geological survey of finland - 2012 (sp_054)

GEOLOGICAL SURVEY OF FINLAND

Special Paper 54 2012

The Archaean of the Karelia Province in Finland

Edited by Pentti Hölttä

Geological Survey of Finland, Special Paper 54

The Archaean of the Karelia Province in Finland

Edited by Pentti Hölttä

Geological Survey of FinlandEspoo 2012

Front cover: Archaean of the Karelia Province in Finland. Report of the GTK project entitled Archaean bedrock modeling.

Unless otherwise indicated, the figures have been prepared by the authors of the article.

ISBN 978-952-217-213-6 (pdf)ISBN 978-952-217-214-3 (paperback)

ISSN 0782-8535

Layout: Elvi Turtiainen OyPrinting house: Tammerprint Oy

Hölttä, P. (ed.) 2012. The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54, 254 pages, 139 figures, 9 tables and 6 appendices.

The Finnish part of the Archaean Karelia Province is divided into several complexes on the basis of lithological, structural, metamorphic and geochro-nological differences between them. These complexes are Ilomantsi, Lentua, Kuopio, Iisalmi, Rautavaara, Manamansalo, Kalpio, Siurua and Ranua. All of these complexes are mostly formed of gneissic granitoids. Neoarchaean rocks dominate, since Palaeoarchaean and Mesoarchaean granitoids (>2.9 Ga) are only locally present in the western and northern parts of the province. The granitoid rocks can be classified, based on their major and trace element com-positions and age, into four main groups, which are the TTG (tonalite-trond-hjemite-granodiorite), sanukitoid, QQ (quartz diorite-quartz monzodiorite) and GGM (granodiorite-granite-monzogranite) groups.

The TTGs share many geochemical features with adakites, and they have a large age span from c. 3.50 to 2.73 Ga. Adakitic plutonic rocks appear to represent a continuous compositional series from TTGs with variable Na

2O/K2O and low Ba+Sr to sanukitoids, which have a high Ba–Sr signature, low Na2O/K2O ratio and uniform HREE pattern. Sanukitoids have a uniform age distribution of 2.74–2.72 Ga. The age of the QQs is c. 2.70 Ga, representing the youngest juvenile Archaean magmatism, and the age of the GGMs c. 2.71-2.66 Ga, representing crustal melting in Neoarchaean collisional events.

Migmatized amphibolites are found as layers and inclusions in TTGs, and their compositional trends indicate that they could represent both partially molten mid-ocean ridge basalts and metamorphosed dykes with some crustal contamination. Metamorphism of the TTG complexes took place under upper amphibolite and granulite facies conditions at 2.70–2.60 Ga. Partial melting of the TTG gneisses yielded leucosomes that are rich in Na2O and have a trond-hjemitic affinity, while leucosomes within granulites are CaO-rich and classify as tonalites.

Reliable concordant U-Pb zircon data obtained for volcanic rocks in the Archaean greenstone belts in Finland indicate distinct age groups for each belt: Suomussalmi 2.94, 2.87 and 2.82 Ga; Kuhmo-Tipasjärvi 2.84–2.80 Ga; Ilo-mantsi-Kovero 2.88 and 2.75 Ga; and Oijärvi 2.82–2.80 Ga. Both the Kuhmo and Tipasjärvi belts contain sedimentary rocks that were deposited after 2.75 Ga, and in the Arola area of the Kuhmo belt a deformed quartzite contains de-trital zircon as young as 2.70 Ga. The sediments in the paragneiss belts within TTG complexes were deposited ca. 2.72 Ga ago. Sm-Nd isotopic results show that volcanic rocks in the Kuhmo and Tipasjärvi belts largely represent newly mantle-derived material. In contrast, in the Suomussalmi belt, Sm-Nd and Pb isotope results indicate a major involvement of significantly older crustal mate-rial (>3 Ga). A minor contribution of older crustal material is also evident in the Ilomantsi belt, where some igneous rocks contain xenocrystic zircon up to 3.3 Ga in age. In the Kuhmo greenstone belt, mafic and ultramafic volcanic rocks show an affinity to oceanic plateau basalts, and seem to derive from a slightly depleted primitive mantle-type source. Ilomantsi komatiites have highly fractionated, LREE-enriched patterns that indicate extensive interaction with the associated felsic volcanics, and both the komatiites and the felsic volcan-ics bear arc signatures. The geochemical data suggest that the greenstone belts store a long-lived (>200 Ma) fragmentary record of geological evolution, pos-sibly in various geodynamic settings, including an oceanic plateau, island arc, back arc/intra-arc and intra-continental rift. Neoarchaean accretion of exot-ic terranes at c. 2.83–2.75 Ga and subsequent collisional crustal stacking at around 2.73–2.68 Ga may have been the mechanism that generated the present structure of the Karelia Province.

4

Keywords (GeoRef Thesaurus, AGI): Karelia Province, gneisses, greenstone belts, geochemistry, absolute age, metamorphism, tectonics, Fennoscandian Shield, Archean, Finland

Pentti HölttäGeological Survey of FinlandP.O. Box 96FI-02151 EspooFinland

E-mail: [email protected]

5

CONTENTS

Preface ................................................................................................................................................ 7 Pentti Hölttä

Archaean complexes of the Karelia Province in Finland ..................................................................... 9Pentti Hölttä, Esa Heilimo, Hannu Huhma, Heikki Juopperi, Asko Kontinen, Jukka Konnunaho, Laura Lauri, Perttu Mikkola, Jorma Paavola and Peter Sorjonen-Ward

The Archaean of the Karelia Province in Finland ............................................................................. 21Pentti Hölttä, Esa Heilimo, Hannu Huhma, Asko Kontinen, Satu Mertanen, Perttu Mikkola, Jorma Paavola, Petri Peltonen, Julia Semprich, Alexander Slabunov and Peter Sorjonen-Ward

The age of the Archaean greenstone belts in Finland........................................................................ 74Hannu Huhma, Irmeli Mänttäri, Petri Peltonen, Asko Kontinen, Tapio Halkoaho, Eero Hanski, Tuula Hokkanen, Pentti Hölttä, Heikki Juopperi, Jukka Konnunaho, Yann Lahaye, Erkki Luukkonen, Kimmo Pietikäinen, Arto Pulkkinen, Peter Sorjonen-Ward, Matti Vaasjoki and Martin Whitehouse

Nd isotopic evidence for Archaean crustal growth in Finland ......................................................... 176Hannu Huhma, Asko Kontinen, Perttu Mikkola, Tapio Halkoaho, Tuula Hokkanen, Pentti Hölttä, Heikki Juopperi, Jukka Konnunaho, Erkki Luukkonen, Tapani Mutanen, Petri Peltonen, Kimmo Pietikäinen and Arto Pulkkinen

Overview of Neoarchaean sanukitoid series in the Karelia Province, eastern Finland .................... 214Esa Heilimo, Jaana Halla and Perttu Mikkola

Geochemical and petrophysical characteristics of plutonic rocks from the Archaean Karelia Province in Finland ...................................................................................... 226Tapio Ruotoistenmäki

Fluid-controlled melting of granulites and TTG-amphibolite associations in the Iisalmi Complex, Central Finland ......................................................................................... 244Franziska Nehring

7

PREFACE

The Karelia Province comprises the southwestern part of the Ar-chaean cratonic nucleus of the Fennoscandian Shield, and records an Archaean history of almost one billion years, from c. 3.5 Ga to 2.6 Ga. Research during the last few decades in both Russia and Finland have greatly improved our knowledge of the evolution of the Archaean crust of the Karelia Province. This volume in the Ge-ological Survey of Finland Special Paper series presents a review of recent research on the Archaean bedrock in Finland and new data, especially regarding age determinations from the greenstone belts.

In the first paper by Hölttä et al., the authors describe the main geological features of the Karelia Province in Finland. They present a regional subdivision of geological complexes which can be used as a basis for discussing field relations, as well facilitating a better understanding of the tectonic classification and evolution of the Archaean bedrock.

The Archaean bedrock of the Karelia Province consists mostly of rather monotonous tonalitic-trondhjemitic-granodioritic (TTG) gneisses which can nevertheless be classified into several distinct lithological and geochemical types, representing distinctly different evolutionary histories. Greenstone belt assemblages in the Karelia Province also seem to represent various geodynamic settings. The second paper by Hölttä at al. present a review and new analytical data on the geochemistry, age relations, metamorphism and palaeo-magnetism of the various components of the Archaean crust and discuss the possible tectonic models which could explain the present structure of the Karelia Province.

The first paper by Huhma et al. provides extensive new data on U-Pb age determinations on zircon from volcanic rocks and meta-sediments in the Archaean greenstone belts and adjacent areas. The second paper by Huhma et al. presents Sm-Nd isotopic data from c. 400 samples which together with the U-Pb zircon ages show that most of the western part of the Karelia Province consists of rela-tively juvenile Neoarchaean crust.

Sanukitoids (or high Mg-granitoids) are distinctive Neoarchaean igneous rocks whose geochemistry differs significantly from that of the Archean TTGs. They are found in Archaean cratons worldwide, and in the central parts of the Karelia Province they form a late to post-tectonic suite which was formed in a narrow time span be-tween 2.74-2.72 Ga. The paper by Heilimo et al. gives a review of the recent studies of the sanukitoids in the Karelia Province.

The geochemical characterstics of many Archaean TTGs closely resemble modern adakites which are felsic rocks that are commonly considered to represent the products of slab-melting in subduction zones. The paper by Ruotoistenmäki considers the geochemical and petrophysicals characteristics and discusses the origin of Archaean plutonic rocks that have geochemical affinities with adakites.

The Archaean of the Karelia Province in FinlandEdited by Pentti HölttäGeological Survey of Finland, Special Paper 54, 7–8, 2012

8

With the exception of the central parts of some greenstone belts, the Archean bedrock in Finland was highly metamorphosed during Neorchaean orogenic processes and underwent partial melting that produced metatexitic and diatexitic migmatites in most rock types. The paper by Nehring describes such migmatisation processes in mafic granulites and adjacent upper amphibolites facies rocks in the Iisalmi Complex in the western part of the Karelia Province.

Espoo, 26 November 2012

Pentti Hölttä

Geological Survey of Finland, Special Paper 54Pentti Hölttä

9

ARCHAEAN COMPLEXES OF THE KARELIA PROVINCE IN FINLAND

byPentti Hölttä 1), Esa Heilimo2), Hannu Huhma1),

Heikki Juopperi3), Asko Kontinen2), Jukka Konnunaho3), Laura Lauri3), Perttu Mikkola2), Jorma Paavola2) and

Peter Sorjonen-Ward2)

Hölttä, P., Heilimo, E., Huhma. H., Juopperi, H., Kontinen, A., Konnunaho, H., Lauri, L., Mikkola, P., Paavola, J. & Sorjonen-Ward, P. 2012. Archaean complexes of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54, 9−20, 3 figures.

In this study we represent new division of the Finnish part of the Archaean Ka-relia Province into nine complexes: Ilomantsi, Lentua, Kuopio, Iisalmi, Rautavaara, Manamansalo, Kalpio, Siurua and Ranua. The easternmost part of the Archaean of Finland, the Ilomantsi complex belongs to the Central Karelia subprovince which is characterized by short Neoarchaean (<2.8 Ga) crustal growth period. Most of the Archaean in central Finland belongs to the Western Karelia subprovince. The Lentua complex is characterized by tonalite-trondhjemite-granodiorite series rocks (TTGs) whose age varies from 2.95 Ga to 2.73 Ga and a narrow N-S trending green-stone belt, the Tipasjärvi- Kuhmo-Suomussalmi belt, where the ages of volcanic rocks vary from c. 2.95 to c. 2.80 Ga. Sanukitoid intrusions with an age of 2.72 Ga occur throughout the Lentua complex. Metasediments with a deposition age close to 2.70 Ga and 2.71-2.69 Ga granodiorite-granite -monzogranite (GGM) series rocks are common in the central and southern parts of the Lentua complex. The Kuopio complex includes the Archaean gneiss domes and tectonic slivers within Proterozoic metasediments and consists of TTG gneisses and migmatites with a few sanukitoid and quartz diorite intrusions. The Iisalmi complex is characterized by Mesoarchaean 3.2 Ga TTGs and amphibolites, c. 2.70 Ga quartz diorite-quartz monzonite (QQ) intrusions and medium pressure (9-11 kbar) granulites metamorphosed at 2.70-2.60 Ga. Chemically altered rocks and pervasive Proterozoic deformation are com-mon in the Rautavaara complex where all dated rocks are Neoarchaean, < 2.80 Ga. The Kalpio complex mainly consists of metasediments that are arkosic gneisses, mica schists/gneisses and gneissic quartzites. The Manamansalo complex is composed of NeoArchaean TTG gneisses with amphibolite layers and micaceous paragneisses. In the Karelia Province the Siurua complex contains the oldest Mesoarchaean and Paleoarchaean rocks in a small area where there are TTGs whose ages range from 3.50 to 2.96 Ga. In the Siurua complex there is a large granulite facies area that was metamorphosed at low pressures (5-6 kbar). TTGs dated from the Ranua complex are 2.83-2.73 Ga. In the eastern part of the complex there is a large area of meta-sediments, and smaller paragneiss localities are also met in the northern parts of the complex. Quartz diorites-quartz monzonites dated at 2.70 Ga are also found in the Ranua complex.

Keywords (GeoRef Thesaurus, AGI): complexes, Karelia Province, Fennoscan-dian shield, Archean, Finland

The Archaean of the Karelia Province in FinlandEdited by Pentti Hölttä Geological Survey of Finland, Special Paper 54, 9–20, 2012

10

1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland2)Geological Survey of Finland, P.O. Box 1237, FI-7021 1 Kuopio, Finland3)Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland


11

Geological Survey of Finland, Special Paper 54Archaean complexes of the Karelia Province in Finland

INTRODUCTION

In this paper we have divided the Finnish part of the Archaean Karelia Province of the Fennos-candian Shield into nine complexes on the ba-sis of lithological, structural, metamorphic and geochronological differences between each other. The usage of the term complex follows the clas-sification of the North American Stratigraphic Code (2005), where a complex is defined as “an assemblage or mixture of rocks of two or more ge-netic classes, i.e., igneous, sedimentary, or metamor-phic, with or without highly complicated structure”.

Reflecting the fact that the Archaean bedrock main-ly consists of rather monotonous gneissic tonalite-trondhjemite-granodiorite series rocks (TTGs), the geological differences between the complexes are in many cases not very prominent, but some lithological, geochemical and age differences do exist from one complex to another. The complex division follows that presented in the digital geo-logical database of Finland (http://www.geo.fi/suomkalliop.html).

KARELIA SUBPROVINCES

Slabunov et al. (2006) and Hölttä et al. (2008) di-vided the Karelia Province into three terranes differing from each other in their lithological, structural and age patterns. These are the Western Karelia terrane, the Central Karelia terrane and the Vodlozero terrane (Fig. 1). The term terrane refers to a fault-bounded crustal block whose geo-

logical history differs from that of the surround-ing areas (e.g. Jones et al. 1983, Jones 1990). As such a relationship between the Karelia “terranes” has not yet been adequately demonstrated and the division is based on differences in geochronology, lithology and geochemistry, we have here used the more neutral term subprovince.

Western Karelia subprovince

We divided the Finnish part of the Western Ka-relia subprovince into eight complexes: the Len-tua, Kuopio, Rautavaara, Iisalmi, Manamansalo, Kalpio, Siurua and Ranua complexes. This divi-sion roughly follows the previous one presented by Sorjonen-Ward and Luukkonen (2005). The division is mostly based on lithological and age dif-ferences. Most rocks in the Western Karelia sub-province are Neoarchaean < 2.80 Ga, but never-theless some complexes show older ages. The oldest

Palaeo-archaean rocks of 3.5 Ga are found in the Siurua complex (Mutanen & Huhma 2003) and Mesoarchaean 3.2 Ga rocks are found in the Iisal-mi complex (Hölttä et al. 2000, Mänttäri & Hölttä 2002). The oldest rocks observed in the Lentua complex are ca 2.95 Ga (Käpyaho et al. 2007, Huhma et al. 2012, Mikkola et al. 2011a). In oth-er complexes Mesoarchaean and Palaeoarchaean rocks have thus far not been found .

Lentua complex

The Lentua complex (Fig. 3) mainly consists of migmatitic and gneissic TTGs representing long crustal growth period that can be divided three age groups of c. 2.95 Ga, 2.83-2.78 Ga and 2.76-2.73 Ga. The oldest TTG rocks are found in the Suomussalmi area in the northern part of the complex (Hyppönen 1983, Vaasjoki et al. 1999, Luukkonen 1985, Käpyaho et al. 2006, 2007, Lauri et al. 2006, Mikkola 2011, Mikkola et al. 2011a). The northern part of the Lentua com-plex, the Taivalkoski-Kuusamo area is separat-ed from the southern part by E-W and SW-NE trending shear zones (Fig. 2). Displacements and rotation seen in the strike of Proterozoic doler-

ite dyke swarms at the fault zone suggest that the shear zones involved at least some Proterozoic tectonic displacement. A distinctive feature of the Taivalkoski-Kuusamo area is the presence of large domains of Eu-enriched leucocratic TTG gneisses.

The southern-southwestern parts of the com-plex are characterized by a relative abundance of gneissose sedimentary rocks, known as Nurmes paragneisses. The paragneisses are mostly migma-titic quartz-biotite-plagioclase gneisses with chemi-cal composition almost identical to the global aver-age for Neoarchaean greywackes. On the basis of the ages of detrital zircon grains their deposition

12

Geological Survey of Finland, Special Paper 54Pentti Hölttä, Esa Heilimo, Hannu Huhma, Heikki Juopperi, Asko Kontinen, Jukka Konnunaho, Laura Lauri, Perttu Mikkola, Jorma Paavola and Peter Sorjonen-Ward

Fig. 1. Generalised geological map of the Archaean of Fennoscandia, modified after Slabunov et al. (2006) and Hölttä et al. (2008).

13


Fig. 2. A generalised lithological map of the Finnish part of the Karelia Province.Basemap © National Land Survey of Finland, licence no 13/MML/12.

14


Fig. 3. Archaean complexes of the Finnish part of the Karelia Province. The geological base map is from Fig. 2.

15


age is close to 2.72 Ga (Kontinen et al. 2007, Hölt-tä et al. 2012, Huhma et al. 2012).

The sanukitoid series intrusions in the Lentua complex are c. 2.72 Ga in age, and they are gen-erally c. 20 Ma younger than sanukitoids in the Ilomantsi complex (Heilimo et al. 2011). Quartz diorites dated at c. 2.70 Ga are locally found in the Lentua complex (Mikkola et al. 2011a). The youngest abundant intrusives are c. 2.70-2.69 Ga granodiorite-granite-monzogranite (GGM) series rocks that are related to metamorphism and melt-ing of the TTG crust in the Neoarchaean (Luuk-konen 1988, Käpyaho et al. 2006, Mikkola 2008, Mikkola et al. 2012).

There are several minor occurences of or-thopyroxene bearing enderbitic and mafic gneisses NE of Lieksa in the southeastern part of the Lentua complex, as in the Tulos granu-lite area on the Russian side of the state border (Slabunov et al. 2006). Metasedimentary rocks locally show granulite facies garnet-orthopyrox-ene-bearing assemblages. Granulites facies or-thopyroxene-bearing TTGs are also found west of Taivalkoski and east of Kianta (Fig. 2).

The Lentua complex includes the Tipasjärvi, Kuhmo and Suomussalmi greenstone belts as well as some minor greenstone occurrences as nar-row interlayers in TTGs such as the Ipatti green-stone belt in the southern part of the complex. Some of these consist of small serpentinite bodies with Ni mineralizations as in Tainiovaara (Pekka-rinen 1980).

The oldest U-Pb zircon ages from volcanic rocks are obtained in the lower units of the Suomus-salmi greenstone belt, being c. 2.95 Ga (Luuk-konen et al. 2002, Huhma et al. 2012). All other dated volcanic rocks in the Tipasjärvi, Kuhmo and Suomussalmi greenstone belts yield ages of c. 2.87-2.80 Ga (Huhma et al. 2012), as do the volcanic rocks in the nearby Kostomuksha greenstone belt in Russia (Bibikova et al. 2005b).

There are a few rare intrusive rock types in the Lentua complex. The age of the Kuohattijärvi layered pyroxenite-gabbro-anorthosite intrusion is unknown but its deformation suggests that it is Archaean. Large Paleoproterozoic c. 2.45 Ga layered mafic intrusions are found in the north-ern parts of the Lentua complex. In the north the complex is autochthonously covered by the c. 2.40 Ga ultramafic and mafic volcanic rocks of the Kuusamo Group overlain by Jatuli-stage cra-tonic-epicratonic, predominantly quartzitic meta-sediments (Silvennoinen 1972).

Rautavaara complex

The Lentua complex is separated in the SW from the Rautavaara complex by SE-NW trending Pro-terozoic shear zone (Fig. 3). In the Rautavaara complex rocks older than 2.75 Ga have not been found thus far but on the other hand only a few datings exist for the rocks of this complex. The dominant rock type is a TTG gneiss with vari-able amounts of amphibolite and biotite-plagio-clase paragneiss as enclaves and schlierens.

The abundance of chemically altered ultra-mafic to felsic rocks is the distinctive feature of the Rautavaara complex. These rocks include cordierite- orthoamphibole rocks and quartz rocks with Al-silicates (andalusite, kyanite, sil-limanite) and cordierite. The oldest, c. 2.75 Ga zircon grains dated in the complex are from a quartz-cordierite rock that is interpreted to derive from chemically altered felsic volcanic rock (Hölt-tä 1997, Paavola 1999, Mänttäri & Hölttä 2002). A quartz diorite from Rokanmäki (Fig. 2) yielded a conspicuously young TIMS zircon age of 2.68 Ga, which may result from a mixture of magmatic and metamorphic zircon grains (Paavola 1999). Other Neoarchaean igneous rocks in the area are 2.72 Ga sanukitoids and 2.66 Ga granites (Halla 2005, Heilimo et al. 2011). At least the western part of the Rautavaara complex underwent granulite faci-es metamorphism at c. 2.68-2.62 Ga, as is indicated by U-Pb ages obtained for metamorphic zircon and monazite. Most of the Rautavaara complex under-went pervasive Paleoproterozoic deformation and related retrograde metamorphism at 1.89 Ga in conditions at around 600°C and 5-6 kbar, which largely destroyed the Archaean granulite facies mineral assemblages (Paavola 1999, Mänttäri & Hölttä 2002).

In the north in the Lahnasjärvi area (Fig. 2) TTGs are parautochthonously overlain by early Proterozoic 2.3-2.1 Ga platform quartzites. In the northwest the complex is in a faulted contact with the Otanmäki-Kuluntalahti sliver of c. 2.05 Ga alkaline to peraluminous granites. Dykes and small bodies of often garnet-bearing c. 1.80 Ga pegmatite granite are found in the Lahnasjärvi area.

Iisalmi complex

The boundary between the Rautavaara and Iisal- mi complexes possibly represents a suture be-tween two tectonic terranes (Fig. 3), based on the drastic differences observed in lithology and ages. Chemically altered lithologies are lacking and MesoArchaean 3.2-3.1 Ga gneisses are found

16


in the Iisalmi complex (Hölttä et al. 2000, Mänt-täri & Hölttä 2002). These migmatitic gneisses comprise intermediate and mafic paleosomes, the latter compositionally resembling MORB-type basalts with flat or slightly LREE depleted rare earth element patterns (Hölttä 1997). The Iisalmi complex was intruded at 2.70 Ga by orthopyrox-ene-bearing quartz diorites, and was deformed and metamorphosed, locally in granulite facies, between c. 2.68-2.62 Ga, obviously together with the Rautavaara complex (Mänttäri & Hölttä 2002). The granulites are mostly garnetiferous two-pyrox-ene mafic and intermediate rocks for which geo-thermometry and geobarometry indicate crystal-lization at c. 800-850oC and 9-11 kbar (Hölttä & Paavola 2000).

Kuopio complex

The Kuopio complex is here defined to include the Archaean gneiss domes and/or tectonic slivers within Proterozoic metasediments in the Kuopio (Fig. 3), Kotalahti and Juojärvi areas (Fig. 2) which may represent tectonic thrusts of Archaean gneisses from an unknown source or root zone (cf. Park & Bowes 1983, Park et al. 1984). The possible thrusting could have been coeval with the c. 1.9 Ga obduction of the Outokumpu allochthon.

The Kuopio complex was intensively tectoni-cally reworked during the Palaeoproterozoic. The Archaean rocks are TTG gneisses and migmatites with some sanukitoid and quartz diorite intru-sions that chemically resemble similar rocks in the Iisalmi and Rautavaara complexes. No age data are available for the sanukitoids in the Kuopio complex, but the quartz diorites display 2.7 Ga ages (Lukkarinen 2008), similar to the Iisalmi and Rautavaara quartz diorites.

Kalpio complex

The Kalpio complex is characterized by the abun-dance of metasedimentary rocks, along with zones of TTGs especially in its western part (Laajoki 1991, Fig. 3). The metasedimentary rocks include arkosic gneisses, mica schists and gneisses as well as gneissic quartzites. Amphibolite layers which may partly represent metamorphosed dykes are com-mon among the metasediments. Serpentinites and metagabbros, locally forming layered ultramafic-mafic sills, occur in the eastern part of the com-plex (Laajoki 1991). Felsic metatuffites whose age probably is c. 2.72 Ga are found in one of the youngest included sedimentary units (Huhma et al. 2000, Laajoki 2005).

The mica schists and gneisses are partly highly

aluminous and display shale-normalised immobile trace element patterns characterized by deep nega-tive Nb anomalies, LREE enrichment and HREE depletion. The patterns are very similar to the aver-age composition of Karelia Province Archaean rocks in Rasilainen et al. (2007), suggesting that the source of the Kalpio sediments was in a simi-lar TTG, sanukitoid and GGM rich crust as that presently exposed in the Western Karelia Province.

U-Pb datings by Vaasjoki et al. (2001) showed that the Kalpio granitoids and gneisses would typically contain dominantly Archaean zircon grains, which also suggests that they would be ei-ther Archaean rocks or Proterozoic paragneisses or gneissic granitoids with abundant inherited Ar-chaean components. Monazite U-Pb ages for the gneisses and granites in the Kalpio complex are in the range of c. 1.81-1.79 Ga (Vaasjoki et al. 2001).

The Kajaani gneiss-granite area SE of Lake Oulunjärvi is here included in the Kalpio com-plex. This connection is based on similar lith-ologies, i.e. the presence of amphibolites-interca-lated arkosite gneisses, mica gneisses and quartzite gneisses. Further support for the Kalpio correlation is provided by the presence of serpentinite-gabbro intrusions in both areas. The eastern part of the Kajaani area is dominated by gneissic TTG rocks. Their southern and eastern margin is tectonic against the A-type gneissic, peralkaline-peralumi-nous Proterozoic granites of 2.05 Ga.

Manamansalo complex

The Manamansalo complex south of the Kalpio complex (Fig. 3) consists of TTG gneisses with am-phibolite and micaceous paragneiss layers. In the SW part of the Manamansalo complex are the Piiparinmäki and Pirttimäki areas which were described as separate complexes by Laajoki and Luukas (1988). The Pirttimäki area is formed of banded schists and quartz-feldspar gneisses with amphibolite layers, whereas the Piiparinmäki area mainly consists of gneissic TTG rocks with abundant amphibolite layers, and with abundant foliated Proterozoic granitoids in its N part. The contacts of these two areas are either lithodemic or tectonic (Laajoki & Luukas 1988).

The Manamansalo complex is still scantily dat-ed. Two age determinations are available from the Manamansalo area, one from a tonalite gneiss and another from its pegmatite bands, giving ages of 2675 ± 2 Ma and 2663 ± 2 Ma, respectively (Vaas-joki et al. 2001). If the U-Pb age on zircon from the tonalite gneiss is not from metamorphic grains it represents the youngest Archaean tonalite so far observed in the Finnish Archaean.

17


One U-Pb age determination on zircon from a tonalite in the southern part of the Pirttimäki area has given an age of 2.73 Ga. Monazite from this tonalite is Palaeoproterozoic, 1.82 Ga (Pie-tikäinen & Vaasjoki 1999). Similar to the Kalpio Complex, Palaeoproterozoic granites and granite pegmatites are abundant in the Manamansalo complex. Similar monazite ages suggest that these complexes jointly experienced a relatively high temperature metamorphic event at the time the Proterozoic granites intruded them.

Siurua complex

The Siurua complex contains the Siurua 3.5 Ga trondhjemitic gneisses which are the oldest rocks observed in the Karelia Province (Fig. 3) so far (Mutanen & Huhma 2003). Low-pressure granulite facies orthopyroxene bearing 2.96 Ga TTG or-thogneisses and amphibolites are found in their vicinity (Lalli 2002, Mutanen & Huhma 2003). The Palaeoarchaean rocks are only found in a re-stricted area, because most age determinations in the adjacent rocks yield Neoarchaean ages. The majority of detrital zircon grains in adjacent par-agneisses are Neoarchaean, 2.74 – 2.72 Ga, Pal-aeoarchaean grains being absent (Huhma et al. 2012).

Ranua complex

The Ranua complex (Fig. 3) consists of TTG rocks and granites dated at 2.82 – 2.73 Ga and 2.70 – 2.62 Ga, respectively (Huhma et al. 2012). The Ranua complex includes the N-S striking Oijärvi green-stone belt which mostly consists of amphibolite facies mafic and ultramafic volcanic rocks and sediments (Sorjonen-Ward & Luukkonen 2005). The existing datings give an age of 2.82-2.80 Ga for the intermediate volcanic rocks of the Oijärvi belt, but a felsic porphyry as young as 2.67 Ga was also found (Huhma et al. 2012). Paragneisses also occur locally in the Ranua complex outside the Oijärvi greenstone belt, and a large proportion of detrital zircon grains in these paragneisses are 2.74 – 2.73 Ga in age, giving the maximum deposition age (Huhma et al. 2012). The extensive Ranua intrusion in the northern part of the com-plex, showing variably dioritic -quartz dioritic com-positions, is dated at 2.70 Ga (Mutanen & Huhma 2003). U-Pb data on metamorphic zircon grains in mafic granulites and leucosomes of migmatites indicate high grade metamorphism at 2.68 – 2.65 Ga (Mutanen & Huhma 2003, Lauri et al. 2011).

Central Karelia subprovince

Ilomantsi complex

The Central Karelia subprovince differs from the surrounding Archaean subprovinces on the basis of the predominantly Neoarchaean < 2.80 Ga age of plutonic and volcanic sequences (Vaasjoki et al. 1993, Huhma et al. 2012), of its relative abundance of sanukitoids and of the geochemistry of vol-canic rocks of the greenstone belts (Hölttä et al. 2012). The Ilomantsi complex refers to the Finn-ish part of the Central Karelia subprovince (Figs. 1 and 3) and it includes the Ilomantsi and Kovero greenstone belts.

The oldest granitoids within the Ilomantsi com-plex are c. 2.76 Ga in age (Sorjonen-Ward & Claoué-Long 1993). The complex is characterized by a relatively high abundance of sanukitoids (Fig. 2), which are lacking in the Belomorian province and westernmost complexes of the Western Kare-lia subprovince. The Central Karelia sanukitoids are strongly differentiated and vary in composi-tion from ultramafic to felsic. They appear to be slightly older (2.75-2.73 Ga) than sanukitoids in the Western Karelia subprovince where sa-nukitoids are mostly between 2.70–2.72 Ga in

age (Vaasjoki et al. 1993, Bibikova et al. 2005a, Lobach-Zhuchenko et al. 2005, 2008, Käpyaho et al. 2006, Heilimo et al. 2010, 2011).

Felsic volcanic rocks in the Ilomantsi, Gimola and Khedozero-Bolsheozero greenstone belts have been dated at 2.75-2.73 Ga (Vaasjoki et al. 1993, Bibikova et al. 2005b). In the Ilomantsi green-stone belt, 2.75 Ga andesites have been interpreted to represent the lowermost stratigraphic unit of the volcanic sequence. Calc-alkaline basalt-an-desite-dacite-rhyolite (BADR) series volcanic rocks, crustal signatures in the geochemistry of ultramafic rocks and high abundances of vol-caniclastic greywackes in the Ilomantsi and Khe-dozero-Bolsheozero greenstone belts indicate that these belts originated in arc type tectonic set-tings (Sorjonen-Ward 1993, Slabunov et al. 2006, Hölttä et al. 2012).

In the Kovero greenstone belt (Fig. 2) the oldest felsic volcanic rock is dated at 2.88 Ga (Huhma et al. 2012). There are also geochemical differ-ences between the volcanic rocks of these two belts, e.g. komatiites in Kovero have flat or slight-ly LREE depleted REE patterns (Tuukki 1991), whereas komatiites in Ilomantsi are LREE en-

18


riched (O’Brien et al. 1993, Hölttä et al. 2012). However, because there are no such tectonic fea-tures between the Ilomantsi and the Kovero belts

that would imply that they represent separate ex-otic terranes, the Kovero belt is also included here in the Central Karelia subprovince.

Vodlozero subprovince

The Vodlozero subprovince (Fig. 3) is cored by the 3.2-3.0 Ga Vodla gneiss complex which con-sists of migmatitic amphibolites and TTGs. Three age groups of greenstone belts are distinguished in Vodlozero: an early (3.01-2.95 Ga) group of the Vedlozero-Segozero, Sumozero-Kenozero and South Vygozero greenstone belts; a 2.9-2.85 Ga group of Vedlozero-Segozero and Sumozero-Ke-nozero belts and post 2.85 Ga greenstones of the Matkalahta belt. The Vodla gneisses were meta-morphosed first at 3.15 Gа and then at 2.85 Gа (Sergeev et al. 2007). The Vodla gneiss complex is bordered in the west by the Vedlozero-Segozero greenstone belt, which is the oldest established convergent ocean-continent transition zone in the Karelia Province (Svetov et al. 2006). In the Vedlozero-Segozero belt 3.05-2.95 Ga island arc type tholeiitic, adakitic and basalt-andesite-dac-ite-rhyolite (BADR) series rocks are juxtaposed with 3.10-2.95 Ga komatiitic-basaltic series that

are interpreted to represent proto-oceanic assem-blages (Svetov et al. 2006). The Matkalahta belt, located in the central part of the Vodlozero sub-province, consists of alternating metasediments (quartz arenites, greywackes and carbonaceous shales) and metavolcanics of basalt-komatiite as-sociation with scarce foliated felsic metavolcanic interbeds. The ages of the detrital zircon from the metasediments vary from 3.33 to 2.82 Ga, yield-ing a maximum deposition age of 2.82 Ga for the Matkalahta belt. The youngest (c. 2.70-2.60 Ga) Archaean rocks are sanukitoids, enderbites and mafic dykes. In the NW part of the Vodlozero subprovince dykes are tholeiitic and ultramafic, but in the central part there are low-Cr silicious gabbronorites, e.g. the Shalskiy dyke whose U-Pb age on baddeleyite is 2.51 Ga (Bleeker et al. 2008) and the Sm-Nd mineral age is 2.61 Ga (Mertanen et al. 2006).

DISCUSSION

The above division of the Karelia Province into complexes has to be considered largely tentative. It does not necessarily represent in its details the Archaean evolution as the Western Karelia Province was largely metamorphosed and de-formed at 1.9 – 1.8 Ga during the Svecofenn-ian orogeny which caused a lot of faulting and block movements and penetrative deformation and retrograde metamorphism in large areas. Large areas have been mapped in detail in 1:100 000 scale. Our data sets are also unevenly distrib-uted. For example, there are still areas, especially in the Ranua and Siurua complexes, that have been mapped only on a large regional scale. The age determinations are also concentrated to the greenstone belts and their adjacent areas. The evolution of the greenstone belts could be better constrained, as the detailed, belt-specific chron-ostratigraphic database, for example, is still in its infancy.

Consequently, we can only tentatively sketch important terrane/tectonic boundaries. One is ob-viously between the Ilomantsi and Lentua com-plexes which marks the boundary of the Western Karelia and Central Karelia subprovince. Anoth-er important terrane boundary might be between the Rautavaara and Iisalmi complexes, noting their very different lithologies and that only Neo-archaean rocks have been dated so far in the Rau-tavaara complex. In addition, the Palaeoarchaean rocks of the Siurua complex may represent an ex-otic tectonic block that has been preserved to the present day. Owing to its small size, it cannot be considered as a separate terrane but rather as an exotic tectonic sliver. However, we hope that the above-presented complex division could work as a useful common tool when we discuss the broader field relations, as well as a basis for better under-standing of the tectonic classification and evolu-tion of this fascinating part of the Earth’s crust.

19


REFERENCES

Bibikova, E. V., Petrova, A. & Claesson, S. 2005a. The tem-poral evolution of sanukitoids in the Karelian Craton, Baltic Shield: an ion microprobe U–Th–Pb isotopic study of zircons. Lithos 79, 129–145.

Bibikova, E. V., Samsonov, A. V., Petrova, A. Yu. & Kirnozova, T. I. 2005b. Archean geochronology of Western Karelia. Stratigraphy and Geological Correlation, 13 (5). 459–475.

Heilimo, E., Halla, J. & Hölttä, P. 2010. Discrimination and origin of the sanukitoid series: Geochemical constraints from the Neoarchean western Karelian Province (Fin-land). Lithos 115, 27–39.

Heilimo, E., Halla, J. & Huhma, H. 2011. Single-grain zircon U–Pb age constraints of the western and eastern sanuki-toid zones in the Finnish part of the Karelian Province. Lithos 121, 87−99.

Hölttä, P. 1997. Geochemical characteristics of granulite fa-cies rocks in the Varpaisjärvi area, central Fennoscandian Shield. Lithos 40, 3 1–53.

Hölttä, P. & Paavola, J. 2000. P-T-t development of Ar-chaean granulites in Varpaisjärvi, Central Finland, I: Effects of multiple metamorphism on the reaction his-tory of mafic rocks. Lithos 50, 97–120.

Hölttä, P., Huhma, H., Mänttäri, I. & Paavola, J. 2000. P-T-t development of Archaean granulites in Varpaisjärvi, Cen-tral Finland, II: Dating of high-grade metamorphism with the U-Pb and Sm-Nd methods. Lithos 50, 12 1–136.

Hölttä, P., Balagansky, V., Garde, A. A., Mertanen,S., Peltonen, P., Slabunov, A., Sorjonen-Ward, P. & White-house, M. 2008. Archean of Greenland and Fennoscan-dia. Episodes 31 (1), 1–7.

Huhma, H., Kontinen, A. & Laajoki, K. 2000. Age of the metavolcanic-sedimentary units of the Central Puolanka Group, Kainuu schist belt, Finland. In: 24. Nordiske Ge-ologiske Vintermøte, Trondheim 6.–9. januar 2000. Geo-nytt 1, 87–88.

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho,T., Hanski., E., Hokkanen. T., Hölttä, P., Juop-peri, H., Konnunaho, J., Lahaye, Y., Luukkonen., E., Pie-tikäinen, K., Pulkkinen, A., Sorjonen-Ward, P. , Vaasjoki, M. & Winehouse, M. 2012. The age of Archean green-stone belts in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Jones, D. L. 1990. Synopsis of late Palaeozoic and Mesozoic terrane accretion within the Cordillera of western North America. In: Dewey, J. F., Gass, I. G., Curry, G. B., Har-ris, N. B. W. & Sengör, A. M. C. (eds) Allochthonous Ter-ranes. Cambridge: Cambridge University Press, 23−30.

Jones, D. L., Howell, P. G., Coney, P. J. & Monger, J. W. 1983. Recognition, character and analysis of tectonostratigraph-ic terranes in western North America. Journal of Geologi-cal Education, 31, 295−303.

Hyppönen, V. 1983. Ontojoen, Hiisijärven ja Kuhmon kartta-alueiden kallioperä. Summary: Pre-Quaternary Rocks of the Ontojoki, Hiisijärvi and Kuhmo Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheets 4411, 4412, 4413. Geological Survey of Finland. 60 p.

Käpyaho, A. Hölttä, P. & Whitehouse, M., 2007. U-Pb zir-con geochronology of selected Neoarchaean migmatites in eastern Finland. Bulletin of the Geological Society of Finland 79 (1), 95–115.

Kontinen, A., Käpyaho, A., Huhma, H., Karhu, J., Matukov, D. I., Larionov, A. & Sergeev, S. A. 2007. Nurmes par-

agneisses in eastern Finland, Karelian craton: provenance, tectonic setting and implications for Neoarchaean craton correlation. Precambrian Research 152, 119–148.

Laajoki, K. 1991. Stratigraphy of the northern end of the early Proterozoic (Karelian) Kainuu Schist Belt and as-sociated gneiss complexes, Finland. Geological Survey of Finland, Bulletin 358. 105 p.

Laajoki, K. 2005. Karelian supracrustal rocks. In: Lehtinen, M., Nurmi, P. A. & Rämö, O. T. (eds.) Precambrian Geol-ogy of Finland – key to the Evolution of the Fennoscan-dian Shield. Amsterdam: Elsevier B.V., 279−342.

Laajoki, K. & Luukas, J. 1988. Early Proterozoic stratigraphy of the Salahmi-Pyhäntä area, central Finland, with an emphasis on applying the principles of lithodemic stra-tigraphy to a complexly deformed and metamorphosed bedrock. Bulletin of the Geological Society of Finland 60 (2), 79–106.

Lalli, K. 2002. Petrography, geochemistry and metamorphic petrology of the Isokumpu area in the Ranua granulite belt. Unpublished Master’s Thesis, University of Oulu. (in Finnish)

Lauri, L. S., Rämö, O. T., Huhma, H., Mänttäri, I. & Räsä-nen, J. 2006. Petrogenesis of silicic magmatism related to the 2. 44 Ga rifting of Archean crust in Koillismaa, eastern Finland. Lithos 86, 137−166.

Lauri, L. S., Andersen, T., Hölttä, P., Huhma, H. & Graham, S. 2011. Evolution of the Archaean Karelian Province in the Fennoscandian Shield in the light of U–Pb zircon ages and Sm–Nd and Lu–Hf isotope systematics. Lon-don: Journal of the Geological Society, 167, 1–18.

Lobach-Zhuchenko, S. B., Rollinson, H. R., Chekulaev, V. P., Arestova, N. A., Kovalenko, A. V., Ivanikov V. V., Guseva, N. S., Sergeev, S. A., Matukov, D. I. & Jarvis K. E. 2005. The Archaean sanukitoid series of the Baltic Shield: geo-logical setting, geochemical characteristics and implica-tions for their origin. Lithos 79, 107–128.

Lukkarinen, H. 2008. Siilinjärven ja Kuopion kartta-aluei-den kallioperä Summary: Pre-Quaternary Rocks of the Siilinjärvi and Kuopio Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheets 3331, 3242. Espoo: Geologian tutkimuskeskus. 228 p. + 2 app. maps. (Electronic publi-cation)

Luukkonen, E. 1988. Moisiovaaran ja Ala-Vuokin kartta-alueiden kallioperä. Summary: Pre-Quaternary Rocks of the Moisiovaara and Ala-Vuokki Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheets 4421 and 4423+4441. Geological Survey of Finland. 90 p.

Luukkonen, E., Halkoaho, T., Hartikainen, A., Heino, T., Niskanen, M., Pietikäinen, K. & Tenhola, M. 2002. Re-port of the GTK project ’The Archaean areas of eastern Finland in the years 1992−2001 in the communities of Suomussalmi, Hyrynsalmi, Kuhmo, Nurmes, Rautavaara, Valtimo, Lieksa, Ilomantsi, Kiihtelysvaara, Eno, Kontio-lahti, Tohmajärvi and Tuupovaara. Geological Survey of Finland, archive report M 19/4513/2002/1. 265 p. (in Finnish)

Luukkonen, E. J. 1985. Structural and U-Pb isotopic study of late Archaean migmatitic gneisses of the Presvecoka-relides, Lylyvaara, Eastern Finland. Transactions of the Royal Society of Edinburgh, Earth Sciences 76, 401–410.

Mänttäri, I. & Hölttä, P. 2002. U-Pb dating of zircons and monazites from Archean granulites in Varpaisjärvi, cen-

20


tral Finland: evidence for multiple metamorphism and Neoarchean terrane accretion. Precambrian Research 118, 101−131.

Mertanen, S., Vuollo, J. I., Huhma, H., Arestova, N. A., Kovalenko, A. 2006. Early Paleoproterozoic-Archean dykes and gneisses in Russian Karelia of the Fennos-candian Shield – new paleomagnetic, isotope age and geochemical investigations. Precambrian Research 144 (3−4), 239−260.

Mikkola, P. 2011. The prehistory of Suomussalmi, eastern Finland: the first billion years as revealed by isotopes and the composition of granitoid suites. Academic Disserta-tion. Geological Survey of Finland 79. 24 [78] p.

Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011a. Archean crustal evolution of the Suomussalmi district as part of the Kianta Complex, Karelia; con-straints from geochemistry and isotopes of granitoids. Lithos 125, 287−307.

Mikkola, P., Salminen, P., Torppa, A., Huhma, H. 2011b. The 2. 74 Ga Likamännikkö complex in Suomussalmi, East Finland: lost between sanukitoids and truly alkaline rocks? Lithos 125, 716−728.

Mutanen, T. & Huhma, H. 2003. The 3. 5 Ga Siurua trond-hjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland. Bulletin of the Geological Society of Finland 75, 5 1–68.

North American Stratigraphic Code 2005. North American Commission on Stratigraphic Nomenclature. AAPG Bulletin, 89, 11, 1547–1591.

O’Brien, H., Huhma, H. & Sorjonen-Ward, P. 1993. Petro-genesis of the late Archean Hattu schist belt, Ilomantsi, eastern Finland: geochemistry and Sr, Nd isotopic com-position. In: Nurmi, Pekka A. & Sorjonen-Ward, Peter (eds.) 1993. Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 147–184.

Paavola, J. 1999. Rautavaaran kartta-alueen kallioperä. Sum-mary: Pre-Quaternary Rocks of the Rautavaara Map-Sheet area. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheet 3343. Geo-logical Survey of Finland. 53 p.

Park, A. F. & Bowes, D. R. 1983. Basement-cover relationships during polyphase deformation in the Svecokarelides of the Kaavi district, eastern Finland. Transactions of the Royal Society of Edinburgh, Earth Sciences 74, 95−118.

Park, A. F., Bowes, D. R., Halden, N. M. & Koistinen, T. J. 1984. Tectonic evolution at an early Proterozoic conti-nental margin: the Svecokarelides of eastern Finland. Journal of Geodynamics 1, 359−386.

Pekkarinen, L. J. 1980. Lieksan Tainiovaaran Ni-esiintymä. Geologi 32 (7), p. 92.

Pietikäinen, K. & Vaasjoki, M. 1999. Structural observa-tions and U-Pb mineral ages from igneous rocks at the Archaean-Palaeoproterozoic boundary in the Salahmi Schist Belt, central Finland: constraints on tectonic evolution. Bulletin of the Geological Society of Fin-land 71 (1), 133−142.

Silvennoinen, A. 1972. On the stratigraphic and structural geology of the Rukatunturi area, northeastern Finland. Geological Survey of Finland, Bulletin 257. 48 p.

Slabunov, A. I., Lobach-Zhuchenko, S. B., Bibikova, E. V., Sorjonen-Ward, P., Balagansky, V. V., Volodichev, O. I., Shchipansky, A. A., Svetov, S. A., Chekulaev, V. P., Arestova, N. A. & Stepanov, V. S. 2006. The Archaean nucleus of the Baltic/Fennoscandian Shield. In: Gee, D. G. & Stephenson, R. A. (eds.) European Lithosphere Dynamics. Geological Society of London, Memoir 32, 627–644.

Sorjonen-Ward, P. & Luukkonen, E. 2005. Archean rocks. In: Lehtinen, M., Nurmi, P.A. & Rämö, O.T. (eds.) The Pre-cambrian Geology of Finland − Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier, 19−99.

Strand, K., Köykkä, J. & Kohonen, J. (eds.) 2010. Guidelines and Procedures for Naming Precambrian Geological Units in Finland. 2010 Edition Stratigraphic Commis-sion of Finland: Precambrian Sub-Commission. Geo-logical Survey of Finland, Guide 55. 41 p.

Svetov, S. A., Kudryashov, N. M., Ronkin, Yu. L., Huh-ma, H., Svetova, A. I. & Nazarova, T. N. 2006. Mesoar-chean island-arc association in the Central Karelian Ter-rane, Fennoscandian Shield: new geochronological data. Doklady Earth Sciences 406 (1), 103–106.

Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen, S. 1993. U-Pb age determinations and sulfide Pb-Pb character-istics from the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 103–131.

Vaasjoki, M., Taipale, K. & Tuokko, I. 1999. Radiometric ages and other isotopic data bearing on the evolu-tion of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland. Bulletin of the Geo-logical Society of Finland 71 (1), 155–176.

Vaasjoki, M., Kärki, A. & Laajoki, K. 2001. Timing of Pal-aeoproterozoic crustal shearing in the Central Fen-noscandian Shield according to U-Pb data from as-sociated granitoids, Finland. Bulletin of the Geological Society of Finland 73 (1−2), 87–101.

21

THE ARCHAEAN OF THE KARELIA PROVINCE IN FINLAND

byPentti Hölttä1), Esa Heilimo2), Hannu Huhma1), Asko Kontinen2),

Satu Mertanen1), Perttu Mikkola2), Jorma Paavola2), Petri Peltonen1,3), Julia Semprich5), Alexander Slabunov4) and

Peter Sorjonen-Ward 2)

Hölttä, P., Heilimo, E., Huhma, H., Kontinen, A., Mertanen, S., Mikkola, P., Paa-vola, J., Peltonen, P., Semprich, J., Slabunov, A. & Sorjonen-Ward, P. 2012. The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54, 21−73, 33 figures and 1 appendix.

The Archaean bedrock of the Karelia Province in Finland is mostly formed of granitoids whose ages vary from c. 3.50 to 2.66 Ga. Neoarchaean rocks dominate, since Paleoarchaean and Mesoarchaean granitoids (>2.9 Ga) are only locally pre-sent in the western and northern parts of the province. The granitoid rocks can be classified, based on their major and trace element compositions and age, into four main groups, which are the TTG (tonalite-trondhjemite-granodiorite), sanukitoid, QQ (quartz diorite-quartz monzodiorite) and GGM (granodiorite-granite-mon-zogranite) groups. Most ages obtained from TTGs are between 2.83–2.72 Ga, and they seem to define two age groups separated by a c. 20 Ma time gap. TTGs are 2.83–2.78 Ga in the older group and 2.76–2.72 Ga in the younger group. Sanuki-toids have been dated at 2.74–2.72 Ga, QQs at c. 2.70 Ga and GGMs at 2.73–2.66 Ga. Based on REE, the TTGs fall into two major groups: low-HREE (heavy rare earth elements) and high-HREE TTGs, which obviously originated at differing crustal depths. Sanukitoids are interpreted in terms of melting of subcontinental metasomatized mantle. The GGM group probably represents partial melting of pre-existing TTG crust.

Migmatized amphibolites are found as layers and inclusions in TTGs. Their composition generally varies from basaltic to andesitic. Basaltic amphibolites (SiO2 < 52 wt%) fall into two main groups on the basis of their trace element con-tents. Rocks of the first group have flat or LREE-depleted trace element patterns, resembling here the present mid-ocean ridge basalts, and have chondritic Nb/La ratios, low Zr/Y ratios and high Ni and Cr. Rocks of the second group are enriched in LILE and LREE. They have subchondritic Nb/La ratios and higher Zr/Y ratios than the first group of basaltic amphibolites. Compatible elements, especially Ni but also Cr, are lower in the LREE-enriched group than in the first group. The sec-ond group of LREE-enriched amphibolites could partly represent metamorphosed dykes with assimilated and/or diffused crustal signatures from their TTG country rocks.

The two largest Archaean greenstone belts are the Suomussalmi-Kuhmo-Tipasjärvi belt and the Ilomantsi belt. The latter is predominantly younger than the other greenstone belts in Finland. In the Ilomantsi greenstone belt, volcanic rocks and related dykes are 2.76–2.72 Ga, whereas in other belts they are mostly 2.84–2.80 Ga, and some are even older. The Kuhmo mafic and ultramafic volcanic rocks show an affinity to oceanic plateau basalts, and seem to derive from a slightly


22

Geological Survey of Finland, Special Paper 54Pentti Hölttä, Esa Heilimo, Hannu Huhma, Asko Kontinen, Satu Mertanen, Perttu Mikkola, Jorma Paavola, Petri Peltonen,Julia Semprich, Alexander Slabunov and Peter Sorjonen-Ward

depleted primitive mantle-type source. Ilomantsi komatiites have highly fractionated, LREE-enriched patterns that indicate extensive interaction with the associated fel-sic volcanics, and both the komatiites and the felsic volcanics bear arc signatures.

Metamorphism of the TTG complexes took place under upper amphibolite and granulite facies conditions at 2.70–2.60 Ga. The pressures of the regional metamorphism were mostly c. 6.5–7.5 kbar, and corresponding temperatures c. 650–740 oC. Medium pressure granulites, equilibrated at c. 9–11 kbar and 800–850 oC, are only found in the Iisalmi complex. The Siurua complex contains mafic granulites that were metamorphosed at c. 6 kbar and 750 oC. In greenstone belts, the metamorphic pressures and temperatures that are given by thermobarometry increase from inner to outer parts. P and T were c. 3–4 kbar and 550–590 oC in the inner parts of the Ilomantsi greenstone belt and c. 5 kbar and 630 oC in the outer parts. A similar increase in metamorphic temperatures was also observed in the Kuhmo belt. The Kuhmo and Oijärvi belts record extremely high pressures of up to 10–13 kbar, and in one locality near the eastern boundary of the Kuhmo belt even 16–17 kbar at 650–690 oC.

Neoarchaean accretion of exotic terranes at c. 2.83–2.75 Ga and subsequent collisional crustal stacking at around 2.73–2.68 Ga may have been the mechanism that generated the present structure of the Karelia Province, although it was again strongly reworked during the Svecofennian orogeny.

Keywords (GeoRef Thesaurus, AGI): Karelia Province, granites, amphibolites, greenstone belts, geochemistry, tectonics, Archean, Finland

1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland2) Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland3) Present address: First Quantum Minerals Ltd, Kaikukuja 1, FI-99600 Sodankylä,

Finland4) Institute of Geology, Karelian Research Centre, RAS, Pushkinskaya St. 11,

Petrozavodsk, 185910 Russia5) Physics of Geological Processes, University of Oslo, Blindern, P.O. Box 1048, 0316

Oslo, Norway


23

Geological Survey of Finland, Special Paper 54 The Archaean of the Karelia Province in Finland

INTRODUCTION

There is no generally accepted geodynamic framework for the Archaean eon, as exists for the modern Earth via plate tectonics and the Wilson cycle (Benn et al. 2006). Nevertheless, it is com-monly held that plate tectonics has been operat-ing in some form at least since the Neoarchaean (e.g. deWit 1998, Condie & Benn 2006). Howev-er, there is considerable controversy concerning many of the fundamental aspects of Archaean plate tectonics, including serious doubts about the applicability of the concept at all (Hamilton 1998, 2011). Some views emphasize the likeli-hood of a much faster convection and ocean floor spreading rate in the Archaean than pres-ently, while others suggest that plate velocities have been fairly similar throughout geological time (Blichert-Toft & Albarede 1994, Kröner & Layer 1994, Blake et al. 2004, van Hunen & van den Berg 2004, Strik et al. 2003, Korenaga 2006). Some recent simulations indicate that only af-ter the development of the post-perovskite layer above the core-mantle boundary, after sufficient cooling of the early Earth, could the core have been able to release enough heat to the upper mantle to enable the rapid motion of plates. The earliest this event could probably have occurred was in the early Palaeoproterozoic (Tateno et al. 2009, Hirose 2010).

However, it is generally thought that the Ar-chaean mantle was hotter than today, and the crit-ical petrological evidence for this was komatiites and their much higher abundance in the Archae-an than in the younger geological environments. Komatiites have been related to mantle plumes and reported to record very high mantle tempera-tures and melting pressures. On the other hand, it has also been argued that komatiites were, simi-larly to modern boninites, produced by hydrous melting at relatively shallow mantle depths in a subduction environment. This alternative inter-pretation predicts that the Archaean mantle was only slightly hotter than the present one (Grove & Parman 2004, Condie & Benn 2006).

Complete ophiolite sequences that would com-pletely verify the existence of Phanerozoic-style oceanic crust are rare in Archaean areas. A Ne-oarchaean, 2.51 Ga ophiolite complex has been described from the North China craton (Kusky et al. 2001, 2004), and greenstone occurrences that share many – although not all - characteristics of modern ophiolites have also been found in oth-er Archaean cratons, including the Belomorian province of the Fennoscandian shield (Kusky & Polat 1999, Corcoran et al. 2004, Puchtel 2004,

Shchipansky et al. 2004). Archaean oceanic crust could have been thicker than Proterozoic and Phanerozoic oceanic crust, resembling that of modern oceanic plateaux. This would explain the rareness of complete modern MORB-type ophiolites, as in this case only the upper basal-tic, pillow lava-dominated sections of the oceanic crust were likely to be accreted or obducted and thus preserved in the rock record (Kusky & Polat 1999). Şengör & Natal’in (2004) pointed out that in many Phanerozoic accretionary orogens, as in the western Altaids, evidence of closed oceans also only occurs in the form of separated fragments of variably complete ophiolitic sequences, without a single example of well-preserved major ophiolite nappe such as those in Oman or Newfoundland. Moreover, as the Altaids cover about as much of the Earth’s land area as the Archaean crust, the rarity of indisputable Archaean ophiolite se-quences already appears a less forceful argument against modern-style plate tectonism. Dilek & Po-lat (2008) and Dilek & Furnes (2011) also argued that the structure of the Archaean oceanic crust differed from that of the modern one; for example the Archaean sheeted dyke systems could be rare because spreading rates and magma supply were necessarily not in such a balance that is needed for their generation.

Tonalite-trondhjemite-granodiorite (TTG) gneisses are the major constituent of the Archae-an crust, and more widespread in the Archaean than in younger regions (Condie & Benn 2006). The petrogenesis of HREE-depleted Archaean TTGs have been interpreted in terms of a process that begins with tectonic thickening and subduc-tion of oceanic crust, followed by progressive metamorphism and partial melting of the basaltic rocks, producing TTG melts that for the most part were in equilibrium with anhydrous, eclogitic resi-dues (Rapp et al. 2003). Foley et al. (2002) argued that even the earliest continental crust formed by melting of amphibolites in subduction zone envi-ronments rather than by the melting of eclogite or magnesium-rich amphibolites in lower parts of thick oceanic crust. Nair and Chacko (2008) pro-posed a model where oceanic plateaux served as the nuclei for Archaean cratons, and that TTGs originated in intraoceanic subduction systems where thinner oceanic lithosphere subducted be-neath the thick oceanic plateaux.

On the basis of isotopic age distribution and εNd data, the most important Archaean crust-forming event was at c. 2.70 Ga, when obviously large volumes of continental crust were formed

24


worldwide. In some theories, this flare-up in crust formation was related to a large-scale mantle overturn event, which gave rise to a large number of plumes (Condie 1998, 2000, Condie & Benn 2006). The period 2.75–2.65 Ga was also a period when the pre-existing continental crust was inten-sively reworked in various Archaean provinces, as in the Kola and Karelia Provinces in the Fennos-candian and Superior Province in the Canadian Shield.

Archaean rocks cover roughly one-third of the Precambrian region in the Fennoscandian Shield. Most of these rocks are Neoarchaean (2.8–2.5 Ga). Mesoarchaean (3.2–2.8 Ga) juvenile or re-worked formations are essential constituents of

the bedrock only locally, and Palaeoarchaean rocks (3.6–3.2 Ga) are, overall, rare. The Neoar-chaean 2.75–2.65 Ga event was very strong, in-cluding juvenile TTG magmatism, sedimentation, metamorphism and crustal melting producing granites. This article provides a review of previous studies and presents new data on the geochemis-try, age determinations, metamorphism and pal-aeomagnetism of the Finnish part of the Archae-an Karelia Province, and discusses the magmatic and tectonic processes that could explain its pre-sent constitution and structure, with an emphasis on the Neoarchaean evolution. All ages referred to are U-Pb zircon ages, unless otherwise stated.

GEOLOGICAL SETTING

The Archaean of Fennoscandia is traditionally divided into Norrbotten, Murmansk, Kola, Be-lomorian and Karelia Provinces (Fig. 1, Slabunov et al. 2006, Hölttä et al. 2008). Lobach-Zhuchen-ko et al. (2005) and Slabunov et al. (2006) subdi-vided the Karelia Province into three terranes: the Vodlozero, the Central Karelia and the Western Karelia (Fig. 1), which they observed with sev-eral singular lithological, structural and age char-acters. We have adopted this provincial division, but instead of the term terrane will use subprov-ince to reflect the uncertainty about the nature of the unit contacts. By definition, a tectonostrati-graphic terrane should be a fault-bounded crustal block whose geological history differs from that of the surrounding areas (Jones et al. 1983, Jones 1990). The Karelia subprovinces clearly differ for their geological histories, but there is as yet little evidence that they are all bounded by major ac-cretionary faults.

Important distinctive characteristics of the Karelia subprovinces include that, on the basis of existing age determinations, Mesoarchaean 3.2–2.8 Ga volcanic rocks and granitoids are common in the Vodlozero subprovince, and are also found in the Western Karelia subprovince,

whereas granitoids and greenstones in the Cen-tral Karelia subprovince are Neoarchaean, ≤ 2.8 Ga, although they may locally contain recycled Mesoarchaean crustal material (Vaasjoki et al. 1993). The Belomorian province east of the Kare-lia Province largely consists of 2.93–2.72 Ga TTG gneisses, greenstones and paragneisses, but locally of occurrences of ophiolite-like rocks and eclog-ites that have not been discovered elsewhere in the Archaean parts of the Fennoscandian Shield (Shchipansky et al. 2004, Volodichev et al. 2004). Reflection seismic studies suggest that the Belo-morian province comprises a stack of eastward-plunging subhorizontal nappes and thrusts, which is separated from the underlying Karelia Province by a major detachment zone (Mints et al. 2004).

Hölttä et al. (2012) divided the Finnish part of the Karelia Province into nine large complexes (Ilomantsi, Lentua, Kuopio, Iisalmi, Rautavaara, Manamansalo, Kalpio, Siurua and Ranua) that were possibly not all separately developed tec-tonostratigraphic terranes, but nevertheless have many distinguishable geological features such as differences in age and lithologies when compared with their neighbouring complexes.

Geochemistry of granitoids and migmatitic amphibolites

Figure 2 presents a lithological map of the Finn-ish part of the Karelia Province, showing that most of the area (c. 80%) consists of TTGs. The rest is mainly comprised of supracrustal rocks in greenstone belts and sedimentary gneisses, and

migmatitic amphibolites in enclaves in the gneiss-ic granitoids. On the basis of field observations, the gneissic granitoids include both true orthog-neisses and TTG migmatites with amphibolite and paragneiss mesosomes.

25


Fig. 1. A generalised geological map of the Archaean (a) of the Fennoscandian shield (b, inset), modified after Slabunov et al. (2006) and Hölttä et al. (2008).

26


Granitoids

Archaean granitoids in the Karelia Province can be divided into four main groups on the basis of their field and petrographic characters, major and trace element compositions and age. These are the TTG (tonalite-trondhjemite-gran-odiorite), sanukitoid, QQ (quartz diorite-quartz monzodiorite) and the GGM (granodiorite-granite-monzogranite) groups (Käpyaho et al. 2006, Mikkola et al. 2011a). For this work, 125 samples from granitoids representing various complexes were analysed for their major and trace elements (Appendix 1). Of these samples, 107 were TTGs and 29 from the QQ rocks. The dataset used in this work also includes Archaean rocks from the Rock Geochemical Database of Finland, where the analytical methods applied in this work are described (Rasilainen et al. 2007).

TTGsTTGs represent the majority of the Archaean bedrock in Finland, and understanding of their origin is thus crucial. It is well recognized that Archaean TTGs share many geochemical fea-tures with adakites, i.e. silica-rich volcanic and plutonic rocks at volcanic arcs that are strongly depleted in Y and heavy rare earth elements, low in high-field-strength elements (HFSE) and high in their Sr/Y and La/Yb ratios (Defant & Drum-mond 1990). The chemical criteria for adakites are listed in the original paper by Defant and Drum-mond (1990), and later, for example, in Richards and Kerrich (2007), who use the following criti-cal composition to define adakite: SiO2 ≥ 56 wt%, Al2O3 ≥ 15 wt%, MgO < 3 wt%, Mg number ~ 50, Na2O ≥ wt 3.5 %, K2O ≤ 3 wt%, K2O/Na2O ~ 0.42, Rb ≤ 65 ppm, Sr ≥ 400 ppm, Y ≤ 18 ppm, Yb ≤ 1.9 ppm, Ni ≥ 20 ppm, Cr ≥ 30 ppm, Sr/Y ≥ 20 and LaN/YbN ≥ 20. Martin and Moyen (2003) divided the adakites into the low silica (<60 wt% SiO2) and high silica (HSA, >60 wt% SiO2) groups, re-lating the HSA group to slab melting with some interaction with mantle-wedge peridotite and the LSA group to melting of wedge peridotites be-forehand metasomatised by slab melts.

Most TTGs in the Karelia Province fulfil the adakite criteria, apart from the Cr and Ni con-tents, which are normally below the detection limits of the XRF analysis used, 30 and 20 ppm, respectively. Mg contents are also normally low, in most of the TTGs in the range of 0.35–0.45, which means that they have gained minor com-ponents from mantle peridotites (Halla 2005, Lobach-Zhuchenko et al. 2005, 2008). Halla et al. (2009) divided the TTGs into two major groups,

low-HREE (heavy rare earth elements) and high-HREE TTGs, which obviously originated at dif-ferent lithospheric depths. Here we follow the proposal of Halla et al. (2009), but instead of the HREE content – which depends, besides melting pressure, on the source composition and post-melting fractionation – we use the (La/Yb)N ratio, as low-HREE rocks generally have high (La/Yb)N ratios. We further divide the low-HREE group into Eu-positive and Eu-negative subgroups. Our dataset demonstrates that the two TTG groups are not separated in compositional space but rath-er represent end members between which there is full compositional continuity.

Moyen (2011) studied a large set of analyses from rocks generally regarded as TTGs, ultimately dividing these rocks into four groups: the potassic group and the high-, medium- and low-pressure groups of ‘proper’ juvenile TTGs. The high-pres-sure group, equivalent to the low HREE group, has TTGs with high Al2O3, Na2O, Sr and low Y, Yb, Nb and Ta. The TTGs of the low-pressure group, equivalent to the high-HREE group, show opposite values in these respects. The potassic group rocks that show enrichment in K and LIL elements are thought by Moyen (2011) to have formed by melting of pre-existing crustal rocks. If the criteria for true TTGs include K2O/Na2O < 0.5 (Martin et al. 2005), c. 20% of our samples col-lected in the field as TTG suite rocks would actui-ally belong to the potassic or transitional TTGs, as these types of rocks were referred to by Cham-pion and Smithies (2007). On the other hand, this is a definitional problem, because in granodiorites the K2O/Na2O ratio is typically 0.5–1, and rocks whose K2O/Na2O is < 0.5 are tonalites and trond-hjemites, i.e. TTs rather than TTGs.

The rocks in the low-HREE group are trond-hjemitic and tonalitic when classified using nor-mative compositions and the QAPF diagram in Streckeisen (1973) or the Ab-An-Or diagram in O’Connor (1965, Fig. 3). In the Eu-negative sub-group, SiO2 is generally 62–74 wt%, mg# 30–55 and Al2O3 15–17 wt%. Most of the samples have fractionated REE patterns with low HREE and high Sr/Y (median 81). They also have high LaN/YbN ratios of 20–120 with a median of 49, show-ing negative Eu anomalies (Fig. 5) and low abun-dances of compatible elements.

SiO2 in the Eu-positive, low-HREE TTGs typi-cally varies from 68–76 wt%, and they often have low abundances of FeO and MgO, which is re-flected in their near-white to light grey colour in outcrops and samples. Mg# is generally 28–55 and Al2O3 14.5–17.5 wt%. These TTGs are associated with negative magnetic anomalies on airborne

27


Fig. 2. A generalised geological map of the Finnish part of the Karelia Province. The inset shows the location of the map area in Finland. Basemap © National Land Survey of Finland, licence no 13/MML/12.

28


Fig. 3. A normative Ab-An-Or diagram (O’Connor 1965) for TTGs and QQs. Open triangles = low-HREE TTGs, black tri-angles = low-HREE, Eu-positive TTGs, crosses = high-HREE TTGs, grey dots = QQs, black dots = orthopyroxene-bearing QQs (enderbites).

55 60 65 70 75

14

16

18

20

SiO2

Al 2

O3

Fig. 4. Al2O3 vs. SiO2 in TTGs and QQs. Symbols are as in Fig. 3.

29


Fig. 5. Trace element patterns of TTGs: a, b = high HREE group, c, d = low HREE group, e, f = Eu-positive group. Diagrams represent 255 analyses where the K2O/Na2O ratio is < 0.5, taken from the Rock Geochemical Database of Finland (Rasilainen et al. 2007). Normalising factors for a, c and e are from Boynton (1984) and for b, d and f from Thompson (1982). The shaded area is for all data.

30


magnetic maps, and especially in the northern part of the Karelia Province in Finland they cov-er large areas (Fig. 2). Most samples show, apart from positive Eu anomalies, strongly fractionated REE patterns with HREE mostly below the detec-tion limits, low Y, Sc and Nb, high Sr/Y, LaN/YbN and Zr/Sm ratios and low abundances of com-patible elements (Figs. 5–7). In outcrops, part of these rocks show diatexitic migmatite structures and seem to represent almost complete fusion of amphibolites, but there are also many occurrenc-es of this group that appear to be homogeneous orthogneisses.

The high-HREE group is normatively grano-dioritic and tonalitic. SiO2 is c. 60–72 wt%, mg# generally 30–55 and Al2O3 15–17 wt%. Al2O3/SiO2

is generally lower in samples of this than the other TTG groups (Fig. 4). Rocks in this group have low Sr/Y ratios (median 22) and higher abundances of compatible elements and HREE than the other TTGs. The LaN/YbN is < 20 with a median of 10. On average, the high-HREE group has higher Nb contents (c. 5–15 ppm) than the low HREE group (c. 1–8 ppm).

SanukitoidsSanukitoid granitoids (most commonly grano-di-orites) with low silica, high K, Ba, Sr and elevated Mg, Cr and Ni contents are relatively common in the Western and Central Karelia subprovinces. As a group they postdate the TTGs, being generally 2.74–2.72 Ga (Fig. 21). These sanukitoids resem-

0 5 10 15 20

05

01

00

150

0 5 10 15 20

050

100

150

La/YbN

YbN

K2O/Na2O<0.5 K2O/Na2O>0.5a b

0 10 20 30 40 50

01

00

20

03

00

40

0

0 10 20 30 40 50

01

00

20

03

00

40

0

Sr/Y

Y

YbN

Y

K2O/Na2O<0.5 K2O/Na2O>0.5c d

Fig. 6. Chondrite-normalized La/Yb vs Yb ratios and Sr/Y vs Y ratios for “true” (a, c) and potassic (b, d) TTGs. Normalising factors are from Thompson (1982). Symbols as in Fig. 3.

31


ble in several aspects Mesozoic mantle-derived high Ba-Sr granitoids in Scotland (Fowler et al. 2008, Halla et al. 2009). They have been related to melting of subcontinental metasomatized man-tle, possibly induced by late- or postorogenic slab breakoff (Lobach-Zhuchenko et al. 2005, 2008, Halla 2005, Halla et al. 2009, Heilimo et al. 2010, 2012). However, given that most of these sanuki-toids emplaced shortly before the main phases of metamorphism and deformation (2.71–2.64 Ga), they should rather be classified as late orogenic. The geochemical data for Karelian sanukitoids are found in Heilimo et al. (2010), U-Pb zircon ages in Heilimo et al. (2011) and Hf, Nd, Pb and O isotope geochemistry in Heilimo et al. (2013).

QQAnother important group of non-TTG grani-toids comprises rocks whose normative composi-tion is mostly quartz dioritic and quartz monzo-nitic, but locally also dioritic and monzodioritic. Rocks belonging to this QQ group are especially found in the Western Karelia subprovince. Most QQ intrusions are located west of the sanukitoids described above, but whether there is a genetic link between the sanukitoid and QQ groups is not yet clear. The QQs include the enderbites in the Iisalmi complex (Hölttä 1997), the Ranua di-orite in the Ranua complex (Mutanen & Huhma 2003) and some smaller plutons in Ranua and in the northern part of the Lentua complex (Mik-kola 2008, Mikkola et al. 2011a). The QQs have zircon U-Pb ages close to 2.70 Ga apart from the 2.68 Ga Rokanmäki intrusion (Paavola 1999) in the Rautavaara complex . εNd values at 2.7 Ga are

positive, for example +0.2 and +1 in the two ana-lyzed enderbites of the Iisalmi complex (Hölttä et al. 2000) and +0.8 in the Ranua diorite (Mutanen & Huhma 2003). Many compositional features in these rocks also fulfil the definition of adak-ites, as SiO2 is in most analysed samples 52–62 wt%, Al2O3 a high 15.4–20.1 wt%, MgO 2.5–4.0 wt%, mg# 44–54, Na2O 3.3–5.4 wt%, K2O 0.8–1.8 wt%, Rb 13–52 ppm, Sr 630–1170 ppm, Sr/Y 21–80, Ba 200–800 ppm, Y < 18 ppm and Yb < 1.9 ppm. Furthermore, Cr in most samples is > 30 ppm and Ni >20 ppm, except for values of 10–28 ppm and 6–13 ppm, respectively, in the Ranua diorite. However, the QQs have only moderately fractionated REE patterns with LaN/YbN ratios of 6–15, and the enderbites in the Iisalmi area, as well as the Naimakangas quartz diorites (located in the Iisalmi complex north of the enderbites) and some diorites in Ranua, have a typically flat HREE (Fig. 8). This type of REE pattern is a distinctive feature of the enderbites and was not observed in any other Archaean igneous rocks, apart from 2.74 Ga alkaline rocks in Suomus-salmi, which have a similar REE distribution but generally higher REE abundances (Mikkola et al. 2011b). The enderbites have lower Rb, U and Th contents than the other quartz diorites, probably because of the loss in these elements during the granulite facies metamorphism that they under-went at 2.7–2.6 Ga (Mänttäri & Hölttä 2002). The Ranua diorite has syenogabbro and alkali gabbro inclusions that have higher P2O5 and REE contents than the enclosing diorites (Fig. 9). Al-though mafic, the gabbroic inclusions do not con-tain more Cr and Ni than the host diorite.

0.0 0.5 1.0 1.5 2.0

01

23

4

0.0 0.5 1.0 1.5 2.0

01

23

4Eu/Eu*

Sm/ZrN

K2O/Na2O <0.5 K2O/Na2O >0.5a b

Fig. 7. Eu/Eu* vs. chondrite-normalised Zr/Sm for “true” (a) and potassic (b) TTGs. Normalising factors are from Thompson (1982). Symbols as in Fig. 3.

32


Ba Th K Nb La Sr P Zr Hf Ti Tb Y Yb

0.1

110

100

1000

0.1

110

100

1000

0.1

110

100

1000

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

110

100

1000

Sam

ple

/ R

EE

chondrite


110

100

1000

Sam

ple

/ R

EE

chondrite


11

01

00

10

00

Sam

ple

/ R

EE

chondrite

Sam

ple

/ chondrite

S

am

ple

/ ch

ondrite

S

am

ple

/ ch

ondrite

Rb Ta Ce Nd Sm Tm

Ba Th K Nb La Sr P Zr Hf Ti Tb Y YbRb Ta Ce Nd Sm Tm

Ba Th K Nb La Sr P Zr Hf Ti Tb Y YbRb Ta Ce Nd Sm Tm

a b

c d

e f

Fig. 8. Trace element patterns of QQs. a, b = Ranua, black triangles denote alkali gabbroic inclusions in diorite-quartz diorite; c, d = enderbites of the Iisalmi complex; e,f = Naimakangas. The shaded area is for all data. Normalising factors are as in Fig. 5

33


(2) (3a) (3b) (4) (5a) (5b)

(6*) (7*) (8*) (9*) (10a*) (10b*)

(6) (7) (8) (9) (10a) (10b)

0 20 40 60 80 100

01

02

03

04

05

0

ANOR

Q’

50 55 60 65 70 75 80

0.4

0.5

0.6

0.7

0.8

0.9

1.0

50 55 60 65 70 75 80

02

46

81

01

2

10 15 20 25 30

05

10

15

20

25

30

6 8 10 12 14 16 1820

02

46

81

01

21

4

Al O +FeO+MgO+TiO2 3 2

AlO

/(Fe

O+

MgO

+T

iO)

23

2

Na O+K O+FeO+MgO+TiO2 2 2

(Na

O+

KO

)/(F

eO+

MgO

+T

iO)

22

2

SiO2

Na

O+

KO

-CaO

22

alkalic

calcicalkali

-calc

icca

lc-alk

alic

SiO2

ferroan

magnesian

tot

tot

FeO

/(Fe

O+

MgO

)

Partial melting of

greywacke

pelite

amphibolite

a

c d

e f

6 7 8 9 10 11 12 13

0.1

0.5

15

10

50

100

Na O+K O+CaO2 2

(Na

O+

KO

)/C

aO2

2

b

Fig. 9. Compositions of the granodiorite-granite-monzogranite series rocks. a Q’-ANOR diagram of Streckeisen & Le Maitre (1979), fields: 2 = alkali feldspar granite, 3 = granite, 4 = granodiorite, 5 = tonalite, 6* = quartz alkali feldspar syenite, 7* = quartz syenite, 8* = quartz monzonite, 9* = quartz monzodiorite/quartz monzogabbro, 10* = quartz diorite/quartz gabbro, 6 = alkali feldspar syenite, 7 = syenite, 8 = monzonite, 9 = monzodiorite/monzogabbro, 10 = diorite/gabbro. b,c = classifica-tions after Frost (2001), d–f : diagrams after Patiño Douce (1999). Symbols: open circles = high HREE GGMs, open triangles = medium HREE GGMs, black circles = low HREE GGMs, diamonds = low HREE GGMs without Eu anomaly, black triangles = low HREE GGMs with positive Eu/Eu*.

34


GGMGranodiorite-granite-monzogranite (GGM) suite rocks dated to 2.73–2.66 Ga are the youngest Neoarchaean rocks occurring in large volumes in the Western Karelia subprovince (Käpyaho et al. 2006). They are relatively weakly deformed, red-dish and medium- to coarse-grained rocks. The diagrams in Figures 9–10 illustrate some of the prime geochemical characteristics of the GGM granites. Analyses for the plots are taken from the Rock Geochemical Database of Finland (Ra-silainen et al. 2007), and they are also presented in Appendix 1. Most of these data are for gran-ites, which are peraluminous and metaluminous, and according to the classification by Frost et al. (2001) mostly magnesian, calc-alkalic and alkali-calcic (Fig. 9). In the classification schema by Patiño Douce (1999) based on the major ele-

ments, these granites have compositions that cor-respond to the experimental dehydration melting products of felsic pelites and greywackes, and some may have reacted with basaltic rocks (Figs. 9d–f, 10). Many of the granites have highly frac-tionated, HREE-depleted patterns with negative or no Eu anomalies, but some are less fraction-ated with relatively high HREE. In Figure 11, the GGMs are classified on the basis of their REE distributions into five groups: high-HREE GGMs with a low Gd/YbN ratio, medium-HREE GGMs, low-HREE GGMs, low-HREE GGMs without an Eu anomaly and low-HREE GGMs with a positive Eu/Eu*. At least part of the gran-ites could represent the melting products of sedi-mentary gneisses. On the other hand, according to experimental studies, dehydration melting of sodic TTG gneisses can also produce granitic to

10 12 14 16 18 20 22 24

0.0

0.1

0.2

0.3

0.4

0 5 10 15

0.0

0.5

1.0

1.5

0.20 0.25 0.30 0.35 0.40

0.8

1.0

1.2

1.4

1.6

CaO+Al O2 3

CaO

/Al O 2

3

CaO+FeO+MgO+TiO2

CaO

/(Fe

O+

MgO

+T

iO)

2

Al O +CaO+Na O+K O2 3 2 2

AlO

/(C

aO+

Na

O+

KO

)2

32

2

HP

LP

HP

LP

R

peraluminous

metaluminous

Dehydration melting of

felsic pelites

greywackes

mafic pelites

a b

c

Fig. 10. Compositions of GGM rocks plotted on the diagrams after Patiño Douce (1999). The curves model the melt compo-sitions that result when high-Al olivine tholeiite is hybridized with metapelite: HP = in high pressure; LP = in low pressure; R = in melt-restite mixing without the addition of basaltic components. Symbols as in Fig. 9.

35


La Ce Pr NdPm Sm Eu Gd Tb Dy Ho Er TmYb Lu

0.1

110

100

1000

Sam

ple/

REE

cho

ndri

te


0.1

110

100

1000


0.1

110

100

1000

Sam

ple/

REE

cho

ndri

te


0.1

110

100

1000


0.1

110

100

1000

Sam

ple

/ R

EE c

hond

rite

a b

c d

e

Fig. 11. Rare earth element patterns of the various GGM rocks. Symbols as in Fig. 9. Normalising factors are after Boynton (1984).

36


granodioritic melts (Patiño Douce 2004, Watkins et al. 2007). Skjerlie et al. (1993) have shown ex-perimentally that when interlayered, the melt productivity of tonalite and pelite increases via the interchange of components that lower the re-quired melting temperatures. Anatectic granites therefore tend to contain material from two or more different source rocks, which is reflected in their isotopic and chemical compositions (Skjer-lie et al. 1993). This could also be the case with the Archaean GGMs, which could represent the melting products of TTGs and paragneisses, and mixing of the derived melts with contemporane-ous mafic magmas. The range in εNd (2700 Ma) values of the CGMs is c. -1.5 to +1.0, indicat-ing that some of them might represent the melt-ing of juvenile 2.72–2.78 TTGs, whereas others could originate from older material. However, in the Suomussalmi area, the average δ18O values of zircon from GGMs are normally only slight-ly higher (6.42 ± 0.10) than that of the TTGs, 6.10 ± 0.19. This means that at least in Suomus-salmi the GGMs do not necessarily have a signifi-cant sedimentary input in their source but rather represent melting products of TTGs (Mikkola et al. 2012). However, in the Suomussalmi area the abundance of exposed sedimentary gneisses is also low, while in other areas they may have had a more significant contribution to GGM genesis.

Amphibolites in gneissic complexes

Amphibolites are a ubiquitous component of nearly all of the studied migmatitic TTG com-plexes, in which they can typically be found as layers and inclusions whose widths vary from a few tens of centimetres to tens of metres. Nor-mally, the gneiss-associated amphibolites are all migmatized, the volume of felsic neosome rang-ing in the exposures from < 10% up to c. 90% (Fig. 12). Extensively melted and deformed am-phibolites closely resemble strongly deformed, plutonic TTGs with amphibolite rafts, making their distinction difficult. In metatexitic amphi-bolites, palaeosomes have mostly amphibolite facies mineral assemblages, typically hornblende-plagioclase-quartz, often with retrograde epidote. In granulite facies areas, amphibolites often have coexisting orthopyroxene and clinopyroxene. Garnet-bearing two-pyroxene mafic and interme-diate granulites, which are common in the Iisalmi complex, represent high-temperature-medium pressure equivalents of the common hornblende amphibolites.

The ages of the amphibolites are problematic to resolve, because they often appear to contain

predominantly metamorphic zircon grains (e.g. Mutanen & Huhma 2003). Intermediate granu-lites and amphibolites in the Iisalmi complex have been dated for their protoliths at c. 3.2 Ga (Paavola 1986, Mänttäri & Hölttä 2002, Lauri et al. 2011), but this complex is older overall than most other areas in the western part of the Kare-lia Province.

In this work, 73 amphibolite samples were col-lected from all Archaean gneissic complexes and were analysed for their major and trace element compositions. The data are presented in Appen-dix 1. On the basis of major element composi-tion, and using the TAS classification, the amphi-bolites are mostly basalts and andesitic basalts. Some amphibolites are andesitic and some have a slightly alkaline character. In the Jensen cation plot, most compositions are in the field of high-Mg tholeiites, and some even in the komatiitic ba-salt field, the latter probably because of cumulus olivine. The Al2O3 contents vary mostly from c. 13–16 wt%. In the komatiitic basalts, the Al2O3 content is c. 10–12 wt%. MgO comprises c. 4–10 wt% in basaltic rocks, c. 11–14 wt% in komatiitic basalts and c. 3–6 wt% in andesites.

Basaltic amphibolites (SiO2 < 52 wt%) fall into two main groups on the basis of their trace ele-ment contents. Samples of the first group have flat or LREE-depleted trace element patterns, resembling those of the present mid-ocean ridge basalts. Further characteristics of these samples are high (Nb/La)N ratios, low Zr/Y ratios and high Ni and Cr contents (Hölttä 1997, Nehring et al. 2009). Samples of the second group are enriched in LILE and LREE (Fig. 13) and have lower Nb/LaN ratios and higher Zr/Y ratios than those in the first group. Compatible elements, especially Ni but also Cr, are lower in the LREE-enriched than in the group of LREE-depleted samples (Fig. 14). Andesitic amphibolites (SiO2 c. 52–60 wt%) have similar flat to LREE-enriched trace element pat-terns to the basalts (Fig. 15). However, unlike the basalts, the (La/Yb)N ratio normally increases and the abundance of compatible elements decreases as a function of increasing SiO2. Cr and Ni con-tents are higher in the komatiitic basalts than in basaltic and andesitic amphibolites (Fig. 14). Some of the komatiitic basalts are also enriched in LREE (Fig. 13).

Condie (2005) used the high field strength ele-ment (HFSE) ratios of Archaean basalts to dem-onstrate their possible mantle source domains, as-suming that their magmatectonic framework was broadly similar to that of young oceanic basalts. He noted that on the basis of the Nb/Th, Zr/Nb, Nb/Y and Zr/Y ratios, most non-arc-type Archae-

37


a b

c d

e f

Fig. 12. Field photographs of migmatitic amphibolites of the Ranua complex. Map coordinates of the photograph sites (Finnish national grid, in KKJ zone 3/YKJ): a: 7274813, 3413614; b: 7271283, 3419703; c, d: 7265242, 3424052; e: 7280653, 3412406; f: 7286789, 3422595.

an basalts from greenstone belts resemble oceanic plateau basalts, which are thought to originate from plumes variably comprising deep primitive and shallow depleted mantle. Figure 16 shows a plot of Nb/Y vs. Zr/Y for the basaltic amphibo-lites in the Finnish part of the Karelia Province. Given the depletion of granulite facies rocks in

U and Th, thorium-based ratios are probably use-less for the high-grade migmatitic amphibolites. As Zr/Nb ratios in all samples of the amphibo-lites are c. 10–30, they probably do not contain recycled oceanic lithospheric material. Most of the analysed amphibolites have LREE-depleted or flat REE patterns, relatively low Zr/Y ratios of

38


Sam

ple

/ P

rim

itive

Mantle

0

.11

10

10

01

00

0

Sam

ple

/ P

rim

itive

Mantle

0.1

110

100

1000

Sam

ple

/ P

rim

itiv

e M

antle

Rb Th Nb Ce Sr Nd Sm Ti Y Lu

0.1

110

100

1000

Sam

ple

/ R

EE

chondrite

La Pr Nd Eu Tb Ho Er Yb Lu

11

01

00

10

00

Sa

mp

le/

RE

E c

ho

nd

rite

11

01

00

10

00

Sa

mp

le/

RE

E c

ho

nd

rite

11

01

00

10

00

Ce Sm Gd Dy TmLa Pr Nd Eu Tb Ho Er Yb LuCe Sm Gd Dy Tm

La Pr Nd Eu Tb Ho Er Yb LuCe Sm Gd Dy Tm

La Pr Nd Eu Tb Ho Er Yb LuCe Sm Gd Dy Tm

Ba U La Pr P Zr Eu Dy Yb

Rb Th Nb Ce Sr Nd Sm Ti Y LuBa U La Pr P Zr Eu Dy Yb

Rb Th Nb Ce Sr Nd Sm Ti Y LuBa U La Pr P Zr Eu Dy Yb

a b

c d

e f

Fig. 13. Trace element patterns of basaltic amphibolites. a, b = LREE-depleted group; c, d = LREE-enriched group; e, f = komatiitic basalts. Normalising factors for a, c and e are from Boynton (1984) and for b, d and f from Sun & McDonough (1989).

39


45 50 55 60 65 70

0200

400

600

800

1000

SiO245 50 55 60 65 70

0100

200

300

400

NiC

r

SiO2

LREE low basalts

LREE high basalts

LREE low basalts

LREE high basalts

komatiitic basaltskomatiitic basalts

a b

Fig. 14. Cr and Ni vs. SiO2 in LREE-depleted basaltic amphibolites (filled circles), LREE-enriched basaltic amphibolites (filled triangles), andesitic amphibolites (open triangles) and dacitic and rhyolitic amphibolites (crosses). Black symbols de-note granulite facies rocks in the Iisalmi and Rautavaara complexes.

Rb Ba Th U Nb La Ce Pr Sr P Nd Zr Sm Eu Ti Dy Y Yb Lu

11

01

00

10

00

Sa

mp

le/

Prim

itive

Ma

ntle

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

11

01

00

10

00

Sa

mp

le/

RE

E c

ho

nd

rite

Fig. 15. Trace element patterns of andesitic amphibolites. Black triangles denote granulite facies rocks in the Iisalmi and Rau-tavaara complexes. Normalising factors as in Fig. 13.

40


c. 1–2, and tendency to plot between the primi-tive and deep depleted mantle compositions in the diagram in Figure 16. A smaller number of the amphibolites are LREE enriched, have Zr/Y ratios of c. 3–5 and define on the Nb/Y vs. Zr/Y diagram a trend towards enriched sources that could be the lithospheric mantle or the continen-tal crust. In the field, some of the amphibolites show dyke-like relationships with the host TTGs (Fig. 12f), suggesting that amphibolites in the sec-ond group could represent metamorphosed and deformed dykes that have chemically reacted with the TTG crust. This is supported by the higher

LILE contents in these amphibolites compared with the first group of amphibolites, which could be restites of the plateau basalts after melting that produced the TTGs.

In terms of primitive mantle-normalized con-tents, granulite facies rocks are depleted, and am-phibolite facies rocks are enriched in U and Th, and there is less enrichment of Ba and especially Rb in granulite than in amphibolite facies rocks (Nehring et al. 2009). This probably reflects a higher degree of melting in granulite facies rocks compared with amphibolites (Nehring et al. 2009).

Greenstone belts

The Karelia Province includes at least sixteen, generally NNW-trending greenstone belts (Slabu-nov et al. 2006). Case studies have proposed dis-tinct formative settings for the individual belts, i.e. an oceanic plateau setting for the Kostomuk-sha belt (Puchtel et al. 1998), an island arc setting

for the Sumozero-Kenozero belt (Puchtel et al. 1999) and a continental rift setting for the Suo-mussalmi-Kuhmo-Tipasjärvi and Matkalahta belts (Luukkonen 1992, Papunen et al. 2009, Kozhevnikov et al. 2006). The Finnish part of the Karelia Province contains three major green-

DEP

1 2 5 10 20

0.0

10

.05

0.1

00

.50

1.0

05

.00

NMORB

Arc

PM

EN

REC

DM

Oceanic PlateauBasalt

PLUME SOURCES

NON-PLUME SOURCES

Zr/Y

Nb/Y

Fig. 16. Nb/Y vs. Zr/Y of basaltic amphibolites. Black circles = LREE depleted basalts, triangles = LREE enriched basalts, grey squares = komatiitic basalts. Abbreviations: PM, primitive mantle; DM, shallow depleted mantle; ARC, arc-related ba-salts; NMORB, normal ocean ridge basalt; DEP, deep depleted mantle; EN, enriched component; REC, recycled component.

41


stone belts, the Suomussalmi-Kuhmo-Tipasjärvi belt, the Ilomantsi belt and the Oijärvi belt (Fig. 2). We have new high-precision geochemical data for komatiitic and associated basaltic rocks from the two first named and largest of the belts (Ap-pendix 1). Komatiites are potentially particularly useful in constraining the geotectonic setting of magmatism, because they represent primitive magmas formed during large degree (>30%) melting of the mantle. Consequently, komatiites tend to have low concentrations of incompatible elements, and it is only interaction of the komati-ites with lithospheric materials during magma ascent and emplacement (and post-emplacement alteration) that may result in marked decoupling of compatible and incompatible elements.

Kuhmo greenstone belt

The Kuhmo greenstone belt forms the central part of the c. 220-km-long Suomussalmi-Kuhmo-Tipasjärvi greenstone belt (Fig. 2). The suprac-rustal succession in the Kuhmo belt starts with rhyolitic-dacitic lavas and pyroclastics, whose

depositional basement and original thickness is unknown. Felsic volcanic rocks occur in two age groups, 2.84–2.82 Ga and c. 2.80 Ga (Huhma et al. 2012a). The felsic volcanics are overlain by an up to one-kilometre-thick sequence of tholeiitic pillow lavas and hyaloclastites, with sporadic lay-ers of Algoma-type BIF and hydrothermal Mg-Fe precipitates in the middle part of the sequence. The tholeitic strata are overlain by a sequence of komatiites (total thickness ~ 500 m), komatiitic basalts (~ 300 m), interlayered high-Cr basalts (~ 250 m) and komatiites, high-Cr basalts (~ 250 m) and finally pyroclastic intermediate-mafic vol-canics (Papunen et al. 1999, 2009).

The Kuhmo greenstone belt is bounded by TTGs, sanukitoids and GGM-suite plutons. Several previous studies have suggested that the Kuhmo greenstone succession was deposited on older continental crust represented by the TTGs (Martin et al. 1984, Luukkonen 1992, Papunen et al. 1999, 2009). However, no unconformity or superposition relationship between the TTGs and the greenstone belt supracrustals has ever been demonstrated. Nor is the concept of an old sialic

60 65 70 75 80 85 90

51

01

52

02

53

03

54

0

AlO

/TiO

23

2

mg#

Fig. 17. Al2O3/TiO2 vs. mg# of komatiites (black symbols) and komatiitic basalts (grey symbols) in Kuhmo (diamonds), Ilo-mantsi (filled circles) and Kovero (filled triangles).

42


basement supported by the more recent isotope geochemical and age data (e.g. Käpyaho et al. 2006, Huhma et al. 2012a). With the exception of one sample from the mesosome of a migma-tite from Lylyvaara, c. 30 km east of the Kuhmo greenstone belt (2942 ± 6 Ma; Käpyaho et al. 2007), all samples from the surrounding TTGs yield crystallisation ages younger than the vol-canic rocks of the greenstone belt. Furthermore, Käpyaho et al. (2006) concluded, based on an extensive Sm-Nd isotope study, that the plutonic rocks in the Kuhmo area represent relatively juve-nile material without a major input from signifi-cantly older crust. Neither do the εNd from +1.2 to +2.4 of intermediate and felsic volcanic rocks in Kuhmo (Huhma et al. 2012b) indicate that they would contain significant amounts of older crus-tal material, as one could expect if they originated in a narrow continental rift as suggested by Papu-nen et al. (2009). However, Mesoarchaean, 2.94 Ga felsic volcanic rocks with negative εNd values exist in the Suomussalmi belt north of the Kuhmo belt (Huhma et al. 2012a, b). This difference sug-gests that the Suomussalmi and Kuhmo belts may represent separate volcanic belts that were juxta-posed just during the Neoarchaean terminal ac-cretional/collisional events.

Ilomantsi greenstone belt

The supracrustal sequence in the Ilomantsi greenstone belt is dominated by sedimentary rocks intercalated with less abundant komati-ites, tholeiites, low-Ti tholeiites, andesites, dac-ites and banded iron formations. The lowermost unit starts with mafic pillow lavas, but predomi-nantly consists of felsic pyroclastic and epiclastic sedimentary rocks. The depositional environment was dominated by two distinct but overlapping felsic volcanic complexes, probably locally suba-erial, but that nevertheless developed within mostly relatively deep, turbidite-dominated ba-sins (Sorjonen-Ward 1993). Thin tholeiitic inter-calations and komatiitic sheet flows occur in the upper part of the succession, typically associated with banded iron formations. The komatiites are generally massive recrystallized in structure, and only locally preserve such relict features as cumu-lus textures or flow top breccias (O´Brien et al. 1993). No primary silicate minerals are preserved in the komatiites, as they have been pervasively altered and recrystallised to tremolite-chlorite-serpentine rocks or chlorite-talc-rich schists. Lo-cally, the komatiites are demonstrably intercalated with felsic volcanic rocks.

Vaasjoki et al. (1993) reported a TIMS U-Pb

age of 2754 ± 6 Ma on zircon from a plagioclase-phyric andesite that represents the stratigraphi-cally lowermost units of the Ilomantsi green-stone belt. The majority of detrital zircon grains in the nearby metasediments are of the same age (Huhma et al. 2012a). Previous studies on the Ilo-mantsi belt have documented a close relationship between volcanism, sedimentation, deformation and pluton emplacement (Sorjonen-Ward 1993) implying rapid c. 2.75 Ga crustal growth in the region. All exposed contacts between supracrus-tal rocks and granitoids have been interpreted to be intrusive (Sorjonen-Ward & Luukkonen 2005), and the granitoids cannot therefore represent the basement to the Ilomantsi greenstone belt, nor a dominant source of the material in the supracrus-tal sequences.

Chemical composition of komatiites in Kuhmo and Ilomantsi

Komatiitic rocks from Kuhmo and Ilomantsi show generally similar major element compositions (Ap-pendix 1), but differ significantly in terms of their trace element concentrations. Both suites have the characteristics of the aluminium-undepleted, Munro-type komatiites, having average Al2O3/TiO2 ratios of c. 18.9 (Kuhmo) and 17.4 (Ilomant-si), but there is considerable scatter, particularly in the Ilomantsi data. Komatiites and komatiitic ba-salts of the Kovero greenstone belt, which flanks the Ilomantsi belt in the SW, have high Al2O3/TiO2 ratios, reflecting their low TiO2 content at a given Al2O3 and MgO level (Figs. 17–18). In both the Il-omantsi and Kuhmo lavas, Ni, Co and Cr increase as a function of MgO and Mg# in a way that is indicative of low-pressure fractionation of olivine and chromite being the main factor controlling compositional variation. This is consistent with the relatively differentiated nature of the lavas, as chromite is usually undersaturated in komatiites with > c. 25% MgO (Barnes & Roeder 2001). Ko-vero komatiites seem to differ from the Ilomantsi and Kuhmo komatiites, having overall higher Cr/MgO ratios (Fig. 18).

Komatiites from the Kuhmo and Ilomantsi belts show distinct variation in their incompat-ible trace element concentrations. The Kuhmo komatiites and komatiitic basalts have generally flat primitive mantle normalised patterns show-ing only moderate depletion in LREE (Fig. 19), as is common for Al-undepleted komatiites. In contrast, Ilomantsi komatiites have highly frac-tionated patterns with high LREE/HREE ratios and distinct negative Nb-Ta and Ti-anomalies. The close similarity in trace element patterns

43


10 15 20 25 30 35

0.2

0.4

0.6

0.8

1.0

10 15 20 25 30 35

01000

2000

3000

4000

5000

6000

7000

10 15 20 25 30 35

500

1000

1500

2000

10 15 20 25 30 35

40

60

80

100

120

140

TiO2

NiCo

Cr

MgO

MgOMgO

MgO

Fig. 18. TiO2 (wt%), Cr, Ni and Co (ppm) vs. MgO of komatiites and komatiitic basalts in Kuhmo, Ilomantsi and Kovero. Symbols as in Fig. 17.

between the komatiites and associated rhyolites and dacites (O’Brien et al. 1993) is a clear indi-cation of extensive interaction of the komatiites with the felsic volcanics. Interestingly, the komati-itic basalts from Ilomantsi show less fractionat-ed incompatible trace element patterns than the komatiites, which is inconsistent with derivation of the basalts from the komatiites by crystal frac-tionation. A likely explanation is that the komati-itic basalts evolved from the komatiitic magma already prior to the eruption, within transient storage chamber(s) at depth. During subsequent eruptions the komatiites assimilated more felsic volcanics than the komatiitic basalts, possibly due to their higher eruption temperatures.

Owing to post-eruption alteration, obviously in multiple episodes, the Kuhmo and Ilomantsi komatiites are disturbed to various degrees in their isotope systems. For example, in a Sm-Nd isotope study by Gruau et al. (1992), it has been shown that the Kuhmo komatiites produce a Sm-Nd isochron yielding an age of c. 1.9 Ga, indica-tive of resetting of the Sm-Nd isotope system of these Archaean rocks during Proterozoic meta-morphism. We have also conducted Sm-Nd stud-ies for both Kuhmo and Ilomantsi komatiites, for most part on samples that we believe represented the least altered materials (Huhma et al. 2012b). The results are nevertheless broadly similar to those of Gruau et al. (1992). Therefore, Sm-Nd

44



0.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.1

110

100


0.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.1

11

01

00


0.0

10.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.0

10.1

110

100

Kuhmo - komatiites Kuhmo - komatiitic basalts

Ilomantsi - komatiites Ilomantsi - komatiitic basalts

Kovero - komatiites Kovero - komatiitic basalts

Fig. 19. Primitive mantle-normalized trace element patterns of komatiites and komatiitic basalts in Kuhmo, Ilomantsi and Kovero. Normalising factors are from Sun and McDonough (1989).

45


isotope analyses for these rocks are unlikely to provide any precise information on their mantle source domains.

Condie (2005) has shown that using ratios of highly immobile elements such as Nb/Th, Zr/Nb, Zr/Y and Nb/Y it is possible to characterise at least some isotopically distinct mantle domains, as they are inferred for young oceanic basalts.. In terms of Nb/Y and Zr/Y ratios, Kuhmo komatiites plot close to the demarcation line between plume and non-plume source compositions (Fig. 20c). Most samples cluster between primitive mantle (PM) and shallow depleted mantle (DM) compositions, and there are many plottings towards the deep depleted plume component (DEP). In the Zr/Nb vs. Nb/Th plot (Fig. 20d), the Kuhmo komatiites also plot close to the oceanic plateau basalts, but at somewhat higher Zr/Y values, probably indicat-ing minor pre-eruption fractionation of chromite (cf. sita). Overall, the Kuhmo komatiites show an

affinity to oceanic plateau basalts derived from a slightly depleted primitive mantle (PM)-type source, with a minor deep plume signature. Im-portantly, these komatiites clearly have not been derived from a depleted MORB-type source, and there is also little indication of enriched and recy-cled mantle components in their source, or input from continental crust during their ascent and eruption.

Radiometric age determinations

U-Pb During the past decades, a large number of ther-mal ionisation mass spectrometry (TIMS) U-Pb age determinations on zircon from Archaean rocks have been carried out at the Isotope Lab-oratory of the Geological Survey of Finland (GTK). Recently, the secondary ion mass spec-trometer (SIMS) of the Nordsim laboratory and


0.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.1

110

100


0.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.1

11

01

00


0.0

10.1

110

100

Sa

mp

le/

Prim

itive

Ma

ntle


0.0

10.1

110

100

Kuhmo - komatiites Kuhmo - komatiitic basalts

Ilomantsi - komatiites Ilomantsi - komatiitic basalts

Kovero - komatiites Kovero - komatiitic basalts

Fig. 20. Zr-Nb-Y-Th-La ratios in the komatiites and komatiitic basalts of Kuhmo and Ilomantsi. Abbreviations (Condie 2005): UC, upper continental crust; PM, primitive mantle; DM, shallow depleted mantle; HIMU, high mu (U/Pb) source; EM1 and EM2, enriched mantle sources; ARC, arc-related basalts; NMORB, normal ocean ridge basalt; OIB, oceanic island basalt; DEP, deep depleted mantle; EN, enriched component; REC, recycled component. Arrows indicate the effects of batch melting (F) and subduction (SUB).

46


multiple-collector inductively coupled plasma mass spectrometer (LA-MC-ICPMS) of GTK have also been used in the age determination of Archaean rocks. Figures 21–22 present most of the zircon age data available from plutonic and volcanic rocks in the Finnish part of the Kare-lia Province. It is evident from the diagrams that TTGs age mostly between 2.83–2.72 Ga, and within this range cluster in two groups separat-ed by a c. 20 Ma time gap; in the older group, TTGs are 2.83–2.78 Ga, and in the younger group 2.76–2.72 Ga. The >2.78 Ga TTGs occur almost exclusively outside the Ilomantsi complex (Fig. 21). In the Ilomantsi greenstone belt, vol-canic rocks and related dykes are 2.76–2.72 Ga. From the Ilomantsi complex there have thus far been only two observations of Mesoarchaean rocks (Huhma et al. 2012a), which is consist-ent with observations from the Central Karelia subprovince in Russia (Lobach-Zhuchenko et al. 2005, Bibikova et al. 2005, Slabunov et al. 2006), suggesting that most of the Central Ka-relia crust is relatively young, c. 2.76–2.72 Ga. However, some porphyritic dykes that intruded into mafic volcanic rocks have older, c. 3.0 Ga zircon populations (Vaasjoki et al. 1993). Two datings for felsic volcanic rocks from the Kovero greenstone belt SW of Ilomantsi give ages of

c. 2.88 Ga (Huhma et al. 2012a). These results in-dicate that the Ilomantsi greenstone belt is not a completely juvenile Neoarchaean formation, but includes at least some reworked Mesoarchaean material. Volcanic rocks in the other greenstone belts are dated mostly at 2.84–2.80 Ga (Huhma et al. 2012a). Mesoarchaean c. 2.95 Ga ages are yielded by some volcanic rocks and TTGs in the northern part of the Lentua complex and by some TTGs in the Siurua complex. In the West-ern Karelia subprovince, rocks whose zircon ages are > 3.0 Ga seem to exist only in the Iisalmi and Siurua complexes (Hölttä et al. 2000, Mutanen & Huhma 2003, Lauri et al. 2011). The GGM suite rocks, mostly of c. 2.73–2.66 Ga, occur all over the studied area. The youngest Neoarchae-an zircon ages are from granulites in the Rauta-vaara and Siurua complexes and leucosomes of migmatites giving ages of c. 2.65–2.63 Ga and c. 2.71–2.65 Ga, respectively. These ages have been interpreted to date the high-grade meta-morphism of lower and mid-crust (Mutanen & Huhma 2003, Mänttäri & Hölttä 2002, Käpyaho et al. 2007, Lauri et al. 2011).

Sm-NdThe TIMS/SIMS/LAMS U-Pb zircon age de-termination localities do not yet evenly cover

Fig. 21. Histogram showing the distribution of the U-Pb ages on zircon of various Archaean lithologies in the Finnish part of the Karelia Province.

47


Fig. 22. Sites for the U-Pb age determination samples (Ma). The base map is from Fig. 2.

48


the Archaean area of Finland (Fig. 22), and some relatively large areas remain untouched. Hence, some surprises may arise with future gap filling, remembering, for example, the small area of the 3.5 Ga Siurua gneisses. Sm-Nd analyses have been carried out from most of the samples used for the U-Pb analyses on zir-con. For this work, many additional TTG sam-ples were analysed to improve the regional cover of the Sm-Nd data. These samples were partly from our own sample sets and partly from the Rock Geochemical Database of Finland (Rasi-lainen et al. 2007). Whole rock chemistry was used to select samples with the least obvious metamorphic alteration. The analytical data are presented by Huhma et al. (2012b). Figure 23 shows the distribution of the TDM model ages on a geological map of the study area.

The various geochemical groups of TTGs ob-served in this work do not correlate with Sm-Nd model ages or εNd values in any simple way. The diagrams in Figure 24 show the REE patterns and the Sm-Nd (TDM) model ages of a large num-ber of the analysed TTGs. Even in the youngest age group, where the model ages are < 2.8 Ga and εNd +0.9 - +2.4, and which thus by and large rep-resents juvenile Neoarchaean materials, all geo-chemical types are represented, and the same pat-tern also holds true in the oldest model age group. The granodioritic 3.5 Ga Siurua gneiss has a high REE content, strongly fractionated REE pattern (sample A1602 in Fig. 24d) and negative εNd(2.7 Ga) of –10.8, in contrast to the 2.96 Ga Isokum-pu granulite facies orthogneiss, which belongs to the HREE-depleted and Eu-positive group (sam-ple A1603 in Fig. 24d and Mutanen & Huhma 2003). With a few exceptions, model ages that are around or older than 3.0 Ga are from the Siurua

complex and from the northern parts of the Len-tua complex, indicating that rocks in these areas include a greater Mesoarchaean component than elsewhere in the Finnish Archaean.

SIMS ages on detrital zircon in paragneissesKontinen et al. (2007) concluded in their study on the Nurmes paragneisses that the deposition of the protolith wackes took place at c. 2.70 Ga, which is in the range observed in U-Pb ages of the youngest dated detrital zircon grains. Nearly 50% of the grains were dated at 2.75–2.70 Ga. The whole rock compositions of the Nurmes paragneisses suggest that the source terrains mainly comprised TTGs and sanukitoid-type plutonic and mafic volcanic rocks. Huhma et al. (2000) an-alysed zircon from metasediments in the Kalpio complex (Hölttä et al. 2012) and found that most zircon grains are c. 2.73 Ga and the others from 2.8 to > 3.0 Ga. Huhma et al. (2012a) analysed detrital zircon in metasediments from five other localities in the Karelia Province, and the results were similar to those from the previous studies. Most of these samples predominantly contain c. 2.73–2.75 Ga zircon grains, which suggests that the Neoarchaean intrusions of this age produced most of the sedimentary detritus. Mesoarchaean 3.2-2.8 Ga zircon grains were rare in all para-gneiss and also other metasedimentary samples.

According to Bibikova et al. (2005), zircon from sanukitoids has higher Th/U ratios (>0.5) than zircon in TTGs (<0.5). Given that most 2.75–2.72 Ga zircon grains from paragneisses have Th/U ra-tios > 0.5 (Fig. 25), sanukitoids indeed may have been one of their main sources, although it has to be noted that high Th/U in zircon is not restricted to sanukitoids, but is also found in samples of the other main rock groups.

Lower crustal xenoliths

Mantle and lower crustal xenoliths recovered from c. 500- to 600-Ma-old kimberlites near the southern boundary of the Lentua complex pro-vide pertinent information on the petrology and physical properties of the lower crust of the Ar-chaean Karelia Province (Hölttä et al. 2000, Pel-tonen et al. 2006). The lower crustal xenoliths are almost exclusively from mafic granulites. Mineral thermobarometry, together with isotopic, pet-rological and seismic velocity constraints, imply that the lower crustal xenoliths are derived from the weakly reflective, high-Vp layer at the base of the crust (40–58 km depth; Hölttä et al. 2000, Pel-tonen et al. 2006). Single grain zircon U–Pb dates

and Nd model ages (TDM) from the xenoliths im-ply that the bottom high velocity layer is a hybrid layer consisting of both Archaean and Protero-zoic mafic granulites. Many of the studied xeno-liths record only Proterozoic zircon ages (2.5–1.7 Ga) and Nd model ages (2.3–1.9 Ga), implying that the lower crust contains a significant juve-nile Palaeoproterozoic component (Hölttä et al. 2000, Peltonen et al. 2006). Only a small fraction of zircon grains separated from the xenoliths give Archaean ages typically in the range of 2.7–2.6 Ga. Mesoarchaean zircon grains are almost ab-sent. The oldest zircon ages, up to c. 3.5 Ga, and Nd TDM model ages of c. 3.7 Ga of the xenoliths

49


Fig. 23. Distribution of the TDM model ages (Ma). The geological base map is from Fig. 2.

are similar to those from the oldest gneisses in the Siurua complex. Based on these data, the lowermost crust probably originated as Archaean

mafic gneisses, but was repeatedly intruded by Proterozoic mafic magmas 2.5–1.80 Ga ago.

50



0.1

110

100

1000

30093014302830293052310831093168325134813026

73.3068.5072.0067.8068.7072.1065.4064.8069.0070.3064.60


0.1

110

100

1000

Sam

ple

/ R

EE

chondrite

65.2073.3054.2067.9072.6060.1070.70

2936

2962

2912

2903293829632960


0.1

110

100

1000

2899

2858

2837

2883

2820

2899

2808

2832

56.0062.6066.9070.8074.1057.8064.9057.9065.50


0.1

110

10

01

00

0

Sam

ple

/ R

EE

ch

ond

rite

2772

27972779

268827682755

2734

2746

56.9064.6070.3070.3070.6057.0068.2058.40

2688-2797 Ma 2808-2899 Ma

2903-2963 Ma 3009-3481 Ma

N94002593

N93001430

155-PSH-04

N95001676

N93001872

N93001846

30-PSH-04

N93002664

A1611

N93002622

N94002606

N94002795

N93002484

N94003658

N94003175

N94003728

147-PSH-04

N94003163

159-PSH-04

35-PSH-04

N95001760

N95001798

N93002713N95001765

A1603

N93002466

47-PSH-04175.1-PSH-04

N95001741

N94003664

N94003191

162-PSH-04

N95001753A1602

A1661

a b

c d

Fig. 24. REE patterns of the samples used for Sm-Nd analyses. The numbers next to the curves are for the model ages and the insets in the upper right corner of the boxes show the SiO2 content of the sample.

51


Fig. 25. Th/U ratios in zircons of the paragneisses, based on analyses by Huhma et al. (2012a). The sample A1243 is from a metasediment which was metamorphosed in granulite facies.

Metamorphism

Amphibolites and paragneisses in TTG complexes

Ubiquitous evidence of melting and migmati-sation of felsic but also mafic rocks within the Western Karelia Province implies it was mostly metamorphosed in upper amphibolite and gran-ulite facies conditions. Partial melting was of-ten extensive, leading to the intense migmatisa-tion that characterizes so many localities. Lower grade rocks are found in the inner parts of the Kuhmo-Suomussalmi and Ilomantsi greenstone belts that often show mid- or low amphibolite fa-cies mineral assemblages, well preserved primary structures and only a little or no migmatisation. Because of the dominance of the mineralogically monotonous gneissic TTG rocks, suitable min-eral assemblages - especially garnet-bearing par-agenesis - for the study of pressure-temperature evolution are not common.

For this work, samples were taken from gar-net-bearing amphibolites and paragneisses that sometimes have a garnet-hornblende-plagio-clase-quartz or garnet-biotite-plagioclase-quartz mineral assemblage. Figures 26 and 27 show the localities for which pressures and temperatures have been obtained, using Thermocalc (Powell et al. 1998) and TWQ (Berman 1988, 1991) av-erage PT calculations and grt-bt-pl-qtz thermo-barometry (Wu et al. 2004). Low P/T granulite facies rocks occur sporadically in all complexes, but medium-pressure granulites, metamorphosed at c. 9–11 kbar and 800–850 oC, are only found

in the Iisalmi complex (Hölttä & Paavola 2000). The Siurua complex comprises mafic granulites with hbl-cpx-opx-pl-qtz±grt assemblages, for which maximum metamorphic pressures and temperatures of c. 6 kbar and 750 oC have been calculated (Lalli 2002). Compared with the mafic pyroxene granulites of the Iisalmi area, garnet is rare in the Siurua mafic granulites, which is also an indication of lower pressures. The granulite occurrences of the Taivalkoski area lack garnet-bearing rocks that would allow reliable PT deter-minations.

Sanukitoid suite granodiorites in the SE part of the Lentua complex locally contain orthopyrox-ene, but it is not clear whether the mineral assem-blages in these rocks were metamorphic or mag-matic (Halla & Heilimo 2009). Amphibolites and paragneisses near these charno-enderbites were metamorphosed in upper amphibolite and granu-lite facies at c. 6.5–7.5 kbar and 670–750 oC. Pres-sures obtained for amphibolites elsewhere in the southern part of the Lentua complex are slightly lower, 4.7–5.5 kbar (Fig. 26).

Metamorphic pressures obtained for the Nur-mes paragneisses and for the amphibolites around are mostly c. 6.5–7.5 kbar, and corresponding temperatures c. 650–740 oC. Many samples give lower temperatures of c. 600 oC, but they prob-ably record post-peak cooling or Proterozoic met-amorphism of the Archaean bedrock, because these rocks are normally migmatised, indicating high metamorphic temperatures.

52


Fig. 26. Metamorphic pressures and temperatures: blue dots = calculated using the garnet-biotite-plagioclase-quartz ther-mobarometer by Wu et al. (2004); green dots = calculated using the Thermocalc average PT method for garnet-hornblende-plagioclase-quartz assemblage. The inset shows the area of Fig. 26b. The geological base map is from Fig. 2.

53


Greenstone belts

Garnet bearing samples form supracrustal rocks in the Ilmomantsi belt that typically have the as-semblage grt-bt-pl-qtz±ms, occasionally with an-dalusite and staurolite or more often their mus-covite-filled pseudomorphs. Grt-bt thermometry for these samples indicates in most cases crystal-lization at c. 550–590 oC, similarly to the results of O’Brien et al. (1993) and Männikkö (1988), and these temperatures are in accordance with the observed mineral associations. In the NW part of the Ilomantsi greenstone belt, sillimanite is also present in pelitic rocks, and temperatures from grt-bt thermometry are also higher than in the SE, being c. 600–625 oC. Pressures indicated by the grt-bt-pl-qtz barometer are c. 3.5–5.5 kbar in the central parts of the greenstone belt but >6 kbar in the NW in the sillimanite-bearing meta-sediments. The lower pressures are of the same order as those obtained by Männikkö (1988) us-ing sphalerite barometry for samples from the Ko-vero greenstone belt SW of Ilomantsi. Garnets in the Ilomantsi belt samples are often zoned, with cores richer in Mg than rims, indicating a pres-sure decrease during garnet growth.

Previous studies on the Kuhmo-Suomussalmi greenstone belt have resulted in evidence of a decrease in metamorphic grade from outer to in-ner parts of the belt. According to Tuisku (1988), geothermometry suggests metamorphic tempera-tures as low as 500 oC for the inner and up to 660 oC for the outer parts of the belt. Pressures ob-tained using the sphalerite barometer applied to sphalerite inclusions in pyrite are mostly between 6–7 kbar but range in some cases as high as c. 13 kbar (Tuisku 1988).

An interesting observation was made for a patch of garnet-bearing amphibolites east of the Kuhmo greenstone belt. Noting the standard tholeiite basaltic whole-rock composition of these amphibolites, it is very surprising that they do not comprise any matrix plagioclase, but only minor albite and oligoclase inclusions in garnet (Fig. 28). The observed ranges of the anorthite content in the plagioclase inclusions in two microana-lysed samples are An10–An30 and An1–An20, indicating that some of the inclusions are almost pure albite. The garnet hosts are rich in grossular (Xgrs 0.25–0.35, Xgrs = Ca/(Fe+Mn+Mg+Ca)) and spessartine (Xsps 0.10–0.12) but Mg-poor (Xprp 0.05–0.09), which indicates that the meta-

Fig. 27. Metamorphic pressures and temperatures in the Iisalmi and Rautavaara complexes, calculated using the TWQ pro-gram, after Hölttä et al. (2000) and Mänttäri and Hölttä (2002) (red dots). Blue dots as in Fig. 26a. Purple and green colours show the zones where the Proterozoic retrogression is pervasive, in purple areas kyanite is the only Al2SiO5 polymorph in peraluminous rocks and in green areas all three Al silicates are found, sometimes coexisting.

54


grt

amphab

Fig. 28. Albite inclusions in garnet in amphibolite east of the Kuhmo greenstone belt.

600 620 640 660 680 7006

7

8

9

10

11

12

13

14

15

16

17

An10

An15

An20

An25

hbl pl

grt hbl ep pl

grt hbl ep

hbl ep pl

grt hbl pl

NCFMASHTO, + mag, qtz, H O2

grt hblpl out

Pkbar

oT C

morphic temperatures were not very high dur-ing garnet crystallization. These rocks often contain epidote, sometimes only as inclusions in garnet but occasionally also in the matrix. The P-T pseudosection in Figure 29, calculated for a typical amphibolite composition in the area, shows the upper stability field of plagioclase in the PT space and compositional isopleths of plagioclase in grt-hbl-ep-pl-qtz and grt-hbl-pl-qtz assemblages (calculations using Ther-mocalc 3.33 software by Powell et al. (1998); http://www.metamorph.geo.uni-mainz.de/ thermocalc/. The pseudosection indicates that plagioclase is not stable at pressures above 13–15 kbar at temperatures of 600–650 °C, and that its composition would change to albitic before de-composition with increasing pressure. If an al-bitic composition An1 of plagioclase is used in the average P calculation, the Thermocalc gives average pressures of c. 16–17 kbar at 600–700 °C.

In the Oijärvi greenstone belt, garnet amphi-bolites were found in one locality, and relatively high average pressures of c. 9.5 kbar were also recorded for these rocks using the grt-hbl-pl-qtz barometer.

Fig. 29. A pseudosection showing the stability fields of gar-net, epidote and plagioclase in a NCFMASHTO system of the composition (mol.%): SiO2 52.350, Al2O3 9.138, CaO 12.598, MgO 11.619, FeO 10.640, Na2O 2.676, TiO2 0.653 and O 0.326.

http://www.metamorph.geo.uni-mainz.de/thermocalc/

http://www.metamorph.geo.uni-mainz.de/thermocalc/

55


Age of Archaean metamorphism

Because the bulk of TTGs and volcanic rocks in the greenstone belts are from juvenile Neoar-chaean additions to the crust, it is not a surprise that signs of Mesoarchaean metamorphic events are difficult to distinguish in the preserved small enclaves of Mesoarchaean rocks. Mänttäri and Hölttä (2002) interpreted a c. 3.1 Ga zircon pop-ulation to be metamorphic in the 3.2 Ga rocks of the Iisalmi complex. Käpyaho et al. (2007) found an obviously metamorphic zircon population of 2.84–2.81 Ga in a palaeosome of a 2.94 Ga mig-matite in the Lentua complex. However, most of the observed high-grade metamorphism and de-formation appears Neoarchaean in age.

To more precisely constrain the age of high-grade metamorphism, zircon grains and grain do-mains from leucosomes of migmatites and from granulites have been dated. The ion probe U-Pb data available on zircon from the leucosomes ap-pear to indicate partial melting over a broad time interval from 2.72–2.67 Ga (Käpyaho et al. 2007). Titanite from amphibolite facies rocks also yields broadly similar U-Pb ages. Zircon grains from leucosomes in the Iisalmi granulites give ages from 2.71–2.65 Ga. Metamorphic monazite and zircon from granulite mesosomes have been dated at 2.64 Ga and 2.68–2.61 Ga, respectively (Hölttä et al. 2000, Mänttäri & Hölttä 2002). In the Siu-rua complex, a TIMS U-Pb age on metamorphic zircon from a mafic granulite is 2.65 Ga and in the Siurua and Ranua complexes leucosomes of migmatitic amphibolites have been dated at 2.68–2.62 Ga (Mutanen & Huhma 2003, Lauri et al. 2011). These age data indicate that migmatisation was a long-lasting event, and mostly coeval with GGM magmatism. The lower crust, represented by the medium-pressure granulites in the Iisalmi complex, retained higher temperatures for a long-er time, which supported relatively late crystal-lization of zircon. The youngest Sm-Nd garnet-whole rock ages in the Iisalmi complex granulites are <2.5 Ga, which indicates that cooling to the closure temperatures of the Sm-Nd system lasted until the Proterozoic era (Hölttä et al. 2000).

Proterozoic metamorphism

The Archaean bedrock in the western part of the Karelia Province underwent a strong reheating

during the Palaeoproterozoic Svecofennian orog-eny. Evidence of this includes, for example, that biotite and hornblende sampled from Archaean rocks have K-Ar ages typically in the rage 1.8–1.9 Ga. Archaean K-Ar mineral ages are only pre-sent in samples from the Iisalmi and Taivalkoski granulites and the Ilomantsi complex (Kontinen et al. 1992, O’Brien et al. 1993). The heating of the Archaean crust has been explained by its bur-ial under a massive overthrust nappe complex ca. 1.9 Ga ago (Kontinen et al. 1992).

Numerous ductile shear zones were developed in the Archaean bedrock during the Svecofenn-ian orogeny. The widths of these shear zones vary from tens of metres to several kilometres (Ko-honen et al. 1991). In many places the Protero-zoic shearing was associated with high hydrous fluid flows and related chemical alteration, which is reflected, for instance, in alkali-deficient com-positions and kyanite- and cordierite-bearing as-semblages in originally TTG rocks (Pajunen & Poutiainen 1999). In the eastern part of the Iis-almi complex (Fig. 27), almost all Archaean rocks were ductilely deformed during the Svecofennian orogeny. This is well demonstrated, for example, by the all-encompassing penetrative deforma-tion of the 2.3–2.1 Ga dolerite dykes common in the Rautavaara area. Many of the dykes show shear folds, schistosity and strong lineations dip-ping mostly to the SW. The foliations and linea-tions seen in the dykes are also equally strongly seen in the surrounding Archaean country rocks. In the Rautavaara complex, Archaean granulite facies mineral assemblages were decomposed in the Proterozoic metamorphism that took place at c. 550–650 oC and 5–6 kbar (Mänttäri & Hölttä 2002). Similar temperatures and pressures for the Proterozoic metamorphic overprint have also been reported in the Lentua complex (Pajunen & Poutiainen 1999). Deformation microstruc-tures in the Koitere sanukitoid granodiorites in the Ilomantsi complex indicate temperatures of 400–500 oC during Proterozoic metamorphism (Halla & Heilimo 2009). In the Rautavaara com-plex, Proterozoic metamorphic zones can even be seen; in retrogressed peraluminous rocks next to the east of the granulites of the Iisalmi complex, kyanite is the only Al2SiO5 mineral, whereas far-ther to the east compositionally similar rocks also contain andalusite and sillimanite (Fig. 27).

Palaeomagnetism

Several palaeomagnetic studies on Archaean rocks have been carried out in the Karelia Prov-

ince, but only in a few cases has stable Archaean remanent magnetization unaffected by Protero-

56


zoic overprinting been revealed. The main use of palaeomagnetic data in Archaean geology has been in reconstructing the past positions and movement of the craton at different times and comparing its position with other similar-aged cratons. Continental reconstructions have been made particularly with the Superior Province because of the considerable geological similarity between these two cratonic masses. This section reviews the palaeomagnetic data from Archaean rocks in Finland and NW Russia and present models of the Archaean plate configurations of the Karelia and the Superior Provinces.

The 2913 ± 30 Ma Shilos metabasalts located NW of Lake Onega in NW Russia, with pre-served remanent magnetization estimated at 2800 Ma (Arestova et al. 2000 and references therein), are the oldest rocks from the Karelia Province for which palaeomagnetic data are presently avail-able. Another case of old remanence is from the NW of Lake Onega, where the 2890 Ma Semch River gabbro-diorite is interpreted to preserve its primary magnetic remanence (Gooskova & Krasnova 1985). However, in both cases the age of remanence is defined based on comparison to the APWP (Elming et al. 1993). Therefore, due to poor age constraints, the data are not used in ei-ther case for continental reconstructions.

The most reliable Neoarchaean palaeomag-netic data from the Karelia Province are obtained from the granulite facies enderbites in the Var-paisjärvi area in the Iisalmi complex (Neuvonen et al. 1981, 1997, Mertanen et al. 2006a) and from the orthopyroxene-bearing sanukitoids of the

Koitere area in the Lentua complex (Mertanen & Korhonen 2008, 2011). Younger, well-defined Neoarchaean data come from the Shalskiy gab-bronorite dyke and granulite-grade gneisses in the Vodlozero subprovince in NW Russia (Krasnova & Gooskova 1990, Mertanen et al. 2006b). Com-mon to all these cases is that they are generally well-preserved from the 1.9–1.8 Ga Svecofennian overprinting, they show high magnetic anomalies compared to surrounding TTG gneisses and their remanence has high stability, the directions of re-manence clearly differing from the known Prote-rozoic remanences.

The Koitere sanukitoids and the Varpaisjärvi enderbites show a steep characteristic remanence component, but in Lieksa the inclination is nega-tive and in Varpaisjärvi positive (Mertanen et al. 2006a, Mertanen & Korhonen 2011). It is inter-preted that the steep remanence directions record the long-lasting Neoarchaean metamorphic event at different times, during which the polarity of the Earth’s magnetic field has reversed at least once. The remanence of the Koitere sanukitoids is regarded as ca. 2.7 Ga (207Pb/206Pb monazite age of 2685 Ma, Halla 2002) and the Varpaisjär-vi granulites as ca. 2.6 Ga (Sm-Nd garnet-whole rock ages 2590-2480, Hölttä et al. 2000). Based on data from Koitere and Varpaisjärvi, the Karelia Province moved from a high polar palaeolatitude of 83° to the palaeolatitude of c. 68°, respectively. The overall data from Koitere and Varpaisjärvi thus imply that at c. 2.7–2.6 Ga the Karelia Prov-ince was located at high palaeolatitudes.

DISCUSSION

Adakitic features of TTGs

The mutual compositional similarity of TTGs and modern adakites has been the basis to sug-gest petrogenetic kinship between the two rock suites (Martin 1999, Martin et al. 2005). Adak-ites are spatially related to subduction, and the most likely source of their parental magmas has been the basaltic part of a subducted oceanic slab. They seem to be related to an environment where the subduction zone is abnormally hot, al-lowing the subducting slab to melt (Moyen 2009). Numerical and petrologic models suggest that partial melting of a subducting slab is possible at 60–80 km depth, but only when the subducting oceanic crust is very young (< 5 Ma) and there-

fore hot, or as a consequence of heating under abnormally high stresses in the subduction shear zone (Defant & Drummond 1990, 1993, Pea-cock et al. 1994). However, according to Guts-cher et al. (2000), most of the known Pliocene-Quaternary adakite occurrences are related to the subduction of 10–45 Ma lithosphere, which, according to numerical models, should not pro-duce melt under normal subduction zone thermal gradients. Gutscher et al. (2000) addressed this by flat subduction that can produce the temperature and pressure conditions necessary for the fusion of moderately old oceanic crust. Variation in the subduction angle has been proposed as a criti-cal factor also controlling the variation observed in geochemical features of the Archaean TTGs.

57


Smithies et al. (2003) proposed that Archaean subduction was predominantly flat and that the subduction regimes thus lacked well-developed mantle wedges that would produce melts or inter-act with possible slab-derived melts, in the latter case increasing the compatible element content and Mg contents of the slab melts.

Recently, the usage of the terms adakite, and especially adakite-like, has been expanded to en-compass a wide range of rocks that exhibit the high Sr/Y and La/Yb ratios but not necessarily the other criteria of the original adakite defini-tion. This loose usage has led Moyen (2009) to recommend that separate, more precise terms should be used to describe these “adakitic” rocks, and the term adakite should be reserved only for the high-silica adakites that closely correspond to the rocks originally described as adakites by Defant & Drummond (1990). Halla et al. (2009) argued that the term adakite should only be used for unmistakable slab melts and therefore not for such rocks as the TTGs in the Karelia Province. Smithies (2000) also argued that despite the many compositional similarities, most Archaean TTGs actually differ from Cenozoic adakites, especially in that they have on average lower Mg# and high-er SiO2 contents, suggesting that, unlike adakitic melts, the TTG melts did not interact with mantle peridotite.

High Sr/Y and La/Yb ratios can have several causes, such as high Sr/Y sources, garnet-present melting and interactions with the mantle (Moyen 2009). Melts with an adakitic geochemical signa-ture can also be generated by normal crystal frac-tionation processes from andesitic parental melts, and slab melting is not mandatory for adakite petrogenesis, but adakites or adakite like rocks can instead originate in various geodynamic set-tings (Castillo et al. 1999, Castillo 2006, Richards & Kerrich 2007, Petrone & Ferrari 2008).

The thickness of Archaean oceanic crust has been estimated at between c. 15 and 45 km (Bickle 1986, Abbott et al. 1994, Ohta et al. 1996), i.e. significantly thicker than typical modern oceanic crust, which is c. 7 km (e.g. Hoffman & Ranalli 1988). Where it was warm and buoyant, it perhaps did not subduct at all, and probably not at a steep angle (Abbott & Hoffmann 1984, Hoffman & Ranalli 1988, Abbott et al. 1994). Björnerud and Austrheim (2004) argued that one likely conse-quence of the higher geothermal gradient during the Archaean was that ocean crust became thor-oughly dehydrated at shallower depths than oc-curs today. The residual, dehydrated crust would thus have been very strong and too buoyant to sink into the mantle.

Modelling by van Hunen et al. (2004) suggests that if mantle temperatures were indeed higher during the Archaean than presently, even flat sub-duction was an unlikely process. If this was the case, the obvious lack of interaction with mantle in many TTGs must be explained in some other way. Halla et al. (2009) attributed the low-HREE TTG group to high-pressure partial melting (>20 kbar) of a garnet-bearing basaltic source with little evidence of subsequent mantle contamina-tion. The high-HREE group was generated by significantly lower pressure melting (c. 10 kbar) of a garnet-poor basaltic crust and shows interac-tion with the mantle by its higher Mg#, Cr and Ni contents. Halla et al. (2009) proposed that the high-HREE TTGs were produced in an incipient, hot subduction zone underneath a thick oceanic plateau/protocrust. For the low-HREE TTGs, they saw a non-subduction setting as probable, proposing that these rocks were generated by deep melting in the lower parts of thick domains of ba-saltic oceanic crust.

TTG melts and PTX relations of their protoliths

There is a general agreement that the Archaean TTG suite rocks were formed by partial melting from a compositionally basaltic-gabbroic source. The process was evidently fluid-absent partial melting of amphibolites at temperatures of 900–1100 oC and over a large pressure range from 10 to 25 kbar. The composition of products from partial melting is controlled by pressure and tem-perature, the composition of the source, water availability during the process and the degree of melting. The composition of the partial melts is further modified, for instance, by magma mixing, fractional crystallization and wall rock contami-nation on their way from the loci of melting to the crystallization sites (Rapp et al. 1991, Martin 1995, Martin & Moyen 2002, Foley et al. 2002, Rapp et al. 2003, Moyen & Stevens 2006, Moyen 2011).

During the fusion process, pressure and tem-perature control the assortment and abundance of the residual minerals, such as garnet and pla-gioclase, and consequently the major and trace el-ement content of the TTG melts. For example, the heavy REE is controlled by residual garnet, which is stable in mafic rocks at pressures above c. 9–12 kbar and increases in abundance with increasing pressure. Sr is controlled by plagioclase, which is stable below c. 15–20 kbar. Nb and Ta depend on the presence of residual rutile, which is stable above c. 16–18 kbar (Foley et al. 2002, Moyen & Stevens 2006, Moyen 2011).

58


In the low-HREE TTG group with positive Eu anomalies, Sr and Sr/Y ratios are high and Nb low. Positive Eu could be explained by plagioclase accumulation, but as TTGs in this group are no more enriched in Al2O3, CaO or Na2O than the other low-HREE TTGs, it is more probable that they represent melting with residual rutile and garnet. In dacitic and rhyolitic melts, the garnet-melt partition coefficients are higher for Sm (2.66) and Gd (10.5) than for Eu (1.5) (Rollinson 1993). Thus, high pressure melting with abundant garnet in the residue would obviously lead to melts that are HREE poor and show a positive Eu/Eu* ra-tio, which is also predicted by experimental work (e.g. Springer & Seck 1997).

The melting temperature strongly depends on the starting composition, and the solidus tem-peratures for arc basalts, tholeiitic basalts and komatiitic basalts are thus very different (Moyen & Stevens 2006). The trace element composition of melts principally depends on their protolith concentrations, but through control of the min-eral composition of the restite, the major element content of the protolith also affects the trace el-ement composition of the coexisting melt. Ac-cording to Nair & Chacko (2008), the increase in residual garnet from 5 to 15 wt% changes the La/Yb ratio in the melt fraction from c. 12 to c. 24. Variation in the La/Yb ratio of the melts may be considerable, even under constant P and T, if there is enough compositional variation in the source. Figure 30 shows simplified pseudosections with melting curves and breakdown curves of am-phibole, orthopyroxene, garnet and rutile for two compositionally deviating samples analysed from amphibolite intercalations in TTGs, representing tholeiitic and komatiitic basalts with 1 wt.% H2O. The pseudosections were constructed using the Perple_X 6.6.6 software (Connolly 1990, 2005, Connolly & Petrini 2002, http://www.perplex.ethz.ch/). The composition has a strong influ-ence on the melting temperature but also on the mineral stability fields. In Na2O and Al2O3-poor komatiitic basalt, plagioclase decomposes at pres-sures that are c. 7–10 kbar lower than in the case of basaltic composition (Fig. 30). This means that in >800oC temperatures komatiitic basalt can pro-duce melts with elevated Sr at pressures that are far below the c. 19–21 kbar range that is broadly the upper stability limit of plagioclase in tholeiitic basalts in these temperatures. Also in komatiitic basalt rutile is present at several kbar lower pres-sures than in tholeiitic basalt, and consequently komatiitic basalt can produce Nb and Ta depleted melts at lower pressures than tholeiitic basalt.

According to the model calculations also the

abundance of garnet is strongly dependent on the composition so that at above c. 10 kbar the komatiitic basalt produces roughly twice as much garnet as the tholeiitic basalt (Fig. 30). Conse-quently in TTG melts the La/Yb ratio may signifi-cantly differ only on the basis of the composition of the protolith.

Sanukitoids and quartz diorites are partly too Mg-rich to represent melts from crustal sources. The high Sr content and low LaN/YbN ratio in-dicate that the quartz diorites originated from a hot and shallow mantle environment, where the temperature was so high that plagioclase was not stable, and the pressure so low that little garnet was present in the residue. Figure 31 shows the proportion of residual garnet during the dehydra-tion melting of amphibolite, and the correspond-ing La/Yb ratios in the derived melts, according to the experimental work of Nair and Chacko (2008). The garnet mode in the residue in the case of QQs and high-HREE TTGs would have been 5–15 wt%, and much higher in low-HREE TTGs. This could reflect higher pressures of melting in the case of the low-HREE TTGs, but could also indicate a compositionally different source, which would promote a higher garnet mode in the resi-due.

In the Archaean Earth, low pressure TTGs could have formed, for example, at the base of thick oceanic plateaus (deWit and Hart 1993, Moyen & Stevens 2006). In the greenstone belts, most sequences of mafic volcanic rocks of pla-teau basalt signatures are not compositionally homogeneous, but typically comprise a variety of compositionally differing tholeiitic and komatiitic basalts and komatiites. In addition, many green-stone belts also contain calc alkaline basalts and andesites-dacites. Modern oceanic plateaux, such as the Kerguelen Plateau, consist of intermedi-ate, felsic and alkaline volcanic rocks, as well as sediments (Frey et al. 2000). It is evident from the above discussion that melting of such heteroge-neous packages would produce melts that would also be compositionally heterogeneous and show variable trace element patterns, even in cases where the melting depth was not very high or highly variable.

Greenstone belts

A picture emerging from previous research sug-gests that the Karelia Province was a collage of TTG and greenstone complexes that originated in various geodynamic settings related to sub-duction, collision, continental rifting and man-tle plumes (Bibikova et al. 2003, Samsonov et al.

59


pl out

melt in

opx out

amph outgrt in grt in

rt in

rt in

opxout

amphout

600 700 800 9000.5

1.5

1.0

2.0

2.5

P[G

Pa]

oT C

0.5

1.5

1.0

2.0

2.5

P[G

Pa]

oT C

650 750 850550 700 800 900650 750 850550

pl out

rt inopx out

grt in

melt in

opx o

ut

pl out

grt in

amph o

ut

melt in

rt in

bt amph grt cpx qtz rt

bt amph grt cpx qtz rt H2O

bt opx amphgrt cpx qtz rt

bt opx amphgrt cpx qtz ilm

bt amph grt cpx qtz ilm

bt amph grt cpx ta rt

bt opx amph plgrt cpx qtz ilm

bt opx amph pl grt cpx ilm

bt opx amph pl cpx ilm

bt opx grt cpx qtz rt H2O

bt opx melt grt cpx qtz rt

bt opx melt grt cpx rt

bt opx amph pl cpx ilm melt

600

bt amph pl cpx ilm qtz H2O

bt amph pl grt cpx ilm qtz H2O

bt pl grt cpxilm qtz H2O

bt grt cpx ilm qtz H2O

bt grt cpx qtz rt H2O

bt g

rt c

px la

w q

tz rt H

2O

bt grt cpx law qtz rt

bt melt pl grt cpx ilm qtz

bt melt grt cpx ilm qtz

bt grt cpx qtz ilm rt melt

bt melt grt cpx qtz rt

bt opx melt pl

grt cpx ilm qtz

bt opx melt pl cpx ilm qtz

bt melt pl grt cpx qtz rt

opx melt pl cpx ilm qtz

Fig. 30. NCKFMASHTi pseudosections for Fe-rich basaltic granulite (psh69b) and komatiitic basalt (psh183) and lower and upper stability limits of various minerals in these two whole-rock compositions. The solution models used in cal-culations were: biotite (TCC), amphibole (GlTrTsPg), garnet (HP), orthopyroxene (HP), clinopyroxene (HP), plagioclase (h), ilmenite (WPH), melt (HP). For the original references see http://www.perplex.ethz.ch/PerpleX_solution_model_glos-sary.html.

Compositions used (in wt.%) are:

psh69b psh183SiO2 59.63 47.30TiO2 1.00 0.35Al2O3 13.53 11.50FeO 9.68 8.54MgO 2.65 14.20

psh69b psh183 CaO 5.49 11.70Na2O 3.45 1.16K2O 1.97 0.92H2O 1.00 1.00

60


2005, Slabunov et al. 2006, Papunen et al. 2009). The greenstone belts have also been interpreted as composite terranes comprising magmatic prod-ucts from various geodynamic settings involving plumes and arc magmatism (Puchtel et al. 1998, 1999). Archaean greenstone belts can be divided into autochthonous to parautochthonous and allochthonous based on their relationship with the underlying basement rocks (Polat & Kerrich 2000, 2006). According to Thurston (2002), evi-dence from the Superior Province suggests that many, if not all, greenstone sequences were in autochthonous or parautochthonous units fed from mantle plumes either in continental rift or continental platform settings. Allochthonous models favour the assembly of greenstone belts by horizontal tectonic transport and accretion of various types of oceanic crust in a plate-tectonic geodynamic regime (e.g. Puchtel et al. 1998, 1999, Percival et al. 2004, Percival et al. 2006, Polat & Kerrich 2006). The presence of such features as fold and thrust complexes, orogen-parallel strike-slip faults and tectonically juxtaposed terranes from different tectonic settings, as well as subduc-tion zone geochemical signatures in part of the plutonics and volcanics in the greenstone belts,

supports the concept that the accretion of alloch-thonous terranes was elemental in the growth of many greenstone belts (Polat & Kerrich 2006).

Many komatiite-bearing sequences in Archae-an greenstone belts have been interpreted as piec-es of dismembered Archaean oceanic plateaux (Kusky & Kidd 1992, Abbott & Mooney 1995, Puchtel et al. 1998). Many greenstone belts are characterized by assemblages that suggest rough-ly coeval plume-type komatiite-tholeiitic basaltic and arc-type calc alkaline volcanism. This situa-tion has been explained in the Karelia Province in terms of a subduction setting where the arc-type plutonic volcanic rocks formed at the margins of plume-generated thick basalt plateaux that were not able to subduct because of their buoyant na-ture (Puchtel et al. 1998, 1999). Interlayering of komatiites with subduction-related volcanics has been explained by the interaction of plume and subduction related magmas in such a subduction regime (Grove & Parman 2004).

Grove and Parman (2004) proposed that Ar-chaean komatiites could have been formed by hydrous melting in a subduction environment, which would easily explain the close spatial and temporal association of many komatiites and is-

0 1 2 3 4 5

02

04

06

08

01

00

12

01

40

Average early Archean TTG

Proportion of residual garnet

510

1520

2530

Average MORB

La/Yb

Yb ppm

Fig. 31. La/Yb ratios of Karelian TTG plotted on the La/Yb diagram after Nair and Chacko (2008), showing the effect of the abundance of residual garnet on the La/Yb ratio of the melt in 20% melt fraction during dehydration melting of amphibolite. Open triangles = low-HREE TTGs, black triangles = low-HREE, Eu-positive TTGs, crosses = high-HREE TTGs, grey dots = QQs, black dots = orthopyroxene-bearing QQs (enderbites).

61


land arc type volcanic rocks. This idea, which is supported by the experimental work of Barr et al. (2009), is still disputable, however. For example, based on their work on komatiites in Ontario and Barberton, Arndt et al. (2004) and Stiegler et al. (2010) saw little evidence for the hypothesis of hy-drous melting.

The Kuhmo greenstone belt – an oceanic plateau?

The basic-ultrabasic volcanics in the Kuhmo greenstone belt consist of komatiites and their evolved counterparts, i.e. komatiitic basalts. The komatiite-basalt sequence is completely devoid of epiclastic and chemical interflow sediments, and it lacks geochemical evidence of contamina-tion by any significantly older continental materi-al. These data suggest an eruptive setting far from continental land masses and hydrothermal vents at oceanic ridges and argues against the origin of the Kuhmo greenstone belt within a continental rift zone, as has been proposed, for instance, by Papunen et al. (2009). Immobile trace element (Zr, Y, Nb, Th) systematics are also inconsistent with the formation in a back-arc setting, but rath-er suggest an oceanic plateau setting and magma derivation from a mantle plume. The Al-undeplet-ed nature and the trace element characters of the komatiites indicate that they were derived from a source more similar to primitive upper mantle rather than that of depleted MORBs. Further-more, there is negligible geochemical evidence for the involvement of crust or enriched or recycled mantle sources (EM1, EM2, HIMU). Condie (2005) stressed the clustering of non-arc-related Archaean basalts, in terms of HFSE ratios, close to the primitive mantle values, and suggested on this basis that Archaean mantle plumes had their main source in the “primitive mantle”. Our find-ings support this conclusion, indicating that the late Archaean mantle was less fractionated, or better stirred, than either the early Archaean and post-Archaean mantle.

The U-Pb zircon data (Huhma et al. 2012a) and the Sm-Nd data (Huhma et al. 2012b) on the Kuhmo volcanic rocks provide no evidence for their deposition on a significantly older base-ment in the Kuhmo region. Felsic volcanic rocks in the central part of the Kuhmo belt formed 2.80 Ga ago, giving the minimum age for the mafic-ultramafic magmatism (Huhma et al. 2012a). We conclude that the Kuhmo komatiites represent fissure-controlled eruptions onto a pre-existing rhyolitic-dacitic-tholeiitic oceanic plateau.

The Ilomantsi greenstone belt – a volcanic arc within an attenuated continental margin?

Komatiites within the Ilomantsi greenstone belt, which is located c. 150 km SSE of the Kuhmo belt, were emplaced within a volcano-sedimen-tary basin. Magmatism was dominated by felsic volcanism in two major pulses and coeval grani-toid plutons. The komatiites were emplaced as thin but extensive sheet flows, and probably also as sills beneath the felsic volcanic edifices. The komatiites and dacites-rhyolites occur intercalat-ed, suggesting that ultrabasic and felsic volcan-ism was coeval. Both the komatiites and the felsic volcanic rocks have distinctly low Nb/Th, sug-gesting that the komatiites contain a significant component assimilated from the felsic volcanic rocks. Alternatively, the komatiites could have in-herited their arc-signature from a subduction-en-riched mantle wedge. However, we consider this model less likely, because the samples enriched in lithophile-incompatible elements are depleted in PGE, which is best explained by the segregation of a sulphide melt from the magma in response to contamination by sulphidic metasediments during emplacement. There is evidence of a sig-nificantly older cryptic granitoid basement in the region in the form of inherited c. 3.0 Ga zircon grains in plutonic and subvolcanic felsic rocks and old TDM ages of metasedimentary units in the Ilomantsi belt (Vaasjoki et al. 1993, Huhma et al. 2012a, b). We suggest that the Ilomantsi volcanic rocks represent arc magmatism within an attenuated continental margin where older basement rocks were assimilated by younger arc magmatism.

Supercontinent reconstruction

Several similarities in their geological evolutions can be cited in support of the concept that the Archaean Superior, Hearne and Karelia Prov-inces were parts of the Neoarchaean-Palaeopro-terozoic supercontinent Superia (Bleeker & Ernst 2006).

Comparison of palaeomagnetic data from the Karelia Province with similar-aged poles from the Superior Province (Mertanen & Korhonen 2011, and references therein) shows that Superior was also located at relatively high palaeolatitudes at 2.68–2.60 Ma (Fig. 32a,b). However, the Karelia and Superior Provinces were significantly separat-ed, as there is a c. 30° difference between the lati-tudes both at 2.68 Ga and 2.60 Ga. Taking into account the maximum errors of the poles from both cratons, the latitudinal distances become

62


shorter, and it may be possible that they were even joined at that time. The relative palaeopositions of the two cratons cannot be resolved unequivo-cally, especially at 2.68 Ga, due to the nearly po-lar position of the Karelia Province, which allows its rotation in several directions with respect to Superior.

The steeply inclined remanence of the Varpais-järvi and Lieksa rocks differs distinctly from the 2.50 Ga remanence of the Shalskiy gabbronorite dyke dated at 2510 ± 1.6 Ma in the Vodlozero subprovince (Bleeker et al. 2008). The Shalskiy dyke, as well as the Shalskiy basement gneisses and Vodla River gneisses ca. 50 km east of the Shalskiy dyke, has a shallow southwards point-ing remanence direction (Krasnova & Gooskova 1990, Mertanen et al. 2006b) which is interpreted to be 2.50 Ga. This remanence direction positions the Karelia Province at a low equatorial palaeo-latitude. The data thus suggest substantial move-ment of the Karelia Province between the time of cooling at c. 2.60 Ga after the high grade meta-morphism and subsequent rifting and minor re-working of the craton at c. 2.50 Ga.

Palaeomagnetic reconstruction between Kare-lia and Superior Provinces at 2.50 Ga is presented in Figure 32c. Compared with the 2.6 Ga configu-ration, the palaeopositions between Karelia and Superior are now completely different. The Supe-rior province had drifted across the equator to the latitude of approximately 20° and rotated clock-wise by about 45°, so that at 2.50 Ga both prov-inces were located near the equator, and the Ka-relia Province along the southern margin of the Superior Province. This reconstruction is in close agreement with the Superia model of Bleeker and Ernst (2006), who suggested that the provinces were together at 2.50 Ga.

Tectonic evolution of the Karelia Province

If the Karelia province was indeed once a part of the supercontinent Superia, then many of the ob-servations and models presented for the evolution of the Superior and Hearne Provinces must also be applicable to the Karelia Province. Several ma-jor characteristics in the crustal architecture and composition of the Superior province have long been considered to provide strong support for the operation of modern-style plate tectonics during the Neoarchaean (e.g. Goodwin 1968, Langford & Morin 1976, Card 1990). Tectonic build-up of the province, mostly between 2.72–2.68 Ga, is in-terpreted in terms of accretionary growth process that involved collisions of many microcontinen-tal blocks and juvenile volcanic arcs (Percival et al. 2006).

Accretionary-type orogeny is often considered one of the main processes behind growth of con-tinental crust with time (Şengör & Natal’in 1996, Cawood et al. 2003, Brown 2009). It may also be applicable to Archaean granite–greenstone ter-ranes, as these are often characterized by linear belt structures in which early accretion of forma-tions from various oceanic tectonic environments and microcontinents is followed by arc-type mag-matism (e.g. Kusky & Polat 1999, Bibikova et al. 2003, Samsonov et al. 2005). Neoarchaean accre-tion of exotic terranes at c. 2.83–2.75 Ga, culmi-nating in a subsequent major collisional event/orogeny at around 2.73–2.67 Ga, may have been the mechanism that generated the basic struc-ture of the Karelia Province, and which was then strongly reworked during the Svecofennian oroge-ny. The subduction events enriched the lithospher-ic mantle in LIL elements. At c. 2.76 Ga, a new volcanic arc began to form above a subduction

Equator

Equator

-60°-60°

-30°

-30°

Equator

-60°

-30°

30°

2.50 Ga

2.68 Ga

2.60 Ga

a b c

Fig. 32. Continental reconstructions between the Karelia and Superior cratons at 2.68 Ga (a), 2.60 Ga (b) and 2.50 Ga (c).

63


zone at the margin of the Western Karelia Prov-ince, represented now by the Ilomantsi plutonic-volcanic complex. A subsequent slab breakoff or some other subduction-related process at c. 2.72 Ga led to melting of the enriched wedge mantle, producing voluminous sanukitoids and also small amounts of TTGs (Lobach-Zhuchenko et al. 2008, Halla et al. 2009, Heilimo et al. 2010, 2011).

Kontinen et al. (2007) interpreted SHRIMP and TIMS U-Pb age determinations on zircon grains from the paragneiss mesosomes and crosscut-ting granitoid plutons to constrain the deposition of protolith wackes to c. 2.70 Ga. Some caution should be taken with this interpretation, as the newly obtained precise age of 2715 ± 2 Ma for the Loso sanukitoid intrusion (Huhma et al. 2012a), which crosscuts the local Nurmes type paragneiss-es, suggests that metamorphic effects may have influenced the youngest ages obtained for detrital zircon grains in the paragneisses. Deposition more likely took place in a short (10 Ma or less) period just before 2715 Ma, and it is possible that dep-osition of the Nurmes sediments and sanukitoid plutonism were partly overlapping events. Trace el-ement and U–Pb data suggest that the source com-prised mainly 2.75–2.70 Ga TTG and/or sanuki-toid-type plutonic and mafic volcanic rocks. The close similarity of the paragneiss and sanukitoid compositions is an important clue to the timing and tectonic setting of the deposition. It is clear that TTG-dominated crust, presently character-izing the Western Karelia subprovince, was not the dominant source of the Nurmes sediments. The presence of MORB-type volcanic intercalations in Nurmes wackes suggests that they were deposited in a back arc or intra-arc setting (Kontinen et al. 2007). The exotic nature of the Nurmes sediments as overthrust must be considered as a serious option.

After the intrusion of the last juvenile grani-toids, the QQ quartz diorites at 2.70 Ga, the crust was deformed and metamorphosed. The related process could have been collisional stacking af-ter closure of ocean basins, which thickened the crust between 2.71–2.64 Ga. Vibroseismic images of the crust, as well as tectonic observations from the exposed bedrock, indicate ductile thrusting and related crustal stacking with tectonic trans-portation from southeast to northwest (Kontinen & Paavola 2006, Korja et al. 2006, Sorjonen-Ward 2006). A similar seismic structure characterised by gently dipping, often listric reflections, is also common in other Neoarchaean cratons, and it is interpreted to result from horizontal compression (van der Velden et al. 2006). Fragments of Meso-archaean (micro)continental fragments, such as

the Siurua and Iisalmi complexes, are present as slices in the thickened Neoarchaean crust. Reflect-ing heat production by radioactive decay in the thickened, predominantly felsic-granitoid crust, a Barrovian-type medium P/T metamorphic frame-work was developed. The middle and lower parts of the crust were partially melted, producing mig-matites and the GGM suite intrusions (Mänttäri & Hölttä 2002, Käpyaho et al. 2007, Lauri et al. 2011).

The thickness of the Neoarchaean crust in the Iisalmi complex was at least c. 40 km on the basis of c. 10–11 kbar pressures from the granulites that represent lower crust and bear evidence of long-term residence at high-temperatures (Mänttäri & Hölttä 2002). The significance of the amphibolite facies high-pressure rocks from the other areas is more problematic to interpret as these rocks re-cord a geothermal gradient that is lower than the normal continental gradient. Apart from Kuhmo garnet-amphibolites, other examples of Archaean high P/T rocks in the Fennoscandian Shield are the eclogites in the Belomorian Province which were metamorphosed at c. 700–800 oC and c. 14–17 kbar, possibly even at pressures exceeding 20 kbar (Volodichev et al. 2004, Mints et al. 20101, Shchipansky et al. 2012), i.e. in an eclogite–high-pressure granulite (E-HPG)-type environment, which is consistent with subduction of crustal rocks into the mantle depths (Brown 2007). In Kuhmo the rocks metamorphosed under high pressure only seem to occur in a restricted area surrounded by amphibolite facies rocks that were metamorphosed at c. 6–7 kbar. Therefore, their exhumation might be explained by similar sub-duction-related tectonic processes that exhume high-pressure rocks at present convergent margins (Beaumont et al. 1996, 1999, Agard et al. 2009).

The Ilomantsi greenstone belts shows low pressure metamorphism at 3.5–5.5 kbar and 550–600 oC, which indicates a gradient that is warmer than the normal continental geotherm. These rocks are juxtaposed with migmatites that normally show pressures of c. 6–8 kbar, and in the Kuhmo amphibolite even 15–16 kbar, which represents the amphibole-epidote eclogite facies in the classification of Brown (2009). The dual-ity of thermal environments is typical for modern plate tectonics, where the belts representing differ-ent gradients are juxtaposed by plate tectonic pro-cesses (Brown 2009). Although the metamorphic structure in the Karelia Province is not quite simi-lar to that in modern subduction-related orogenic belts, the significant differences in the metamor-phic gradient between adjacent domains is easy to explain by subductional/collisional processes that

64


assembled rocks representing various geodynamic settings.

One major problem is that we do not currently have a clear conception of the extent to which the present crustal structure is due to Archaean accre-tion/thickening or to Palaeoproterozoic orogenic events. Nevertheless, at least the western and east-ern parts of the Karelia Province were strongly reworked in the Palaeoproterozoic Svecofennian and Lapland–Kola orogenies, when it was com-pressionally thickened and subjected to medium P/T type amphibolite facies metamorphism at 1.9–1.8 Ga (Kontinen et al. 1992, Daly et al. 2001, 2006, Bibikova et al. 2001). One manifestation of the Palaeoproterozoic reworking is the anomaly patterns on airborne magnetic maps, such as in Fig. 33. The general E–W strike of foliation and magnetic banding in the northern part of the Lentua complex suddenly changes to a roughly N–S direction in the Siurua and Ranua com-plexes when crossing over the Palaeoproterozoic

Kainuu schist belt, which forms the boundary between the eastern and western complexes (Fig. 33). A Palaeoproterozoic rotation component is implied, as the same happens with the strikes of the Palaeoproterozoic dyke swarms contained in the two terranes (Vuollo & Huhma 2005). In the pristine Superior Province, Palaeoproterozoic dolerites tend to occur in radiating swarms where the strikes of individual dykes remain much the same over hundreds of kilometres (Ernst & Bu-chan 2001). In marked contrast, dolerite dykes in the Western Karelia subprovince often abruptly change their strikes from one domain to another, reflecting block movements after their emplace-ments mostly between 2.45–1.95 Ga. Tectonic transport to the N–NE during the Svecofenn-ian orogeny at 1.9–1.8 Ga and related ductile to brittle Proterozoic deformation involving uplifts and rotations of rigid blocks largely caused the present framework of linear structures in the Ar-chaean bedrock.

Fig. 33. Airborne magnetic map of the northern part of the Karelia Province in Finland. Dashed lines are for the general strike of foliation.

65


CONCLUSIONS

1. The Western Karelia Province mostly consists of Neoarchaean gneissic granitoids, while Pal-aeoarchaean and Mesoarchaean granitoids (>2.9 Ga) are only locally present. The granitoid rocks are classified into four main groups, which are the TTG (tonalite-trondhjemite-granodiorite), sa-nukitoid, QQ (quartz diorite-quartz monzodior-ite) and GGM (granodiorite-granite-monzogran-ite) groups. Most ages obtained from TTGs are between 2.83–2.72 Ga, and they seem to define two age groups separated by a c. 20 Ma time gap. TTGs are 2.83–2.78 Ga in the older group and 2.76–2.72 Ga in the younger group. Sanukitoids have been dated at 2.74–2.72 Ga, QQs at c. 2.70 Ga and GGMs at 2.73–2.66 Ga. Based on REE, the TTGs fall into two major compositional groups, low-HREE TTGs and high-HREE TTGs, which obviously originated at different crustal depths, but the composition of the protolith has a signifi-cant effect on the REE patterns. Sanukitoids are interpreted as products of melting of subconti-nental metasomatized mantle. The GGM group represents partial melting of pre-existing TTG crust that also caused high-grade metamorphism and migmatisation.

2. Existing isotope data on volcanic rocks of the Kuhmo greenstone belt do not provide much evi-dence for their deposition on significantly older basement in intracratonic environment. The composition of the komatiites in Kuhmo indi-cates that they were derived from primitive upper mantle, representing fissure-controlled eruptions onto a pre-existing oceanic plateau. The volcanic rocks in the Ilomantsi greenstone belt represent arc magmatism within an attenuated continental margin where older basement rocks were assimi-lated by younger arc magmatism. Metamorphic evolution of the greenstone belts differs from that of the surrounding migmatites, indicating late-tectonic juxtaposition of greenstone belts and TTG migmatites.

3. Neoarchaean accretion of exotic terranes at c. 2.83–2.75 Ga and subsequent crustal stacking at around 2.73–2.68 Ga is a possible mechanism that largely generated the present structure of the Karelia Province, although it was again strongly reworked during the Svecofennian orogeny.

ACKNOWLEDGEMENTS

Jaana Halla is thanked for a critical review that greatly improved the manuscript.

REFERENCES

Abbott, D. H. & Hoffman, S. E. 1984. Archean plate tectonics 529–549. revisited 1: Heat flow, spreading rate, and the age of sub-ducting oceanic lithosphere and their effects on the origin and evolution of continents. Tectonics 3, 429–448.

Abbott, D., Burgess, L., Longhi, J. & Smith, W. H. F. 1994. An empirical thermal history of the Earth’s upper man-tle. Journal of Geophysical Research 99, 13835–13850.

Abbott, D. H. & Mooney, W. D. 1995. Crustal Structure and Evolution: Support for the Oceanic Plateau Model of Continental Growth. Reviews of Geophysics, Supple-ment, US National Report to the IUGG, 231–242.

Agard, P., Yamato, P., Jolivet, L. & Burov, E. 2009. Exhuma-tion of oceanic blueschists and eclogites in subduction zones: Timing and mechanisms. Earth-Science Reviews 92, 53–79.

Arestova, N. A., Gooskova, E. G. & Krasnova, A. F. 2000. Pal-aeomagnetism of the Shilos Structure rocks in the South-ern Vygozero greenstone belt, East Karelia. Fizika Zemli (Earth Physics − English translation) 5, 70−75.

Arndt, N. T., Lesher, C. M., Houl, M. G., Lewin, E. & Lacaze, Y. 2004. Intrusion and Crystallization of a Spinifex-Tex-tured Komatiite Sill in Dundonald Township, Ontario. Journal of Petrology 45, 2555–2571.

Barnes, S. J. & Roeder, P. L. 2001. The range of spinel com-positions in terrestrial mafic and ultramafic rocks. Jour-nal of Petrology, 42, 2279−2302.

Barr J. A., Grove T. L. & Wilson A. H. 2009. Hydrous komati-ites from Commondale, South Africa: An experimental study. Earth and Planetary Science Letters 284, 199–207.

Beaumont, C., Ellis, S., Hamilton, J. & Fullsack P. 1996. Mechanical model for subduction-collision tectonics of Alpine-type compressional orogens. Geology 24, 675–78.

Beaumont, C., Ellis, S. & Pfiffner, A. 1999. Dynamics of sediment subduction-accretion at convergent margins: short-term modes, long-term deformation, and tectonic implications. Journal of Geophysical Research 104, 17573–602.

Benn, K., Mareschal, J.-C. & Condie, K. C. 2006. Introduc-tion: Archean Geodynamics and Environments. In: Benn,

66


K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Ge-odynamics and Environments. Geophysical Monograph 164, 1–5.

Berman, R. G. 1988. Internally-consistent thermodynamic data for stoichiometric minerals in the system Na2O-K2O-CaO-MgO-FeO-Fe2O3-Al2O3-SiO2-TiO2-H2O-CO2. Journal of Petrology 29, 445−522.

Berman, R. G. 1991. Thermobarometry using multiequilib-rium calculations: a new technique with petrologic appli-cations. Canadian Mineralogist 29, 833–855.

Bibikova, E., Skiöld, T., Bogdanova, S., Gorbatschev, R. & Slabunov, A. 2001. Titanite-rutile thermochronometry across the boundary between the Archaean Craton in Karelia and the Belomorian Mobile Belt, eastern Baltic Shield. Precambrian Research 105, 315–330.

Bibikova, E. V., Samsonov, A. V., Shchipansky, A. A., Bogina, M. M., Gracheva, T. V. & Makarov, V. A. 2003. The His-ovaara Structure in the Northern Karelian Greenstone Belt as a Late Archean Accreted Island Arc: Isotopic Geochronological and Petrological Evidence. Petrology 11 (3), 261–290.

Bibikova, E. V., Petrova, A. & Claesson, S. 2005. The tem-poral evolution of sanukitoids in the Karelian Craton, Baltic Shield: an ion microprobe U–Th–Pb isotopic study of zircons. Lithos 79, 129–145.

Bickle, M. J. 1986. Implications of melting for stabilisation of the lithosphere and heat loss in the Archaean. Earth and Planetary Science Letters 80, 314–324.

Björnerud, M. G. & Austrheim, H. 2004. Inhibited eclogite formation: The key to the rapid growth of strong and buoyant Archean continental crust. Geology 32, 765–768.

Blake, T. S., Buick, R., Brown, S. J. A. & Barley, M. E. 2004. Geochronology of a Late Archaean flood basalt prov-ince in the Pilbara Craton, Australia: constraints on ba-sin evolution, volcanic and sedimentary accumulation, and continental drift rates. Precambrian Research 133, 143–173.

Bleeker, W. & Ernst, R. 2006. Short-lived mantle generated magmatic events and their dyke swarms: the key unlock-ing Earth’s palaeogeographic record back to 2.6 Ga. In: Hanski, E., Mertanen, S., Rämö, O. T. & Vuollo, J. (eds.), Dyke Swarms − Time Markers of Crustal Evolution. Proceedings of the Fifth International Dyke Confer-ence 2005 Rovaniemi, Finland, 31 July−3 Aug. 2005 & Fourth International Dyke Conference, Kwazulu-Natal, South Africa 26−29 June 2001. London: Taylor & Fran-cis Group, 3−26.

Bleeker, W., Hamilton, M. A. Ernst, R. E. & Kulikov, V. S. 2008. The search for Archean-Paleoproterozoic supercra-tons; new constraints on Superior-Karelia-Kola correla-tions within supercraton Superia, including the first ca. 2504 Ma (Mistassini) ages from Karelia. 33rd Interna-tional Geological Congress, Abstracts.

Blichert-Toft, J. & Albarede, F. 1994. Short-lived chemical heterogeneities in the Archean mantle with implications for mantle convection. Science 263, 1593–1596.

Bornhorst, T. J., Rasilainen, K. & Nurmi, P. A. 1993. Geo-chemical character of lithologic units in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) 1993. Geological devel-opment, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 133–145.

Brown, M. 2007. Metamorphic conditions in orogenic belts:

A record of secular change. International Geology Re-view 49, 193–234.

Brown, M. 2009. Metamorphic patterns in orogenic systems and the geological record. In: Cawood, P. A. & Kröner, A. (eds.) Earth Accretionary Systems in Space and Time. London: The Geological Society, Special Publications, 318, 37–74.

Card, K. D. 1990. A review of the Superior Province of the canadian shield, a product of Archean accretion. Pre-cambrian Research 48, 99−156.

Castillo, P. R. 2006. An overview of adakite petrogenesis. Chinese Science Bulletin 51, 3, 257—268.

Castillo, P. R., Janney, P. E. & Solidum, R. U. 1999. Petrology and geochemistry of Camiguin Island, southern Philip-pines: insights to the source of adakites and other lavas in a complex arc setting. Contributions to Mineralogy and Petrology 134, 33–51.

Cawood, P., Kröner, A. & Windley, B. 2003. Accretionary orogens: definition, character, significance. Geophysical Research Abstracts 5.

Condie, K. C. 1998. Episodic continental growth and super-continents: a mantle avalanche connection? Earth and Planetary Science Letters 163, 97–108.

Condie, K. C. 2000. Episodic continental growth models: afterthoughts and extensions. Tectonophysics 322, 153–162.

Condie, K. C. 2005. High field strength element ratios in Ar-chean basalts: a window to evolving sources of mantle plumes? Lithos 79, 491– 504.

Condie, K. C. & Benn, K. 2006. Archean geodynamics: simi-lar to or different from modern geodynamics. In: Benn, K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Ge-odynamics and Environments. Geophysical Monograph 164, 47–60.

Connolly, J. A. D 1990. Multivariable phase-diagrams - an algorithm based on generalized thermodynamics. Ameri-can Journal of Science 290, 666−718.

Connolly, J. A. D. 2005. Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation. Earth and Planetary Science Letters 236, 524−541.

Connolly, J. A. D. & Petrini, K. 2002. An automated strategy for calculation of phase diagram sections and retrieval of rock properties as a function of physical conditions. Journal of Metamorphic Geology 20, 697−708.

Corcoran, P. L., Mueller, W. U. & Kusky, T. M. 2004. Inferred ophiolites in the Archean Slave Craton. In: Kusky, T. M. (ed.) Precambrian ophiolites and related rocks. Develop-ments in Precambrian Geology 13, 363–404.

Daly, J. S., Balagansky, V. V., Timmerman, M.J., Whitehouse, M.J., de Jong, K., Guise, P., Bogdanova, S., Gorbatschev, R. & Bridgwater, D. 2001. Ion microprobe U-Pb zircon geochronology and isotopic evidence supporting a trans-crustal suture in the Lapland Kola Orogen, northern Fen-noscandian Shield. Precambrian Research 105, 289–314.

Daly, J. S., Balagansky, V. V., Timmerman, M. J. & White-house, M. J. 2006. The Lapland-Kola Orogen: Palaeo-proterozoic collision and accretion of the northern Fen-noscandian lithosphere. In: Gee, D. G. & Stephenson, R. A. (eds.) European Lithosphere Dynamics. Geological Society of London, Memoir 32, 579–598.

de la Roche, H., Leterrier, J., Grandclaude, P. & Marchal, M. 1980. A classification of volcanic and plutonic rocks us-ing R1R2-diagram and major element analyses – its rela-tionships with current nomenclature. Chemical Geology 29, 183–210.

67


Defant, M. J. & Drummond, M. S. 1990. Derivation of some modern arc magmas by melting of young subducted lith-osphere. Nature 367, 662−665.

Defant, M. J. & Drummond, M. S. 1993. Mount St. Helens: potential example of the partial melting of the subducted lithosphere in a volcanic arc. Geology 21, 547–550.

deWit, M. J. 1998. On Archean granites, greenstones, cratons and tectonics: does the evidence demand a verdict? Pre-cambrian Research 91, 181–226.

deWit, M. J. & Hart, R. A. 1993. Earth’s earliest continen-tal lithosphere, hydrothermal flux and crustal recycling. Lithos 30, 309–335.

Dilek, Y. & Polat, A. 2008. Suprasubduction zone ophiolites and Archean tectonics. Geology 36, 431–432.

Dilek, Y. & Furnes, H. 2011. Ophiolite genesis and global tectonics: Geochemical and tectonic fingerprinting of an-cient oceanic lithosphere. Geological Society of America Bulletin 123, 387–411.

Elming, S.-Å., Pesonen, L. J., Leino, M. A. H., Khramov, A. N., Mikhailova, N. P., Krasnova, A. F., Mertanen, S., Bylund, G. & Terho, M. 1993. The drift of the Fen-noscandian and Ukrainian Shields during the Precam-brian: a Palaeomagnetic analysis. Tectonophysics 223, 177–198.

Ernst, R. E. & Buchan, K. L. 2001. The use of mafic dike swarms in identifying and locating mantle plumes. In: Ernst, R. E. & Buchan. K. L. (eds.) Mantle Plumes: Their Identification Through Time. Geological Society of America Special Paper 352, 247−265.

Foley, S., Tiepolo, M. & Vannucci, R. 2002. Growth of early continental crust controlled by melting of amphibolite in subduction zones. Nature 417, 837−840.

Fowler, M. B., Kocks, H., Darbyshire, D. P. F. & Greenwood, P. B. 2008. Petrogenesis of high Ba-Sr plutons from the Northern Highlands Terrane of the British Caledonian Province. Lithos 105, 129–148.

Frey, F. A., Coffin. M. F., Wallace, P. J., Weis, D., Zhao, X., Wise, S. W. Jr., Wähnert, V., Teagle, D. A. H., Sacco-cia, P. J., Reusch, D. N. , Pringle, M. S., Nicolaysen, K. E., Neal, C. R., Müller, R. D., Moore, C. L., Mahoney, J. J., Keszthelyi, L., Inokuchi, H., Duncan, R. A., Delius, H., Damuth, J. E., Damasceno, D., Coxall, H. K., Borre, M. K., Boehm F., Barling, J., Arndt N. T. & Antretter, M. 2000. Origin and evolution of a submarine large igne-ous province: the Kerguelen Plateau and Broken Ridge, southern Indian Ocean. Earth and Planetary Science Let-ters 176, 73−89.

Frost, B. R., Barnes, C. G., Collins, W. J., Arculus, R. J., Ellis, D. J. & Frost, C. D. 2001. A geochemical classification for granitic rocks. Journal of Petrology 42, 2033−2048.

Glebovitsky V. A. 1997. The Early Precambrian of Russia. Harwood Academic. 261 p.

Goodwin, A. M. 1968. Archean protocontinental growth and early crustal history of the Canadian shield. 23rd Interna-tional Geological Gongress, Prague 1968. Vol. 1, 69−89.

Gooskova, E. G. & Krasnova, A. N. 1985. Palaeomagnetism of the basic Archean and Proterozoic intrusions of the eastern part of the Baltic Shield. Izvestia Akademii Nauk SSSR, ser Fizika Zemli (Earth Physics − English transla-tion) 21, 366−373.

Grove, T. L. & Parman, S. W. 2004. Thermal evolution of the Earth as recorded by komatiites. Earth and Planetary Sci-ence Letters 219, 173–187.

Gutscher, M.-A., Maury, R., Eissen, J.-P. & Bourdon, E. 2000. Can slab melting be caused by flat subduction? Geology 28, 6, 535–538.

Halla, J. 2002. Origin and Paleoproterozoic reactivation of Neoarchean high-K granitoid rocks in eastern Finland. PhD thesis, University of Helsinki, Finland. Annale Academica Scientiarium Fennicae, Geologica−Geo-graphica 163. 105 p.

Halla, J. 2005. Late Archean high-Mg granitoids (sanuki-toids) in the southern Karelian domain, eastern Finland: Pb and Nd isotopic constraints on crust-mantle interac-tions. Lithos 79, 161–178.

Halla, J. & Heilimo, E. 2009. Deformation-induced Pb isotope exchange between Kfeldspar and whole rock in Neoarchean granitoids: implications for assessing Proterozoic imprints. Chemical Geology 265, 303–312.

Halla, J., van Hunen, J., Heilimo, E. & Hölttä, P. 2009. Geo-chemical and numerical constraints on Neoarchean plate tectonics. Precambrian Research 174, 155–162.

Hamilton, W. B. 1998. Archean magmatism and tectonics were not products of plate tectonics. Precambrian Re-search 91, 143–179.

Hamilton, W. B. 2011. Plate tectonics began in Neoprotero-zoic time, and plumes from deep mantle have never oper-ated. Lithos 123, 1–20.


Heilimo, E., Halla, J. & Huhma, H. 2011. Single-grain zircon U–Pb age constraints of the western and eastern sanuki-toid zones in the Finnish part of the Karelian Province. Lithos 121, 87−99.

Heilimo, E., Halla, J. & Mikkola, P. 2012. Overview of Neo-archaean sanukitoid series in the Karelian Province, east-ern Finland. In: Hölttä, P. (ed.) The Archaean of the Ka-relia Province in Finland. Geological Survey of Finland, Special Paper 54.

Heilimo, E., Halla, J., Andersen, T. & Huhma, H. 2013.Neo-archean crustal recycling and mantle metasomatism: Hf–Nd–Pb–O isotope evidence from sanukitoids of the Fennoscandian shield. Precambrian Research (in press). Available at: http://dx.doi.org/10.1016/j.precamres. 2012.01.015

Hirose, K. 2010. The Earth’s missing ingredient. Scientific American 302, 6, 58−65.

Hoffman, P. F. & Ranalli, G. 1988. Archean oceanic flack tec-tonics. Geophysical Research Letters 15 (10), 1077–1080.

Hölttä, P. 1997. Geochemical characteristics of granulite facies rocks in the Varpaisjärvi area, central Fennoscan-dian Shield. Lithos 40, 31–53.

Hölttä, P. & Paavola, J. 2000. P-T-t development of Archae-an granulites in Varpaisjärvi, Central Finland, I: Effects of multiple metamorphism on the reaction history of mafic rocks. Lithos 50, 97–120.

Hölttä, P., Huhma, H., Mänttäri, I. & Paavola, J. 2000. P-T-t development of Archaean granulites in Varpaisjärvi, Central Finland, II: Dating of high-grade metamorphism with the U-Pb and Sm-Nd methods. Lithos 50, 121–136.

Hölttä, P., Balagansky, V., Garde, A. A., Mertanen,S., Pel-tonen, P., Slabunov, A., Sorjonen-Ward, P. & Whitehouse, M. 2008. Archean of Greenland and Fennoscandia. Epi-sodes 31 (1), 1–7.

Hölttä, P., Heilimo, E., Huhma, H., Juopperi, H., Kontinen, A., Konnunaho, J., Lauri, L,, Mikkola, P., Paavola, J. & Sorjonen-Ward, P. 2012. Archaean complexes of the Ka-relia Province in Finland. In: Hölttä, P. (ed.) The Archae-an of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

68


Howell, D. G. 1989. Tectonics of Suspect Terranes. New York: Chapman and Hall. 232 p.

Huhma, H., Kontinen, A. & Laajoki, K. 2000. Age of the metavolcanic-sedimentary units of the Central Puolanka Group, Kainuu schist belt, Finland. In: 24. Nordiske Geologiske Vintermøte, Trondheim 6.−9. januar 2000. Geonytt 1, 87–88.

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halko-aho, T., Hanski., E., Hokkanen. T., Hölttä, P., Juopperi, H., Konnunaho, J., Lahaye, Y., Luukkonen., E., Pietikäi-nen, K., Pulkkinen, A., Sorjonen-Ward, P. , Vaasjoki, M. & Winehouse, M. 2012a. The age of Archean greenstone belts in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Fin-land, Special Paper 54.

Huhma, H., Kontinen, A., Mikkola, P., Halkoaho, T., Hokka-nen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Luukko-nen, E., Mutanen, T. Peltonen, P., Pietikäinen, K. & Pulk-kinen, A. 2012. Nd isotopic evidence for Archean crustal growth in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.


Jones, D. L. 1990. Synopsis of late Palaeozoic and Mesozoic terrane accretion within the Cordillera of western North America. In: Dewey, J. F., Gass, I. G., Curry, G. B., Har-ris, N. B. W. & Sengör, A. M. C. (eds.) Allochthonous Ter-ranes. Cambridge: Cambridge University Press, 23−30.

Jones, D. L., Howell, P. G., Coney, P. J. & Monger, J. W. 1983. Recognition, character and analysis of tectonostrati-graphic terranes in western North America. Journal of Geological Education, 31, 295−303.

Käpyaho, A., Mänttäri, I. & Huhma, H. 2006. Growth of Archaean crust in the Kuhmo district, eastern Finland: U-Pb and Sm-Nd isotope constraints on plutonic rocks. Precambrian Research 146, 95–119.

Käpyaho, A. Hölttä, P. & Whitehouse, M. 2007. U-Pb zircon geochronology of selected Neoarchaean migmatites in eastern Finland. Bulletin of the Geological Society of Finland 79 (1), 95–115.

Kontinen, A., Paavola, J. & Lukkarinen, H. 1992. K-Ar ages of hornblende and biotite from Late Archaean rocks of eastern Finland − interpretation and discussion of tec-tonic implications. Geological Survey of Finland, Bulle-tin 365. 31 p.

Kontinen, A. & Paavola, J. 2006. A preliminary model of the crustal structure of the eastern Finland Archaean complex between Vartius and Vieremä, based on con-straints from surface geology and FIRE 1 seismic survey. In: Kukkonen, I. T. & Lahtinen, R. (eds.) 2006. Finn-ish Reflection Experiment FIRE 2001−2005. Geological Survey of Finland, Special Paper 43, 223–240.

Kontinen, A., Käpyaho, A., Huhma, H., Karhu, J., Matukov, D. I., Larionov, A. & Sergeev, S. A. 2007. Nurmes parag-neisses in eastern Finland, Karelian craton: provenance, tectonic setting and implications for Neoarchaean craton correlation. Precambrian Research 152, 119–148.

Korenaga, J. 2006. Archean geodynamics and the thermal evolution of Earth. In: Benn, K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Geodynamics and Environ-ments. Geophysical Monograph 164, 7–32.

Korja, A., Lahtinen, R., Heikkinen, P. & Kukkonen, I. T. 2006. A geological interpretation of the upper crust along FIRE 1. In: Kukkonen, I. T. & Lahtinen, R. (eds.) 2006. Finnish Reflection Experiment FIRE 2001−2005. Geo-logical Survey of Finland, Special Paper 43, 45–76.

Kozhevnikov, V. N., Berezhnaya, N. G., Presnyakov, S. L. Lepekhina, E. N. Antonov, A. V. & Sergeev, S. A. 2006. Geochronology (SHRIMP-II) of zircon from Ar-chean lithotectonic associations in the greenstone belts of the Karelian craton: implications for stratigraphic and geodynamic reconstructions. Stratigraphy and Geologi-cal Correlation 14(3), 240–259.

Krasnova, A. F. & Gooskova, E. G. 1990. Geodynamic evo-lution of the Wodlozero block of Karelia according to palaeomagnetic data. Izvestiya. Earth Physics 26, 80−85.

Kröner, A. & Layer, P. W. 1994. Crust formation and plate motion in the early Archean. Science 256, 1405–1411.

Kusky, T. M. & Kidd, W. S. F. 1992. Remnants of an Archean oceanic plateau, Belingwe greenstone belt, Zimbabwe. Geology 20, 43–46.

Kusky, T. M. & Polat, A. 1999. Growth of granite-greenstone terranes at convergent margins, and stabilization of Ar-chean cratons. Tectonophysics 305, 43–73.

Kusky, T. M., Li, J.-H. & Tucker, R. D. 2001. 2.505-Billion-Year-Old Oceanic Crust and Mantle The Archean Dong-wanzi Ophiolite Complex, North China Craton. Science 292, 1142−1145.

Kusky, T. M., Li, J. H., Raharimahefa, T. & Carlson, R. W. 2004. Origin and emplacement of Archean ophiolites of the Central Orogenic Belt, North China Craton. In: Kusky, T. M. (ed.) Precambrian ophiolites and related rocks. Developments in Precambrian Geology 13, 223–282.

Laajoki, K. 1991. Stratigraphy of the northern end of the early Proterozoic (Karelian) Kainuu Schist Belt and as-sociated gneiss complexes, Finland. Geological Survey of Finland, Bulletin 358. 105 p.

Laajoki, K. & Luukas, J. 1988. Early Proterozoic stratigraphy of the Salahmi-Pyhäntä area, central Finland, with an emphasis on applying the principles of lithodemic stra-tigraphy to a complexly deformed and metamorphosed bedrock. Bulletin of the Geological Society of Finland 60 (2), 79–106.

Lalli, K. 2002. Petrography, geochemistry and metamor-phic petrology of the Isokumpu area in the Pudasjärvi granulite belt. Unpublished Master’s Thesis, University of Oulu. (in Finnish)

Langford, F. F. &Morin, J. A. 1976. The development of the Superior Province of northwestern Ontario by merging island arcs. American Journal of Science 276, 1023−1034.

Lauri, L. S., Rämö, O. T., Huhma, H., Mänttäri, I. & Räsänen, J. 2006. Petrogenesis of silicic magmatism related to the 2. 44 Ga rifting of Archean crust in Koillismaa, eastern Finland. Lithos 86, 137−166.

Lauri, L. S., Andersen, T., Hölttä, P., Huhma, H. & Graham, S. 2011. Evolution of the Archaean Karelian Province in the Fennoscandian Shield in the light of U–Pb zircon ages and Sm–Nd and Lu–Hf isotope systematics. Lon-don: Journal of the Geological Society, 167, 1–18.

Lobach-Zhuchenko, S. B., Rollinson, H. R., Chekulaev, V. P., Arestova, N. A., Kovalenko, A. V., Ivanikov V. V., Guseva, N. S., Sergeev, S. A., Matukov, D. I. & Jarvis K. E. 2005. The Archaean sanukitoid series of the Baltic Shield: geo-logical setting, geochemical characteristics and implica-tions for their origin. Lithos 79, 107– 128.

Lobach-Zhuchenko, S. B., Rollinson, H., Chekulaev, V. P.,

69


SavatenkoV, V. M., Kovalenko, A.V., Martin, H., Gu-seva, N. S. & Arestova, N. A. 2008. Petrology of a late Archaean, highly potassic, sanukitoid pluton from the Baltic Shield: Insights into late Archaean mantle metaso-matism. Journal of Petrology 49 (3), 393–420.

Luukkonen, E. J. 1985. Structural and U-Pb isotopic study of late Archaean migmatitic gneisses of the Presvecoka-relides, Lylyvaara, Eastern Finland. Transactions of the Royal Society of Edinburgh, Earth Sciences 76, 401–410.

Luukkonen, E. 1988. Moisiovaaran ja Ala-Vuokin kartta-alueiden kallioperä. Summary: Pre-Quaternary Rocks of the Moisiovaara and Ala-Vuokki Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheets 4421 and 4423+4441. Geological Survey of Finland. 90 p.

Luukkonen, E. J. 1992. Late Archaean and early Proterozoic structural evolution in the Kuhmo-Suomussalmi terrain, eastern Finland. Publications of the University of Turku, Series A. II. University of Turku, Biologica−Geographi-ca−Geologica 78. 115 p.

Luukkonen, E., Halkoaho, T., Hartikainen, A., Heino, T., Niskanen, M., Pietikäinen, K. & Tenhola, M. 2002. Re-port of the GTK project ’The Archaean areas of eastern Finland’ in the years 1992−2001 in the communities of Suomussalmi, Hyrynsalmi, Kuhmo, Nurmes, Rauta-vaara, Valtimo, Lieksa, Ilomantsi, Kiihtelysvaara, Eno, Kontiolahti, Tohmajärvi and Tuupovaara. Geological Survey of Finland, archive report M 19/4513/2002/1. 265 p. (in Finnish)

Männikkö, K. H. 1988. Myöhäisarkeeisen Koveron liuske-jakson länsiosan deformaatio ja metamorfoosi. Pohjois-Karjalan malmiprojekti. Oulu: Oulun yliopisto, Raportti 15. 108 p.

Mänttäri, I. & Hölttä, P. 2002. U-Pb dating of zircons and monazites from Archean granulites in Varpaisjärvi, cen-tral Finland: evidence for multiple metamorphism and Neoarchean terrane accretion. Precambrian Research 118, 101−131.

Martin, H. 1995. The Archean grey gneisses and the genesis of the continental crust. In: Condie, K.C. (ed.) The Ar-chean crustal evolution: Amsterdam: Elsevier, 205–259.

Martin, H. 1999. The adakitic magmas: modern analogues of Archaean granitoids. Lithos 46, 411–429.

Martin, H. & Moyen, J.-F. 2002. Secular changes in tonalite-trondhjemite-granodiorite composition as markers of the progressive cooling of Earth. Geology, 30, 4, 319–322.

Martin, H., Smithies, R. H., Rapp, R., Moyen, J.-F. & Cham-pion, D. 2005. An overview of adakite, tonalite–trond-hjemite–granodiorite (TTG), and sanukitoid: relation-ships and some implications for crustal evolution. Lithos 79, 1–24.

Mertanen, S., Pesonen, L. J., Hölttä, P. & Paavola, J. 2006a. Palaeomagnetism of Palaeo-proterozoic dolerite dykes in central Finland. In: Hanski, E., Mertanen, S., Rämö, O. T. & Vuollo, J. (eds.) Dyke Swarms − Time Markers of Crustal Evolution, Proceedings of the Fifth Interna-tional Dyke Conference, IDC5, Rovaniemi, Finland, 31 July−3 August 2005. Taylor & Francis Group/ Balkema, 243−256.

Mertanen, S., Vuollo, J. I., Huhma, H., Arestova, N. A. & Ko-valenko, A. 2006b. Early Paleoproterozoic-Archean dykes and gneisses in Russian Karelia of the Fennoscandian Shield–new paleomagnetic, isotope age and geochemi-cal investigations. Precambrian Research 144 (3−4), 239−260.

Mertanen, S. & Korhonen, F. 2008. Archean-Paleoprote-

rozoic configuration of Laurentia and Baltica focusing on paleomagnetic data from Baltica. 33rd International Geological Congress, 6−14 August 2008, Oslo, Norway. Abstracts.

Mertanen, S. & Korhonen, F. 2011. Paleomagnetic constraints on an Archean – Paleoproterozoic Superior–Karelia con-nection: new evidence from Archean Karelia. Precambri-an Research 186, 193–204.

Mikkola, P. 2008. Koillis-Kainuun kallioperä. Summary: Pre-Quaternary rocks of Northeast Kainuu. Geological Survey of Finland, Report of Investigation 175. 53 p. + 5 app. (Electronic publication)

Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011a. Archean crustal evolution of the Suomussalmi district as part of the Kianta Complex, Karelia; con-straints from geochemistry and isotopes of granitoids. Lithos 125, 287−307.

Mikkola, P., Salminen, P., Torppa, A. & Huhma, H. 2011b. The 2. 74 Ga Likamännikkö complex in Suomussalmi, East Finland : lost between sanukitoids and truly alka-line rocks? Lithos 125, 716−728.

Mikkola, P., Lauri, L. S. & Käpyaho, A. 2012. Neoarchean leucogranitoids of the Kianta Complex, Karelian Prov-ince, Finland: Source characteristics and processes re-sponsible for the observed heterogeneity. Precambrian Research 206–207, 72–86.

Mints, M. V., Berzin, R. G., Suleĭmanov, A. K., Zamozhn-yaya, N. G., Stupak, V. M., Konilov, A. N., Zlobin, V. L. & Kaulina, T. V. 2004. The deep structure of the early Precambrian crust of the Karelian craton, southeast-ern Fennoscandian shield: results of investigation along CMP profile 4B. Geotectonics 38 (2), 87–102.

Mints, M. V., Belousova, E. A., Konilov, A. N., Natapov, L. M., Shchipansky, A. A. Griffin, W. L., O’Reilly, S. Y., Do-kukina, K. A. & Kaulina, T. V. 2010. Mesoarchean sub-duction processes: 2.87 Ga eclogites from the Kola Pen-insula, Russia. Geology 38, 739–742.

Moyen, J.-F. 2009. High Sr/Y and La/Yb ratios: The mean-ing of the “adakitic signature”. Lithos 112, 556–574.

Moyen, J.-F. 2011. The composite Archaean grey gneisses: Petrological significance, and evidence for a non-unique tectonic setting for Archaean crustal growth. Lithos 123, 21−36.

Moyen, J.-F. & Stevens, G. 2006. Experimental constraints on TTG petrogenesis: implications for Archean geodynam-ics. In: Benn, K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Geodynamics and Environments. Geophysical Monograph 164, 149–176.

Mutanen, T. & Huhma, H. 2003. The 3. 5 Ga Siurua trond-hjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland. Bulletin of the Geological Society of Finland 75, 51–68.

Nair, R. & Chacko, T. 2008. Role of oceanic plateaus in the initiation of subduction and origin of continental crust. Geology 36 (7), 583–586.

Nehring, F., Foley, S. F., Hölttä, P. & Kerkhof, A. M. van den 2009. Internal differentiation of the Archean continental crust: fluid-controlled partial melting of granulites and TTG-amphibolite associations in central Finland. Jour-nal of Petrology 50 (1), 3–35.

Neuvonen, K. J., Korsman, K., Kouvo, O. & Paavola, J. 1981. Paleomagnetism and age relationship of the rocks in the Main Sulphide Ore Belt in central Finland. Bulletin of the Geological Society of Finland 53, 109−133.

Neuvonen, K. J., Pesonen, L. J. & Pietarinen, H. 1997. Rema-nent Magnetization in the Archaean Basement and Cut-

70


ting Diabase Dykes in Finland, Fennoscandian Shield. Geophysica 33(1), 111−146.

O’Brien, H., Huhma, H. & Sorjonen-Ward, P. 1993. Petro-genesis of the late Archean Hattu schist belt, Ilomantsi, eastern Finland: geochemistry and Sr, Nd isotopic com-position. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) 1993. Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 147–184.

Ohta, H., Maruyama, S., Takahashi, E., Watanabe, Y. & Kato, Y. 1996. Field occurrence, geochemistry and petrogenesis of the Archean Mid-Oceanic Ridge Basalts (AMORBs) of the Cleaverville area, Pilbara Craton, Western Aus-tralia. Lithos 37, 199–221.

Paavola, J. 1986. A communication on the U-Pb and K-Ar age relations of the Archaean basement in the Lapinlah-ti-Varpaisjärvi area, central Finland. Geological Survey of Finland, Bulletin 339, 7−15.

Paavola, J. 1999. Rautavaaran kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Rautavaara Map-Sheet area. Geological map of Finland 1:100 000, Explanation to the Map of Pre-Qauternary Rocks, Sheet 3343. Geological Survey of Finland. 53 p.

Paavola, J. 2003. Vieremän kartta-alueen kallioperä. Sum-mary: Pre-Quaternary Rocks of the Vieremä Map-Sheet area. Geological map of Finland 1:100 000, Explanation to the Map of Pre-Qauternary Rocks, Sheet 3342. Geo-logical Survey of Finland. 40 p. + 2 app. maps.

Pajunen, M. & Poutiainen, M. 1999. Palaeoproterozoic pro-grade metasomatic-metamorphic overprint zones in Archaean tonalitic gneisses, eastern Finland. In: Stud-ies related to the Global Geoscience Transects/SVEKA Project in Finland. Bulletin of the Geological Society of Finland 71 (1), 73−132.

Papunen, H., Halkoaho, T. & Luukkonen, E. 2009. Archaean evolution of the Tipasjärvi-Kuhmo-Suomussalmi Green-stone Complex, Finland. Geological Survey of Finland, Bulletin 403. 68 p. + App. data cd.

Patiño Douce, A. E. 1999. What do experiments tell us about the relative contribution of crust and mantle to the origin of granitic magmas. Geological Society Special Publica-tion 168, 55−76.

Patiño Douce, A. E. 2004. Vapor-absent melting of tonalite at 15–32 kbar. Journal of Petrology 46 (2), 275–290.

Peacock, S. M., Rushmer, T. & Thompson, A. B. 1994. Partial melting of subducting oceanic crust. Earth and Planetary Science Letters 121, 227–244.

Peltonen, P., Mänttäri, I., Huhma, H. & Whitehouse, M. J. 2006. Multi-stage origin of the lower crust of the Kare-lian craton from 3. 5 to 1. 7 Ga based on isotopic ages of kimberlite-derived mafic granulite xenoliths. Precam-brian Research 147, 107−123.

Percival, J. A., McNicoll, V., Brown, J. L. & Whalen, J. B. 2004. Convergent margin tectonics, central Wabigoon subprovince, Superior Province, Canada. Precambrian Research 132, 213−244.

Percival, J., Sanborn-Barrie, M., Skulski, T., Stott, G. M., Helmstaedt, H. & White, D. J. 2006. Tectonic evolution of the western Superior Province from NATMAP and Lithoprobe studies. Canadian Journal of Earth Sciences, 43, 1085−1117.

Petrone, C. M. & Ferrari, L. 2008. Quaternary adakite - Nb-enriched basalt association in the western Trans-Mexican Volcanic Belt: is there any slab melt evidence? Contribu-tions to Mineralogy and Petrology 156, 73–86.

Pietikäinen, K. & Vaasjoki, M. 1999. Structural observa-tions and U-Pb mineral ages from igneous rocks at the Archaean-Palaeoproterozoic boundary in the Salahmi Schist Belt, central Finland: constraints on tectonic evo-lution. Bulletin of the Geological Society of Finland 71 (1), 133−142.

Polat, A. & Kerrich, R. 2000. Archean greenstone belt mag-matism and the continental growth-mantle evolution connection: constraints from Th-U-Nb-LREE systemat-ics of the 2.7 Ga Wawa subprovince, Superior Province, Canada. Earth and Planetary Science Letters 175, 41−54.

Polat, A & Kerrich, R. 2006. Reading the geochemical fin-gerprints of Archean hot subduction volcanic rocks. In: Benn, K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Geodynamics and Environments. Geophysical Monograph 164, 198−213.

Powell, R., Holland, T. J. B. & Worley, B. 1998. Calculating phase diagrams involving solid solutions via non-linear equations, with examples using THERMOCALC. Jour-nal of Metamorphic Geology 16, 577–588.

Puchtel, I. 2004. 3.0 Ga Olondo Greenstone Belt in the Aldan Shield, E. Siberia. In: Kusky, T. (ed.) Precambrian Ophi-olites and Related Rocks. Developments in Precambrian Geology 13. Amsterdam: Elsevier, 405–423.

Puchtel, I. S., Hofmann, A. W., Mezger, K., Jochum, K. P., Shchipansky, A. A. & Samsonov, A. V. 1998. Oceanic pla-teau model for continental crustal growth in the Archae-an: a case study from the Kostomuksha greenstone belt, NW Baltic shield. Earth and Planetary Science Letters 155, 57–74.

Puchtel, I. S., Hofmann, A. W., Amelin, Yu. V., Garbe-Schön-berg, C. D., Samsonov, A. V. & Shchipansky, A. A. 1999. Combined mantle plume–island arc model for the forma-tion of the 2.9 Ga Sumozero-Kenozero greenstone belt, SE Baltic Shield: isotope and trace element constraints. Geochimica et Cosmochimica Acta 63, 3579–3595.

Rapp, R. P., Watson, E. B. & Miller, C. F. 1991. Partial melt-ing of amphibolite/eclogite and the origin of Archaean trondhjemites and tonalites. Precambrian Research 51, 1–25.

Rapp, R. P., Shimizu, N. & Norman, M. D. 2003. Growth of early continental crust by partial melting of eclogite. Na-ture 425 (9), 605−609.

Rasilainen, K, Lahtinen, R. & Bornhorst, T. 2007. Rock geo-chemical database of Finland, Manual. Geological Sur-vey of Finland, Report of Investigation 164. 38 p.

Richards, J. P. & Kerrich, R. 2007. Adakite-like rocks: their diverse origins and questionable role in metallogenesis. Economic Geology 102 (4), 537−576.

Samsonov, A. V., Bogina, M. M., Bibikova, E. V., Petrova, A.Y u. & Shchipansky, A. A. 2005. The relationship between adakitic, calc-alkaline volcanic rocks and TTGs: implica-tions for the tectonic setting of the Karelian greenstone belts, Baltic Shield. Lithos 79, 83–106.

Şengör, A. M. C. & Natal’in, B. A. 1996. Turkic-type orogeny and its role in the making of the continental crust, An-nual Review of Earth and Planetary Science 24, 263–337.

Şengör, A. M. C. & Natal’in, B. A. 2004. Phanerozoic ana-logues of Archaean oceanic basement fragments: Altaid ophiolites and ophirags. In: Kusky, T. (ed.) Precambrian Ophiolites and Related Rocks. Developments in Precam-brian Geology 13. Amsterdam: Elsevier, 675–726.

Şengör, A. M. C., Sinan, Ö. M., Keskin, M., Sakınç, M., Özbakır, A. D. & Kayan, İ. 2008. Eastern Turkish high plateau as a small Turkic-type orogen: Implications for post-collisional crust-forming processes in Turkic-type

71


orogens. Earth-Science Reviews 90, 1–48.Sergeev, S. A., Bibikova, E. V., Matukov, D. I. & Lobach-

Zhuchenko, S. B. 2007. Age of the magmatic and meta-morphic processes in the Vodlozero Complex, Baltic Shield: an ion microprobe (SHRIMP II) U–Th–Pb iso-topic study of zircons. Geochemistry International 45(2), 198–205.

Shchipansky, A. A., Samsonov, A. V., Bibikova, E. V., Baba-rina, I. I., Konilov, A. N., Krylov, K. A., Slabunov, A. I. & Bogina, M. M. 2004. 2.8 Ga boninite-hosting partial su-prasubduction ophiolite sequences from the North Kare-lian greenstone belt, NE Baltic Shield, Russia. In: Kusky, T. (ed.) Precambrian Ophiolites and Related Rocks. De-velopments in Precambrian Geology 13, 425–487.

Shchipansky, A. A., Khodorevskaya, L. I., Konilov A. N. & Slabunov A. I. 2012. Eclogites from the Belomorian Mo-bile Belt (Kola Peninsula): geology and petrology. Rus-sian Geology and Geophysics 53, 1–21.

Skjerlie, K. P., Patiño Douce, A. E. & Johnston A. D. 1993. Fluid absent melting of a layered crustal protolith: impli-cations for the generation of anatectic granites. Contri-butions to Mineralogy and Petrology 114, 365–378.

Slabunov, A. I., Lobach-Zhuchenko, S. B., Bibikova, E. V.,

Sorjonen-Ward, P., Balagansky, V. V., Volodichev, O. I., Shchipansky, A. A., Svetov, S. A., Chekulaev, V. P., Aresto-va, N. A. & Stepanov, V. S. 2006. The Archaean nucleus of the Baltic/Fennoscandian Shield. In: Gee, D. G. & Ste-phenson, R. A. (eds.) European Lithosphere Dynamics. Geological Society of London, Memoir 32, 627–644.

Smithies, R. H. 2000. The Archaean tonalite-trondhjemite-granodiorite (TTG) series is not an analogue of Ceno-zoic adakite. Earth and Planetary Science Letters 182, 115–125.

Smithies, R. H., Champion, D. C. & Cassidy, K. F. 2003. For-mation of Earth’s early Archaean continental crust. Pre-cambrian Research 127, 89–101.

Sorjonen-Ward, P. 1993. An overview of structural evolution and lithic units within and intruding the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) 1993. Geological devel-opment, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 9–102.

Sorjonen-Ward, P. 2006. Geological and structural frame-work and preliminary interpretation of the FIRE 3 and FIRE 3A reflection seismic profiles, central Finland. In: Kukkonen, I. T. & Lahtinen, R. (eds.) 2006. Finnish Re-flection Experiment FIRE 2001−2005. Geological Sur-vey of Finland, Special Paper 43, 105–159.

Sorjonen-Ward, P. & Claoué-Long, J. 1993. Preliminary note on ion probe results for zircons from the Silvevaara gran-odiorite, Ilomantsi, eastern Finland. In: Autio, S. (ed.) 1993. Geological Survey of Finland, Current Research 1991−1992. Geological Survey of Finland, Special Paper 18, 25–29.

Sorjonen-Ward, P. & Luukkonen, E. 2005. Archean rocks. In: Lehtinen, M., Nurmi, P. A. & Rämö, O. T. (eds.) The Pre-cambrian Geology of Finland - Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier, 19−99.

Springer, W. & Seck, H. A. 1997. Partial fusion of basic granulites at 5 to 15 kbar: implications for the origin of TTG magmas. Contributions to Mineralogy and Petrol-ogy 127, 30–45.

Stiegler, M. S., Lowe, D. R. & Byerly, G.R. 2010. The Petro-genesis of Volcaniclastic Komatiites in the Barberton

Greenstone Belt, South Africa: a Textural and Geochem-ical Study. Journal of Petrology, 1−26.

Streckeisen, A. & Le Maitre, R. W. 1979. A chemical approxi-mation to the modal QAPF classification of the igneous rocks. Neues Jahrbuch für Mineralogie, Abhandlungen 136, 169–206.

Strik, G., Blake, T. S., Zegers, T. E., White, S. E. & Lan-gereis, C. G. 2003. Palaeomagnetism of flood basalts in the Pilbara Craton, Western Australia: Late Archaean continental drift and the oldest known reversal of the geomagnetic field. Journal of Geophysical Research 108 (B12), 2551, EMP 2-1-2-21.

Svetov, S. A., Kudryashov, N. M., Ronkin, Yu. L., Huhma, H., Svetova, A. I. & Nazarova, T. N. 2006. Mesoarchean island-arc association in the Central Karelian Terrane, Fennoscandian Shield: new geochronological data. Doklady Earth Sciences 406 (1), 103–106.

Tateno, S., Hirose, K., Sata, N. & Ohishi, Y. 2009. Determi-nation of post-perovskite phase transition boundary up to 4400 K and implications for thermal structure in D″ layer. Earth and Planetary Science Letters 277, 130–136.

Thurston, P. 2002. Autochthonous development of Superior Province greenstone belts? Precambrian Research 115, 11−36.

Tuisku, P. 1988. Geothermobarometry in the Archean Kuhmo-Suomussalmi greenstone belt, eastern Finland. In: Marttila, E. (ed.) 1988. Archaean geology of the Fen-noscandian Shield: Proceedings of a Finnish-Soviet sym-posium in Finland on July 28-August 7, 1986. Geological Survey of Finland, Special Paper 4, 171−172.

Tuukki, P. A. 1991. Arkeeinen Koveron liuskejakso ja sen mafisten ja ultramafisten kivien geokemia ja petrogenesis. Pohjois-Karjalan malmiprojekti. Oulu: Oulun yliopisto, Raportti 28. 129 p.

Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen, S. 1993. U-Pb age determinations and sulfide Pb-Pb characteris-tics from the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) 1993. Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 103–131.

Vaasjoki, M., Taipale, K. & Tuokko, I. 1999. Radiometric ages and other isotopic data bearing on the evolution of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland. Bulletin of the Geological Society of Finland 71 (1), 155–176.

Vaasjoki, M., Kärki, A. & Laajoki, K. 2001. Timing of Pal-aeoproterozoic crustal shearing in the Central Fennos-candian Shield according to U-Pb data from associated granitoids, Finland. Bulletin of the Geological Society of Finland 73 (1−2), 87–101.

van der Velden, A. J., Cook, F. A., Drummond, B .J. & Goleby, B. R. 2006. Reflections of the Neoarchean: a global per-spective. In: Benn, K., Mareschal, J.-C. & Condie, K. C. (eds.) Archean Geodynamics and Environments. Geo-physical Monograph 164, 255–265.

van Hunen, J., van den Berg, A. & Vlaar, N. J. 2004. Various mechanisms to induce present-day shallow flat subduc-tion and implications for the younger Earth: a numeri-cal parameter study. Physics of the Earth and Planetary Interiors 146, 179–194.

Volodichev, O. I., Slabunov, A. I., Bibikova, E. V., Konilov, A. N. & Kuzenko, T. I. 2004. Archean Eclogites in the Belomorian Mobile Belt, Baltic Shield. Petrology 12 (6), 540–560.

72


Vuollo, J. & Huhma, H. 2005. Paleoproterozoic mafic dikes in NE Finland. In: Precambrian geology of Finland : key to the evolution of the Fennoscandian Shield. Develop-ments in Precambrian geology 14. Amsterdam: Elsevier, 195−236.

Watkins J. M., Clemens, J. D. & Treloar, P. J. 2007. Archaean TTGs as sources of younger granitic magmas: melting of sodic metatonalites at 0.6–1.2 GPa. Contributions to

Mineralogy and Petrology 154, 91–110.Winter, J. D. 2001. Igneous and metamorphic petrology.

PNew Jersey: Rentice Hall. 697 p.Wu, C.-M., Zhang, J. & Ren, L.-D. 2004. Empirical garnet–

biotite–plagioclase–quartz (GBPQ) geobarometry in m edium- to high-grade metapelites. Journal of Petrology 45 (9) , 1907–1921.

Appendix 1. Chemical analyses of granitoids. amphibolites and volcanic rocks of the greenstone belts. Missing or zero values are below detection limits or not analyzed. Analyses NA1-13 are from Paavola (2003). A1602 and A1611 from Mutanen and Huhma (2003) and A1661 from Lauri et al. (2006).

TTGs and QQs.Map

coordinateswt.% ppm

Sample Northing (KKJ)

Easting (KKJ)

SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 Sum of oxides

S Cl Cu Zn Ga Sr Ba Pb Ce Co Cr Dy Er Eu Gd Hf Ho La Lu Nb Nd Ni Pr Rb Sc Sm Ta Tb Th Tm U V Y Yb Zr

XRF ICP-MS

low-HREE TTGs, Eu-negative

27-PSH-04 7295076 3409888 65.20 0.60 16.20 3.79 0.05 1.36 3.03 4.54 3.81 0.27 98.84 277 161 0 73 27 1074 2591 34 123 7.41 12.20 1.87 0.88 1.39 4.69 5.10 0.36 67.60 0.12 4.88 46.50 5.52 13.10 73.40 5.07 6.82 0.23 0.53 8.10 0.10 0.47 52.90 9.61 0.69 214.00

47-PSH-04 7288134 3429931 72.00 0.34 14.20 2.30 0.04 0.81 1.87 3.85 4.10 0.09 99.60 140 35 28 272 827 52 85.3 4.39 13.3 1.71 0.75 0.79 3.02 3.98 0.27 61.5 0.11 9.22 31.7 9.16 9.13 172 3.41 4.29 0.83 0.39 31.0 0.15 2.95 26.0 9.27 0.75 126

70.1-PSH-04 7335466 3437280 69.20 0.35 15.80 2.79 0.06 1.04 3.07 5.00 1.92 0.10 99.32 58 26 472 461 17.20 6.63 8.28 0.91 0.52 0.52 1.63 2.74 0.18 6.65 0.00 1.61 7.74 5.76 1.68 130.00 5.30 1.56 0.00 0.20 1.36 0.00 0.00 38.00 4.78 0.40 82.10

33-PSH-04 7251572 3443602 71.00 0.32 15.40 2.65 0.06 1.04 1.74 5.14 1.91 0.09 99.35 70 49 24 345 538 22.20 4.87 5.23 1.22 0.40 0.56 1.76 2.80 0.17 10.30 0.00 2.21 10.30 0.00 2.67 45.90 4.02 1.85 0.00 0.20 1.96 0.00 0.61 29.00 4.64 0.35 94.90

N93001872 7336660 3444840 70.60 0.28 15.50 2.61 0.05 1.02 2.75 4.98 1.83 0.11 99.73 59 414 409 34.7 5.8 1.29 0.67 0.64 2.05 1.69 0.2 18.4 0.1 4.02 17.2 4.49 82 4.92 2.49 0.41 0.28 2.97 0.1 0.81 33.5 7.24 0.58 64.4

99-PSH-04 7332874 3458005 64.50 0.65 16.00 4.24 0.08 2.73 2.02 5.10 3.45 0.30 99.07 95 23 741 1374 203 10.30 7.04 4.05 1.31 3.24 11.20 4.14 0.57 115.00 0.18 5.68 102.00 8.37 26.90 83.80 7.99 14.60 0.32 1.14 8.87 0.17 1.04 67.00 16.10 0.98 169.00

96-PSH-04 7326669 3469776 64.80 0.65 16.30 4.18 0.06 2.02 4.29 4.98 1.57 0.21 99.07 100 68 24 896 988 54.60 12.10 9.02 1.72 0.82 1.38 3.67 3.48 0.32 27.80 0.10 2.86 27.00 7.47 6.15 28.30 7.88 4.62 0.00 0.41 0.65 0.12 0.23 81.70 7.60 0.68 135.00

145-PSH-04 7314783 3474729 68.10 0.41 16.00 3.33 0.06 1.52 2.85 5.56 1.35 0.12 99.29 60 79 24 497 804 45.50 7.72 5.96 1.15 0.50 0.79 2.21 2.08 0.13 25.90 0.00 1.95 19.40 0.00 5.23 27.70 8.03 2.78 0.00 0.25 1.53 0.00 0.00 51.40 4.75 0.15 83.30

102.1-PSH-04 7300662 3477529 71.00 0.26 15.70 1.87 0.03 0.65 2.44 5.20 2.14 0.10 99.39 76 32 27 533 781 45.30 3.92 0.00 0.86 0.29 0.63 1.65 3.09 0.17 27.30 0.00 2.72 16.50 0.00 4.65 63.00 2.68 2.04 0.00 0.19 5.92 0.00 0.34 18.30 4.69 0.32 122.00

101-PSH-04 7304590 3478318 71.00 0.26 15.80 1.85 0.04 0.69 2.55 5.30 1.85 0.10 99.44 45 25 525 676 38.50 3.67 6.02 0.97 0.35 0.42 1.63 2.82 0.15 15.00 0.00 2.85 9.31 5.28 2.97 67.10 2.99 1.74 0.26 0.18 6.32 0.00 0.71 19.10 4.56 0.34 107.00

A1602 7267090 3480520 70.30 0.45 15.60 2.33 0.02 0.92 3.17 4.48 1.83 0.03 99.13 170 52 22 311 503 32 213 5.6 1.9 0.6 1.35 6.77 6.9 0.27 123 0.1 5.2 75.8 8 22.2 57 3.6 10 0.2 0.59 46 0.1 2 32 7.5 0.55 294

113-PSH-04 7270043 3484343 71.00 0.27 15.60 1.97 0.03 0.67 2.62 4.93 2.18 0.10 99.37 120 44 24 483 773 33 41.60 3.98 0.00 0.98 0.50 0.64 1.69 2.88 0.17 22.80 0.00 2.87 14.30 0.00 4.19 53.40 2.93 2.28 0.00 0.23 5.16 0.00 0.37 21.90 4.92 0.44 115.00

119-PSH-04 7273941 3484649 71.20 0.25 15.70 1.85 0.03 0.63 2.55 5.04 2.02 0.09 99.36 77 40 23 490 853 31 32.90 3.37 0.00 0.93 0.49 0.50 1.83 2.94 0.17 17.00 0.00 2.48 12.40 0.00 3.29 51.70 2.95 1.77 0.00 0.21 4.65 0.00 0.43 20.30 6.04 0.54 119.00

135.1-PSH-04 7300169 3487254 68.40 0.38 16.70 2.69 0.05 0.94 3.46 5.24 1.31 0.15 99.31 91 61 22 652 572 64.70 5.71 6.93 1.54 0.66 0.84 2.80 3.49 0.28 27.40 0.11 3.94 20.40 5.98 5.59 57.30 3.57 3.43 0.31 0.33 6.85 0.10 2.29 34.40 8.51 0.74 145.00

103-PSH-04 7286222 3488817 70.30 0.28 16.10 2.07 0.04 0.79 2.92 5.11 1.69 0.08 99.40 69 47 27 584 619 53.00 4.30 5.59 1.17 0.59 0.71 2.17 3.40 0.23 29.20 0.11 2.47 19.10 0.00 5.41 51.30 2.93 2.47 0.00 0.25 8.03 0.00 0.50 23.80 6.59 0.53 123.00

162-PSH-04 7215005 3491679 64.80 0.54 16.70 4.32 0.07 2.55 3.68 4.52 2.20 0.28 99.64 118 70 27 587 700 120 10.6 24.7 2.20 0.83 1.19 4.62 4.22 0.36 65.0 0.11 3.55 43.8 20.1 12.4 68.1 7.97 6.11 0.2 0.54 11.4 0.10 0.31 62.8 9.23 0.67 170

N94002795 7174620 3492960 70.80 0.39 16.20 1.83 0.02 0.63 2.86 5.79 1.11 0.07 99.70 160 34 602 638 85 5.4 0.96 0.31 0.81 3.34 5.35 0.13 42.6 0.1 1.83 34.9 9.35 29.7 1.34 4.89 0.2 0.34 12.4 0.1 0.4 25.1 3.81 0.21 224

170.2-PSH-04 7166515 3495778 70.60 0.34 15.00 2.70 0.05 0.64 2.09 4.29 3.48 0.12 9 9.31 152 53 29 217 675 41 96.30 4.76 8.87 2.60 1.23 0.68 3.84 6.76 0.47 55.40 0.20 19.00 30.30 6.37 9.06 176.00 5.64 4.39 1.09 0.50 21.60 0.18 4.07 15.00 13.90 1.10 237.00

171.1-PSH-04 7170924 3495952 68.60 0.45 16.00 3.09 0.05 1.18 3.49 4.83 1.50 0.12 99.30 289 62 26 378 511 52.70 7.78 7.97 1.35 0.50 0.72 2.32 4.46 0.24 29.10 0.00 4.02 19.70 11.40 5.20 49.20 5.58 2.62 0.00 0.29 6.16 0.00 0.32 39.60 6.83 0.62 171.00

115-PSH-04 7266784 3496539 72.30 0.24 15.10 1.72 0.03 0.52 2.39 4.71 2.35 0.08 99.42 121 36 23 363 660 34.00 3.12 0.00 1.13 0.34 0.58 1.52 2.85 0.14 20.50 0.00 3.18 13.80 0.00 3.88 68.30 2.79 1.90 0.00 0.27 7.14 0.00 0.38 16.90 4.32 0.29 97.20

90-PSH-04 7331415 3502859 69.70 0.27 16.00 1.92 0.03 0.72 2.60 4.61 3.49 0.09 99.43 165 125 27 27 405 1044 90.50 4.26 0.00 1.33 0.54 0.60 3.02 3.14 0.22 48.00 0.00 2.51 33.90 5.42 9.50 80.70 3.34 4.33 0.00 0.31 19.90 0.00 0.33 24.70 4.93 0.39 113.00

91.1-PSH-04 7327823 3504736 73.40 0.22 14.70 1.48 0.02 0.62 2.86 5.07 1.03 0.10 99.49 84 22 23 417 334 61.40 2.93 6.44 0.78 0.49 0.62 2.02 1.72 0.14 39.40 0.00 1.99 22.00 0.00 6.50 25.20 2.96 2.54 0.00 0.22 4.75 0.00 0.00 12.90 3.74 0.19 59.70

182-PSH-04 7086928 3505776 68.30 0.44 15.50 3.36 0.06 1.87 2.96 4.88 1.77 0.13 99.25 266 145 25 64 25 357 296 52.00 10.10 12.10 1.30 0.51 0.65 2.29 2.91 0.22 28.10 0.00 4.59 19.70 18.90 5.60 72.70 6.91 2.68 0.34 0.28 9.67 0.00 1.26 50.10 5.86 0.39 113.00

155-PSH-04 7197685 3508558 70.30 0.19 17.10 1.15 0.01 0.54 3.52 5.86 0.91 0.07 99.64 71 25 21 1079 456 50.2 3.07 16.4 0.24 0.15 0.46 1.12 1.98 0.1 28.5 0.1 0.55 16.5 4.79 22.3 0.71 1.46 0.2 0.1 2.28 0.1 0.2 14.6 1.25 0.15 91.7

183.1-PSH-04 7086291 3510075 69.40 0.32 16.50 2.33 0.04 0.87 3.51 5.24 1.07 0.11 99.39 61 0 60 25 567 372 0 31.40 4.19 0.00 0.89 0.31 0.57 1.75 3.35 0.14 15.20 0.00 2.16 13.00 0.00 3.44 49.40 2.96 2.01 0.00 0.17 2.11 0.00 0.31 28.10 4.27 0.34 115.00

177-PSH-04 7148157 3510818 65.50 0.62 16.40 4.29 0.06 1.97 3.80 4.45 1.81 0.17 99.07 276 0 87 28 461 477 0 34.40 11.80 13.30 0.78 0.41 0.54 1.67 3.06 0.16 17.50 0.00 3.48 13.70 18.40 3.73 66.80 7.63 2.06 0.00 0.22 1.45 0.00 0.00 73.70 4.60 0.36 108.00

140-PSH-04 7294281 3510825 73.30 0.24 14.60 1.67 0.02 0.66 2.85 4.64 1.37 0.06 99.42 202 0 25 22 365 436 0 105 3.61 6.96 0.71 0.18 0.71 2.05 3.76 0.10 64.90 0.00 2.18 31.30 0.00 10.20 41.90 2.05 3.31 0.00 0.25 15.50 0.00 0.29 17.40 2.77 0.27 141.00

175.1-PSH-04 7160836 3517091 67.80 0.48 15.90 3.55 0.05 1.52 3.21 4.88 1.77 0.20 99.35 124 224 50 28 326 343 117 8.37 13.8 2.37 0.98 0.87 4.37 5.69 0.42 62.1 0.13 9.55 38.5 17.4 11.5 119 8.49 5.42 0.23 0.54 12.0 0.12 0.69 44.9 11.1 0.83 226

193.1-PSH-04 7080204 3519163 61.70 0.77 15.90 6.35 0.10 3.03 4.21 3.86 2.53 0.44 98.90 1435 274 92 111 29 376 474 0 124 19.00 0.00 3.99 2.19 1.88 8.34 4.37 0.75 59.20 0.29 7.11 60.80 11.20 14.90 86.30 17.90 9.89 0.62 0.94 15.10 0.33 1.20 142.00 23.30 1.90 150.00

N94003664 7122480 3538130 72.10 0.27 15.20 2.13 0.05 0.84 1.99 5.58 1.49 0.11 99.76 30 451 643 78.7 4.6 2.75 1.21 0.76 4.12 3.77 0.5 41.6 0.1 4.19 30.4 8.48 42.4 4.99 4.68 0.24 0.56 10.2 0.14 1.39 22.9 12.4 0.68 129

PSH$-2006-41.1 7268633 3550618 67.60 0.47 16.50 3.46 0.05 1.21 3.93 4.65 1.27 0.17 99.31 70 69 23 222 398 66.5 8.45 1.54 0.71 0.81 3.25 4.61 0.31 38.4 6.75 23.1 6.83 53.2 5.62 3.73 0.47 0.39 17.9 1.19 39.7 7.98 0.72 197

N94003728 7214700 3556940 57.90 0.80 17.10 7.31 0.08 7.69 0.72 4.00 1.69 0.30 97.59 67 34 69 113 213 12 40 7.25 3.12 3.22 13.7 4.13 1.23 99.2 0.37 6.64 108 28 27 71.8 28.4 18.9 0.28 1.71 5.56 0.38 2.03 85.8 35.3 2.48 171

A1661 7282484 3557732 64.60 0.71 16.30 4.93 0.07 1.87 4.64 4.44 1.66 0.19 99.41 67 200 30 66 24 516 830 21 105 31.00 2.43 1.28 1.27 3.88 0.00 0.41 61.10 0.14 3.00 36.00 24.00 10.80 41.00 9.77 5.00 0.51 5.11 0.15 0.22 73.00 11.80 0.81 270.00

PSH$-2006-57 7310511 3576510 73.30 0.25 14.20 2.20 0.04 0.72 3.06 4.27 1.29 0.07 99.41 306 34 21 372 397 59.8 3.92 0.80 0.41 0.53 2.18 4.32 0.16 36.6 2.95 21.9 28 6.51 39.4 3.83 2.91 0.2 0.24 14.8 0 0.66 16.7 3.70 0.30 155

N95001741 7305143 3577816 68.70 0.44 15.90 2.96 0.04 1.17 3.17 4.72 2.15 0.13 99.38 160 61 382 961 71 8.1 33 1.09 0.38 0.7 2.74 3.26 0.18 42.9 0.1 4.81 22.5 6.78 69.2 3.68 3.1 0.21 0.32 11.8 0.1 0.45 38.1 4.44 0.3 167

N95001765 7278218 3605233 70.70 0.37 15.60 2.38 0.04 1.02 3.21 4.49 1.83 0.12 99.76 42 570 560 88 36.3 5.2 1.09 0.54 0.45 1.56 3.02 0.21 18.8 0.1 2.67 12.4 3.88 68.2 4.16 1.96 0.22 0.22 7.29 0.1 14.1 27.4 5.39 0.5 133

N94003163 7042789 3608691 65.20 0.56 17.30 4.01 0.06 1.58 2.79 5.64 2.26 0.21 99.61 81 33 702 741 72.7 9.4 1.69 0.97 0.99 3.37 4.8 0.35 38.9 0.14 6.27 29.1 8.44 72 6.17 4.5 0.37 0.41 8.34 0.14 1.24 39.2 11 0.98 173

N95001798 7250790 3612308 72.60 0.24 15.00 1.97 0.04 0.54 2.53 5.43 1.25 0.08 99.68 67 327 315 43.7 3.8 0.82 0.38 0.51 1.69 3.61 0.15 25.3 0.1 3.27 13.3 4.11 48.7 2.98 2.11 0.2 0.22 7.69 0.1 0.8 15.8 4.6 0.37 163

N95001676 7339208 3621792 70.30 0.27 15.40 2.59 0.05 0.86 2.37 4.82 2.75 0.10 99.51 130 32 631 1417 68.8 4 0.86 0.42 0.68 1.98 2.41 0.16 36.5 0.1 3.84 23.5 7.27 63 2.25 2.84 0.24 0.25 6.62 0.1 1.03 21.9 4.62 0.47 103

N95001760 7267858 3624201 67.90 0.51 15.80 3.85 0.07 1.30 3.60 5.04 1.59 0.19 99.85 85 279 322 31 77 9.2 33 1.64 0.69 0.82 3.08 4.16 0.31 48.8 0.11 6.17 25.5 7.78 85.1 6.97 3.38 0.62 0.35 8.46 0.1 1.8 44.1 9.33 0.63 196

N94003175 7059053 3633080 64.90 0.58 17.00 4.00 0.06 1.70 4.77 4.86 1.68 0.20 99.75 76 660 826 81 10.7 2.91 1.11 1.5 4.95 4.5 0.46 37.7 0.16 4.77 37.4 9.99 48.8 7.93 6.5 0.43 0.54 4.35 0.16 0.65 64 13.8 1.07 181

PSH-03-80.2 7054221 3635795 63.60 0.89 16.70 4.45 0.06 1.35 3.93 4.89 2.51 0.49 98.88 75 29 70 24 675 1608 175 9.13 3.44 1.12 2.54 8.64 8.07 0.50 82.4 0.14 11.4 68.6 0 18.8 63.5 6.51 11.3 0.55 0.93 23.4 0.14 1.98 72.2 15.9 1.01 385

PSH-03-61.1 7046618 3651298 70.20 0.38 15.20 2.78 0.04 1.21 3.06 4.59 1.70 0.13 99.29 74 61 28 413 481 80.0 8.33 0.64 0.31 0.95 2.28 3.66 0.14 38.7 3.18 26.7 0 7.92 69.7 4.04 3.55 0.2 0.24 7.46 0.37 40.5 3.57 0.32 147

PSH-03-95.1 7025498 3653737 67.70 0.45 15.70 3.18 0.04 1.43 3.62 5.00 1.83 0.15 99.11 79 80 69 29 627 526 42.5 7.70 0.86 0.40 0.81 2.23 2.79 0.14 21.0 1.89 18.4 0 4.84 58.2 4.22 2.70 0.2 0.23 3.91 0.26 48.5 4.91 0.36 107

PSH-03-49 7043528 3661417 70.50 0.25 15.60 1.81 0.02 0.84 3.03 4.61 2.55 0.13 99.34 162 44 24 685 1507 40.7 4.65 1.71 0.88 1.08 3.60 2.11 0.30 21.3 1.86 20.6 0 4.92 48.7 7.51 4.06 0.2 0.39 0.84 0.10 0.20 26.7 8.11 0.53 74

PSH-03-17 7025513 3667774 64.50 0.52 15.60 4.11 0.07 2.28 3.92 4.40 3.04 0.25 98.70 100 86 27 830 1416 32 93.9 10.6 42 2.41 1.03 1.61 5.16 4.18 0.43 49.9 0.16 4.13 40.7 20 11.0 76.3 9.23 6.24 0.20 0.58 6.59 0.11 0.37 75.2 12.3 0.95 164

PSH-03-9 7028671 3680461 63.50 0.52 16.50 4.35 0.08 2.41 4.37 4.77 2.15 0.30 98.96 455 84 25 914 1433 44 90.5 11.9 40 3.51 1.30 1.75 5.86 4.76 0.52 41.4 0.20 3.58 41.3 0 10.5 51.3 13.5 7.07 0.2 0.70 6.32 0.18 0.52 76.7 14.8 1.35 163

PSH-03-7.1 7027237 3683425 64.20 0.58 16.00 4.28 0.07 2.17 4.15 4.66 2.63 0.29 99.02 224 99 32 954 1752 37 95.9 11.9 40 2.56 0.96 1.64 5.09 4.46 0.42 47.3 0.12 3.41 38.7 23 10.6 55.1 10.5 6.13 0.2 0.56 7.41 0.16 0.26 79.4 11.8 0.98 163

N93002484 7012294 3707655 74.10 0.13 14.30 1.49 0.02 0.42 1.13 4.52 3.54 0.07 99.72 26 126 369 67 100 3 3.28 0.83 0.46 6.71 4.69 0.43 48.2 0.1 6.14 39.7 11.2 109 4.6 8.31 0.4 0.85 36.1 0.1 5.18 13 12.3 0.59 165

PSH$-2006-72.1 7235260 3566345 66.50 0.59 15.50 4.01 0.06 2.24 3.76 4.39 1.78 0.21 99.04 714 286 32 65 26 654 1246 87.6 13.9 73 1.95 0.96 1.22 4.19 4.35 0.40 49.5 0.14 6.39 34.2 28 9.71 54.4 8.40 4.63 0.36 0.49 13.8 0.13 0.66 66.3 9.81 0.87 159

PSH$-2006-66 7245197 3544603 70.70 0.37 15.70 2.07 0.03 1.27 3.95 5.10 0.23 0.11 99.52 79 30 23 460 123 34.6 7.91 0.76 0.24 0.59 1.62 2.71 0.12 16.3 2.47 13.3 3.52 4.91 6.69 1.74 0.2 0.20 6.36 0 0.25 39.8 2.56 0.17 93.4

PSH$-2006-67 7276204 3572480 70.20 0.48 15.40 2.80 0.04 1.09 3.53 4.38 1.36 0.13 99.41 142 68 21 396 604 62.9 7.53 1.17 0.50 0.98 2.55 3.97 0.22 36.6 3.45 20.8 6.21 39.2 4.73 2.76 0.20 0.32 3.00 0 0.45 39.8 6.11 0.46 151

PSH$-2006-63 7286307 3588739 70.50 0.33 15.60 2.36 0.04 0.81 3.35 4.89 1.41 0.13 99.42 212 65 23 278 352 94.2 5.29 1.00 0.35 0.69 3.13 4.35 0.16 57.2 4.61 32.0 10.2 52.3 3.04 3.89 0.26 0.35 18.1 0 0.75 23.2 4.40 0.47 174

PSH$-2006-59 7291022 3575518 70.90 0.35 15.30 2.56 0.03 0.79 2.60 5.06 1.66 0.11 99.37 200 50 25 323 454 58.3 4.63 0.78 0.33 0.54 1.83 4.75 0.13 25.2 3.31 15.3 37 4.57 62.0 5.69 2.19 0.2 0.21 14.9 0 0.75 29.3 3.21 0.16 190

PSH$-2006-77 7299037 3561654 69.60 0.47 15.40 2.77 0.05 1.10 1.97 4.11 3.75 0.11 99.34 175 59 20 271 1219 59.6 7.60 0.81 0.32 0.75 2.05 4.57 0.11 36.6 6.69 20.1 6.18 115 4.67 2.25 0.34 0.21 13.1 0 1.26 32.2 3.45 0.29 183

PSH$-2006-35 7303241 3571417 69.20 0.44 15.80 2.81 0.05 1.13 3.13 4.96 1.66 0.14 99.31 138 121 74 24 459 688 55.2 7.62 1.18 0.59 0.68 2.27 3.55 0.21 31.9 3.05 20.2 5.99 58.8 5.18 3.05 0.23 0.25 9.94 0 0.25 40.0 5.57 0.43 138

PSH$-2006-55 7316147 3572392 70.10 0.45 15.20 2.73 0.04 1.05 2.94 4.34 2.40 0.09 99.34 88 67 26 373 943 49.0 7.87 32 0.91 0.37 0.6 1.72 2.84 0.14 29.5 3.44 15.7 4.66 65.7 4.69 1.87 0.2 0.24 3.79 0 0.40 41.9 3.60 0.36 106

low HREE TTGs, Eu-positive

49.1-PSH-04 7286461 3393302 71.80 0.24 15.40 2.12 0.02 0.55 2.80 4.91 1.60 0.06 99.49 0 126 0 28 24 548 423 0 15.40 3.27 5.02 0.17 0.00 0.48 0.50 3.52 0.00 9.22 0.00 1.80 5.09 0.00 1.56 36.80 1.99 0.83 0.00 0.00 0.86 0.00 0.00 22.50 1.58 0.15 144.00

25-PSH-04 7295535 3408151 70.70 0.29 15.80 2.02 0.02 0.74 3.21 5.01 1.45 0.09 99.34 0 86 0 37 21 564 448 0 20.60 4.55 6.36 0.30 0.23 0.52 0.67 2.75 0.00 12.40 0.00 2.31 6.81 0.00 1.98 46.60 2.36 0.95 0.00 0.10 1.03 0.00 0.20 25.80 1.49 0.15 99.00

22.2-PSH-04 7288098 3408396 70.50 0.23 16.60 1.48 0.02 0.76 2.84 5.24 1.73 0.07 99.48 0 88 0 27 25 499 887 0 13.40 3.27 0.00 0.19 0.00 0.54 0.27 2.19 0.00 9.75 0.00 1.00 4.38 0.00 1.23 41.40 1.58 0.56 0.00 0.00 0.00 0.00 0.27 16.50 1.14 0.15 80.60

4.4-PSH-04 7268811 3421259 73.70 0.17 14.70 1.27 0.02 0.55 2.81 5.34 0.89 0.02 99.47 0 77 0 22 0 457 570 0 8.67 1.89 0.00 0.00 0.00 0.27 0.52 2.41 0.00 5.36 0.00 0.80 3.52 0.00 0.97 17.70 1.18 0.50 0.00 0.00 0.00 0.00 0.00 9.92 0.54 0.15 83.20

42-PSH-04 7304441 3430880 71.60 0.27 15.20 1.87 0.02 0.60 2.17 4.44 3.05 0.10 99.31 0 81 0 33 22 469 1783 0 63.40 3.55 10.40 0.42 0.21 0.81 1.42 5.00 0.00 39.50 0.00 1.60 19.50 5.94 6.24 58.40 2.35 2.27 0.00 0.15 5.28 0.00 0.28 21.00 1.66 0.23 186.00

A1603 7279400 3476550 73.30 0.14 14.80 1.28 0.02 0.44 2.61 4.17 2.79 0.04 99.59 14 22 15 449 970 17.2 2.4 0.29 0.15 0.35 0.66 1.7 0.1 11.4 0.1 0.7 5.83 5 1.7 59 1.8 0.69 14 1.5 0.15 66

N93001430 7246350 3479710 64.60 0.52 17.60 4.22 0.06 1.60 4.96 4.85 1.08 0.15 99.64 180 230 30 57 555 384 17.6 10.7 0.75 0.34 0.59 1.38 1.83 0.16 9.16 0.1 1.33 8.24 2.06 11.3 8.02 1.42 0.16 60.2 4.33 0.31 73.8

160.1-PSH-04 7195644 3493400 76.40 0.18 12.70 1.62 0.04 0.62 1.55 4.12 2.26 0.02 99.50 0 100 0 39 22 131 434 0 19.90 2.96 7.01 0.60 0.31 0.53 0.83 2.12 0.10 11.90 0.00 3.63 5.90 0.00 1.89 56.10 1.76 0.93 0.00 0.12 0.56 0.00 0.00 11.20 3.06 0.15 67.40

180-PSH-04 7083277 3497879 72.90 0.31 14.40 2.30 0.04 0.82 3.48 4.06 0.99 0.06 99.36 132 162 0 29 22 408 371 0 31.10 5.73 7.29 0.13 0.00 0.62 0.76 2.87 0.00 19.00 0.00 1.63 9.21 6.41 2.74 32.40 2.26 0.89 0.00 0.00 1.47 0.00 0.00 28.00 1.53 0.15 114.00

157-PSH-04 7198968 3503463 72.20 0.24 15.70 1.49 0.02 0.60 3.01 5.57 0.63 0.05 99.52 0 190 0 33 20 650 476 0 20.70 3.41 12.10 0.00 0.00 0.47 0.59 4.17 0.00 11.10 0.00 0.70 7.49 0.00 2.10 14.40 0.87 1.02 0.00 0.00 0.00 0.00 0.00 15.90 0.93 0.15 155.00

PSH-03-78.1 7039815 3636685 72.30 0.29 14.70 2.14 0.03 0.88 3.05 4.64 1.41 0.08 99.51 123 47 24 183 277 22.7 6.93 0.67 0.32 0.57 1.24 2.64 0.11 12.5 4.78 7.65 0 2.12 69.4 2.52 1.27 0.70 0.14 0.98 0.34 30.7 3.16 0.17 124

PSH-03-113.1 7021518 3654963 70.70 0.29 15.30 2.43 0.04 0.91 2.83 5.07 1.74 0.06 99.36 105 123 56 24 282 400 19.6 6.06 0.42 0.23 0.52 0.99 2.75 11.3 4.45 7.28 0 1.99 87.8 4.11 1.07 0.36 0.10 1.51 0.55 30.2 2.44 0.15 108

PSH$-2006-74.2 7230285 3555279 71.00 0.29 15.20 2.08 0.04 1.29 3.59 4.97 1.00 0.08 99.54 0 180 0 43 21 431 311 0 12.5 7.9 0 0.25 0.2 0.36 0.46 2.79 8.21 2.37 3.72 28 1.13 32.5 0.96 0.55 0.34 41.1 2.07 0.30 107

PSH$-2006-72.3 7235270 3566333 68.00 0.34 17.00 2.48 0.03 0.94 3.85 5.27 1.24 0.12 99.27 322 49 22 690 856 17.4 5.13 0.98 0.49 0.71 1.75 3.05 0.21 9.27 1.65 7.75 2.00 34.5 4.38 1.61 0.22 0.88 0 25.1 5.32 0.48 128

PSH$-2006-47 7260179 3542391 70.50 0.32 15.80 2.32 0.04 0.70 2.99 4.83 1.87 0.09 99.45 0 0 0 54 24 404 930 0 20.8 5.19 0 0.41 0.26 0.73 0.91 2.44 12.6 1.72 7.47 0 2.12 44.4 3.7 1.04 0.12 0.23 26.3 2.24 0.24 107

PSH$-2006-65.1 7260301 3542182 70.60 0.28 16.10 1.84 0.03 0.77 3.40 4.93 1.46 0.08 99.49 0 0 0 47 24 494 537 0 19.5 4.05 0 0.32 0.17 0.55 0.98 2.43 11.9 1.84 7.62 0 1.93 36.3 3.91 1.01 0.1 0.5 0.36 19.7 1.99 0.16 89.6

PSH$-2006-71 7263785 3591919 72.20 0.25 15.20 1.62 0.03 0.57 2.05 5.41 2.02 0.08 99.43 0 0 0 35 0 419 660 0 24.4 3.61 0 0.34 0.15 0.51 0.95 3.51 11.3 2.21 8 0 2.1 67.4 2.84 1.24 0.14 6.91 0.69 15.8 2.07 0.15 129

PSH$-2006-69 7267268 3596120 73.30 0.24 15.10 1.45 0.02 0.61 2.99 4.76 1.07 0.02 99.56 0 112 0 39 0 499 777 0 10.2 3.85 0 0.61 0.3 4.53 6.36 1.51 3.61 0 1 37.5 1.36 0.5 1.89 0.74 15.1 1.13 0.15 150

PSH$-2006-70 7267943 3593479 72.60 0.22 15.20 1.77 0.02 0.58 2.90 3.93 2.06 0.07 99.36 0 0 0 57 23 359 1714 32 12.1 3.11 0 0.26 0.54 0.68 3.95 6.58 3.22 4.7 0 1.21 92.1 2.33 0.74 2.08 0.32 13 1.61 0.26 141

PSH$-2006-62 7285425 3581572 69.60 0.26 17.10 1.69 0.03 0.67 3.19 5.00 1.88 0.10 99.52 0 77 0 44 24 420 517 0 21 3.2 0 0.61 0.26 0.66 1.39 4.57 0.13 12.6 4.46 7.82 0 2.09 65.2 3.72 1.37 0.29 0.19 3.56 1.14 13.1 3.62 0.26 203

PSH$-2006-26 7286396 3549314 73.80 0.12 14.50 1.11 0.02 0.26 1.97 3.69 3.99 0.03 99.49 0 167 0 28 21 281 1334 0 11.7 1.54 0 0.15 0.72 0.32 1.86 8.02 0.74 3.48 0 1 45.6 0.95 0.33 0.52 7 0.7 0.15 48.7

PSH$-2006-27 7286655 3548799 74.50 0.11 14.40 0.93 0.02 0.21 1.93 3.93 3.44 99.46 0 0 0 29 0 287 1371 0 13.8 1.88 0 0.35 0.48 0.65 2.44 7.82 1.27 5.07 0 1.41 70.9 1.27 0.78 1.3 0.2 6.89 1.7 0.15 77.9

PSH$-2006-61.1 7286873 3579654 72.50 0.27 15.00 1.73 0.02 0.76 2.60 4.57 2.05 0.03 99.53 104 135 48 25 271 553 34 49.3 4.17 31 0.46 0.26 0.48 1.03 6.88 29.7 3.57 15.7 4.87 60.5 3.41 1.44 0.13 21.5 1.29 17.4 1.70 0.15 279

PSH$-2006-29 7290673 3550903 68.10 0.56 16.10 3.29 0.03 1.35 3.86 4.44 1.46 0.14 99.33 0 102 0 84 27 457 629 0 40 8.58 38 0.67 0.18 0.86 1.42 3.14 0.12 23.1 2.78 14.7 0 3.77 38.1 3.08 1.59 0.16 0.57 48 3.22 0.25 113

PSH$-2006-50 7294387 3537983 69.30 0.33 16.70 2.08 0.02 0.72 3.64 5.16 1.38 0.14 99.47 0 210 0 38 26 742 678 0 25.8 4.95 0 0.48 0.2 0.62 1.62 5.01 0.11 14.7 1.93 10.5 0 2.96 15 2.98 1.57 0.18 0.22 23.9 2.95 0.23 205

PSH$-2006-32 7295276 3569495 69.90 0.14 17.40 0.91 0.01 0.30 2.93 5.53 2.43 0.03 99.58 0 72 0 28 28 412 795 54 54.1 1.44 0 0.34 0.68 1.35 3 32.4 1.32 16.2 0 5.04 39.6 1.32 1.81 0.14 11.3 0.35 5.98 1.38 0.15 105

PSH$-2006-51 7295342 3533520 71.70 0.34 14.90 2.46 0.04 0.74 3.42 4.65 1.21 0.04 99.50 0 85 0 72 23 278 300 0 20.8 5.1 0 0.39 0.15 0.58 0.93 3.91 12.3 3.62 7.49 0 2.03 23.2 4.91 0.93 0.12 0.26 29.5 2.34 0.21 158

PSH$-2006-49.1 7295700 3541314 64.70 0.14 20.60 1.03 0.02 0.56 4.60 6.37 1.42 0.05 99.49 0 84 0 0 23 883 1301 0 13 2.16 0 0.29 0.15 1.32 0.39 1.63 9.01 0.77 3.94 0 1.22 21.6 0.94 0.34 13.4 1.06 0.18 71.5

PSH$-2006-33.1 7297528 3571879 70.50 0.31 15.90 1.87 0.03 0.86 2.68 5.45 1.74 0.10 99.44 0 111 0 52 28 541 613 0 22.6 5.01 0 0.3 0.48 0.82 3.47 12.7 1.68 7.67 0 2.36 44.4 3.02 1.27 0.26 25.3 1.58 0.15 110

PSH$-2006-81 7303346 3563601 68.90 0.28 17.50 1.25 0.02 0.70 2.28 5.01 3.45 0.02 99.41 0 126 0 35 25 417 1735 54 57.4 3.03 0 0.29 1.14 1.46 4.50 36.7 2.38 16.5 0 5.63 65.7 1.69 1.75 0.15 10.1 0.31 16.7 1.38 0.15 163

PSH$-2006-34 7304422 3568974 73.20 0.18 15.50 1.21 0.02 0.19 3.14 5.00 1.06 99.50 0 84 0 30 24 455 342 32 26.4 1.63 0 0.13 0.63 0.63 4.3 17.3 1.56 8.05 0 2.39 22.5 0.97 0.7 3.1 0.21 22.6 0.93 0.15 167

PSH-03-57 7049503 3662258 72.10 0.38 14.50 2.05 0.04 0.83 2.94 4.52 1.96 0.07 99.39 159 130 35 25 285 753 26.3 6.23 0.82 0.74 0.69 1.38 3.51 0.17 15.6 0.12 4.49 9.07 0 2.56 39.2 2.74 1.40 0.27 0.17 0.98 0.32 35.9 5.47 0.68 157

high-HREE TTGs

30-PSH-04 7251640 3455324 68.20 0.52 15.30 4.47 0.08 1.73 2.87 4.48 1.96 0.12 99.73 63 85 23 242 489 32.9 10.4 13.5 2.05 1.35 0.64 2.53 3.64 0.43 15.1 0.19 5.07 14.7 13.8 3.73 55.5 8.77 2.65 0.63 0.42 6.02 0.17 0.93 59.6 12.4 1.21 130

159-PSH-04 7193494 3494215 73.30 0.41 13.60 3.26 0.05 0.62 3.21 4.13 1.00 0.07 99.66 218 47 21 200 222 45.3 5.21 13.4 2.64 1.71 0.99 3.19 4.78 0.58 25.0 0.24 5.68 16.3 4.60 43.7 9.46 2.85 0.30 0.47 2.69 0.26 0.46 22.0 16.1 1.82 210

161-PSH-04 7199563 3495132 67.50 0.56 15.40 4.25 0.09 1.41 3.73 4.19 1.88 0.16 99.17 0 211 0 72 29 259 403 0 46.60 9.29 13.00 3.47 2.26 0.79 4.28 4.72 0.81 24.40 0.32 6.52 18.90 9.38 5.02 49.20 9.84 3.59 0.31 0.59 2.11 0.35 0.00 45.10 22.00 2.14 193.00

147-PSH-04 7189686 3505754 65.50 0.81 15.20 5.89 0.08 1.95 4.77 4.61 0.59 0.22 99.62 223 174 22 77 23 471 350 72.9 12.0 8.16 4.02 2.11 1.37 5.62 6.49 0.73 31.9 0.27 5.36 36.0 6.86 8.87 6.31 14.4 6.14 0.24 0.78 1.04 0.28 0.28 80.4 20.9 1.87 280

N93002713 7088720 3569860 60.10 0.58 16.70 6.00 0.13 4.46 2.74 4.12 3.30 0.31 98.44 210 190 89 34 374 580 76.1 17.9 135 5.26 3.01 1.16 6.36 4.36 0.97 36.6 0.42 10 37.6 42 9.31 76.4 14.3 7.52 0.93 0.93 12.7 0.44 2.99 99.2 30.9 2.8 174

N95001753 7319762 3579539 69.00 0.71 13.90 4.66 0.08 1.83 3.07 3.39 2.54 0.23 99.41 130 110 67 158 424 85.9 9.1 66 5.44 2.97 1.35 6.84 7.92 1.07 43.7 0.42 11.6 38.6 9.9 85.7 11.9 7 1.05 1.04 13.6 0.39 2.39 67.8 31.9 2.83 346

N94002606 7103485 3619776 66.90 0.47 15.90 4.33 0.08 1.64 4.17 4.49 1.62 0.14 99.74 170 70 337 574 35 11.6 2.6 1.43 0.9 3.33 3 0.54 17.5 0.17 5.28 17 4.36 48.7 10.6 3.5 0.24 0.49 2.73 0.19 0.2 53.6 15.6 1.21 125

N94003191 7074206 3631667 65.40 0.66 15.60 5.50 0.11 1.95 4.64 4.23 1.42 0.29 99.80 170 140 27 67 234 184 77.4 12.1 12 7.51 1.93 11.4 6.38 2.57 38.4 1.21 15.7 40.4 10.2 58.6 16.8 10.2 2.94 1.95 16.7 1.2 6.01 71.4 86 8.04 259

PSH-03-83.1 7052044 3632456 71.20 0.18 15.30 1.78 0.04 0.89 2.76 4.68 2.52 0.06 99.40 159 27 533 805 42.2 4.71 1.39 0.73 0.45 1.83 1.17 0.25 20.8 0.14 2.94 16.1 0 4.34 62.0 2.95 2.53 0.2 0.31 5.48 0.13 17.3 8.79 0.83 91

PSH-03-80.1 7054221 3635795 63.90 0.51 16.30 4.99 0.07 2.58 3.76 4.12 2.67 0.13 99.04 83 84 28 513 786 47.3 16.5 57 2.38 1.04 1.01 3.91 3.27 0.44 22.3 0.17 4.97 22.2 26 5.13 79.8 12.5 3.98 0.44 0.46 2.75 0.17 0.41 86.3 13.4 1.12 124

N93002466 7029555 3641442 68.50 0.44 15.50 4.31 0.09 1.18 4.13 3.81 1.66 0.15 99.77 68 220 400 36.9 9 3.85 2.31 0.79 4.02 6.15 0.73 18.9 0.32 5.4 17.1 4.41 68.9 12.9 3.67 0.47 0.64 4.86 0.3 1.44 38.3 22.7 2.03 278

PSH-03-70 7026737 3642943 69.50 0.25 16.00 2.44 0.05 1.32 3.02 4.88 1.86 0.07 99.39 68 62 23 337 297 16.9 6.60 1.16 0.79 0.42 1.79 2.79 0.29 8.74 0.13 2.38 7.44 33 1.88 93.9 4.69 1.74 0.43 0.28 3.33 0.10 0.76 19.7 8.01 0.77 116

PSH-03-68.1 7031234 3644757 68.70 0.48 15.50 3.39 0.05 1.18 4.00 4.49 1.38 0.11 99.28 152 59 24 295 270 22.4 8.18 2.16 1.12 0.75 2.63 3.17 0.43 10.8 0.13 4.55 10.6 0 2.50 52.2 7.24 2.38 0.31 0.34 1.98 0.18 0.55 46.2 11.9 1.14 167

PSH-03-69.1 7030508 3649199 66.90 0.49 15.30 4.45 0.09 1.70 4.26 3.96 1.86 0.15 99.16 75 79 24 290 286 35.5 11.2 2.44 1.36 0.75 3.47 3.29 0.48 16.7 0.19 4.45 14.8 0 3.82 86.5 13.1 2.93 0.35 0.47 6.63 0.18 1.03 64.9 14.3 1.39 146

PSH$-2006-43 7270819 3549555 65.00 0.59 17.00 4.19 0.08 1.59 3.93 4.74 1.90 0.16 99.17 90 574 103 28 406 516 34 38.6 9.94 30 2.28 0.93 0.75 2.80 4.61 0.41 20.3 0.11 6.29 16.2 4.09 55.9 8.93 2.83 0.55 0.45 5.24 0.15 0.49 62.0 10.8 0.94 195

PSH$-2006-38 7283040 3555974 66.80 0.55 16.10 3.87 0.06 1.55 4.40 4.45 1.29 0.18 99.25 307 88 78 24 423 426 39.3 9.87 36 1.50 0.82 0.93 2.49 5.10 0.30 21.7 0.13 5.42 16.9 4.32 29.5 7.90 2.34 1.61 0.35 0.72 0.33 67.2 8.15 0.90 211

PSH$-2006-80.1 7301635 3562090 67.10 0.55 14.30 4.92 0.06 3.41 3.08 2.45 3.17 0.11 99.16 183 62 25 272 942 49.9 14.8 92 2.12 1.17 0.67 3.06 4.46 0.48 30.2 0.2 9.28 18.8 43 5.59 139 12.0 3.23 0.95 0.45 19.8 0.17 3.90 76.8 12.6 1.22 177

PSH-03-105.1 7032731 3634137 71.60 0.34 15.10 2.55 0.04 0.82 2.82 4.86 1.19 0.09 99.42 70 69 25 285 302 27.7 5.23 1.22 0.56 0.53 1.95 3.98 0.22 16.3 0.11 3.40 11.5 0 3.01 54.3 4.03 1.97 0.47 0.24 3.79 0.10 0.85 27.6 7.28 0.68 167

QQs

NA1 7089800 3500800 63.20 0.71 15.90 5.21 0.09 2.77 3.61 4.73 1.66 0.23 98.11 24 109 22 695 821 59.7 43 2.18 1.12 1.16 3.55 0.41 27.8 0.18 28 7.35 44 12.2 4.58 0.47 1.18 0.18 0.33 116 13.1 1.2 205

NA2 7091100 3500220 59.20 0.66 17.10 5.99 0.11 2.76 5.37 4.81 1.08 0.21 97.29 100 107 23 687 732 37.6 42 2.86 1.44 1.27 3.86 0.56 15.7 0.18 23.3 5.4 22 16.1 4.88 0.57 0.22 135 15.3 1.31 174

NA3 7090650 3501600 61.80 0.72 16.80 4.87 0.08 2.63 4.15 5.29 1.33 0.25 97.92 92 25 660 783 45.3 40 2.47 1.14 1.25 4.06 0.47 18.4 0.15 27.8 6.6 43 11.4 5.11 0.52 0.16 127 13.4 1.05 174

NA4 7092530 3502340 57.00 0.84 18.30 6.39 0.11 2.97 6.48 5.42 0.42 0.29 98.22 200 80 86 25 904 189 35.8 37 3.14 1.58 1.47 4.79 0.56 14 0.21 27.2 5.55 14 14.6 5.71 0.61 0.21 161 17.1 1.43 169

NA5 7093450 3503600 57.40 0.83 17.60 6.41 0.10 3.00 5.70 4.84 1.07 0.30 97.24 25 107 32 838 597 49.4 34 2.96 1.5 1.34 4.47 0.55 20.7 0.18 30.1 7 24 14.1 5.82 0.6 0.21 163 16.5 1.36 179

NA6 7095400 3505600 51.80 0.84 20.10 6.61 0.10 3.68 8.06 5.29 0.36 0.40 97.24 240 90 98 32 1203 204 33.8 52 3.19 1.54 1.64 5.07 0.57 12.5 0.18 25.5 25 5.4 16.8 5.57 0.61 0.21 160 16.5 1.26 105

NA7 7095750 3505600 60.10 0.77 16.30 5.88 0.13 3.22 5.09 3.87 1.92 0.24 97.53 113 22 633 479 55.5 55 3.39 1.66 1.47 5.57 0.66 22.3 0.22 35.9 8.11 122 14.8 6.56 0.71 0.24 0.54 141 18.5 1.46 164

NA8 7094120 3507200 62.00 0.72 16.90 4.93 0.08 2.48 5.14 4.82 0.94 0.22 98.23 190 81 29 798 599 50.8 43 3.02 1.45 1.28 5.17 0.56 20.8 0.19 32 21 7.29 52 11.7 6.04 0.64 0.66 0.22 131 16.2 1.32 204

NA9 7093480 3507600 54.80 0.81 18.50 7.00 0.11 3.47 6.52 5.02 0.79 0.31 97.32 160 117 28 909 500 61.4 43 3.31 1.49 1.52 5.05 0.58 27 0.2 34.6 8.4 43 16.7 5.92 0.68 1.17 0.2 159 16.6 1.35 179

NA10 7092680 3508380 59.50 0.78 17.80 5.54 0.10 2.77 5.53 4.99 0.85 0.28 98.13 180 140 23 88 31 874 642 48.8 34 3.38 1.52 1.4 5.32 0.6 19.3 0.17 32.6 7.16 52 12.3 6.54 0.68 0.19 130 16.8 1.26 213

NA11 7090940 3508250 51.80 0.99 19.10 7.06 0.13 3.95 7.13 5.30 0.82 0.29 96.56 130 190 106 33 1034 344 51.4 71 3.97 1.82 1.72 6.01 0.72 19 0.24 34.6 24 7.75 22 18.1 7.06 0.77 0.79 0.28 0.22 193 20.3 1.72 174

NA12 7097810 3513450 51.80 0.96 19.30 7.37 0.13 4.00 5.98 5.51 1.29 0.33 96.67 100 137 31 808 401 40 44 3.5 1.59 1.67 5.2 0.62 15.4 0.2 28.8 22 6.15 51 18.1 6.1 0.65 0.22 173 17.7 1.45 194

NA13 7097280 3514100 58.30 0.75 17.80 6.14 0.10 2.90 5.54 4.91 1.17 0.25 97.86 70 28 90 30 784 510 36.7 35 1.93 1.01 1.16 3.07 0.34 16.4 0.11 19.2 4.63 30 11.7 3.71 0.41 1.48 0.14 0.38 148 10.2 0.85 93

35-PSH-04 7283902 3417477 54.20 0.77 15.50 8.08 0.13 6.03 7.14 4.30 1.84 0.22 98.22 66 168 22 115 28 763 446 56.5 26.5 85.7 5.08 2.58 1.79 8.43 2.75 1.04 20.1 0.38 9.43 40.0 71.1 8.39 54.3 25.1 8.48 0.64 1.05 1.06 0.40 0.54 157 28.4 2.45 99.2

N93001846 7248480 3463070 57.00 0.89 16.40 7.36 0.14 5.49 5.31 4.55 1.77 0.24 99.15 86 108 360 572 64.5 18.2 195 6.09 3.38 1.84 7.91 5.24 1.12 28 0.52 16.8 40.2 58 9.29 44.9 24 8.38 2.45 1.09 3.9 0.5 2.88 145 33.8 3.61 212

94-PSH-04 7320457 3470936 61.00 0.62 17.70 5.28 0.09 2.67 4.92 5.41 1.21 0.21 99.10 83 99 27 677 614 34.3 11.9 13 1.76 1.15 1.16 3.7 2.26 0.36 15.1 0.16 2.71 20.9 7.53 4.5 27.9 11.7 4.05 0.46 0.65 0.15 98.9 10.3 0.83 97.6

146-PSH-04 7321528 3475274 57.90 0.77 16.90 6.87 0.12 3.80 6.51 4.32 1.32 0.32 98.82 222 23 98 27 924 645 48.1 20.2 27.5 2.31 1.26 1.33 4.24 1.57 0.47 22.7 0.15 3.47 24.8 13.3 5.97 26.2 17.9 4.53 0.5 1.52 0.18 0.29 141 13.3 1.1 59.4

93-PSH-04 7322356 3476703 54.40 0.92 18.80 7.48 0.13 3.39 7.43 4.92 0.88 0.37 98.72 161 152 121 32 1104 564 61.5 17.5 9.86 3.66 2.02 1.83 6.34 3.81 0.65 25.5 0.22 3.71 38.1 6.88 8.23 15.8 17.9 7.12 0.83 0.69 0.26 139 18.7 1.73 150

A1611 7322230 3476750 56.00 0.77 18.10 7.73 0.13 2.98 6.92 4.73 0.90 0.34 98.60 210 11 105 23 1047 665 62.8 15 30 3.76 1.87 1.75 5.98 3.2 0.67 27.3 0.23 4.3 36.2 6 8.58 14 16 6.65 0.2 0.72 0.6 0.26 0.2 126 20 1.63 142

N94003658 7129400 3501150 57.80 0.79 17.10 7.67 0.11 3.36 6.79 4.91 1.13 0.19 99.85 270 59 374 317 33 8.6 51 3.99 2.4 1.33 4.84 3.28 0.81 13.3 0.34 5.65 21 36 4.63 28.7 21.2 4.61 0.48 0.68 0.85 0.35 0.64 130 22.9 2.36 126

N93002622 7095070 3512530 62.60 0.62 16.00 5.09 0.09 2.47 5.07 4.80 1.15 0.19 98.08 74 579 509 47.2 11.8 47 2.15 1.22 1.02 3.38 3.38 0.39 20.2 0.15 3.45 22.2 34 5.59 29.7 11.4 3.69 0.22 0.46 2.02 0.18 0.2 87.4 12.8 1.19 150

PSH-92-79 7058550 3520870 60.73 0.79 18.04 4.98 0.07 2.50 5.74 5.14 0.78 0.33 99.09 70 294 8 109 28 1045 755 43.7 23 2.28 1.16 1.54 4.81 0.41 19.5 0.15 2 26.8 17 6.1 2 12 4.74 0.54 0.08 0.14 0.03 111 13 1.07 144

N93002664 7042270 3533520 58.40 0.79 17.20 6.32 0.09 3.17 6.11 4.75 1.29 0.31 98.43 310 540 25 89 771 591 67.1 14.6 69 3.12 1.59 1.56 5.05 3.84 0.58 28 0.18 4.11 35.9 31 8.86 27.2 15.4 6.67 0.2 0.68 0.5 0.21 0.2 109 16.8 1.34 159

PSH-92-12 7032300 3540750 56.22 0.76 18.66 6.47 0.10 3.60 6.81 5.04 0.98 0.31 98.95 390 245 21 126 27 808 560 63.7 47 4.86 2.66 2.02 7.17 0.89 23.9 0.32 2 40.5 25 9.18 3 20 8.37 0.96 0.2 0.31 0.08 148 28 2.11 158

PSH-92-9.1 7031920 3541290 58.29 0.67 17.78 6.01 0.09 3.50 6.48 4.80 0.97 0.29 98.88 390 262 25 100 35 778 594 47.5 58 3.76 1.89 1.5 6.79 0.75 17.8 0.28 5 31.3 26 7.01 3 21 7.2 0.82 0.11 0.27 0.07 148 25 1.75 235

PSH-92-9.2 7031920 3541290 58.37 0.75 17.75 5.80 0.09 3.33 6.06 4.80 1.09 0.28 98.32 250 422 92 30 761 537 38 58 4 2.23 1.33 5.79 0.72 15.2 0.25 3 24.7 20 5.29 13 16 5.8 0.69 0.08 0.24 0.1 136 20 1.62 197

PSH-92-3.4 7029400 3542000 61.66 0.65 17.37 4.98 0.09 2.76 5.53 4.79 1.04 0.27 99.14 90 234 5 92 27 797 591 43.1 56 2.95 1.47 1.21 4.87 0.54 16.9 0.19 4 26.9 18 6.14 14 13 5.94 0.64 0.04 0.18 0.03 115 17 1.14 144

PSH-92-5.8 7031000 3542850 57.21 0.81 18.69 6.21 0.09 3.15 6.27 4.76 1.39 0.30 98.87 1210 256 11 109 31 766 885 51.8 45 3.97 1.98 1.63 6.13 0.7 20.8 0.24 2 33.7 23 7.62 27 22 7.29 0.81 0.17 0.29 0.22 134 20 1.82 248

N94002593 7106131 3658934 56.90 1.04 18.00 7.98 0.10 2.61 5.50 4.32 2.56 0.29 99.30 400 230 22 140 33 604 583 61.5 19.4 2.93 1.1 1.44 5.01 3.85 0.5 30 0.12 5.31 31.6 7.82 113 10.8 6.1 0.29 0.61 4.07 0.16 0.44 131 13.7 0.92 168

Gabbroic inclusions in the Ranua quartz diorite

144.1-PSH-04 7312710 3474626 48.70 1.33 17.60 10.20 0.16 5.23 8.25 4.57 1.19 0.65 97.88 156 189 28 148 26 1168 632 152 28.2 21.8 5.54 2.42 2.73 10.6 4.63 0.94 68.8 0.32 4.87 75.4 13.3 18.1 26.6 24.6 12.6 1.23 2.42 0.36 0.31 205 26.5 2.01 186

144.2-PSH-04 7312710 3474626 44.70 1.71 15.70 12.99 0.21 6.97 9.80 3.33 0.88 0.70 96.99 443 146 32 181 31 703 330 117 36.6 30.2 6.73 3.12 3.28 12.5 5.66 1.23 50.1 0.41 5.44 70 16.3 15.3 22.8 33.4 14.2 1.47 2.73 0.42 0.32 272 33.6 2.73 241

AmphibolitesSample Northing

(KKJ)Easting

(KKJ)SiO2 TiO2 Al2O3 FeO MnO MgO CaO Na2O K2O P2O5 Sum of

oxidesS Cl Cu Zn Ga As Sr Ba Pb Ce Co Cr Dy Er Eu Gd Hf Ho La Lu Nb Nd Ni Pr Rb Sc Sm Ta Tb Th Tm U V Y Yb

XRF ICP-MS

Basalts

134.2-PSH-04 7278375 3476541 50.40 1.09 14.70 11.62 0.21 6.65 9.63 3.30 0.73 0.08 98.41 540 189 53 133 25 105 121 11.1 46.2 118 3.42 2.36 0.77 3.52 1.78 0.84 5.41 0.37 2.65 7.69 111 1.49 4.97 37.7 2.50 0.33 0.57 1.25 0.33 1.38 284 22.7 2.16

148.1-PSH-04 7192031 3504475 47.00 0.96 17.50 11.79 0.16 6.05 5.79 3.79 2.37 0.13 95.54 282 198 39 360 1070 61.3 32.1 182 4.14 1.97 1.47 5.37 1.76 0.72 30.9 0.26 6.12 29.6 58.4 7.17 56.7 19.7 5.67 0.41 0.77 0.82 0.27 0.35 168 21.0 1.72

150.2-PSH-04 7193373 3519647 50.60 1.02 14.70 11.23 0.26 6.32 9.63 2.71 0.96 0.14 97.57 261 161 25 139 103 21.3 42.4 204 3.42 2.06 0.87 3.78 1.61 0.76 9.22 0.30 4.84 11.8 84.9 2.68 39.1 40.1 3.12 0.36 0.57 1.64 0.31 0.88 293 20.3 2.14

166.1-PSH-04 7257589 3495545 51.90 0.43 15.20 11.05 0.23 6.90 8.49 2.62 0.69 0.15 97.65 114 190 28 82 640 14.0 39.1 171 2.92 1.91 0.55 2.30 0.56 0.64 6.01 0.30 5.78 7.93 60.1 1.69 17.5 45.3 2.28 0.41 0.44 0.82 0.31 0.54 172 18.9 2.00

175.3-PSH-04 7160836 3517091 51.90 1.77 12.90 12.48 0.17 4.81 9.07 2.98 1.27 0.20 97.56 913 733 295 82 30 338 258 37.5 43.0 25.4 5.55 3.36 1.27 5.97 3.51 1.13 17.3 0.47 7.16 20.4 42.4 4.70 23.6 37.5 4.53 0.38 0.95 3.43 0.46 0.37 295 31.9 2.91

178.1-PSH-04 7145042 3508646 49.30 1.44 13.50 12.08 0.19 6.91 8.99 3.37 0.89 0.15 96.82 650 543 86 99 257 101 27.4 46.5 90.2 4.09 2.24 1.17 4.84 2.37 0.83 11.9 0.27 8.88 16.0 88.0 3.67 13.5 36.6 3.67 0.48 0.66 1.33 0.32 0.24 284 21.5 1.82

190-PSH-04 7096414 3517642 51.90 1.26 13.30 13.25 0.24 4.88 7.79 3.15 1.19 0.14 97.12 258 195 86 153 25 214 241 16.0 48.1 41.2 4.41 2.79 1.08 4.09 2.28 0.97 7.71 0.42 4.91 10.2 67.5 2.12 48.8 41.8 3.21 0.35 0.72 2.80 0.41 0.60 350 27.4 2.69

21-PSH-04 7280410 3419488 51.50 0.56 13.60 9.10 0.17 6.91 11.50 2.88 0.47 0.04 96.73 3499 60 203 90 26 888 103 11.1 47.9 341 2.31 1.57 0.92 1.99 1.04 0.58 6.37 0.27 2.30 5.83 121 1.37 14.2 34.3 1.68 0.40 1.10 0.23 2.43 188 15.6 1.55

22.1-PSH-04 7288098 3408396 47.60 1.40 14.00 12.36 0.19 6.54 9.69 3.31 1.07 0.11 96.27 410 142 24 90 28 148 117 15.6 48.8 127 5.06 3.15 1.20 4.62 2.56 1.06 6.76 0.43 3.99 11.5 88.6 2.24 18.5 40.7 3.70 0.23 0.78 1.09 0.45 0.55 350 29.1 2.82

5-2-VJ-86 7033040 3548300 49.38 0.52 17.06 9.25 0.17 6.48 10.66 3.02 0.26 0.05 96.85 660 79 69 104 25 304 85 17 14.3 18 1.84 0.92 0.54 2.18 0.37 5.86 0.19 2 7.88 37 1.81 1 42 1.94 0.3 0.05 0.13 0.01 203 12 1.17

70.2-PSH-04 7335466 3437280 49.10 0.92 13.90 10.85 0.21 8.01 8.20 0.80 3.47 0.11 95.58 121 20 169 22 414 496 13.3 47.2 146 3.96 2.60 0.84 3.75 2.00 0.86 6.05 0.39 3.50 9.19 122 1.81 259 43.4 2.65 0.29 0.59 3.29 0.35 0.88 261 22.3 2.29

8.1-PSH-04 7265242 3424052 47.60 1.11 15.70 10.11 0.13 7.18 8.93 3.33 1.68 0.30 96.07 856 171 74 134 30 239 310 15.9 43.8 75.0 2.60 1.60 0.93 3.02 1.66 0.56 6.91 0.17 3.28 11.5 88.5 2.21 52.5 30.9 2.96 0.20 0.46 0.63 0.19 0.36 252 13.7 1.22

PSH$-2006-64 3548904 7270375 51.80 0.76 14.40 10.62 0.18 7.20 9.54 3.09 0.80 0.06 98.44 580 198 33 136 21 213 159 18.4 43.4 328 3 1.81 0.77 2.75 1.31 0.61 10.9 0.27 2.66 8.66 106 2.02 5.21 37.1 2.02 0.28 0.45 0.75 0.24 0.29 228 15.4 1.58

PSH-03-30 7047328 3641329 47.60 0.87 17.70 9.26 0.15 6.27 9.16 3.56 1.44 0.26 96.27 1251 66 60 176 27 556 394 36.9 31.9 51 3.45 2.17 1.40 4.75 2.46 0.75 16.9 0.31 2.68 22.0 20 4.94 37.5 22.2 4.54 0.67 1.75 0.30 0.26 207 20.9 1.81

PSH-03-35.1 7036978 3654061 52.00 0.88 13.40 9.76 0.19 7.32 9.31 2.85 0.62 0.07 96.40 76 128 20 334 79 11.2 42.7 241 3.45 2.14 0.86 3.25 1.50 0.70 4.80 0.33 2.78 8.87 149 1.74 14.9 40.6 2.60 0.56 0.52 0.30 0.33 236 19.5 2.12

PSH-03-44 7040779 3664210 50.20 0.95 13.10 11.10 0.21 6.86 10.14 2.93 0.59 0.07 96.14 238 558 58 128 24 151 107 19.4 52.0 102 3.73 2.46 0.95 3.54 1.51 0.82 8.37 0.34 2.1 10.8 74 2.46 5.11 56.7 2.45 0.56 0.34 334 22.0 2.31

PSH-90-13.2 7027700 3532860 43.32 0.71 13.66 18.29 0.55 6.05 10.88 2.38 0.42 0.09 96.35 5840 431 582 143 27 75 87 13 15.6 170 3.69 2.41 0.87 3.06 0.75 7.53 0.36 3 8.82 93 2.03 6 0 2.41 0.54 n.d. 0.33 n.d. 264 18 2.5

PSH-90-27.1 7029780 3546860 50.54 0.50 15.49 8.57 0.16 6.70 10.82 3.11 0.29 0.06 96.24 300 82 26 89 25 264 89 17 16.7 27 1.98 1.31 0.65 2.58 0.51 7.06 0.16 3 9.61 45 2.19 0 0 1.9 0.39 n.d. 0.16 n.d. 187 13 1.35

PSH-90-3.2 7038000 3535550 47.14 1.00 15.16 11.72 0.21 7.15 10.30 2.71 0.60 0.08 96.07 1750 125 181 113 16 123 99 17 13.6 150 4.17 2.71 0.88 3.88 0.86 5.49 0.37 1 7.9 129 1.83 3 45 2.87 0.61 0.25 0.35 0 319 23 2.28

PSH-90-37.7 7028450 3547310 48.69 0.54 14.82 9.23 0.19 6.80 10.50 3.20 0.28 0.06 94.31 140 244 0 127 18 215 126 17 15.2 51 2.38 1.44 0.71 2.26 0.5 6.54 0.2 4 8.78 50 2.11 4 0 1.91 0.4 n.d. 0.2 n.d. 224 11 1.43

130-PSH-04 7336033 3436865 48.40 0.96 13.60 11.62 0.23 8.45 7.94 1.95 2.81 0.06 96.01 137 55 144 197 282 8.95 50.3 191 3.46 2.16 0.71 2.78 1.47 0.77 4.19 0.35 2.12 6.74 172 1.28 219 42.5 2.16 0.55 0.31 282 21.5 2.40

181-PSH-04 7088104 3501008 46.10 0.69 13.70 11.09 0.20 9.99 12.05 1.88 0.45 0.05 96.20 295 87 55 109 23 161 81 7.44 49.5 335 2.30 1.59 0.67 1.91 1.05 0.58 3.70 0.20 1.50 4.80 169 0.93 6.53 51.3 1.40 0.42 0.23 270 14.4 1.64

184-PSH-04 7082241 3528086 49.60 0.97 15.80 10.49 0.37 4.46 13.27 1.78 0.33 0.06 97.13 5682 452 94 102 25 104 60 6.27 58.7 197 3.23 2.55 0.71 3.17 1.06 0.72 2.28 0.39 2.04 6.33 167 1.06 3.23 47.4 2.10 0.53 0.36 297 21.9 2.35

185.1-PSH-04 7081555 3527826 48.20 1.05 14.60 12.43 0.20 7.77 10.28 2.51 0.18 0.07 97.29 83 28 78 22 334 40 5.76 50.5 161 3.35 2.16 0.73 3.16 1.35 0.77 1.67 0.34 1.74 6.23 114 0.94 2.20 42.6 2.20 0.55 0.32 276 21.0 2.17

191.1-PSH-04 7072092 3518919 45.70 1.04 14.20 12.89 0.22 8.44 12.07 1.74 0.30 0.06 96.66 1009 504 77 121 144 54 10.1 57.7 212 3.92 2.71 0.82 3.52 1.23 0.82 3.48 0.40 1.90 7.73 167 1.49 1.90 49.4 2.68 0.57 0.39 318 24.1 2.42

191.2-PSH-04 7072092 3518919 49.80 1.11 16.20 10.76 0.30 4.90 11.91 3.06 0.30 0.07 98.41 1402 110 93 103 23 106 60 5.91 55.8 171 3.74 2.48 0.76 2.94 1.72 0.80 1.74 0.37 1.90 5.98 145 1.02 2.40 45.6 2.05 0.56 0.32 293 23.4 2.61

192-PSH-04 7074043 3511060 46.30 0.97 14.20 12.65 0.21 8.14 11.91 2.32 0.25 0.07 97.01 1664 180 146 106 97 38 6.85 51.9 215 3.45 2.29 0.73 2.64 1.38 0.76 2.13 0.35 1.65 5.97 141 1.08 0.81 43.1 2.00 0.50 0.30 276 21.0 2.30

20-PSH-04 7282728 3423895 48.70 0.87 13.80 11.94 0.21 7.84 9.38 2.52 0.51 0.06 95.83 90 58 97 169 149 6.31 49.9 150 3.12 2.32 0.69 2.65 1.54 0.70 2.19 0.35 1.86 5.61 126 0.97 18.2 45.1 1.85 0.47 0.34 279 20.1 2.05

49.2-PSH-04 7286461 3393302 47.60 0.81 14.20 11.13 0.18 7.89 9.66 3.19 0.76 0.05 95.47 95 32 93 21 103 77 8.72 50.0 209 3.35 2.06 0.76 2.44 1.56 0.74 3.88 0.32 1.69 7.04 143 1.30 12.2 41.7 1.83 0.52 0.33 253 18.3 2.00

5-PSH-04 7275650 3413629 46.10 0.64 15.80 9.89 0.16 9.53 10.49 2.43 1.21 0.03 96.28 215 44 79 22 95 77 5.37 49.4 279 1.86 1.31 0.52 1.57 0.65 0.43 2.37 0.17 1.22 4.06 212 0.79 33.4 30.9 1.05 0.29 0.18 181 11.4 1.23

7-1-VJ-86 7037700 3533200 48.35 0.87 16.09 11.41 0.20 7.19 10.95 2.56 0.13 0.07 97.82 1070 566 117 93 16 79 49 13 7.19 277 3.3 2.24 0.75 3 0.74 2.65 0.4 2 5.51 158 1.06 1 41 2.11 0.52 0.39 0.34 0.16 274 18 2.16

PSH$-2006-45 3559160 7263765 49.50 1.15 14.90 11.52 0.22 7.57 10.10 2.21 0.52 0.08 97.77 270 161 77 125 20 106 89 8.2 52.6 250 3.74 2.42 0.87 3.61 1.47 0.8 2.76 0.35 2.53 7.04 146 1.45 8.83 42.2 2.2 0.21 0.56 0.34 313 21.8 2.55

PSH$-2006-83.2 3491568 7256767 50.70 1.21 16.10 10.99 0.17 6.54 9.74 2.35 0.47 0.11 98.37 892 106 81 111 344 386 12.3 44.9 231 4.13 2.80 0.93 3.98 1.95 0.95 4.85 0.37 2.90 8.59 102 1.75 3.97 40.4 2.49 0.65 0.40 0.27 309 23.8 2.49

PSH-03-51.1 7042512 3663804 49.50 0.94 14.30 11.76 0.24 5.86 12.91 1.17 0.20 0.05 96.92 1645 65 111 21 110 70 7.33 57.7 219 4.47 2.65 0.79 3.36 1.46 0.95 3.03 0.40 1.81 6.31 145 1.07 1.92 58.2 2.06 0.60 0.42 333 27.8 2.86

PSH-03-97.5 7033349 3653109 49.30 1.37 14.40 12.18 0.22 6.62 8.82 2.44 1.03 0.11 96.49 1331 241 80 119 27 114 190 14.2 53.3 0.019 5.65 3.30 1.27 4.69 3.14 1.15 6.32 0.48 3.61 11.4 123 2.15 41.7 49.3 3.59 0.27 0.83 0.54 0.45 0.29 362 33.7 3.12

PSH-90-12.1 7023550 3537100 48.29 0.91 15.91 10.44 0.26 5.12 12.09 3.10 0.43 0.08 96.63 1770 134 133 105 19 128 92 19 7.68 254 3.64 2.61 0.82 3.54 0.82 3.1 0.37 3 6.72 156 1.24 5 50 2.13 0.55 0.19 0.31 0.11 294 22 2.08

PSH-90-44.1 7049200 3516250 45.89 0.76 14.38 11.62 0.24 7.31 13.43 2.10 0.21 0.04 95.98 610 92 38 100 19 94 35 11 5.86 288 3.11 2.14 0.72 2.88 0.72 1.97 0.31 3 4.91 143 1 1 0 1.87 0.55 n.d. 0.35 n.d. 274 20 1.89

PSH-90-5.4 7040520 3535940 47.77 1.64 14.07 12.97 0.25 6.01 10.98 2.63 0.30 0.15 96.77 1150 148 81 155 26 117 89 20 22.9 191 7.26 5.28 1.71 6.79 1.52 8.1 0.72 5 16.6 77 3.5 0 50 5.29 1.26 0.07 0.74 0.03 399 44 4.58

PSH-90-66.1 7061150 3526600 45.41 0.85 13.88 11.01 0.20 8.17 11.88 2.20 0.67 0.06 94.33 500 171 44 115 15 76 76 12 11 378 3.64 2.41 0.83 3.54 0.88 4.19 0.35 1 8.11 157 1.47 4 0 2.25 0.53 n.d. 0.38 n.d. 304 19 2.47

PSH-90-66.4 7061150 3526600 45.18 0.61 13.92 10.68 0.27 8.85 13.47 1.30 0.07 0.04 94.39 430 52 53 83 12 68 29 11 3.21 437 3.24 2.28 0.54 2.21 0.8 0.8 0.34 3 3.6 135 0.64 4 54 1.53 0.47 0 0.38 0.02 255 20 2.52

PSH-90-90 7041030 3544450 47.78 1.09 16.28 10.19 0.23 5.89 11.67 2.81 0.12 0.07 96.13 1830 303 117 110 21 107 51 15 4.43 329 3.69 2.55 0.73 3.31 0.82 1.3 0.37 1 5.1 212 0.83 3 54 1.89 0.55 0.38 0 371 21 2.26

PSH-90-94.3 7067150 3529970 45.65 0.84 14.20 11.41 0.20 7.48 12.51 1.99 0.37 0.06 94.71 770 66 90 100 23 94 44 16 6.45 304 3.97 2.28 0.9 3.28 0.8 2.35 0.34 0.5 6.14 163 1.16 6 0 1.94 0.62 n.d. 0.43 n.d. 288 17 2.49

Komatiitic basalts

PSH-03-24.1 7029373 3630838 48.30 0.89 11.20 9.57 0.18 12.20 9.49 1.92 1.58 0.11 95.44 142 134 164 295 21.2 54.4 493 2.95 1.61 0.89 3.27 1.29 0.55 11.7 0.20 2.64 13.7 180 3.01 50.6 50.9 2.83 0.46 0.65 0.21 0.51 295 15.6 1.02

183.2-PSH-04 7086291 3510075 47.30 0.35 11.50 8.54 0.18 14.20 11.66 1.16 0.92 0.01 95.81 355 86 42 64 128 1.90 55.7 679 1.34 0.81 0.30 1.10 0.28 0.65 0.15 0.56 1.58 310 0.37 18.2 45.7 0.84 0.2 0.18 0.5 0.12 0.2 189 8.30 0.80

189.2-PSH-04 7096661 3532852 47.70 0.66 10.40 11.37 0.22 12.60 9.97 1.71 0.94 0.04 95.61 94 156 25 102 122 10.3 58.7 725 2.45 1.36 0.71 2.04 1.04 0.44 2.68 0.18 1.93 7.85 318 1.72 35.9 34.7 2.09 0.2 0.36 0.5 0.21 0.25 195 13.8 1.54

PSH$-2006-78 3561914 7301700 49.30 0.80 11.70 10.17 0.15 13.50 7.00 1.89 2.43 0.03 96.96 334 126 75 438 25.9 59.3 1079 3.4 2.03 0.72 4.06 1.84 0.74 10.7 0.27 4.91 16.4 390 3.76 98.8 35.5 3.38 0.56 0.61 1.61 0.26 0.48 210 18.4 1.93

PSH-03-28.1 7041034 3627235 48.40 0.39 11.10 11.15 0.24 10.70 10.01 1.70 1.13 0.01 94.83 93 168 20 82 123 24.3 50.0 1039 7.48 4.87 0.48 5.23 1.01 1.59 8.75 0.74 5.62 12.8 276 3.25 38.9 36.3 3.82 2.43 1.04 2.09 0.74 1.14 178 54.3 5.13

Andesitic basalts

170.3-PSH-04 7166515 3495778 52.60 1.07 13.60 11.22 0.19 5.54 8.57 3.44 0.84 0.08 97.15 488 340 91 195 27 126 85 226 12.6 40.6 101 3.73 2.61 0.83 3.73 1.78 0.91 5.40 0.39 3.95 8.61 71.2 1.66 16.9 38.8 2.55 0.49 0.66 2.30 0.40 1.77 277 24.3 2.62

171.2-PSH-04 7170924 3495952 55.90 0.94 14.60 9.22 0.16 5.43 7.65 3.18 0.68 0.07 97.84 1701 356 166 99 26 153 202 19.7 37.4 99.4 3.77 2.31 0.83 3.30 2.32 0.83 7.94 0.38 3.71 11.3 70.4 2.57 16.2 35.0 2.88 0.29 0.63 1.39 0.35 0.25 275 23.3 2.32

193.2-PSH-04 7080204 3519163 53.00 0.89 10.60 11.32 0.21 8.27 9.81 1.98 0.71 0.11 96.90 1240 358 51 126 178 61 25.9 52.7 383 2.47 1.41 0.93 3.60 2.29 0.45 12.3 0.14 4.02 13.8 196 3.33 7.81 26.3 2.79 0.21 0.47 1.48 0.18 0.84 179 12.8 0.98

3.1-PSH-04 7271283 3419703 54.80 0.63 15.70 8.53 0.15 5.57 7.17 4.63 1.12 0.16 98.46 138 113 24 159 142 35.4 24.5 110 4.87 2.75 1.25 5.16 2.94 0.95 14.5 0.41 5.38 20.9 90.4 4.86 29.0 22.6 4.50 0.35 0.84 0.5 0.39 0.2 140 26.4 2.54

4.3-PSH-04 7268811 3421259 53.50 0.96 15.00 9.85 0.17 4.36 7.92 3.65 1.42 0.15 96.98 6390 190 282 114 24 312 338 17.3 34.2 56.1 2.89 1.92 1.05 3.67 1.87 0.69 7.68 0.28 3.76 11.3 50.4 2.25 32.2 30.8 2.64 0.28 0.49 0.62 0.31 0.31 219 20.1 1.94

43.1-PSH-04 7309666 3435356 52.80 1.41 14.40 7.91 0.14 8.89 5.41 2.12 3.71 0.26 97.04 232 167 39 99 26 228 1083 77.1 34.9 143 3.55 1.89 1.86 5.72 3.98 0.70 37.0 0.21 13.6 36.4 158 9.24 91.6 21.5 6.11 0.81 0.76 10.7 0.24 2.26 161 17.6 1.33

77.2-PSH-04 7281986 3483078 52.60 1.21 13.60 12.32 0.22 6.02 8.41 3.00 0.81 0.11 98.31 120 288 30 174 30 149 101 18.7 43.7 99.4 5.29 2.82 1.01 4.50 2.26 1.06 9.60 0.48 3.85 11.2 69.4 2.38 13.4 43.6 2.93 0.24 0.79 1.42 0.45 0.84 325 29.7 2.77

91.2-PSH-04 7327823 3504736 53.70 1.19 13.90 11.03 0.17 5.38 7.68 1.73 2.17 0.08 97.03 163 122 24 432 384 9.46 38.7 66.4 4.32 2.84 0.95 3.54 2.18 0.91 3.99 0.46 3.02 7.91 69.5 1.60 68.0 37.2 2.86 0.2 0.69 0.5 0.39 0.2 272 24.9 2.82

PSH$-2006-37 3556349 7282311 56.70 0.98 16.70 7.29 0.14 4.13 6.74 4.47 1.40 0.25 98.80 76 143 115 27 461 317 52.2 24 0.0112 4.03 2.29 1.33 4.98 3.47 0.82 22.3 0.37 8.73 28.6 7.16 43 16.7 5.23 0.3 0.81 0.74 0.31 1.06 133 22.4 2.34

PSH$-2006-72.2 3566346 7235244 53.60 0.94 15.50 9.54 0.14 5.09 8.75 3.97 0.82 0.12 98.48 906 288 62 97 28 504 326 32.5 36 0.0179 3.96 2.46 1.33 5.41 2.3 0.86 12.9 0.35 4.46 21.3 0.007 4.66 12.5 32.8 4.45 0.27 0.81 1.93 0.33 0.73 228 21.4 2.06

PSH-90-65.1 7054360 3537500 57.06 1.15 14.33 8.23 0.18 3.31 8.34 3.13 1.73 0.36 97.82 200 92 0 112 22 110 629 21 41.5 34 6.21 3.39 1.42 5.97 1.2 19.2 0.49 9 23.4 13 5.43 40 0 5.29 0.97 n.d. 0.58 n.d. 181 37 3.85

PSH-90-72.1 7030680 3547110 53.90 0.61 14.42 9.53 0.18 5.82 9.18 2.23 0.45 0.08 96.40 1440 158 35 118 22 232 120 23 23.5 33 2.6 1.75 0.86 2.58 0.53 10.7 0.27 1 11.2 38 2.8 0 0 2.56 0.43 n.d. 0.27 n.d. 206 16 1.46

Rhyodacites and

179.1-PSH-04 7075136 3498485 64.30 0.76 15.70 5.71 0.10 2.87 3.12 3.44 2.59 0.12 98.71 4077 254 64 94 28 323 578 56.7 26.9 118 3.80 1.87 1.00 4.77 3.44 0.73 27.2 0.32 5.27 26.2 81.4 6.63 80.5 19.8 4.71 0.40 0.69 8.42 0.27 1.50 131 20.0 2.04

PSH$-2006-64.1 3548902 7270369 68.00 0.44 16.20 3.03 0.04 1.39 4.15 4.57 1.29 0.15 99.26 893 145 50 50 421 597 40.1 8.87 0.004 0.85 0.42 0.59 1.88 3.26 0.17 22.8 1.75 14.3 4.12 34.4 6.13 1.94 0.26 4.1 0.26 40.1 4.06 0.3

PSH$-2006-65.2 3542180 7260301 67.20 0.38 15.10 4.31 0.07 3.43 2.37 2.91 3.27 0.10 99.13 96 126 23 344 858 19.9 14.3 0.0156 0.91 0.42 0.45 1.62 2.61 0.18 10.2 3.32 9.42 0.0074 2.32 88.0 9.17 1.68 0.32 0.21 4.31 1.13 47.2 4.77 0.39

PSH-03-46.1 7040756 3663942 69.30 0.47 16.00 2.33 0.04 1.05 3.10 5.29 1.57 0.16 99.31 215 57 23 739 643 42.0 6.49 0.003 1.65 0.72 0.90 3.16 3.07 0.31 20.5 4.14 19.4 4.98 52.0 5.00 3.44 0.27 0.38 1.83 0.20 37.3 8.26 0.45

10.1-PSH-04 7257618 3429116 56.80 0.57 15.70 8.06 0.16 4.88 4.86 2.34 3.41 0.07 96.85 181 132 28 319 357 27.9 28.6 47.2 3.41 2.11 0.98 4.19 7.22 0.74 10.9 0.32 3.86 15.8 67.0 3.79 161 28.2 3.80 0.33 0.64 0.5 0.27 0.47 131 19.0 1.94

PSH-90-69.6 7030260 3547250 59.63 1.00 13.53 9.68 0.14 2.65 5.49 3.45 1.97 0.18 97.72 930 211 8 128 23 280 767 23 57.3 27 4.12 2.04 1.32 4.73 0.81 26.8 0.37 7 25.8 13 6.69 24 0 5.13 0.71 n.d. 0.31 n.d. 272 20 1.95

172-PSH-04 7177648 3492703 59.60 0.97 15.00 7.72 0.10 3.45 5.68 4.09 1.73 0.23 98.56 150 57 27 252 334 56.0 23.6 45.3 5.19 3.07 1.23 5.66 5.18 1.15 25.5 0.44 8.98 28.1 44.2 6.62 59.8 20.7 5.55 0.68 0.89 5.65 0.45 0.98 133 30.2 2.77

Metavolcanic rocks of the greenstone belts

Komatiites and komatiitic basalts

Ilomantsi, Hattu (reanalysed from O'Brien et al. 1993)Sample Northing

(KKJ)Easting

(KKJ)SiO2 TiO2 Al2O3 FeO MgO MnO CaO Na2O K2O P2O5 Sum of

oxidesAs Ba Cl Cr Cu S V Zn Ba Ce Co Cu Dy Er Eu Ga Gd Hf Ho La Lu Nb Nd Pb Pr Rb Sc Sm Sr Ta Tb Th Ti Tm U

XRF ICP-MS

KJP-87-80.2 6997601 3717957 40.50 0.16 4.17 9.02 34.30 0.14 2.35 0.07 0.00 0.07 90.78 23 3448 20 335 94 88 0.3 2.28 101 17.4 0.49 0.37 0.14 3.98 0.51 0.28 0.08 0.97 0.05 0.49 1.78 5.75 0.36 0.29 18.4 0.42 47 0 0.06 0.12 845 0.03 0.03

HJO-86-30 6995360 3715648 43.90 0.23 4.23 8.94 35.00 0.14 1.86 0.07 0.02 0.15 94.54 20 3631 65 721 97 110 4.23 5.19 86.8 69.8 0.55 0.4 0.24 4.62 0.83 0.38 0.13 2.2 0.06 0.83 3.25 1.56 0.68 1.02 19.3 0.89 114 0 0.11 0.25 1264 0.05 0.08

HJO-86-32 6994985 3715775 42.90 0.28 4.07 9.34 33.50 0.12 1.00 0.07 0.02 0.11 91.41 85 3286 20 192 100 86 71.6 3.28 88.1 8.5 0.69 0.44 0.23 4.58 0.88 0.54 0.15 1.23 0.06 0.84 2.76 1.21 0.5 1.07 17.9 0.58 75.6 0 0.11 0.21 1603 0.05 0.07

KJP-87-80.1 6997601 3717957 43.10 0.44 7.60 7.93 26.80 0.16 6.52 0.07 0.04 0.21 92.87 32 2004 20 60 131 89 17.8 16.1 55.9 8.21 1.81 0.92 0.51 8.59 2 1.02 0.35 7.12 0.15 1.45 9.92 2.12 2.19 1.51 21.3 2.02 115 0 0.27 1.15 2424 0.12 0.1

KJP-87-99 6992144 3716279 47.00 0.43 7.04 15.91 11.90 0.38 9.80 1.25 0.22 0.15 94.08 805 142 2227 20.00 350 123 107.00 118 12.6 64.9 29.7 2.09 1.11 0.54 8.93 2.29 1.5 0.44 5.29 0.17 2.32 7.24 3.41 1.68 6.55 22.8 1.71 83.8 0.02 0.36 1.19 2365 0.16 0.35

L05092835 6989805 3717661 46.50 0.48 7.39 9.95 17.50 0.22 9.08 0.62 0.11 0.13 91.98 40 1662 0 160 96 28.7 7.61 1.7 2.68 1.39 0.83 10.9 2.56 1.43 0.52 2.56 0.22 1.94 6.84 2.1 1.21 2.1 29 2.35 67 0.42 0.93 2660 0.23 0.22

KJP-87-16 7003931 3712603 48.50 0.49 5.31 11.15 20.00 0.23 8.07 0.10 0.02 0.05 93.92 20 1279 21 61 105 147 5.3 22.5 85 60 1.65 0.75 0.6 9 2.36 1.44 0.27 9.97 0.1 3.82 11.8 3.35 2.9 0.42 16.6 2.22 62.9 0.14 0.3 1.66 2783 0.09 0.4

KJP-87-14.2 7003532 3712622 40.50 0.63 10.40 9.64 21.80 0.18 7.44 0.07 0.03 0.21 90.90 26 61 2327 20 60 133 180 4.65 29.6 86.7 0.98 1.64 1.07 0.53 15.9 2.52 1.85 0.33 15.3 0.15 4.24 14.2 1.5 3.59 0.85 25.9 2.65 27.4 0.08 0.34 2.05 3530 0.16 0.41

HJO-87-79.1 6988788 3717137 50.20 0.54 9.41 11.06 13.70 0.20 7.62 2.65 0.40 0.16 95.94 167 60 1429 20.00 98 164 131.00 172 13.6 53.5 2.29 2.67 1.58 1.06 15 3.14 1.7 0.56 5.97 0.23 2.46 9.39 2.32 1.9 12.3 26.4 2.66 186 0.06 0.42 1.74 3251 0.23 0.47

Ilomantsi, Kovero

12-TTU-06 6943898 3675060 40.60 0.10 3.29 10.17 37.80 0.16 0.61 0.07 0.00 92.79 29 3522 316 66 71 3.78 0.84 128 14 0.53 0.33 3.15 0.33 0.12 0.51 0.21 0.72 2.38 0.12 0.39 15.5 0.29 583

11-TTU-06 6943935 3675034 40.20 0.19 5.29 10.26 32.80 0.13 2.38 0.07 0.00 91.32 5943 2649 100 67 1.85 1.2 138 109 0.47 0.33 6.14 0.33 0.5 0.6 1 3.87 0.2 0.54 19.3 0.38 1.69 1100

9-TTU-06 6943932 3675037 45.40 0.20 5.61 8.52 27.30 0.15 6.73 0.07 0.00 93.99 4529 1423 92 57 1.92 1.67 95.7 32.2 0.86 0.63 0.14 6.09 0.61 0.19 0.58 0.6 1.72 2.21 0.32 0.2 18.3 0.68 17.5 0.14 1190

19-TTU-06 6943879 3675073 42.30 0.16 5.09 10.08 32.60 0.12 3.45 0.07 0.00 93.87 2520 1488 87 60 1.06 1.34 129 40.4 0.93 0.53 4.78 0.5 0.59 0.18 0.63 0.12 0.29 1.6 1.47 0.22 0.33 21 0.42 7.05 0.11 906

7-TTU-06 6943939 3675038 43.90 0.22 7.18 9.00 26.10 0.15 6.37 0.07 0.00 92.99 3440 1651 100 61 0.86 1.47 106 84.7 1.22 0.74 6.62 0.86 0.26 0.58 0.44 1.44 1.03 0.28 0.23 27.1 0.64 5.72 0.17 1300

10-TTU-06 6943926 3675037 38.90 0.19 5.62 10.89 32.40 0.13 2.98 0.07 0.00 91.19 23 5909 2151 110 64 6.04 4.49 127 86.7 0.53 0.35 6.04 0.51 0.5 0.13 2.58 0.54 2.39 2.57 0.5 0.5 19.2 0.63 6.28 1070

24-TTU-06 6943812 3675114 46.60 0.35 9.69 11.34 14.90 0.23 10.50 0.82 0.16 0.02 94.61 47 58 76 1912 20 60 186 107 41.5 3.58 66.6 7.59 1.49 1.03 0.27 9.51 1.38 0.68 0.34 1.72 0.2 0.61 3.01 1.93 0.53 12.2 46.5 1 54.2 0.27 2280 0.15 0.2

22-TTU-06 6943813 3675108 47.50 0.33 8.71 10.98 15.70 0.21 10.20 0.78 0.24 0.02 94.67 68 89 1872 20 60 186 113 58.8 3.03 72.3 25.3 1.54 0.96 0.29 8.8 1.18 0.68 0.32 1.6 0.14 0.67 2.52 1.97 0.43 24.2 42.6 0.85 48.1 0.21 2100 0.14 0.2

23-TTU-06 6943815 3675110 49.00 0.34 9.65 10.71 15.00 0.19 8.33 1.10 0.30 0.02 94.63 40 87 92 1308 50 60 185 93 76.8 2.96 68 55.8 1.57 1.12 0.22 8.71 1.21 0.75 0.34 1.59 0.18 0.64 2.41 3.25 0.48 34.8 43.3 0.85 78.3 0.25 2120 0.15 0.2

L05092828 6957665 3692097 51.40 0.57 11.50 9.36 9.97 0.18 8.56 3.79 0.21 0.03 95.57 94.6 613 61.3 1070 239 83.7 70.5 3.58 68.6 2.08 1.29 0.44 10.5 1.68 0.88 0.43 1.31 0.21 1.07 3.16 1.9 0.59 4 50.2 1.19 100 0.3 3320 0.19

25-TTU-06 6943815 3675118 47.40 0.39 10.30 11.97 13.50 0.30 10.30 1.12 0.10 0.02 95.40 32 77 1574 20 60 190 162 21 3.36 79.3 26.5 1.64 1.17 0.38 10.8 1.27 0.79 0.39 1.39 0.18 0.67 2.65 2.65 0.49 2.2 45.5 1.02 44.2 0.27 2370 0.17 0.2

Kuhmo

L03072898 7133098 3601208 41.10 0.23 4.73 9.30 30.60 0.21 5.66 0.00 0.01 0.02 91.86 23 7191 57 112 215 0 2.83 112 47.6 0.66 0.49 0.11 6.43 0.55 0.1 0.13 0.71 0.05 0.37 1.36 0.39 0.3 0.42 16.7 0.33 1.07 0.02 0.12 0.26 1200 0.05 0

10-PTP-03 7130564 3602049 41.40 0.16 3.08 7.16 36.70 0.13 1.85 0.00 0.01 0.02 90.51 25 3003 180 64 72 0 2.38 112 7.44 0.71 0.43 0.06 4.13 0.43 0.02 0.11 0.74 0.07 0.48 1.22 0 0.34 0.46 10.6 0.26 4.93 0.01 0.09 0.17 934 0.05 0

4-PTP-03 7127563 3601670 42.60 0.37 8.62 10.00 24.20 0.17 5.60 0.08 0.02 0.03 91.69 2558 94 100 150 98 3.07 2.71 92.5 81.3 1.37 0.95 0.27 8.41 1.15 0.41 0.31 0.74 0.12 0.72 2.4 5.17 0.38 1.12 30.9 0.63 15.7 0 0.21 0.01 2380 0.11 0

L03072900 7204190 3608706 45.80 0.39 14.20 9.03 12.40 0.18 11.10 1.49 0.22 0.04 94.85 65 190 935 112 190 171 76 39.5 2.91 78 110 1.36 0.88 0.35 11.9 1.16 0.18 0.26 0.79 0.14 0.79 2.6 2.95 0.45 6.69 39.8 0.68 156 0.03 0.19 0.06 2330 0.14 0

2A-PTP-03 7127610 3601579 45.70 0.36 7.18 9.14 21.50 0.17 8.24 0.11 0.01 0.03 92.44 293 26 81 2466 13 38 141 84 14 2.09 26.2 0 1.56 0.91 0.2 7.4 1.25 0.51 0.31 0.58 0.11 0.8 2.55 0.36 0.35 0.58 23 0.8 7.09 0.06 0.23 0.13 1829 0.14 0.03

2F-PTP-03 7127619 3601588 46.30 0.33 6.90 8.87 21.70 0.17 8.35 0.12 0.01 0.02 92.77 302 19 74 2505 6 45 139 79 1.94 1.69 68.6 12.8 1.12 0.76 0.21 8.16 1.04 0.34 0.27 0.52 0.12 0.95 1.97 0.88 0.32 0.38 26 0.58 7.69 0.02 0.18 0.1 1853 0.13 0.06

25-PTP-03 7133092 3601277 51.10 0.37 14.80 6.25 11.20 0.16 10.93 2.16 0.98 0.02 97.97 0 187 72 454 32 4 168 81 157 3.38 30.8 12.6 1.89 0.97 0.34 10.9 1.4 0.5 0.36 1.45 0.13 0.61 2.9 32.6 0.46 41 32.4 0.98 124 0.03 0.25 0.3 1733 0.13 0.1

53-PTP-03 7151046 3598464 43.80 0.35 7.30 10.15 22.60 0.22 7.11 0.05 0.02 0.02 91.62 15 22 94 2499 0 0 140 147 3.11 1.66 55.5 0 1.45 0.77 0.22 8.22 1.09 0.46 0.31 0.57 0.11 0.6 1.83 0 0.29 0.54 23.7 0.81 5.05 0.05 0.21 0.1 1824 0.12 0.38

2G-PTP-03 7127619 3601588 44.50 0.40 8.24 10.45 20.50 0.18 8.03 0.26 0.02 0.02 92.60 262 21 68 2612 15 107 178 97 1.06 2.52 124 15.9 1.51 0.93 0.21 8.75 1.33 0.54 0.35 1 0.18 0.77 2.58 0.94 0.45 0.19 30.4 0.94 6.6 0.02 0.23 0.06 2269 0.2 0.03

56-PTP-03 7123890 3603424 46.00 0.65 12.90 12.20 10.50 0.27 10.30 0.94 0.27 0.05 94.08 70 220 890 51 890 256 113 53.1 6.29 85.2 52.8 2.76 1.88 0.61 15.5 2.46 0.63 0.53 2.03 0.26 1.43 5.43 7.41 0.94 8.83 45.3 1.98 69.3 0.07 0.4 0.18 3990 0.25 0

2H-PTP-03 7127619 3601588 44.50 0.41 8.09 10.69 20.00 0.19 8.16 0.32 0.02 0.02 92.40 28 16 90 2545 7 9 158 93 1.4 2.49 74.8 5.68 1.74 1.05 0.34 9.46 1.41 0.68 0.36 0.85 0.13 0.82 2.11 1.89 0.46 0.18 33.2 0.86 7.33 0.04 0.23 0.1 2575 0.13 0.08

12-PTP-03 7129321 3600846 45.30 0.54 10.60 10.81 15.80 0.20 10.04 0.78 0.30 0.04 94.41 0 96 134 1487 16 7 208 193 81.5 3.77 59.8 0 2.45 1.37 0.39 10.6 2.29 0.59 0.53 1.36 0.22 1.12 3.71 2.89 0.58 9.29 32.9 1.34 20.4 0.09 0.33 0.13 2728 0.26 0.08

2I-PTP-03 7127619 3601588 45.10 0.48 9.54 11.71 16.60 0.20 8.60 1.32 0.05 0.03 93.63 11 24 136 2185 17 10 203 83 3.17 2.97 77.9 0 1.97 1.21 0.47 11.3 1.49 0.69 0.37 1.17 0.17 0.94 3.39 2.36 0.49 0.31 35.8 1.2 12.8 0.04 0.29 0.09 2860 0.17 0.06

2B2-PTP-03 7127619 3601588 44.10 0.37 7.95 9.62 22.40 0.21 6.80 0.20 0.04 0.02 91.71 0 26 78 2545 6 0 145 93 3.91 2.38 82.5 7.38 1.48 0.88 0.33 8.51 1.09 0.58 0.29 1.06 0.14 0.68 2.13 3.53 0.41 2.05 29.3 1.07 14 0.01 0.22 0.08 2051 0.14 0

2B1-PTP-03 7127619 3601588 48.70 0.57 11.60 10.88 12.60 0.20 7.86 3.02 0.07 0.03 95.53 1 27 160 668 18 47 225 66 8.59 2.87 65.6 7.94 2.13 1.56 0.49 12.6 1.87 0.77 0.46 0.97 0.2 0.99 2.99 7.83 0.56 0.31 45.3 1.16 72.1 0.1 0.31 0.07 3420 0.22 0.02

7D-PTP-03 7128010 3602258 43.00 0.47 8.33 10.85 21.50 0.17 6.98 0.07 0.01 0.04 91.42 1 20 58 1973 0 0 174 76 2.43 4.2 86.8 0 1.93 1.15 0.39 9.6 1.68 0.77 0.43 1.42 0.2 3.81 3.07 1.6 0.62 0.37 30.2 1.18 10.1 0.31 0.32 0.17 2875 0.17 0.07

2D-PTP-03 7127619 3601588 47.40 0.56 11.30 11.15 13.60 0.19 7.84 2.56 0.07 0.03 94.70 9 40 163 815 6 16 218 69 15 2.72 64.2 36.9 2.12 1.43 0.38 12.2 1.65 0.79 0.4 1.05 0.19 1.06 2.74 4.55 0.46 0.23 43.8 1.04 55 0.05 0.29 0.1 3462 0.21 0.08

2C-PTP-03 7127619 3601588 47.50 0.58 11.30 11.24 13.40 0.20 7.96 2.63 0.07 0.03 94.91 6 26 184 816 15 55 231 74 5.87 4.1 64.9 22.7 2.3 1.33 0.51 12.5 1.92 0.87 0.5 1.53 0.2 1.13 3.95 8.1 0.67 0.27 43.8 1.31 58.4 0.04 0.31 0.12 3578 0.21 0.05

13-PTP-03 7105965 3618236 47.20 0.62 12.00 10.30 12.10 0.23 11.20 1.73 0.18 0.05 95.61 57 140 1123 235 111 35.8 6.78 72.3 13 2.45 1.65 0.58 13.4 2.46 0.74 0.6 2.23 0.25 1.67 4.86 3.21 0.97 2.3 43.1 1.42 146 0.1 0.36 0.15 3940 0.27 0

7B-PTP-03 7128010 3602258 44.70 0.46 8.24 10.63 19.90 0.20 8.13 0.25 0.03 0.03 92.57 2 20 56 2195 4 0 168 104 3.87 3.8 83.7 0 2.26 1.35 0.38 10.9 1.72 0.93 0.4 1.8 0.16 0.83 3.29 3.09 0.62 0.66 34.1 1.25 8.6 0.03 0.3 0.12 1604 0.17 0.04

7F-PTP-03 7128010 3602258 44.60 0.44 7.96 10.39 19.90 0.20 8.17 0.22 0.02 0.03 91.93 2 20 45 1924 11 6 157 98 4.93 3.09 86.5 6.6 2.05 1.31 0.34 10.3 1.36 0.79 0.39 1.26 0.21 0.7 2.87 5.14 0.56 0.36 28.6 1.06 8.8 0.04 0.31 0.08 1860 0.22 0.08

7E-PTP-03 7128010 3602258 40.50 0.59 10.10 12.72 20.20 0.20 6.51 0.13 0.02 0.05 91.02 0 22 52 1632 116 86 217 108 14.4 6.48 91.1 99.9 2.06 1.44 0.46 11.8 1.9 0.74 0.45 2.91 0.23 1.35 4.57 2.89 0.93 0.24 33.7 1.41 7.17 0.11 0.35 0.15 3441 0.21 0.03

2E-PTP-03 7127619 3601588 47.40 0.58 11.10 11.41 12.80 0.19 8.61 2.74 0.10 0.02 94.95 6 30 216 1445 45 261 231 70 11 3.29 66.4 24.3 2.47 1.53 0.5 13.6 1.8 0.9 0.57 1.24 0.23 1.15 3.54 4.38 0.54 0.43 45.6 1.36 40.5 0.08 0.33 0.18 3645 0.21 0.04

48-PTP-03 7175646 3604213 44.00 0.75 12.30 12.40 13.80 0.20 7.41 1.80 0.04 0.06 92.76 46 1136 130 160 254 122 25.9 6.58 83.9 113 2.88 1.81 0.55 15.4 2.55 0.86 0.62 2.1 0.23 1.51 5.33 0.37 0.97 0.44 38.6 1.74 40.6 0.08 0.44 0.24 4650 0.26 0.04

7C-PTP-03 7128010 3602258 48.40 0.63 10.90 10.99 14.10 0.19 7.15 2.63 0.07 0.04 95.10 6 31 68 886 31 113 222 74 13.1 4.63 65.9 20.8 2.75 1.68 0.78 11.6 2.39 0.79 0.6 1.79 0.27 1.57 4.3 3.37 0.79 1.69 40.9 1.47 40.5 0.09 0.39 0.18 3775 0.26 0.07

52-PTP-03 7151793 3598324 45.50 0.75 10.90 13.65 11.10 0.28 11.49 1.24 0.40 0.05 95.36 7 128 259 773 10 1 247 160 110 9.05 51.8 0 3.02 1.76 0.82 13.2 3.69 1.38 0.66 4.08 0.23 1.58 7.2 6.62 1.24 11.4 31.9 2.23 111 0.11 0.52 0.42 3794 0.31 0.57

47-PTP-03 7171190 3603261 48.70 0.66 13.00 10.80 11.10 0.18 6.87 3.03 0.09 0.05 94.48 38 694 65 270 247 94 18.7 13.4 76.7 61.5 3.05 1.7 0.63 14.4 2.5 0.73 0.66 6.02 0.25 2.27 8.01 1.36 1.78 1.2 47 1.77 112 0.14 0.42 1.39 4130 0.24 0.37

7A-PTP-03 7128010 3602258 48.50 0.66 11.90 10.52 12.20 0.18 7.41 3.27 0.06 0.04 94.74 1 27 66 938 83 76 220 70 8.72 5.96 66.7 88.4 2.62 1.74 0.6 14 2.31 1.09 0.55 2.18 0.29 1.75 5.19 7.44 0.9 0.43 44.4 1.52 83.3 0.14 0.42 0.18 4314 0.27 0.11

36-PTP-03 7137847 3600713 48.90 1.12 5.84 11.00 11.90 0.36 13.30 1.86 0.45 0.06 94.79 255 360 53 172 860 265 136 247 14.5 84.9 170 3.07 1.63 1.15 12.2 3.97 1.58 0.63 5.53 0.18 3.53 11.6 7.18 2.14 9.48 55.7 3.28 63.1 0.24 0.57 1.23 6780 0.22 0.35

Basalts

Ilomantsi, Hattu (reanalysed from O'Brien et al. 1993)Sample Northing

(KKJ)Easting



XRF ICP-MS

HJO-86-116 6990234 3717430 48.50 0.89 14.50 11.46 8.92 0.18 9.02 2.97 0.18 0.07 96.69 57 300 100 60 309 113 42.6 6.13 45.8 120 3.21 1.97 0.64 17.1 2.7 0.99 0.71 2.35 0.29 1.71 4.85 1.88 0.97 2.45 47.6 1.89 199 0 0.47 0.23 4885 0.28 0.04

HJO-86-117 6990137 3717484 49.50 0.95 14.20 11.75 8.95 0.19 9.15 2.41 0.15 0.07 97.32 54 183 107 87 306 128 27.5 6.28 48 101 3.56 2.21 0.7 17.3 2.79 1.12 0.77 2.38 0.32 1.58 5.66 1.14 1.01 1.11 45.6 2 101 0 0.51 0.27 5385 0.32 0.06

HJO-86-20 6991638 3717464 52.40 1.71 11.70 19.47 2.41 0.26 6.13 3.07 0.22 0.20 97.57 58 212 30 25 578 85 225 44.3 18.4 38.6 32.2 9.3 5.98 1.73 26.3 7.72 3.39 2.11 6.67 0.88 6.15 15.2 1.27 2.84 1.46 44.9 5.6 86.7 0.31 1.44 0.58 10750 0.87 0.17

HJO-86-21 6991432 3717334 50.50 2.01 12.40 18.57 3.78 0.24 5.62 4.34 0.19 0.13 97.78 39 142 30 20 173 299 117 32.5 10.2 56.8 9.07 5.94 3.74 1.27 21.8 5.13 2.19 1.28 3.46 0.57 3.45 9.87 0 1.75 3.09 52.7 3.29 70.8 0.14 0.89 0.39 12420 0.55 0.08

HJO-87-90 6992863 3716656 49.40 0.68 13.40 10.16 10.20 0.17 10.42 2.00 0.11 0.06 96.60 38 642 49 206 225 93 23.2 6.41 51.5 76.9 2.71 1.73 0.54 13.4 2.57 1.2 0.59 2.57 0.24 1.85 5.53 1.43 1.04 0.79 38.2 1.67 126 0.02 0.4 0.2 3877 0.24 0.08

KJP-87-13.1 7003524 3712682 51.90 0.80 13.20 7.20 6.53 0.18 11.96 3.71 0.14 0.06 95.68 60 463 37 247 254 75 56.1 8.43 41 45.4 3.01 1.82 0.69 14.3 2.51 1.21 0.67 3.35 0.27 2.16 6.42 1 1.25 1.42 39.7 2.03 370 0.04 0.46 0.25 5050 0.26 0.07

KJP-87-13.2 7003524 3712682 52.50 1.16 14.10 9.45 7.32 0.16 9.47 3.63 0.20 0.09 98.07 79 74 258 815 308 86 67 11.2 41.7 255 4.41 2.41 0.99 18 4.08 1.68 0.89 3.9 0.35 3.41 8.97 2.11 1.8 4.21 41.8 2.77 252 0.09 0.56 0.38 7029 0.38 0.08

KJP-87-38 6993925 3718179 49.90 0.83 13.70 9.11 9.96 0.14 10.59 2.51 0.46 0.06 97.26 94 594 85 188 261 91 75.5 7.95 44.3 89.1 3.16 1.96 0.72 15.5 2.78 1.24 0.63 3.09 0.31 2.11 6.55 2.33 1.24 20.4 42.2 1.93 178 0.07 0.47 0.25 4943 0.32 0.09

KJP-87-97 6991758 3717879 48.10 0.93 15.50 12.64 7.52 0.19 8.99 2.99 0.27 0.07 97.20 59 131 241 39 60 275 141 42.8 5.1 49.3 33.8 2.7 1.9 0.7 15 2.55 0.99 0.65 1.89 0.25 1.62 5 3.36 0.8 9.93 38.7 1.56 309 0 0.42 0.11 4959 0.26 0

L05092836 6993925 3718025 48.40 0.97 16.10 8.01 7.59 0.19 11.40 1.99 0.88 0.08 95.61 142 454 60 650 323 79 137 8.51 3.51 2.03 0.75 16.7 2.95 1.42 0.66 3.15 0.3 2.44 6.88 5.35 1.33 35.5 47.7 2.13 159 0.47 5420 0.29

L05092826 6972729 3723586 51.10 0.99 14.80 10.08 5.71 0.24 10.30 2.15 0.28 0.08 95.73 50 209 0 330 109 37.1 8.85 3.95 2.65 0.84 17.2 3.49 1.36 0.85 3.16 0.39 2.09 7.6 7.79 1.47 6.88 53 2.64 163 0.56 5770 0.39

PAN-86-11 6993835 3718183 51.80 0.88 14.20 8.13 7.99 0.17 11.36 2.50 0.52 0.07 97.62 148 443 57 1302 269 62 130 8.52 41.9 80.5 3.03 1.93 0.71 14.9 2.79 1.27 0.66 3.56 0.25 2.16 6.45 3.41 1.29 17.4 40.9 2.12 224 0 0.49 0.36 4976 0.28 0.12

PAN-86-17 6990733 3718027 51.80 1.02 13.80 10.97 7.10 0.15 9.67 2.35 0.28 0.08 97.22 93 64 149 117 452 302 112 77.6 7.34 44.2 120 3.6 2.26 0.8 18.5 2.83 1.46 0.75 2.73 0.35 2.07 6.3 2.18 1.11 6.13 47.5 2.03 120 0.08 0.53 0.3 6179 0.34 0.14

PAN-86-20 6992281 3717925 50.30 1.07 13.70 13.16 6.65 0.20 8.83 3.20 0.29 0.08 97.48 73 96 88 26 82 315 120 55.5 6.21 48.6 32.3 4.09 2.7 0.73 19.2 2.9 1.17 0.95 2.39 0.4 2.3 5.31 1.26 0.92 5.81 46.7 1.85 247 0.06 0.61 0.28 6474 0.38 0.08

PAN-86-23 6992196 3717388 51.20 1.27 13.90 14.71 5.97 0.19 6.65 3.84 0.22 0.12 98.07 73 88 30 275 1520 244 139 63.9 21.3 59 253 3.97 2.4 1.2 18.4 4.28 1.79 0.81 8.54 0.35 5.88 14.3 2.49 3.15 2.84 20 3.79 169 0.26 0.67 0.83 7748 0.3 0.22

PAN-86-33 6972844 3710939 49.00 0.74 15.00 9.12 4.98 0.21 15.58 2.52 0.37 0.05 97.57 102 60 374 39 957 231 75 98.8 7.45 48.7 40.4 2.75 1.75 0.64 18 2.58 1.21 0.57 3.42 0.24 1.85 5.92 3.41 1.14 10.8 39 1.97 417 0.05 0.43 0.19 4662 0.23 0.14

PAN-86-5 6993806 3713266 47.70 1.18 14.50 13.40 7.38 0.22 9.70 2.74 0.37 0.15 97.34 42 155 63 316 20 60 223 151 137 12.7 45.2 28.8 3.67 1.91 0.99 20.4 3.48 2.17 0.74 5.6 0.26 2.02 8.93 5.16 1.88 8 29.5 2.53 320 0.01 0.55 2.16 6843 0.26 0.5

PAN-86-6 6993806 3713256 49.10 1.15 14.00 12.47 7.84 0.19 9.54 2.58 0.27 0.14 97.28 62 147 81 278 35 64 219 145 133 16.2 44.2 38.3 3.48 1.9 1.14 18.8 4.35 1.74 0.7 7 0.23 1.83 11.8 4.28 2.36 6.16 27.3 3.48 359 0 0.58 2.15 6605 0.24 0.48

Ilomantsi, Kovero

1-TTU-06 6943963 3675029 51.00 1.66 16.20 12.33 5.54 0.13 6.65 4.38 0.34 0.14 98.36 91 176 153 37 60 411 71 82.6 11.3 50 47.7 6.42 3.96 1.24 20.6 5.69 2.94 1.38 4.32 0.6 4.93 10.7 2.77 1.94 15.2 50.7 3.7 147 0.32 0.98 0.73 10200 0.62 0.23

21-TTU-06 6943873 3675083 49.80 0.77 13.60 14.85 6.64 0.23 8.28 3.06 0.27 0.05 97.55 76 233 30 20 217 327 209 59.8 6.42 54.7 20.5 3.18 2.04 0.6 14.9 2.58 1.44 0.71 2.49 0.33 1.43 4.86 5.36 1.02 8.69 53.8 1.95 83.2 0.2 0.49 0.5 4590 0.31 0.2

2-TTU-06 6943950 3675033 50.30 1.60 15.90 11.34 7.40 0.12 5.60 4.47 0.24 0.13 97.10 68 102 148 611 510 410 85 54.9 15.8 51.2 614 5.24 3.61 1.04 18.2 4.83 2.49 1.2 6.4 0.55 4.52 11.3 3.38 2.31 11.8 46.1 3.35 110 0.27 0.84 0.72 9490 0.51 0.24

3-TTU-06 6943949 3675038 50.30 1.56 15.70 13.59 6.25 0.15 5.11 3.86 0.67 0.13 97.31 134 166 134 190 3652 402 196 130 15 51.9 216 5.5 3.4 1.18 20.4 4.83 2.45 1.15 5.98 0.51 4.05 11.4 2.37 2.25 28.6 45.2 3.73 106 0.22 0.86 0.65 9060 0.5 0.2

4-TTU-06 6943951 3675038 49.20 1.52 15.40 13.77 6.35 0.13 5.90 3.80 0.51 0.12 96.69 109 223 139 20 60 391 60 95.7 12.6 53 45.5 6.04 3.88 1.29 21.7 5.16 2.65 1.29 4.46 0.6 4.38 10.5 1.78 2.04 22.6 45 3.78 121 0.28 0.95 0.64 9060 0.53 0.2

5-TTU-06 6943943 3675036 49.50 1.58 15.00 12.87 6.10 0.15 7.64 3.53 0.79 0.12 97.28 231 270 138 33 95 402 73 231 13.3 51 45.5 5.87 3.8 1.18 18.5 5.63 2.51 1.29 4.6 0.6 4.44 10.6 2.51 2.01 37.4 47.6 3.99 176 0.26 0.96 0.64 9470 0.55 0.2

L05092832 6943625 3670167 47.20 0.94 14.50 11.79 8.09 0.21 9.49 2.62 0.20 0.07 95.11 64.5 255 45.1 162 299 100 37.1 6.74 3.47 2.12 0.61 15.5 2.77 1.01 0.72 2.49 0.31 2 5.88 3.35 1.09 3.38 39.2 2.14 102 0.51 5490 0.32

L05092833 6946736 3673527 47.60 0.54 13.70 9.99 9.69 0.19 10.80 1.66 0.46 0.04 94.67 107 762 183 892 229 78.5 80 3.85 2.09 1.37 0.41 12.6 1.79 0.62 0.44 1.38 0.21 1 3.21 1.31 0.59 17.5 37.9 1.31 98.5 0.32 3130 0.21

L05092827 6958504 3660662 50.80 0.88 15.20 8.97 6.31 0.22 10.30 3.27 0.30 0.08 96.33 104 300 211 5230 271 104 105 10 3.02 1.94 0.7 18.4 2.95 1.43 0.62 3.99 0.26 2.81 7.31 3.94 1.49 11.2 40.1 2.17 164 0.45 0.59 5230 0.27

L05092830 6945739 3676428 52.00 0.61 12.50 11.88 6.61 0.19 8.53 2.78 0.26 0.05 95.41 123 336 31 0 275 74.3 99.1 4.28 2.51 1.85 0.52 12.7 2.39 0.84 0.58 1.48 0.27 1.18 3.78 2.07 0.7 4.43 46.1 1.55 156 0.45 3420 0.25

11-PTP-03 7129344 3600704 50.20 0.67 13.60 10.83 5.62 0.22 11.15 3.06 0.21 0.04 95.60 0 56 214 2096 9 0 251 68 30.2 1.83 45 0 3.35 2.03 0.42 9.05 2.27 1.07 0.7 0.45 0.3 1.35 2.59 13.2 0.38 0.66 40.2 1.42 131 0.1 0.46 0.09 3334 0.33 0.09

Kuhmo

20-PTP-03 7127527 3601305 50.20 0.89 13.40 11.15 7.39 0.22 11.37 1.84 0.27 0.07 96.80 1 25 231 273 191 1313 268 138 25.1 10 38.6 154 4.26 2.41 0.89 16.3 3.77 1.63 0.8 4.44 0.31 2.37 8.17 23.8 1.26 2.09 38.2 2.42 87.7 0.14 0.62 0.88 4621 0.36 0.25

22-PTP-03 7129486 3600780 51.20 0.83 14.00 8.94 7.14 0.17 10.51 3.49 0.14 0.06 96.48 0 49 130 543 5 0 268 89 28.4 9.11 41.9 0 3.88 2.37 0.66 14 3.7 1.28 0.79 3.52 0.32 2.15 6.88 9.22 1.26 0.62 40.6 2.61 129 0.14 0.57 0.42 4136 0.35 0.18

27-PTP-03 7142159 3605087 45.30 0.61 17.70 9.63 9.60 0.15 10.03 2.07 0.66 0.04 95.79 0 95 121 245 24 69 181 80 77.1 4.59 43.9 12.6 2.32 1.52 0.53 14.6 2.27 1.07 0.56 1.91 0.25 1.26 4.39 3.66 0.64 30.5 23.8 1.49 115 0.1 0.35 0.15 3112 0.24 0.19

37-PTP-03 7141009 3603962 50.30 0.64 14.30 10.07 7.89 0.19 12.32 1.06 0.21 0.05 97.03 2 63 159 364 121 2393 261 94 36.7 5.32 38.6 100 3.56 1.99 0.58 13.8 2.57 1.08 0.63 2.32 0.33 1.27 4.54 1.94 0.84 2.54 43 1.77 74.8 0.08 0.47 0.57 3248 0.31 0.14

42-PTP-03 7147046 3598074 49.90 0.77 13.80 10.26 8.07 0.25 11.01 2.74 0.31 0.06 97.17 0 114 135 316 14 0 268 329 105 7.06 39.6 0 4.32 2.3 0.63 15.4 3.5 1.17 0.92 3.28 0.32 1.65 6.12 8.91 1.08 3.86 41.8 2.35 216 0.12 0.56 0.48 4051 0.34 0.21

75-PTP-03 7239736 3606637 49.80 0.72 16.10 7.77 9.80 0.15 7.51 2.86 0.05 0.05 94.81 39 1193 41 210 299 96 17 3.76 89.3 40.2 2.46 1.67 0.55 17.2 2.29 0.49 0.48 1.05 0.2 1.09 4.08 6.3 0.67 0.82 54.6 1.19 143 0.05 0.35 0.06 4300 0.21 0.01

88-PTP-03 7233958 3624564 53.40 1.00 14.70 7.17 8.92 0.11 7.04 3.87 0.27 0.09 96.57 0 131 169 351 68 29 168 69 118 16.8 34.1 59.7 2.87 1.29 0.99 16.9 3.96 0.94 0.54 7.72 0.11 3.54 10.1 1.33 2.12 10.4 16.3 2.83 367 0.22 0.5 0.83 4718 0.17 0.15

Andesites and dacites (reanalysed from O'Brien et al. 1993)

Ilomantsi, HattuSample Northing

(KKJ)Easting



XRF ICP-MS

HJO-86-101 6991270 3716009 68.10 0.40 15.70 3.57 1.17 0.06 3.03 4.74 2.18 0.15 99.10 987 34 2457 62 63 1034 29 6.83 39.2 1.41 0.71 0.56 20.5 2.34 3.24 0.28 15.5 0.13 4.48 14.2 18 3.65 50.6 5.97 2.69 657 0.36 0.29 7.86 2318 0.1 1.76

HJO-86-105 6991447 3716381 65.50 0.64 16.40 5.49 0.74 0.10 2.83 5.06 1.98 0.26 98.98 757 109 60 108 101 781 49.6 12.6 16.4 2 1.01 0.97 23.5 3.25 4.1 0.39 23.9 0.16 5.09 24.3 13.5 5.88 73.8 11.3 4.09 974 0.28 0.41 6.1 3678 0.13 1.15

HJO-86-107 6990879 3716638 65.80 0.72 15.10 7.26 2.76 0.08 1.17 2.94 1.78 0.08 97.68 424 211 66 4370 163 124 423 31.5 35.9 71.4 2.49 1.42 0.85 19.2 2.57 2.8 0.49 14.8 0.22 4.49 14.9 10.9 3.58 67.8 20.5 3 190 0.27 0.43 3.6 4181 0.2 1.12

HJO-86-121 6989430 3717788 67.60 0.57 15.40 4.73 1.74 0.06 2.94 4.04 1.86 0.10 99.05 437 115 37 1824 114 112 420 27.4 16.9 58.3 1.68 1.1 0.7 18.4 2.08 2.72 0.37 13.6 0.15 2.9 13.4 17.9 3.06 64 13.1 2.29 501 0.24 0.29 3.68 3046 0.14 1.01

HJO-86-22 6991366 3717206 62.30 1.04 11.10 14.00 1.03 0.17 3.99 4.05 0.11 0.36 98.15 40 176 141 39 84 27.5 30.6 13.8 8.05 14.3 9.38 2.33 28.6 12.5 6.32 3.16 10.1 1.36 9.59 27.8 0.17 5.06 2.84 32 9.44 75.4 0.55 2.31 1 7048 1.33 0.2

HJO-86-23 6991520 3717289 62.80 0.53 15.70 5.24 4.80 0.07 3.03 6.40 0.04 0.18 98.80 29 187 60 111 64 14.2 13.9 14.6 2.58 1.82 1.02 0.83 20 2.1 2.65 0.36 6.16 0.16 3.49 8.61 0 1.93 0.53 13 1.77 81.7 0.15 0.31 1.9 3166 0.16 0.18

HJO-86-28 6995272 3715712 66.40 0.28 15.60 2.99 1.75 0.06 2.06 5.98 3.74 0.16 99.03 2167 82 60 62 75 2300 29.9 8.09 30.5 1.49 0.76 0.55 23.2 2.26 3.28 0.26 13.4 0.11 5.45 14.7 20.1 3.53 77.7 7.15 2.83 1614 0.28 0.3 3.15 1713 0.1 1.47

HJO-87-122.2 6976030 3715460 65.40 0.62 16.80 4.44 2.12 0.07 3.88 4.20 1.43 0.17 99.14 473 63 34 106 91 107 467 16.7 5.88 8.53 1.3 0.67 0.73 22.3 1.7 3.23 0.26 7.51 0.09 5.35 9.43 18.6 2.04 61.6 6.54 1.92 600 0.24 0.27 4.41 3549 0.1 1.06

HJO-87-56 6988866 3716432 71.20 0.30 15.40 2.49 1.11 0.05 4.51 3.42 0.89 0.07 99.43 403 34 60 50 58 424 16.2 8.78 12 0.76 0.41 0.36 19.8 1.32 2.65 0.19 8.71 0.06 1.79 7.27 4.34 1.75 29 6.2 1.34 338 0.12 0.19 1.14 1797 0.05 0.36

HJO-87-79.2 6988788 3717136 55.40 0.73 12.80 8.19 9.67 0.15 5.39 5.33 0.30 0.14 98.10 121 849 60 190 95 123 18.4 50.2 3.22 3.02 1.89 0.94 14.7 3.35 2.04 0.64 8.68 0.26 2.96 12.2 3.88 2.64 9.01 34.7 2.89 410 0.13 0.52 1.63 4536 0.27 0.49

KJP-87-12.1 7003497 3712733 55.10 0.76 16.60 8.22 3.38 0.10 4.82 4.25 3.10 0.38 96.71 905 92 64 2967 153 111 962 82.2 23.1 63.5 3.65 1.83 2.02 22.1 6.45 4.64 0.74 37.9 0.25 6.32 40.8 10 10.1 123 17.5 7.62 791 0.27 0.84 7.72 4491 0.28 1.81

KJP-87-12.2 7003497 3712733 59.20 0.60 18.30 4.41 1.04 0.07 4.13 7.34 3.08 0.32 98.50 1107 70 100 68 111 1101 97.5 5.58 4.18 2.67 0.99 2.01 19.1 5.96 4.58 0.5 45.6 0.14 6.97 48 14.8 11.5 96.7 6.62 8.29 990 0.38 0.7 8.94 3394 0.13 2.07

KJP-87-14.1 7003532 3712642 65.70 0.55 16.90 3.32 0.94 0.04 2.76 5.90 2.91 0.25 99.27 1188 60 55 100 1206 70 5.4 31.6 1.57 0.61 1.37 23.6 4.09 4.09 0.25 33.4 0.05 5.67 35.8 13.1 8.51 88.5 3.77 5.99 814 0.32 0.46 5.06 3199 0.07 1.34

KJP-87-60 7006433 3711274 57.80 0.93 16.20 8.42 1.77 0.12 4.47 4.66 2.62 0.60 97.59 978 126 101 369 168 105 1050 99.6 25.1 94.8 4.37 1.9 2.2 20.5 7.25 4.86 0.75 46.6 0.27 8.05 49.3 22.3 12.1 86.1 19.2 8.83 1041 0.39 0.9 9.97 5674 0.3 1.77

L05092834 6994261 3711500 64.80 0.65 15.80 5.54 2.45 0.09 4.64 1.83 2.22 0.35 98.36 1000 98 0 128 94 903 77 3.66 1.61 1.81 20.10 6.27 3.75 0.63 35.9 0.23 4.88 39.60 10.40 9.87 86.60 14.10 7.29 690 0.30 0.80 5.14 3210 0.22 0.89

P403 6994026 3712609 66.30 0.69 14.20 6.87 3.23 0.07 2.80 2.64 1.82 0.09 98.72 64 436 209 220 57 2553 151 161 449 30.2 29.3 62.9 2.45 1.4 0.8 17.7 2.87 2.62 0.49 14.5 0.18 3.55 14.6 10.8 3.55 61.3 19.2 2.92 211 0.18 0.42 3.42 4052 0.21 0.94

P415 6993769 3713334 68.60 0.36 15.00 3.38 1.13 0.10 2.73 4.11 3.58 0.15 99.14 1319 30 54 1960 65 93 1453 64 7.97 82.1 2.15 1.01 0.92 21.7 3.71 4.21 0.4 33.5 0.15 4.95 26.6 37.5 6.97 102 7.36 4.48 452 0.26 0.46 9.56 2246 0.15 3.01

P535 6971469 3714088 62.50 0.86 16.20 7.61 3.97 0.08 1.24 1.55 3.35 0.12 97.48 367 334 27 2944 175 142 386 37.6 36.5 40.6 2.91 1.59 0.89 20.8 3.47 3.63 0.61 17.6 0.27 6.14 17.3 12.6 4.29 132 22.4 3.61 123 0.43 0.55 5.45 4999 0.25 1.68

PAN-86-1 6993748 3713319 71.90 0.37 14.90 3.72 0.59 0.12 0.69 3.77 2.91 0.16 99.12 667 2478 62 94 673 51.7 7.33 7.34 2.03 1 0.99 20.8 3.82 3.78 0.39 27.6 0.16 4.66 23.8 13 5.77 75.3 6.31 4.17 281 0.27 0.5 8.69 2140 0.11 2.54

PAN-86-14 6990288 3716005 63.20 0.67 19.20 4.16 0.47 0.07 4.23 4.68 2.11 0.24 99.03 1347 62 166 108 82 1348 75.6 8.9 4.44 2.52 1.12 1.06 24 3.85 3.55 0.43 37.7 0.16 5.31 31.5 14.2 8.02 56 11 5 1058 0.24 0.48 8.87 3875 0.14 1.25

PAN-86-2 6993787 3713277 66.60 0.44 16.50 3.94 1.59 0.06 3.88 3.74 2.18 0.18 99.11 824 34 673 77 80 814 60 9.28 20 1.92 0.98 1.01 22 3.66 3.24 0.36 30.8 0.13 3.42 26.4 19.6 6.78 66.1 8.12 4.32 748 0.18 0.44 7.27 2426 0.11 1.96

PAN-86-3 6993757 3713279 57.80 0.90 14.70 6.72 5.65 0.12 7.22 3.97 1.17 0.54 98.80 500 403 60 171 100 513 88.4 26.1 9.29 3.35 1.47 2.04 22.2 6.53 2.77 0.61 36.4 0.17 5.01 47.1 12.9 11.3 32.8 20.1 7.98 997 0.23 0.74 5.76 5627 0.19 1.37

PAN-86-4 6993816 3713276 61.90 0.72 15.60 6.01 3.45 0.11 5.26 5.30 0.56 0.17 99.07 264 148 60 137 87 261 33.5 25.3 22.9 2.08 1.07 1.04 21.1 3.1 2.77 0.4 13.9 0.15 2.68 15.7 7.72 3.79 13.6 14.2 3.42 383 0.09 0.42 4.23 4100 0.15 1.07

PAN-86-7 6993815 3713246 68.40 0.42 16.20 3.12 2.12 0.04 3.30 3.99 1.47 0.16 99.23 1143 56 60 71 81 1188 19 8.28 29.8 1.38 0.57 0.72 23.1 1.78 3.41 0.27 8.64 0.11 3.1 8.7 14.9 2.16 46.8 7.69 1.76 757 0.2 0.25 7.85 2475 0.1 1.98

PAN-86-8 6993866 3713254 74.90 0.06 14.80 0.87 0.10 0.04 1.35 5.79 1.60 0.01 99.52 873 675 30 56 928 10.2 0.57 13.1 0.86 0.29 0.45 24.5 1.4 2.5 0.13 5.43 0.03 5.69 5.73 11 1.26 39.8 1.04 1.44 348 0.46 0.18 1.95 425 0.02 1.94

Ilomantsi, Kovero

26-TTU-06 6943876 3675205 74.40 0.25 11.80 4.41 1.45 0.07 2.03 2.84 1.70 0.05 99.00 203 66 30 660 1078 35 43 209 39.5 21.6 665 1.15 0.95 0.34 14.7 1.47 4.15 0.28 18 0.23 4.61 13.9 9.75 4.16 48.3 4.18 2.07 54.9 0.52 0.23 13.4 1470 0.15 3.41

27-TTU-06 6943871 3675209 68.70 0.52 12.90 6.67 1.92 0.12 2.99 2.47 2.06 0.15 98.50 299 91 36 371 7341 63 68 307 68.3 45.3 345 3.84 2.28 0.92 18.5 5.05 4.62 0.75 32.9 0.34 5.57 26.8 12.6 7.43 56.9 9.11 4.61 99.7 0.42 0.68 8.64 3200 0.31 2.71

28-TTU-06 6943874 3675216 71.80 0.31 12.00 6.15 2.05 0.10 2.01 3.75 0.53 0.08 98.77 108 77 30 285 3467 38 165 113 28.4 47.8 302 2.95 1.67 0.67 15.4 3.22 5.67 0.52 15.5 0.26 7.72 13.7 18.7 3.24 14.8 6.34 2.77 67.8 0.56 0.51 13.6 1930 0.22 3.35

6-TTU-06 6943942 3675036 56.80 1.23 16.40 6.03 4.24 0.08 9.72 4.21 0.22 0.12 99.04 146 116 123 190 98 301 76 129 36.1 35.6 217 5.24 3.35 1.54 24.4 5.25 2.91 1.05 11.4 0.5 4.75 17.7 7.64 3.91 14.6 36.7 4.47 334 0.38 0.86 4.3 7360 0.46 1.23

73

74

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho, T., Hanski, E., Hokkanen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Layahe, Y., Luukkonen. E., Pietikäinen. K., Pulkkinen, A., Sorjonen-Ward, P., Vaasjoki, M. & Whitehouse, M. 2012. The age of the Archaean greenstone belts in Finland. Geological Survey of Finland, Special Paper 54, 74−175, 69 figures, 1 table and 4 appendices.

Reliable concordant U-Pb zircon data obtained for volcanic rocks in the Ar-chaean greenstone belts in Finland indicate distinct age groups for each belt: Suomussalmi 2.94, 2.87 and 2.82 Ga; Kuhmo-Tipasjärvi 2.84–2.80 Ga; Ilomantsi- Kovero 2.88 and 2.75 Ga; and Oijärvi 2.82–2.80 Ga. The relative abundance of rocks within these age groups still remains unclear. Results from the Kuhmo belt indicate that the age of felsic and gabbroic rocks in the central part of the belt (Kellojärvi area) is 2798 ± 2 Ma, which is also the minimum age for the local mafic-ultramafic magmatism, including komatiites. Tholeiitic mafic rocks in the Kuhmo belt, as represented by the Moisiovaara gabbro, are 2823 ± 6 Ma in age, which is considered the maximum age for the komatiites.

Both the Kuhmo and Tipasjärvi belts contain sedimentary rocks that were de-posited after 2.75 Ga, and thus at least 50 Ma after the volcanism. Still younger sediments have been found in the Arola area of the Kuhmo belt, where a deformed quartzite contains detrital zircon as young as 2.70 Ga. The sediments in the parag-neiss belts were deposited ca. 2.72 Ga ago.

Sm-Nd isotopic results show that volcanic rocks in the Kuhmo and Tipasjärvi belts largely represent newly mantle-derived material. The bulk of the granitoids surrounding the belt postdate the volcanic rocks, and the isotope results as a whole suggest that the contribution of older crustal material was negligible and does not support the existence of continental basement during the formation of the suprac-rustal rocks within these belts. In contrast, in the Suomussalmi belt, Sm-Nd and Pb isotope results indicate a major involvement of significantly older crustal mate-rial (>3 Ga). A minor contribution of older crustal material is also evident in the Ilomantsi belt, where some igneous rocks contain xenocrystic zircon up to 3.3 Ga in age. Altogether, the isotope results suggest that the schist belts store a long-lived (>200 Ma), fragmentary record of geological evolution, possibly in various geodynamic settings, including an oceanic plateau (Kuhmo, Tipasjärvi), island arc (Ilomantsi), back arc/intra-arc (paragneiss belts) and intra-continental rift (Suo-mussalmi).

Keywords (GeoRef Thesaurus, AGI): schist belts, greenstone belts, absolute age, U/Pb, Sm/Nd, isotopes, lead, Archean, Finland


THE AGE OF THE ARCHAEAN GREENSTONE BELTS IN FINLAND

byHannu Huhma1), Irmeli Mänttäri1), Petri Peltonen1,4), Asko Kontinen2), Tapio Halkoaho2), Eero Hanski5), Tuula Hokkanen1), Pentti Hölttä1),

Heikki Juopperi3), Jukka Konnunaho3), Yann Lahaye1), Erkki Luukkonen2), Kimmo Pietikäinen3), Arto Pulkkinen1),

Peter Sorjonen-Ward2), Matti Vaasjoki1,a) and Martin Whitehouse6)

75

Geological Survey of Finland, Special Paper 54The age of the Archaean greenstone belts in Finland

1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland2) Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland3) Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland4) Present address: First Quantum Minerals Ltd, Kaikukuja 1, FI-99600 Sodankylä,

Finland5) Department of Geosciences, P.O. Box 3000, FI-90014 University of Oulu,

Finland6) Swedish museum of Natural History, P.O. Box 50007, SE-10405 Stockholm,

Swedena) deceased


76

Geological Survey of Finland, Special Paper 54Hannu Huhma, Irmeli Mänttäri, Petri Peltonen, Asko Kontinen, Tapio Halkoaho, Eero Hanski, Tuula Hokkanen, Pentti Hölttä, Heikki Juopperi, Jukka Konnunaho et al.

INTRODUCTION

The age and other characteristics of the Archae-an volcano-sedimentary belts, especially their re-lationship with the surrounding granitic-gneissic terrains, are essential in modelling the evolution of the Archaean lithosphere. From the Finn-ish Archaean bedrock, multi-grain zircon U-Pb TIMS analyses have been available for decades (e.g. Kouvo 1958, Wetherill et al. 1962, Hyppönen 1983). Although often being imprecise, these data have provided useful constraints for the geologi-cal evolution of the Archaean crust. Precise mul-ti-grain dating has often been difficult because of the presence of xenocrystic zircon and/or effects of metamorphism. A frequent problem is also

that suitable materials for dating are scarce, and the identification of their protoliths may also be difficult because of strong metamorphic effects. The Sm-Nd and Rb-Sr methods have turned out to be even more problematic in the dating of Ar-chaean volcanic rocks. Primary igneous miner-als are commonly unavailable, and the very strict assumptions required for whole-rock dating are usually difficult to verify.

Recently, a large amount of new U-Pb data has been obtained from the Archaean schist/ green-stone belts in Finland, including the Suomussal-mi, Kuhmo, Tipasjärvi, Ilomantsi (Hattu), Kove-ro and Oijärvi belts (Fig. 1). The aim of this paper

Fig. 1. (a) Major Archaean tectonic provinces of the central part of Finland and adjacent Russian Karelia. (b) Generalized geological map of central Finland (from Kontinen et al. 2007) showing the main Archaean units. OGB/SGB/KGB/TGB/IGB/KoGB = Oijärvi/ Suomussalmi/ Kuhmo/ Tipasjärvi/ Ilomantsi/ Kovero greenstone belt.

77


is to present these results together with some new data on Archaean granitoids and paragneisses outside the greenstone belts. The U-Pb results from ca. 60 samples consist of ca. 600 analyses by SIMS, 200 analyses by LA-MC-ICPMS and 170 analyses using TIMS. These results construct a much-improved basis for constraining the Ar-chaean evolution in Finland and the entire Fen-noscandian Shield. As practically all samples are from deformed and metamorphosed rocks,

mostly metamorphosed under amphibolite fa-cies conditions, the “meta” prefix is not generally used. Sample sites are shown on bedrock maps (e.g. Fig. 4), which are based on GTK’s database (1:1 000 000, DigiKP 200) (http://www.geo.fi/en/bedrock.html). Sample co-ordinates are given in the associated paper on Sm-Nd isotopes (Huhma et al. this volume; also http://geomaps2.gtk.fi/ac-tivemap/ ).

METHODS

Sampling for the present isotope studies was mostly carried out in conjunction with extensive mapping projects, and the samples should thus be well chosen and relevant in solving major geo-logical problems. Samples for the isotope studies were washed, crushed, washed again using a Wil-fley table, and treated with methylene iodide and Clerici® solutions to separate the heavy miner-als. Non-magnetic heavy fractions were separated with a Frantz isodynamic separator. Zircons were selected for analysis by hand-picking. Some of the fractions were air-abraded (Krogh 1982) for TIMS (thermal ionization mass spectrometer) U-Pb analyses, and for some recent analyses, zircons were treated using the chemical abra-sion method by Mattinson (2005). When apply-ing the CA-TIMS technique, we largely followed the steps described by Schoene et al. (2006), in which zircon was placed in a furnace at 900 oC for 60 hours in beakers before being transferred to Teflon microcapsules, placed in high-pressure vessels, and leached in 29M HF for 12 hours. The decomposition of minerals and extraction of U and Pb for multi-grain TIMS analyses mainly fol-lowed the procedure described by Krogh (1973). 235U-208Pb-spiked and unspiked isotopic ratios were measured using a VG Sector 54 or non-commercial mass-spectrometers at the Geologi-cal Survey of Finland, Espoo. The measured lead and uranium isotopic ratios were normalized to the accepted values of SRM 981 and U500 stand-ards. Common-lead corrections were carried out using the age-related Pb isotope composition of the Stacey and Kramers (1975) model and errors of 0.2 (for 206Pb/204Pb and 208Pb/204Pb) and 0.1 (207Pb/204Pb). The measured Pb blank was 10–50 pg. The U-Pb age calculations were performed using the PbDat and the Isoplot/Ex programs (Ludwig 1991, 2003).

For SIMS and LA-MC-ICPMS analyses, zir-con grains were hand-picked under a binocular

microscope, mounted in epoxy resin, sectioned approximately in half and polished. Back-scat-tered electron images (BSE) and cathodolumi-nescence (CL) pictures of the zircons were taken using SEM to target the analysis spots. Most of the in situ SIMS (secondary ion mass spectrom-etry) U-Pb analyses were performed on the Nor-dic Cameca IMS 1270 at the Swedish Museum of Natural History, Stockholm (Nordsim facil-ity). The spot diameter for the 4-8 nA primary O2

- ion beam was 25-15 μm (latter values apply for recent data) and oxygen flooding in the sample chamber was used to increase the production of Pb+ ions . Three counting blocks, each including four cycles of the Zr, Pb, Th, and U species of interest, were measured from each spot. The mass resolution (M/ΔM) was 5400 (10%). The raw data were calibrated against a zircon standard (91500; Wiedenbeck et al. 1995) and corrected for modern common lead (T=0; Stacey & Kramers 1975). For the detailed analytical procedure, see Whitehouse et al. (1999) and Whitehouse and Kamber (2005). All the errors in age reported in the text and fig-ures are given at the 2σ level.

The measurements by LA-MC-ICPMS were performed utilizing the Nu Plasma HR multicol-lector ICPMS at the Geological Survey of Fin-land in Espoo. A technique very similar to that described by Rosa et al. (2009) was applied, with the exception that a New Wave UP193 Nd:YAG laser microprobe was used. Samples were ab-lated in He gas (gas flow = 0.2–0.3 l/min) using a low-volume teardrop-shaped (< 2.5 cm3) la-ser ablation cell (Horstwood et al. 2003). The He aerosol was mixed with Ar (gas flow = 1.2 l/min) in a teflon mixing cell prior to entry into the plasma. The gas mixture was optimized daily for maximum sensitivity. All analyses were carried out in static ablation mode. Ablation conditions were the following: beam diameter generally 25 μm, pulse frequency 10 Hz, beam energy density

http://www.geo.fi/en/bedrock.html


http://geomaps2.gtk.fi/activemap/

http://geomaps2.gtk.fi/activemap/

78


1.4 J/cm2. A single U–Pb measurement included 30 s of on-mass background measurement, fol-lowed by 60 s of ablation with a stationary beam. Masses 204, 206 and 207 were measured in sec-ondary electron multipliers, and 238 in an extra high-mass Faraday collector. The geometry of the collector block does not allow simultane-ous measurement of 208Pb and 232Th. Ion counts were converted and reported as volts by the Nu Plasma time-resolved analysis software. 235U was calculated from the signal at mass 238 using a natural 238U/235U ratio of 137.88. Mass number 204 was used as a monitor for common 204Pb. In ICPMS analysis, 204Hg mainly originates from the He supply. The observed background counting rate on mass 204 was ca. 1200 (ca. 1.3×10−5 V), and had been stable at that level during the year prior to the measurements. The contribution of 204Hg from the plasma was eliminated by on-mass background measurement prior to each analysis. Age-related common-lead (Stacey & Kramers 1975) correction was used if the analysis showed common-lead contents above the detection limit. Signal strengths on mass 206 were typically >10−3 V, depending on the uranium content and age of the zircon. Two calibration standards were run in duplicate at the beginning and end of each analytical session, and at regular intervals during sessions. Raw data were corrected for the back-ground, laser-induced elemental fractionation, mass discrimination and drift in ion counter gains

and reduced to U–Pb isotope ratios by calibration to concordant reference zircons of known age, us-ing protocols adapted from Andersen et al. (2004) and Jackson et al. (2004). Standard zircons GJ-01 (609 ± 1 Ma; Belousova et al. 2006) and an in-house standard, A1772 (2711 ± 3 Ma/TIMS; 2712 ± 1 Ma/SIMS, see below), were used for cali-bration. The calculations were performed off-line, using an interactive spreadsheet program written in Microsoft Excel/ VBA by T. Andersen (Rosa et al. 2009). To minimize the effects of laser-induced elemental fractionation, the depth-to-diameter ratio of the ablation pit was kept low, and isotopi-cally homogeneous segments of the time-resolved traces were calibrated against the corresponding time interval for each mass in the reference zircon. To compensate for drift in instrument sensitivity and Faraday vs. electron multiplier gain during an analytical session, a correlation of signal vs. time was assumed for the reference zircons. A descrip-tion of the algorithms used is provided in Rosa et al. (2009). Plotting of the U-Pb isotopic data and age calculations were performed using the Isoplot/Ex 3 program (Ludwig 2003). All the ages were calculated with 2σ errors and without decay constants errors.

For a few samples the dating was carried out at VGESEI in St Petersburg using SHRIMP II and methods described by Williams (1998) and Lario-nov et al. (2004).

U-Pb ON IN-HOUSE ZIRCON STANDARDS

Zircon grains from two rock samples are used at GTK as an in-house standard for LA-MC-ICPMS analysis. These samples are a Proterozoic pyroxene-bearing granite, A382 (Voinsalmi, Ran-tasalmi; Patchett & Kouvo 1986), and an Archae-an gabbro, A1772 (Änäkäinen, Lieksa), which have both yielded relatively concordant multi-grain TIMS Pb/U results. Both samples contain euhedral, oscillatory-zoned, prismatic zircon, but in A382 some grains have distinct core domains.

Multi-grain TIMS analyses on A382 have yielded concordant or nearly concordant data (Appendix 2). Excluding the CA-TIMS data, four concordant analyses give an age of 1877 ± 2 Ma. The two CA-TIMS analyses on coarse-grained zircon grains give a slightly older 207Pb/206Pb age of ca. 1885 Ma, whereas CA-TIMS analysis on fine-grained zircon is not distinct from the origi-nal data. Fifty-six analyses on 49 grains were per-formed using SIMS (Nordsim) in Stockholm (Ap-

pendix 1). The common-lead content is low and most analyses are concordant within error. Re-gression of all 56 analyses yields an age of 1879 ± 2 Ma. Concordant data points give an age of 1877 ± 2 Ma (Fig. 2a), which is considered the age of magmatic zircon.

Isotopic compositions of a few analyses from A382 are slightly off the concordia, and consider-ing only these data, an average 207Pb/206Pb age of 1882 ± 3 Ma can be calculated (Fig. 2b). These in-clude analyses on high-U core domains, but no age difference was obtained between cores and rims. Although no distinctly older cores were found in the SIMS study, the larger database acquired by LA-MC-ICPMS contains a few analyses that give ages well above 1.9 Ga. This may explain the slightly older age obtained for the CA-TIMS data above. Consequently, there are potential problems in using sample A382 as a standard. However, it has been observed that optically good-quality,

79


20201980

19401900

18601820

1780 53

17b

15

10

06b

06

02b

02

0150

30

0.29

0.31

0.33

0.35

0.37

0.39

0.41

4.6 5.0 5.4 5.8 6.2207Pb/235U

206 Pb

/238 U

A382 Discordant dataIntercepts at

0 ± 0 & 1882 ± 3 MaMSWD = 2.1 n=9

data-point error ellipses are 2σ

1920

1900

1880

1860

1840

0.32

0.33

0.34

0.35

0.36

5.05 5.15 5.25 5.35 5.45 5.55 5.65207Pb/235U

206Pb238U

A382Concordia Age = 1877 ± 2 Ma

n=44, NORDSIM0nly concordant data incl.


Fig. 2b. Concordia diagram of discordant zircon analyses from the Voinsalmi granite A382.

Fig. 2a. Concordia diagram of zircon analyses from the Voinsalmi granite A382. Concordant SIMS data give an age of 1877 ± 2 Ma.

80


simple prismatic zircons in A382 are devoid of these problems.

The three TIMS analyses on sample A1772 are slightly discordant and yield an upper intercept age of 2711 ± 3 Ma and a lower intercept at 421 ± 200 Ma (Appendix 2). The age obtained by the ion probe (Nordsim) is 2712 ± 1 Ma and is based on 54 concordant or nearly concordant U-Pb analyses on 46 zircon grains (Appendix 1, Fig. 3). Only two analyses of the whole data set are dis-tinct and provide slightly younger ages (n3565-44, n3565-48). The data reveal that the U content in

zircon is relatively high (average 700 ppm) and the amount of common lead extremely low. Despite the high U content, most analyses are concordant within error. However, strictly taken there are still several data points slightly below the concordia, which should not appear in a perfect Pb/U stand-ard. Heterogeneity is also evident in the Th/U ra-tio, which ranges from 0.01 to 1.2 (Appendix 1). For dating of Archaean zircons, it is, however, most critical to reliably measure the 207Pb/206Pb ra-tio, and in this respect zircon A1772 is very useful.

27702750

27302710

26902670

26502630

n3565-48

n3565-44

0.47

0.49

0.51

0.53

0.55

12.2 12.6 13.0 13.4 13.8 14.2207Pb/235U

206Pb238U

A1772average 207Pb/206Pb age

2712 ± 1 MaMSWD = 2.4 n=54

NORDSIM


Fig. 3. Concordia diagram of zircon SIMS analyses from the Änäkäinen gabbro A1772.

81


SUOMUSSALMI GREENSTONE BELT

The Suomussalmi greenstone belt forms the northern part the discontinuous Tipasjärvi-Kuhmo-Suomussalmi (TKS) greenstone com-plex, running as a ca. 200-km-long, N–S-trend-ing zone of supracrustal rocks in eastern Finland (Fig. 1). Although the Archaean age of these belts has been known since the early work of Kouvo and Tilton (1966), there have still been problems in constraining the detailed evolution of the su-pracrustal sequences within the belt and their relationship with the adjacent granitoid rocks. Based on Rb-Sr and Pb-Pb studies, Vidal et al. (1980) and Martin and Querré (1984) argued that the Suomussalmi greenstone belt was ca. 2.65–2.5 Ga old. However, U-Pb ages on zircon have shown that the volcanic rocks from the Kuhmo and Tipasjärvi greenstone belts are ca. 2.79–2.80 Ga in age (Hyppönen 1983, Vaasjoki et al. 1999), whereas even a much older age of ca. 2.97 Ga was obtained for felsic volcanic rocks from the Suo-mussalmi greenstone belt in the Saarikylä-Luo-ma area (Vaasjoki et al. 1999).

Traditionally, the Suomussalmi greenstone belt has been divided into the Luoma and Saarikylä Groups (Piirainen 1988, Engel & Dietz 1989, Luukkonen et al. 2002, Sorjonen-Ward & Luuk-konen 2005), which in the Saarikylä area were

thought to be separated predominantly by a N–S-trending mylonitic zone with intense albite-sericite alteration. The Luoma Group in the west mainly consists of sedimentary and volcanic rocks of an-desitic-dacitic composition, while in the Saarikylä Group (= Saarikylä Formation of the Suomus-salmi Group in the current geological map), maf-ic-ultramafic volcanic rocks are more dominant. Small mineralizations (Ag-Zn-Pb, Au, Ni, PGE) have been the reason for more detailed work in the Saarikylä-Luoma area (Kopperoinen & Tuokko 1988, Luukkonen et al. 2002). All rocks in the Suo-mussalmi belt are metamorphosed and deformed at amphibolite facies, but primary structures are still visible in places.

Field observations in the Saarikylä-Luoma area suggest that some rocks that were previously regarded as volcanic are rather of mixed volcanic-sedimentary in origin. The age of 2.97 Ga obtained by Vaasjoki et al. (1999) may thus represent that of detrital zircon. In order to unravel the problems re-lated to the distincly old age of the Luoma Group, ion-microprobe dating was conducted on the origi-nal and three other related samples. The new SIMS data and additional U-Pb data obtained by TIMS and LA-MC-ICPMS, together with Sm-Nd re-sults, are presented in this paper.

U-Pb geochronology of the Suomussalmi greenstone belt

This study concentrates on the Saarikylä-Luoma area, from where the original sample (A1191 Ala-Luoma, Vaasjoki et al. 1999) representing the Luoma Group was obtained. Three samples (A1192, A1467, A1593), originally thought to belong to the Saarikylä Group, were picked ca. 1 km east of the sampling site of A1191. Accord-ing to the current understanding of the local stra-tigraphy, these samples also represent the Luoma Group (Fig. 4B). Two further samples from the area (A1428, A260) were collected ca. 2 km south of the sampling site of A1191. We also report data on two samples from the eastern Tormua branch of the Suomussalmi belt (A1429, A1821), and results from the volcanogenic country rock of the Kuikkapuro Au prospect in Kiannanniemi (A1701x) (Fig. 4).

A1191 Ala-Luoma volcanogenic sediment

Sample A1191-Ala-Luoma was originally inter-preted as a felsic volcanic rock from the Luoma Group, but subsequent field observations have demonstrated a volcanoclastic sedimentary ori-

gin for this lithology. Sample A1191 is a fine-grained grey rock with metamorphic mineralogy.

The zircon grains are pale brown and translu-cent and under the binocular microscope, appear euhedral with simple prismatic surfaces domi-nating. The crystal edges are somewhat abraded, which is in accordance with the sedimentary na-ture of the rock, but does not suggest a particu-larly long distance of transport prior to deposi-tion. Practically all crystals contain cracks, faint oscillatory zoning occurs occasionally, and a few crystals contain metamict zones within the crys-tals (Fig. 5).

The ion probe analyses obtained are relatively few (analysed in 2000, n759, Appendix 1) and form two groups. The U-Pb data on seven grains suggest an age of ca. 2.95 Ga, while two grains seem to be younger with an age of ca. 2.82 (Fig. 6a). As these two grains show magmatic oscilla-tory zoning and therefore are not metamorphic in origin, they should constrain the age of deposition to be significantly younger than the bulk of zircon.

In order to further study the significance of the youngest zircon grains in A1191, we also per-

82


Fig. 4. Geological map of the Suomussalmi area showing the locations of the samples used for U-Pb dating (red star – this study; other samples are granidoids, published by Mikkola et al. 2011a). Igneous ages with 2-sigma errors are given in Ma af-ter the sample number. The large map is based on the 1:1 000 000 geological map (Korsman et al. 1997), where the greenstone belt consists of three main rock types: mafic metavolcanic rocks (brown), ultramafic metavolcanic rocks (green) and inter-mediate-felsic metavolcanic rocks (yellow). Granitoids surrounding the greenstone belts are divided into TTGs and intrusive rocks (stippled). The inset map is based on GTK DigiKP 200. For a more detailed legend see: Bedrock of Finland – DigiKP. Digital map database [Electronic resource]. Espoo: Geological Survey of Finland [referred 31.5.2011]. Version 1.0. Available at: http://www.geo.fi/en/bedrock.html.


83


Fig. 5. BSE images of zircon A1191 (2.95 Ga), A1428 (2.82 Ga), A1429 (2.82 Ga) and A1467 (2.94 Ga).

formed LA-MC-ICPMS analyses on the original SIMS mount. The new U-Pb data show that only the two grains, originally observed by SIMS, give ages of ca. 2.82 Ga, whereas all other grains yield dates ca. 2.95 Ga (Appendix 3, Fig. 6b). Thus, considering both the SIMS and LA-MC-ICPMS data, there are only two grains out of 33 that yield-ed an age of ca. 2.82 Ga. As the multi-grain TIMS age estimate is also close to 2.95 Ga, we consider it is possible that the presence of 2.82 Ga grains is due to contamination during sample process-ing, and thus should not be used for constraining the age of deposition, unless further studies prove otherwise. In any case, the bulk of the material in the Ala-Luoma rock A1191 is from ca. 2.95 Ga sources.

A260 Haaponen greywacke

Sample A260-Haaponen is an old greywacke sam-ple from the GTK archives, which was collected ca. 2 km south of A1191 and is also regarded as a representative of the Luoma Group. The exact co-

ordinates of the sample are not known. In hand specimen, the rock is fine-grained and grey, simi-lar to A1191. Mineral separation yielded abundant brown, mostly euhedral zircon grains. The popula-tion is fairly homogeneous and signs of abrasion are limited. Two multi-grain TIMS analyses car-ried out in 1983 (at GTK by O. Kouvo and cowork-ers) are discordant and plot roughly on the chord defined by the TIMS data on sample A1191, sug-gesting a common main source of zircon for these volcanogenic sedimentary rocks (Fig. 6a).

A1428 Mesa-aho quartz porphyry

Sample A1428-Mesa-aho is from a quartz-plagi-oclase porphyry, located ca. 2.5 km SSW of the site of sample A1191 (Fig. 12). Based on field evidence, the Mesa-aho rock is considered as an almost concordant, foliated felsic dyke within the volcanoclastic sediments of the Luoma Group. The rock is coarser-grained than the samples treated above, containing deformed quartz and plagioclase phenocrysts in a fine-grained matrix.

84


Saarikylä-Luoma volcanogenic sedimentary rocks

2400

2600

2800

3000

A260A & B

0.3

0.4

0.5

0.6

0.7

8 10 12 14 16 18 20 22

207Pb/235U

206 Pb

/238 U

A1191 NORDSIMca. 2.95 Ga (7 grains)

Vaasjoki et al 1999:A1191 TIMS data

Intercepts at 962 ± 102 & 2966 ± 9 Ma

MSWD = 1, n=4

33003200

31003000

29002800

27002600

0.4

0.5

0.6

0.7

0.8

11 13 15 17 19 21 23 25207Pb/235U

206 Pb

/238 U

A1191LA-MC-ICPMS

24 grains ca. 2.95 Ga& 2 grains ca. 2.82 Ga


Fig. 6a. Concordia diagram of zircon analyses from the volcanosedimentary rocks of the Saarikylä-Luoma area: Error ellipses – SIMS data on A1191, squares – TIMS data on A1191 (Vaasjoki et al. 1999), triangles – TIMS data on A260.

Fig. 6b. Concordia diagram of LA-MC-ICPMS analyses on zircon A1191. The two analyses at ca. 2.82 Ga are from the same grains that were measured by SIMS and yielded similarly younger ages than the other grains.

85


Sample A1428 yielded abundant zircon grains, which are pale brown-reddish in colour, mostly short and small (<100 μm) in size. Many grains have sharp crystal edges. SEM study showed no inner structures apart from a relatively faint zon-ing (Fig. 5).

The results of three TIMS U-Pb analyses on A1428 are fairly close to the concordia and pro-vide an upper intercept age of 2817 ± 4 Ma (Ap-pendix 2, Fig. 7). Ion microprobe analyses (n762, Appendix 1) on eight crystals are also nearly con-cordant and define an upper intercept at 2816 ± 12 Ma (Fig. 7). Uranium concentrations are rather low, and there is only small variation in the apparent Th/U ratios. It should be noted, how-ever, that all isotope analyses for this sample were performed using the heaviest fraction (density > 4.3), and that zircon in the other samples in this study generally also consists of less dense mate-rial. Typically, there is a good negative correlation between density and the U content (and the de-gree of metamictization and discordancy).

A1467 felsic volcanic rock

Sample A1467 was collected ca. 200 m east of the shear zone that was formerly considered to

mark the tectonic contact between the Luoma and Saarikylä Groups. Originally, A1467 was thought to represent the Saarikylä Group felsic volcanic rocks and correlate with the earlier sample A1192, which has yielded very discordant zircon U-Pb re-sults (Vaasjoki et al. 1999, also Fig. 8). According to the current understanding of the local stratig-raphy, these samples also represent the Luoma Group (Fig. 4B). In hand specimen, the samples are pale grey, strongly altered schists. Thin section studies reveal that they contain quartz and feld-spar phenocrysts or aggregates in a sheared matrix of fine-grained quartz and sericite.

The zircon grains in the sample are turbid, brownish in colour and principally consist of simple prismatic-pyramidal, euhedral, elongated crystals. Backscatter electron images demonstrate a clear oscillatory zoning within most crystals, but in some cases this is missing, and it seems that in some crystals such unzoned domains may form ill-defined “cores” surrounded by areas with oscil-latory zoning (Fig. 5). Virtually all crystals also contain numerous cracks and corroded areas. Part of these domains lie on the fringes of the crystals, but they also occur within their core parts, and the corrosion seems to advance not only along cracks but also along seemingly undisturbed

A1428 Mesa-aho porphyry

28402800

27602720

26802640

2600

0.43

0.45

0.47

0.49

0.51

0.53

0.55

0.57

0.59

11.5 12.5 13.5 14.5 15.5

207Pb/235U

206 Pb

/238 U

NORDSIMIntercepts at

326 ± 360 & 2816 ± 12 MaMSWD = 0.97, n=8

A1428 TIMSIntercepts at

453 ± 160 & 2817 ± 4 MaMSWD = 0.08, n=3

Fig. 7. Concordia diagram of zircon analyses from the Mesa-aho felsic porphyry (A1428): Error ellipses – SIMS data, dia-monds – TIMS data.

86


crystallographic zones.Five TIMS analyses of the zircon grains (Ap-

pendix 2) are very discordant and show a relatively high amount of common lead. They form a poorly defined, linear trend on the concordia diagram (Fig. 8) and suggest an upper intercept age of ca. 2.95 Ga. The obtained ion microprobe data (n761, Appendix 1) confirm this estimate. Excluding one analysis, the eight data points available define an age of 2940 ± 12 Ma. One analysis (n761-01) was deliberately carried out on a metamict area and is grossly discordant, and has high common lead, thus giving an obvious reason for the large discord-ances observed in the multi-grain TIMS analyses. If this discordant analysis is rejected, the remaining seven analyses give intercepts at 2943 ± 20 and 320 ± 480 Ma (MSWD = 4.7). One grain (n761-02) is clearly older than the others (ca. 3.2 Ga), but SEM observations do not show any obvious differences with the rest of the grains. It should be noted that analyses of the “cores” with negligible oscillatory zoning plot within the main group.

A1593 felsic porphyry

Sample A1593 (KJP-96-105) is from a quartz porphyry outcrop located ca. 150 m south of the

sampling site of A1467 (Fig. 4). Based on field relationships, A1593 should represent the same association as A1467, but compared to A1467 or A1192, the rock is clearly less altered. It is char-acterized by bluish quartz phenocrysts 2–5 mm in diameter and occurs as a more coarse-grained foliated felsic layer (perhaps altered ash-flow) within the volcanoclastic sediments of the Luo-ma Group.

The sample yielded very little zircon, and no attempt was made to date this mineral. However, a few grains of monazite were obtained from the sample. A TIMS U-Pb analysis on monazite gave a nearly concordant result with a 207Pb/206Pb age of 2942 ± 3 Ma (Appendix 2). This is compatible with the zircon U-Pb results from the other two samples (Fig. 8) and, in fact, is by far the oldest monazite age obtained on any rock from Finland.

A1429 Kilpasuo andesite, Tormua

The Kilpasuo sample represents the fine-grained, intermediate volcanic rocks found in the eastern branch of the Suomussalmi belt, also known as the Tormua belt (Fig. 4). Only a small number of small, brown, euhedral zircon grains were ob-tained from this sample. The three TIMS analy-

Felsic volcanic rocks

3200

2800

2400

2000

1600

1200

A1192

n761-02a

0.0

0.2

0.4

0.6

0 4 8 12 16 20 24

207Pb/235U

206 Pb

/238 U

A1467 NORDSIMIntercepts at

205 ± 130 & 2940 ± 12 MaMSWD = 4.3, n=8

A1593 Monazite2942 ± 3 Ma

Fig. 8. Concordia diagram of zircon and monazite analyses from the felsic volcanic rocks of the Saarikylä-Luoma area: Error ellipses – SIMS data A1467 zircon, squares – TIMS data on A1467 zircon, triangles – TIMS data on A1192 zircon (Vaasjoki et al. 1999), diamond – A1593 monazite.

87


ses are discordant and yield intercepts at 2774 ± 6 and 440 ± 160 Ma. An analysis using chemical abrasion was not successful, since hardly any zir-con was left after the treatment. The U-Pb analy-ses by LA-MC-ICPMS are, however, concordant and give an age of 2822 ± 7 Ma (Appendix 3, Fig. 9). The result, based on analyses utilizing the Ar-chaean in-house standard (A1772), is considered a reliable age estimate for zircon and the Kilpa-suo volcanic rocks in the Tormua belt.

A1821 Tormua gabbro

Sample A1821 was collected from a gabbroic rock that is thought to represent the coarse-grained in-ner part of a tholeiitic lava flow within the Tor-mua belt (Fig. 4). Only a small amount of zircon was obtained from this sample. In the density fraction d > 4.2 g cm-3, most grains are weakly brownish and translucent. They have forms vary-ing from long to short with prismatic faces (l:w 2-4) (zircon 07 in Fig. 14J) or more ragged and formless surfaces in more equant grains (zircon 06 in Fig. 14J). The density fraction 4.0-4.2 g cm-3 also includes a few transparent and more round-ish zircon crystals. In BSE images, the zircon grains frequently show pale inner domains with voids and/or dense, white spots potentially result-ing from exsolution. The grains are corroded,

and the rims have irregular boundaries, dark BSE and frequent microcracks. In places darker, faint spots or bands also occupy the pale inner zircon domains. Zircon grain #07 represents the least corroded/altered zircon example of the long prism type (Fig. 14J).

A total of 16 zircon domains were analysed by SIMS from the Tormua gabbro (Appendix 1). Four analyses were rejected because of the high common-lead contents. In spite of the variety of analysed zircon domain types, ten of the 12 data points cluster at 2866 ± 4 Ma, which is consid-ered the age of magmatic zircon and the age of the gabbro (Fig. 10).

A1701x Kuikkapuro

In connection with the research on the Kuikka-puro Au-prospect in the Kiannanniemi area, two samples were collected from drill-core R361 from host rocks below the mineralized zone (Fig. 4). Sample #1 (=A1701x) from the depth interval 44.50–45.50 m is a biotite-plagioclase-amphibole schist and sample #2 from the depth interval 97.00–99.70 m a biotite-garnet-amphibole schist. Both samples yielded mostly fine-grained zircon, which is generally dark brown, translucent and euhedral. In sample #2, some grains are turbid and pale.

A1429 Kilpasuo andesite, Tormua

29602920

28802840

28002760

27202680

0.46

0.50

0.54

0.58

0.62

0.66

12.5 13.5 14.5 15.5 16.5 17.5207Pb/235U

206Pb238U

A1429 LA-MC-ICPMSConcordia Age = 2822 ±7 Ma ,n=10


TIMS Intercepts at440 ± 160 & 2774 ± 6 Ma

MSWD = 2.0, n=3

Fig. 9. Concordia diagram of zircon LA-MC-ICPMS (error ellipses) and TIMS analyses on zircon from the Kilpasuo andesite (A1429).

88


A1821 Tormua gabbro

2900

2800

2700

2600

2500

0.40

0.44

0.48

0.52

0.56

0.60

0.64

10 12 14 16 18207Pb/235U

206 Pb

/238 U

Intercepts at783 ± 170 & 2863 ± 6 Ma

MSWD = 1.8 n=12


A1821 SIMS Concordia Age 2866 ± 4 Ma ,n=10

Fig. 10. Concordia plot showing zircon SIMS U-Pb isotopic results from the Tormua gabbro sample A1821, Suomussalmi, eastern Finland.

A1701c Kuikkapuro volcanic rocks

30202980

29402900

28602820

27802740

2700

0.49

0.51

0.53

0.55

0.57

0.59

0.61

13 14 15 16 17 18 19207Pb/235U

206 Pb

/238 U


A1701c Concordia Age 2815 ±4 Ma , n=8/11 (host rock#1)

Kuikkapuro host rock#2:6 analyses range from 2.81 to 3.53 Ga

host rock #13 analyses ca. 2.85 Ga

n2524-05a

Fig. 11. Concordia plot showing zircon SIMS U-Pb isotopic results from Kuikkapuro rocks in Kiannanniemi. Error ellipses – sample 4511/98/R361/44.50-45.50, diamonds – sample 4511/98/R361/97.00-99.70 (analysis n2524-05a plots outside the figure).

89


Eight SIMS analyses from sample #1 are con-cordant and give an age of 2815 ± 4 Ma, but three analyses are slightly older at 2.85 Ga (Appendix 1, Fig. 11). The six analyses carried out on sam-ple #2 scatter from 2.81 to 3.53 Ga. Four of these suggest an age of ca. 2.96 Ga.

Due to alteration, it is difficult to judge the ul-timate origin of these schists, but the rocks in the

Kiannanniemi area are mostly volcanogenic. We are inclined to think that the youngest, apparently magmatic zircons define the age of volcanism at 2815 ± 4 Ma. The older zircons are considered xenocrystic and thus suggest an involvement of older crustal material in the petrogenesis of the Kiannanniemi volcanic rocks.

Discussion on the Suomussalmi greenstone belt data

As mentioned earlier, the supracrustal rocks of the Luoma Group have been considered older than the rocks of the Saarikylä Group/Forma-tion (Piirainen 1988, Engel & Dietz 1989, Vaasjo-ki et al. 1999, Sorjonen-Ward & Luukkonen 2005, Papunen et al. 2009). In the Saarikylä-Luoma area, the boundary between these two units was thought to be principally along the N–S-trending mylonitic zone with intense albite-sericite altera-tion. According to the current view presented on the geological map of the Saarikylä-Luoma area, the boundary is now adjusted so that the bulk of the felsic rocks in the west are considered part of

the Luoma Group, and the mafic-ultramafic rocks eastwards are assigned to the Saarikylä Formation (formerly Group) of the Suomussalmi Group (Fig. 4B). Accordingly, the Luoma Group contains fel-sic volcanogenic rocks, which are ca. 2.94 Ga old. This is strongly supported by the U-Pb age of 2942 ± 3 Ma obtained from monazite in sample A1593.

The Suomussalmi belt also contains significant-ly younger felsic volcanogenic rocks, which formed ca. 2.82 Ga. These include the Mesa-aho porphy-ry (A1428), a volcanogenic rock in the Kiannan-niemi area (A1701x), and the Kilpasuo andesite (A1429) in the Tormua branch, ca. 15 km ENE of

Archean volcanic rocks/ galenas & least radiogenic whole rocks

3000

2000

10000

Ala-Luoma galenas

Taivaljärvi galenas

14.2

14.6

15.0

15.4

15.8

16.2

12 14 16 18206Pb/204Pb

207Pb204Pb

Suomussalmi/ Luoma Group2.94 Ga reference isochron

(4 galenas & 8 wr)

Suomussalmi/ Saarikylä Fm2.82 Ga reference isochron

Tipasjärvi/ TaivaljärviAge = 2834 ± 90 MaMSWD = 4.2 n=12(4 galenas & 8 wr)

S&K

Fig. 12. Diagram showing the Pb isotope composition for galenas and whole rock samples from the Luoma Group (blue squares) and Saarikylä Formation (green triangles) from the Suomussalmi belt, compared with Pb isotope results from the Tipasjärvi belt (red dots). Data are from Vaasjoki et al. (1999), and with only the least radiogenic whole rock analyses (206Pb/204Pb < 19) plotted. The evolution of the average terrestrial lead isotope composition by Stacey and Kramers (1975) is shown for reference (S&K).

90


the Saarikylä area (Fig. 4). The 2866 ± 4 Ma gab-bro from Tormua (A1821) represents the third age group obtained in the belt. The relative abundance of these age groups remains unclear. The two age groups obtained in the Saarikylä-Luoma area are also found in granitoids west of the greenstone belt (A1856 and A1857 in Fig. 4, Mikkola et al. 2011a).

In any case, the contribution of material at least as old as 2.94 Ga in the Suomussalmi green-stone belt is significant. In addition to U-Pb re-sults, this becomes evident from the Sm-Nd data presented by Huhma et al. (this volume). This old age is also supported by lead isotope results (Vidal et al. 1980, Vaasjoki 1981, Vaasjoki et al. 1999). This is shown in Fig. 12, where lead iso-tope compositions of galena from the Ala-Luoma sulphide mineralization together with associated Luoma Group whole-rocks samples seem to plot roughly on a 2.94 Ga reference isochron. This sug-gests that the isotopic composition measured from galena (206Pb/204Pb = 13.60, 207Pb/204Pb = 14.87, 208Pb/204Pb = 33.47) records the initial composition for the felsic rocks at 2.94 Ga. As this plots far above the average terrestrial evolution curve by Sta-cey and Kramers (1975), it means that the source for lead had an extended evolution in a high-U/Pb environment before 2.94 Ga. The diagram also shows isotope compositions for a few mafic rocks from the Saarikylä Formation. Four of them plot below the Luoma chord and suggest that the initial Pb isotope composition was clearly distinct from Luoma, and in fact similar to the composition ob-tained for galena from the VMS-type Taivaljärvi

deposit in the 2.8 Ga Tipasjärvi greenstone belt (Vaasjoki et al. 1999). As is shown in Figure 12, the isotopic composition of associated whole-rocks samples plots roughly on a 2.8 Ga isoch-ron, suggesting that galena (206Pb/204Pb = 13.41, 207Pb/204Pb = 14.65, 208Pb/204Pb = 33.13) records the initial isotope composition for the Tipasjärvi volcanic rocks. As is shown by Huhma et al. (this volume), these volcanic rocks have yielded posi-tive, depleted mantle-type initial εNd(2800) values. It is thus possible that the Pb isotope composition measured from the Taivaljärvi galena could repre-sent a depleted mantle value at 2.8 Ga, or at least gives the maximum value, provided that some old upper crustal lead was involved. High Pb concen-trations in crust-derived compared to mantle-de-rived materials make Pb very sensitive to crustal contamination compared to Nd. In fact, the Pb isotope composition of the Taivaljärvi galenas is more radiogenic than the composition of 2.8 Ga model mantle (Stacey & Kramers 1975, Zartman & Doe 1981).

It should be noted that in this discussion we have used only the results of the least radiogenic analyses (206Pb/204Pb < 19), which should be more important when evaluating the initial isotope composition of the system. More radiogenic data scatter considerably, which is obviously due to metamorphic effects, and the data as a whole yield younger age estimates for the Luoma Group sam-ples (Vaasjoki et al. 1999). Based on the isotope results presented here, it is conceivable that crust as old as 3.5-3.6 Ga may have existed in the area.

KUHMO AND TIPASJÄRVI GREENSTONE BELTS

The Kuhmo greenstone belt forms the central part of the N–S-trending Tipasjärvi-Kuhmo-Suomussalmi greenstone complex in eastern Fin-land (Fig. 1). The geology and geochemistry of the belt has been summarized by Papunen et al. (2009), who also provide references to previous studies. One of the key localities is the Kellojär-vi-Siivikkovaara area (Fig. 13), where relatively abundant komatiitic lava flows and cumulates oc-cur and have been extensively studied.

Previous U-Pb zircon data suggest that the volcanic rocks in the Kuhmo and Tipasjärvi greenstone belts are ca. 2.79-2.80 Ga old, while

the surrounding granitoids are generally younger (Hyppönen 1983, Luukkonen 1988, Vaasjoki et al. 1999, Käpyaho et al. 2006). However, due to discordant and slightly heterogeneous data, the errors in the ages of greenstone belt samples are often fairly large. Therefore, new analyses using up-to-date methods have also been performed on samples utilized in previous studies. New data in-cluding U-Pb analyses by SIMS, TIMS and LA-MC-ICPMS are presented in this paper. The Sm-Nd isotope results are discussed in the associated paper by Huhma et al. (this volume).

91


Fig. 13. Geological map of the Kuhmo greenstone belt showing the locations of the samples used for U-Pb dating (red star – this study; other samples – Hyppönen 1983, Luukkonen 2001, Käpyaho et al. 2006, 2007, Kontinen et al. 2007, Heilimo et al. 2011; also: http://geomaps2.gtk.fi/activemap/). Igneous ages with 2-sigma errors are given in Ma after the sample number (red – volcanic rocks of the main belt). The map is based on the 1:1 000 000 geological map (Korsman et al. 1997), where the greenstone belt consists of four main rock types: mafic metavolcanic rocks (brown), ultramafic metavolcanic rocks (green), intermediate-felsic metavolcanic rocks (yellow) and metasediments (blue). Granitoids surrounding the greenstone belts are divided into TTGs and intrusive rocks (stippled).

92


We present new U-Pb results on eighteen sam-ples from the Kuhmo greenstone belt, includ-ing samples from the Ruokojärvi and Pitkäperä belts, which are located slightly east of the main Kuhmo belt (Fig. 13). The samples include ten felsic-intermediate volcanic, three gabbroic and four sedimentary rocks.

A1346 Lampela andesite

Sample A1346-Lampela represents a fine- to medi-um-grained volcanic unit of an intermediate com-position, which occurs in the Kellojärvi area in the middle part of the Kuhmo greenstone belt and is assigned to the Mäkisensuo Formation on the geo-logical map (Fig. 13). The sample yielded a small amount of fine-grained, pale zircon. The fraction d > 4.5 g/cm3 contains a few small, weakly reddish, transparent and some large, turbid grains. In the density fraction 4.3–4.5 g/cm3, the zircon popula-tion is homogeneous and mostly consists of equant (~100 μm), translucent grains. In BSE images, most zircon grains reveal weak oscillatory zoning (Fig. 14C). Inclusions are very common.

The previous multi-grain U-Pb TIMS analyses show a relatively high amount of common lead and provide fairly discordant results (Appendix 2). However, in the analysis using chemical abra-sion (Mattinson 2005), the common-lead content was very low and the result nearly concordant with a 207Pb/206Pb age of 2797 ± 2 Ma. The six TIMS analyses are on a chord, giving an upper intercept age of 2801 ± 4 Ma and a lower inter-cept at 766 ± 31 Ma (Fig. 15).

A total of 13 zircon domains from the coarser-grained fraction were analysed using secondary ion mass spectrometry (Appendix 1). From these analyses, one was rejected due to a high amount of common lead. On a concordia diagram (Fig. 15), ten analyses largely from faintly zoned zircon grains plot in a cluster with a concordia age of 2798 ± 4 Ma. The distinct core and rim domains are coeval. Analysis #12 from a structurally ho-mogeneous zircon domain indicates a margin-ally younger age of ca. 2.76 Ga. Zircon from this sample was also analysed by MC-ICPMS using a laser with a spot diameter of 35 µm and the GJ and in-house A382 standards. Ten analyses pro-vide practically similar and, within 2-sigma error, mostly concordant results, which give an average 207Pb/206Pb age of 2794 ± 8 Ma (Appendix 3, Fig. 15). All three methods thus give consistent results, and the age of 2798 ± 4 Ma may be used as an eruption age of this volcanic rock.

A1560 Huuhilonkylä felsic rock

Sample A1560-Huuhilonkylä was collected ca. 2 km south of the Lampela andesite and represents a medium-grained, felsic rock that occurs in the middle of the Kellojärvi ultramafic complex (Fig. 13). In hand specimen, sample A1560 looks fairly similar to sample A1346 from Lampela. Accord-ing to Papunen et al. (2009), the age relation-ship between the Kellojärvi ultramafic complex and this felsic rock has only been observed in a drill-core, where a felsic rock is seen to intrude a marginal pyroxenite of the Kellojärvi complex as dykes.

A large amount of euhedral zircon was obtained from the Huuhilonkylä sample. Most grains are translucent and reddish, with zoning typical of magmatic zircon grains. In the fine-grained, heavy fraction (+4.3/ < 75 µm), some grains are colour-less and clear (analysis A1560F). The six previous multi-grain TIMS analyses give scattered and dis-cordant U-Pb results with 207Pb/206Pb ages up to 2.78 Ga. Instead, the result using the CA-TIMS method is concordant at 2798 ± 2 Ma (Fig. 16). The scatter of the data is not due to zircon inher-itance but obviously due to metamorphic effects, which are most prominent in analysis #A1560F.

The concordant zircon analysis is considered to date the magmatic event at 2798 ± 2 Ma. Provid-ed that the age relationships referred to above are valid, the obtained date would give the minimum age for the Kellojärvi ultramafic complex.

A1418 Niittylahti gabbro

Sample A1418-Niittylahti was collected from a gabbro-anorthosite body also located in the mid-dle of the Archaean Kellojärvi ultramafic com-plex (Fig. 13). It has been considered to be the latest magmatic phase in the Kellojärvi complex, but as it is chemically distinct from the associated ultramafic rocks, it may instead represent a dis-tinctly later intrusive phase. The gabbro yielded a large amount of principally long (l:w ~3-8), weakly yellowish brown, mostly turbid zircon with ragged surfaces. The grain size varies from large (300 µm) to fine (<100 µm), and the mor-phology of the zircon is typical for zircon grains in gabbroic rocks, with abundant resorption fea-tures (Fig. 14A). Some grains show weak longitu-dinal compositional zoning and some have fairly diffuse pale and darker domains in BSE.

From the Niittylahti gabbro, a total of 21 zir-con domains were dated by SIMS (Appendix 1).

U-Pb geochronology of the Kuhmo greenstone belt

93


Fig. 14. BSE images of selected zircon crystals and grains. Analysis numbers and spot sites are marked in the figures. A) Kuhmo, A1418 Niittylahti gabbro: Rather unaltered (14a) and altered (02a) 2.79 Ga gabbroic zircon and gabbroic zir-con giving a younger age of 2.74 Ga. B) Kuhmo, A1377 Siivikko felsic xenolith in komatiite: ~2.80-2.79 Ga analyses from a sector zoned grain 03 (a and b) and oscillatory-zoned crystal (10a) from the coarser grain-size faction. BSE pale, homogeneous rim zircon phases with a mean age of 2.77 Ga.C) Kuhmo, A1346 Lampela andesite: Magmatic 2.80 Ga zir-con with a pale, quite homogeneous inner domain (10b) and a weakly zoned outer domain (10a). An age of 2.76 Ga was measured from a structurally homogeneous grain (12a). D) Kuhmo, A1774 Hetteilä#2 mica schist: ~2.74 Ga magmat-ic zircon (05a and 02 a) and an older rounded 2.79 Ga core (04a). E) Kuhmo, A1773 Hetteilä#1 intermediate volcanic rock: ~2.83 Ga rounded cores and zoned grains (02a, 09a, and 03a) and a 2.67 Ga metamorphic rim. F) Kuhmo, A1746 Petäjäniemi metasediment: An oscillatory zoned magmatic (13) and a probable metamorphic zircon (01) plotting on the same discordia line with an upper in-tercept age of 2847 ± 9 Ma. A younger age of 2.74 Ga was measured from a low-U zoned zircon 12. G) Kuhmo, A1771 Kellojärvi gabbro-norite: ~2.81 Ga typi-

cal gabbroic zircon (13) and a BSE pale and homogeneous slightly younger, recrystallized (?) grain with an age of 2.78 Ga. Zircon core 02a was dated at 1.1 Ga.H) Ilomantsi, A1626 Rasisuo gabbro: 06 represents an equi-dimensional grain with a rather homogeneous internal struc-ture and 02 and 11a are from weakly zoned gabbroic zircon. Both types are coeval and plot in the same 2756 ± 4 Ma clus-ter.I) Ilomantsi, A1627 Rasisuo felsic tuff: 2.88–2.87 Ga zoned (longitudinal and oscillatory) zircon 04a and 06a, 13a homo-geneous grain with rim remnants. J) Suomussalmi, A1821 Tormua gabbro: 05a BSE dark irreg-ular rim without reasonable U-Pb data and the 2.87 Ga BSE pale core domain (06a), 2.85 Ga darker domain of an euhe-dral grain, and an example of phase separation (no analysis). K) Suomussalmi, A120 Ruokojärvi dacite: 08 and 24 exam-ples of rejected analyses on another major zircon type (~2.83 Ga?). 3.13–3.12 Ga cores (31a and 03a) and a 2.98 Ga weakly zoned rim (03b). L) Ranua, A1782 Käärmevaara gabbro: 2.81–2.80 Ga gab-broic zircon (05, 07 and 08) representing the most unaltered types and a younger ~2.70 Ga metamorphic grain (09a). M) Ranua, A1783 Puljunlehto dacite: 2.83–2.82 Ga magmat-ic grains (04a and 05a) and a younger 2.79 Ga metamorphic (07a) grain. An age of 2.78 Ga was also measured from the weakly zoned zircon 03 (contamination or ancient lead loss?).

94


A1346 Lampela andesite

2850

2750

2650

2550

0.40

0.44

0.48

0.52

0.56

0.60

10.0 11.0 12.0 13.0 14.0 15.0 16.0207Pb/235U

206Pb238U

LA-MC-ICPMSPb/Pb age 2794 ± 8 Ma

MSWD = 1.12 n=10


A1346 SIMS Concordia Age = 2798 ± 4 Ma

n=10 (/12)

TIMS Intercepts at 766 ± 31 & 2801 ± 4 Ma

MSWD = 1.3 n=6

CA-TIMSPb/Pb 2797±2 Ma

Fig. 15. Concordia diagram of zircon analyses from the Lampela andesite (A1346): Red error ellipses – SIMS data, blue filled ellipses – TIMS data, black error ellipses – ICPMS data.

A1560 Huuhilonkylä porphyry

2300

2400

2500

2600

2700

2800

A1560A +4.3 >75 clear a16h

A1560B +4.3 >75 clear

A1560C 4.2-4.3 a16h

A1560D 4.0-4.2 <75 a6h

A1560E +4.3 >75 clear a24h

A1560F +4.3 <75 water-clear a16h

A1560G +4.3 CA-TIMS

0.38

0.42

0.46

0.50

0.54

0.58

8 10 12 14 16207Pb/235U

206Pb238U

Intercepts at329 ± 480 & 2794 ± 21 Ma

MSWD = 18 n=4

A1560 CA-TIMS: 2798 ± 2 Ma(concordant analysis A1560G)

Fig. 16. Concordia diagram of zircon U-Pb TIMS analyses from the Huuhilonkylä felsic porphyry (A1560).

95


Two of the analyses were rejected because of high common-lead proportions. Fifteen analyses plot in a tight cluster and 14 of them determine a con-cordia age of 2788 ± 4 Ma (Fig. 17).

One analysis (12a, Fig. 14A) from a structur-ally homogeneous, long grain enveloped by an al-teration rim is concordant at 2.74 Ga, and analysis n2251-19a is quite distinct, suggesting an age of ca. 1.9 Ga. The latter analyses probably register meta-morphic effects. This interpretation receives some support from the relatively old lower intercept age obtained by the TIMS analyses (see below).

The six TIMS analyses show a fairly high amount of common lead and provide discordant results (Appendix 2). The data plot on a chord that gives intercepts at 2757 ± 8 Ma and 1400 ± 30 Ma. Chemical abrasion of this turbid zircon was not successful, since hardly any material was left after the treatment. The analysis has high com-mon lead and yielded reversely discordant result. The available isotope data thus suggest that this gabbro could be marginally younger than the ul-tramafic Kellojärvi complex.

A1771 Kellojärvi gabbro

The gabbroic sample A1771-Kellojärvi was col-lected from a drill-core in the middle of the

Kellojärvi ultramafic complex (M52/4411/03/R315/286.95-293.0) (Fig. 13). The gabbro-norite belongs to the heterogeneous sequence composed of gabbro, pyroxenite and anorthosite with pe-ridotite interlayers. These rocks may represent a “hybrid” sequence, which developed from komatiitic magma via contamination with older felsic crustal material.

Mineral separation yielded a large amount of fairly coarse-grained, mostly turbid, grey-pig-mented, long, subhedral to anhedral zircon with ragged surfaces. In BSE images (Fig. 14G), the zircon grains show either compositional zoning or a homogeneous internal structure. Many larger and long grains show signs of corrosion and al-teration.

From the Kellojärvi gabbronorite, a total of 13 zircon domains were analysed by SIMS (Appen-dix 1). All data are concordant and their radio-genic lead proportions are high enough for U-Pb ages. However, most data range between 2.80 and 2.74 Ga and do not allow precise age calculation. There are also three grains with distinct ages, one at 3.23 Ga and two ca. 1.0 Ga. The 1.0 Ga grains are dark and homogeneous in BSE images. They have low U and probably represent unusual meta-morphic zircon. One multi-grain U-Pb analysis was also carried out using the TIMS technique

A1418 Niittylahti gabbro

2800

2700

2600

2500

2400

2300

0.34

0.38

0.42

0.46

0.50

0.54

0.58

8 10 12 14 16207Pb/235U

206 Pb

/238 U

A1418 TIMS Intercepts at

1400 ± 30 & 2757 ± 8 MaMSWD = 1.3, n=6

A1418 SIMSConcordia age = 2788 ± 4 Ma, n=14

Fig. 17. Concordia diagram of zircon analyses from the Niittylahti gabbro (A1418): Error ellipses – SIMS data, diamonds – TIMS data.

96


A1771 Kellojärvi gabbro

2680

2720

2760

2800

2840

2880

A1771 TIMS

0.49

0.51

0.53

0.55

0.57

0.59

12.5 13.5 14.5 15.5 16.5207Pb/235U

206 Pb

/238 U

A1771 SIMS & TIMSIntercepts at

1391 ± 240 & 2776 ± 13 MaMSWD = 1.5, n=11


A1771 SIMS: 2.74-2.80 Ga5 oldest analyses:

2798 ±8 Ma

Fig. 18. Concordia diagram of zircon analyses from the Kellojärvi gabbro (A1771): Open error ellipses – SIMS data.

and yielded a discordant result, although consist-ent with the bulk of the SIMS data. Combining all data, intercepts with concordia at 2776 ± 13 and 1391 ± 240 Ma can be calculated (Fig. 18). It is conceivable that metamorphic effects are sig-nificant in this sort of turbid zircon, and in fact, there is a good negative correlation between the calculated age and U content. Thus, the real mag-matic age of zircon could be closer to the oldest obtained dates, which give a concordia age of 2798 ± 8 Ma (n = 5).

A1377 Siivikko felsic rock

Sample A1377-Siivikko represents felsic rock fragments of a granodioritic composition, up to a few metres in diameter, which occur as in-clusions within komatiitic lava flows in the Sii-vikko area south of the Kellojärvi ultramafic complex (Fig. 13). The outcrops containing these inclusions were shortly described by Pa-punen et al. (1998). Papunen et al. (2009) in-terpreted the felsic bodies as large xenoliths captured from wall rocks by the komatiitic magma. Another interpretation is that they rep-resent fragments of boudinaged felsic dykes. The Siivikko sample yielded a reasonable amount of pale, transparent to translucent zircon grains

varying in morphology from long prismatic to equant. In BSE images (Fig. 14B), the zircon crystals typically show longitudinal or oscillatory zoning and less frequently sector zoning. Equant grains typically have pale, homogeneous, non-fractured rims enveloping darker BSE cores.

A total of 15 zircon domains were analysed by SIMS from sample A1377 (Appendix 1). Exclud-ing three discordant analyses, the U-Pb data plot in a cluster and give an average 207Pb/206Pb age of 2786 ± 8 Ma (Fig. 19). The high MSWD of 8 sug-gests, however, a scatter in excess of analytical er-ror. The darker BSE, zoned zircon domains tend to give older apparent ages, and their U concen-trations are frequently the lowest in the data set. Four of these define a concordia age of 2797 ± 4 Ma, and combined with the remaining three, give an average 207Pb/206Pb age of 2795 ± 7 Ma. Four of the structurally homogeneous pale BSE domains, which are mostly obvious rims, yield a concordia age of 2771 ± 8 Ma, but one similar pale domain (n2248-03a) has a 207Pb/206Pb age of 2800 ± 6 Ma, being the same age as obtained from the inner part of this same grain (n2248-03b). Three previous TIMS U-Pb analyses on multigrain zircon sam-ples are very discordant (Appendix 2, Fig. 19).

Our best interpretation is that the age of 2797 ± 4 Ma records the timing of the primary crys-

97


A1377 Siivikko felsic fragment in komatiite

2100

2300

2500

2700

2900

A1377 TIMS

0.3

0.4

0.5

0.6

6 8 10 12 14 16 18207Pb/235U

206Pb238U


A1377 SIMSaverage Pb/Pb age

2786 ± 8 MaMSWD = 8.1 (n=12)

Reference line433 & 2783 Ma

Magmatic zirconaverage Pb/Pb age

2795 ± 7 MaMSWD = 2.2 (n=7)

Pale rim domains2.77-2.79 Ga (n=5)

Fig. 19. Concordia diagram of zircon analyses from the Siivikko felsic fragment (A1377): Error ellipses – SIMS data, dia-monds – TIMS data.

tallization of the felsic rock A1377, and the pale zircon domains were affected by a later metamor-phic event. In principle, the metamorphic effect could have been related to the capture by the komatiitic magma, but more likely it is related to general metamorphic events in the area, which are also recorded by many other samples dealt with in this study. This interpretation would also be consistent with the discordant analyses from this sample. In fact, the results from the samples dis-cussed above suggest that the komatiites cannot be younger than 2798 ± 2 Ma. The initial εNd(2797) of +2.0 shows that the felsic rock represents ju-venile mantle-derived material (Huhma et al. this volume).

A2027 Siivikkovaara quartz porphyry dyke

Sample A2027 represents a felsic dyke intruding the komatiites in the Siivikkovaara area (Han-ski 1980). The sample yielded abundant zircon grains, which are light-coloured, fairly transpar-ent, euhedral to subhedral prisms or fragments. Both TIMS and LA-MC-ICPMS have been used for U-Pb dating (Appendices 2 and 3).

An analysis carried out using the chemical abra-sion TIMS method is practically concordant at 2795 ± 2 Ma, and together with other two slightly

discordant analyses plot on a chord, which gives intercepts at 2797 ± 5 Ma and 1082 ± 110 Ma. The LA-MC-ICPMS data are also concordant, and using all data an age of 2800 ± 5 Ma can be calculated. Although within the error quoted, two analyses (8a, 13a) seem to give marginally older ages. Rejecting these, the age would be 2795 ± 5 Ma (Fig. 20). In BSE or CL images, no distinct cores were found. Combining all data available, an age of 2795 ± 3 Ma is considered as the best esti-mate for zircon and the porphyry dyke, providing a minimum age for the country rock komatiites.

A511 Katerma rhyolite

Sample A511-Katerma represents a large rhyolitic rock formation located several km south of the Kellojärvi ultramafic complex (Fig. 13). Based on seven discordant multi-grain TIMS analyses, a U-Pb age of 2798 ± 15 Ma was reported by Hyp-pönen (1983). Zircon grains in this sample are euhedral, pale and mostly turbid crystals, which typically have resorbed surfaces. An analysis us-ing the CA-TIMS technique provides a nearly concordant result with a 207Pb/206Pb age of 2797 ± 2 Ma (Appendix 2). The common-lead content in this analysis is very low compared to the older data. All eight analyses available are roughly on a

98


A2027 Siivikkovaara porphyry dike

29202880

28402800

27602720

26802640

0.44

0.48

0.52

0.56

0.60

12 13 14 15 16 17207Pb/235U

206 Pb

/238 U

LA-MCICPMSaverage Pb/Pb age

2800 ± 5 MaMSWD = 0.95 n=22 (all)


Concordia Age = 2795 ± 5 Man=20


MSWD = 0.006 n=3

Fig. 20. Concordia diagram of zircon analyses from the Siivikkovaara felsic dyke (A2027): Large red error ellipses – LA-MC-ICPMS data, small black error ellipses – TIMS data.

A511 Katerma rhyolite

2800

2700

2600

2500

2400

2300

A511H +4.2 CA***

A511G +4.6

A511F 3.8-4.0A511E 4.0-4.1/<75

A511D 4.0-4.1/>75

A511C +4.1/long

A511B +4.6

A511A +4.1

0.32

0.36

0.40

0.44

0.48

0.52

0.56

8 10 12 14 16207Pb/235U

206 Pb

/238 U

A511 TIMS Intercepts at 294 ± 38 & 2799 ± 5 Ma

MSWD = 1.9 n=8

Hyppönen 1983: Intercepts at286 ± 94 & 2798 ± 15 Ma (n=7, A511H excluded)

Fig. 21. Concordia diagram of zircon U-Pb TIMS analyses from the Katerma rhyolite (A511).

99


chord, which gives intercept ages at 2799 ± 5 and 294 ± 38 Ma (Fig. 21). The upper intercept age can be considered a reliable eruption age for the Katerma rhyolite.

A788 Polvilampi rhyolite

Sample A788-Polvilampi represents a large fel-sic volcanic unit located several kilometres north of the Kellojärvi complex (Fig. 13). Hyppönen (1983) called this rock quartz-feldspar schist and reported an age of 2810 ± 48 Ma, which was based on four discordant U-Pb TIMS analyses on zircon. Abundant zircon in this rock consists of euhedral grains often showing sharp crystal edges and well-developed zoning, which are typi-cal features of zircon grains in igneous rocks.

A CA-TIMS analysis on zircon from A788 yield-ed a nearly concordant result with a 207Pb/206Pb age of 2795 ± 2 Ma (Appendix 2). Combining all TIMS U-Pb analyses, an upper intercept age of 2800 ± 11 Ma can be calculated (Fig. 22).

Zircon from this sample was also analysed us-ing SIMS (SHRIMP) at VSEGEI, St. Petersburg (Appendix 4). Sixteen U-Pb analyses are nearly concordant and yield an upper intercept age of 2788 ± 14 Ma. Combining all SIMS and TIMS data produces intercepts with concordia at 2799 ± 5 and 397 ± 50 Ma. The date of 2799 ± 5 Ma can be considered as the age of sample A788, and gives the timing of the related felsic volcanism.

A976 Moisiovaara gabbro

Sample A976-Moisiovaara is a coarse-grained, tholeiitic mafic rock, which was taken from a sill intruding banded tholeiitic amphibolites in the northern part of the Kuhmo greenstone belt, ca. 30 km north of the Kellojärvi complex (Fig. 13). According to Luukkonen (1988), these volumi-nous layered tholeiitic mafic-ultramafic sills pre-dominate in the lower stratigraphic part of the greenstone belt and may be 10 km long and up to 800 m thick.

Based on discordant and slightly heterogene-ous TIMS analyses on zircon, Luukkonen (1988) reported a U-Pb age of 2790 ± 18 Ma for the Moi-siovaara gabbro. Abundant zircon grains available from sample A976 mostly consist of turbid, grey, subhedral-anhedral crystals, being fairly typical igneous zircon from a gabbroic rock. In the heavy fraction, translucent, simple euhedral zircon prisms were also found. The CA-TIMS analyses on zircon are not perfectly concordant, but the 207Pb/206Pb ages of 2811 ± 3 Ma and 2806 ± 3 Ma should provide an absolute minimum age. Using

all ten TIMS analyses, the intercept ages are 2815 ± 16 and 1102 ± 150 Ma, but the scatter is rather large (Fig. 23). A special feature of the zircon in A976 is the high Th/U ratio (inferred from radio-genic 208Pb/206Pb, Appendix 2).

Zircon from sample A976 was also analysed using laser MC-ICPMS. All 16 data points are practically condordant within 2-sigma error, and fifteen of them give an average 207Pb/206Pb age of 2823 ± 6 Ma. One analysis (A976-10a) gives a slightly younger Pb/Pb age and is close to the bulk of the TIMS data (Appendix 3, Fig. 23). The data as a whole suggest that the scatter in TIMS analy-ses is more likely due to metamorphic effects than older xenocrystic zircon. The Th/U ratio in the CA-TIMS data is lower than in the other analyses (Luukkonen 1988), and it is thus conceivable that these CA-TIMS analyses do not record the age of solely magmatic zircon. It should be noted that the MC-ICPMS analyses were carried out during the same session using the same standards as with sample A1346, on which the TIMS and SIMS analyses confirm the accuracy of the MC-ICPMS 207Pb/206Pb ages. We are inclined to consider the average 207Pb/206Pb age of 2823 ± 6 Ma as the best available estimate for the age of magmatic zircon and emplacement of the Moisiovaara gabbro.

A1773 Hetteilä intermediate volcanic rock

Sample A1773-Hetteilä is a fine-grained felsic rock from the Vuosanka area, where supracrus-tal rocks seem to form a separate N–S-trending belt just east of the main Kuhmo greenstone belt. The sample was collected from a drill core (M52/4412/02/R416/6.20-8.80).

Partly due to the small sample size, mineral separation yielded only a few medium to fine-grained, pale coloured, transparent to translucent zircon grains with a rather rounded morphology. Short prismatic crystals are uncommon. In BSE images (Fig. 14E), the zircon is mostly rounded and/or corroded and shows a diffuse composi-tional structure/zoning. Only some zircon grains display clear oscillatory zoning or a rather homo-geneous internal structure. A thin pale outer rim surrounds almost all zircon grains. Some titanite grains were also obtained from this sample, sug-gesting an igneous origin for the rock.

A total of 15 zircon domains were analysed (Appendix 1) from A1773 using the secondary ion microprobe (Nordsim). One analysis was rejected because of its high degree of reverse discordancy. The U-Pb data cluster in two groups with a good correlation with the analysed zircon domain type. The cores and zoned grains have ages around

100


A788 Polvilampi felsic volcanic rock

2500

2600

2700

2800

0.40

0.44

0.48

0.52

0.56

0.60

10 11 12 13 14 15 16207Pb/235U

206Pb238U

A788 Intercepts at 397 ± 50 & 2799 ± 5 Ma

MSWD = 1.9 n=21(SIMS + TIMS)

Fig. 22. Concordia diagram of zircon analyses from the Polvilampi rhyolite (A788): Error ellipses – SIMS data (SHRIMP), diamonds – TIMS data.


2900

2800

2700

2600

2500

A976J &K CA-TIMS

0.42

0.46

0.50

0.54

0.58

0.62

10 12 14 16207Pb/235U

206 Pb

/238 U

LA-MC-ICPMS Pb/Pb age 2823 ± 6 Ma ,MSWD = 1.2, n=15


TIMS Intercepts at 1102 ± 150 & 2815 ± 16 Ma

MSWD = 10, n=10

Fig. 23. Concordia diagram of zircon U-Pb TIMS (solid error ellipses) and LA-MC-ICPMS (open ellipses) analyses from the Moisiovaara gabbro (A976). The length of grain 7 is ca. 200 µm.

101


2.85–2.80 Ga and the outermost pale rims with low Th/U determine an age of 2678 ± 3 Ma (Fig. 24). A wide pale rim (01a) with a very high U con-tent (6600 ppm) gives an age of ca. 530 Ma.

Provided that the rock is of a purely igneous origin, the average Pb/Pb age of 2836 ± 6 Ma obtained from the zoned magmatic zircon prob-ably gives the age of the felsic rock A1773, and the younger rims register a metamorphic event at 2.68 Ga. The rounded morphology of these zircon grains probably originates from postmag-matic resorption, which is common in Archaean zircon in eastern Finland.

A1774 Hetteilä mica schist

Sample A1774-Hetteilä represents a fine-grained mica schist unit from the same drill core (M52/4412/02/R416, depth 94.80–96.65) from which the other Hetteilä sample (A1773) was taken. Rocks in the drill-cores between these two samples are mostly amphibolites.

The sample yielded a small amount of pale, typically fine-grained (75–100μm), short prismatic to round and equant zircon grains. In general, the population looks homogeneous, and the rounded

morphology of some grains is compatible with their assumed detrital origin. In BSE images (Fig. 14D), the majority of the zircon grains are dark and show different types of oscillatory zoning (broad and smooth or narrow and sharp). Some grains have separate cores and rims, while oth-ers show rather homogeneous internal structures. Several zircon grains are surrounded by remnants of a thin pale rim. Inclusions are common.

Ten zircon domains were analysed from A1774 using the SIMS (Nordsim) (Appendix 1). Most of the data show minor discordance and moderate to low U concentrations. Analyses from the oscilla-tory-zoned zircon grains plot on the same chord, suggesting an age of ca. 2.74 Ga (Fig. 25). Zircon core n2557-04a (see Fig. 14D) and grain n2557-10a are ca. 2.79 Ga old. Provided that the rock sampled by A1774 is of a sedimentary origin, the data constrain the deposition after 2.74 Ga, which would imply a considerably younger time of for-mation than what was obtained for the 2.84 Ga rock above (A1773), and a tectonic break between the two sequences.

In fact, this would be consistent with the pres-ence of 2.75 Ga detrital zircons in the sedimenta-ry samples in the Ronkaperä Formation discussed

A1773 Hetteilä#1 volcanic rock

2880

2840

2800

2760

2720

2680

2640

2600

0.47

0.49

0.51

0.53

0.55

0.57

11.5 12.5 13.5 14.5 15.5 16.5207Pb/235U

206 Pb

/238 U


Low Th/U rims:Concordia Age = 2678 ±3 Ma, n=4

A1773 SIMS average Pb/Pb age:2836 ± 6 Ma, MSWD = 1.14, n=9

Fig. 24. Concordia diagram of zircon SIMS analyses from the Hetteilä intermediate volcanic rock A1773. Analysis n2556-01a is outside the range of the figure.

102


A1774 Hetteilä#2 felsic rock

28402800

27602720

26802640

26002560

0.42

0.46

0.50

0.54

0.58

11 12 13 14 15 16207Pb/235U

206Pb238U



MSWD = 1.8, n=7

A1774 SIMS8 analyses ca. 2.74 Ga2 analyses ca. 2.79 Ga

Fig. 25. Concordia diagram of zircon SIMS analyses from the Hetteilä felsic rock A1774.

below. A similar situation was also observed in the Tipasjärvi schist belt, where a sedimentary rock from the Kokkoniemi Formation contains abundant 2.74 Ga zircons, while the volcanic rocks lower in the lithostratigraphy of the belt are ca. 2.8 Ga old.

A1746 Petäjäniemi sedimentary rock

Fine-grained, laminar metasediments occur at Petäjäniemi, north-east of Lake Ontojärvi. In the stratigraphy these rock are above the mafic-ultramafic volcanic rocks. Two samples for iso-tope studies were collected from the same out-crop (AAK-03-109). Of these, A1746 represents a fairly homogeneous felsic layer and A1747 was taken from a heterolithic exposure consisting of alternating, thin (few mm to few cm) felsic and mafic mica rich layers. However, no zircon grains were recovered from A1747.

A very small amount of mainly colourless to red-tinted, transparent to translucent zircon grains was separated from sample A1746. These grains are either short prismatic or oval-shaped (w:l~1.5-2.5; 100-200 μm) without distinct crystal faces. Although homogeneous under a stereomi-croscope, the population is heterogeneous in BSE

images (Fig. 14F). Several short zircon grains are clear and show weak, smooth zoning (metamor-phic grains?), whereas some longer prismatic crys-tals show evident magmatic oscillatory zoning with occasional zone-controlled alteration (mag-matic grains). A few distinct cores were detected. Signs of abrasion are generally minor. However, some grains have a slightly rounded morphology compatible with a detrital origin.

A total of 18 zircon domains were dated from the Petäjäniemi sediment sample A1746 (Appen-dix 2). One analysis was rejected due to a high common-lead content. The U-Pb analyses define two age groups, at ca. 2.85 Ga and 2.74 Ga (Fig. 26). Assuming that the 14 older grains have a common origin, an upper intercept age of 2847 ± 9 Ma can be calculated (together with a lower in-tercept of 582 ± 270 Ma, MSWD = 3.5). The 2.74 Ga ages were measured from a weakly oscillatory-zoned, euhedral grain n2246-12a (Fig. 14F) and from a BSE-darker, homogeneous, metamorphic rim phase of zircon 09 having a 2.86 Ga core. The ages obtained register both igneous and meta-morphic events that are considered to predate the deposition of the Petäjäniemi sediment.

Before drawing broader inferences, one should remember that only very few zircons were found

103


in this rock and the number of analyses is also small. Nevertheless, deposition of this sediment after the main volcanic phase in the Kuhmo greenstone belt is possible, being reminiscent of the case observed at Vuosanka (A1744-Hetteilä), Rakennuslahti (83-PGN-90 below) and Tipasjär-vi (A1748-Aarreniemi below), and also consistent with the stratigraphic scheme (e.g. Papunen et al. 2009).

83-PGN-90 (A2102) Rakennuslahti greywacke

A fairly large area of the southern part of the Kuhmo greenstone belt is dominated by the meta-sedimentary rocks assigned to the Ronkaperä For-mation. In this work, this predominantly metat-urbidite unit is represented by the metagreywacke sample 83-PGN-90 from Rakennuslahti (Fig. 13). The sample was collected from a sandy layer in an outcrop of metaturbidite schist dominated by 5–15-cm-thick, gray-coloured, massive sandy layers. The rock has a blastoclastic-schistose tex-ture, in which the largest obvious relict clastic grains are up to 0.5 mm in size and mainly consist of monocrystalline quartz. The present mineral composition is quartz, plagioclase, biotite and chlorite with minor ilmenite, apatite, tourmaline and zircon.

Zircon in this sample mainly consists of eu-hedral crystals, which show clear magmatic zon-ing. Signs of abrasion are generally limited. The MC-ICPMS U-Pb data on 45 zircon grains were originally obtained utilizing only the GJ1 and Proterozoic (A382) in-house standards. Later, ten of these grains were re-analysed using the Archae-an in-house standard (A1772) for calibration. It turned out that the data on these two sessions are indistinguishable (Appendix 3). The ages range from ca. 2.74 Ga up to 3.2 Ga, and nearly half of the analysed grains are close to 2.75 Ga in age (Fig. 27). It seems evident that the deposition of this sedimentary rock took place after the main volcanic phases of the Kuhmo greenstone belt and subsequent to ca. 2.75 Ga.

A1753 Arola quarzite

Sample A1753 (55-PTP-03) represents the quartz-ites that occur as a relatively narrow, ca. 1- km-long, apparently fault-bound sliver in the central part of the Kuhmo greenstone belt (Fig. 13). The rock is a reddish, sericite-bearing, blastoclastic, laminar and deformed quartzite. A fair amount of zircon obtained from a relatively small sam-ple consists of mostly euhedral, slightly rounded, brownish grains.

A1746 Petäjäniemi sedimentary rock

2000

2200

2400

2600

2800

3000

0.2

0.3

0.4

0.5

0.6

0.7

5 7 9 11 13 15 17 19207Pb/235U

206 Pb

/238 U


A1746 SIMS14 analyses ca. 2.85 Ga2 analyses ca. 2.74 Ga

Fig. 26. Concordia diagram of zircon SIMS analyses from the Petäjäniemi sediment sample A1746.

104


Ronkaperä Formation greywacke

3400

3200

3000

2800

2600

2400

0.35

0.45

0.55

0.65

0.75

8 12 16 20 24 28207Pb/235U

206 Pb

/238 U


83-PGN-90LA-MC-ICPMS

Youngest 25 zirconsca. 2750 Ma

Fig. 27. Concordia diagram of zircon LA-MC-ICPMS analyses from the Rakennuslahti greywacke sample 83-PGN-90. The length of grain 39a is ca. 100µm.

Zircon in this sample was analysed using SIMS (SHRIMP) at VSEGEI, St. Petersburg. Most of the 22 U-Pb analyses are concordant within error and show a large range of ages from 2.70 to 3.45 Ga (Appendix 1, Fig. 28). Half of the dates con-centrate on ca. 2.70 Ga and were obtained from oscillatory zoned zircon domains. They probably derive from felsic magmatic rocks, and the data thus suggest that the deposition of the Arola quartzite took place after ca. 2.70 Ga. Granitoids and felsic dykes crosscutting the volcanic rocks of the greenstone belt in the Arola area have yielded U-Pb zircon age of ca. 2.74–2.73 Ga and are thus significantly older (samples A402, A572, A1702, A1707, Hyppönen 1983, Käpyaho et al. 2006, Heilimo et al. 2011) than the Arola quartzite. Evi-dently, the Arola quartzite is much younger than any other supracrustal unit in the Kuhmo green-stone belt.

It is notable that the Arola quartzite is clearly deformed. However, observing that most Protero-zoic metadiabase dykes just west of the Kuhmo greenstone belt are pervasively schistose, even a Proterozoic age of this quartzite could be specu-lated. The presence of 2.22 Ga gabbro-wehrlite sills within the middle part of the Kuhmo belt (Hanski et al. 2010) suggests that the 2.2 Ga ero-

sion level was not much higher than the present erosion level. Over the whole Karelia Province, these sills are restricted to <1–2 km below the Pal-aeoproterozoic Kainuu-Jatuli quartzites.

A1213, A1254 Pitkäperä meta-andesites

The Pitkäperä samples A1213 and A1254 repre-sent andesitic rocks in a location ca. 10 km east of the main Kuhmo greenstone belt, where they form a 4-km-long, NE-trending belt (Fig. 13). The geology and geochemistry of the rocks in the Pitkäperä area have been described by Luuk-konen (2001). The samples collected for dating are fine- to medium-grained rocks mainly consist-ing of plagioclase, quartz and biotite.

Mineral separation yielded only a small amount of fine-grained zircon grains, which are short, pale, fairly transparent and euhedral. Abundant titanite was also obtained from these samples. The previous conventional TIMS results are dis-cordant, but data after chemical abrasion are fair-ly close to concordia and yield 207Pb/206Pb ages of ca. 2.83 Ga (Appendix 2).

The MC-ICPMS analyses on zircon A1254 provide a concordant age at 2847 ± 8 Ma (Fig. 29), which is close to the upper intercept age of

105


2842 ± 5 Ma obtained from the TIMS data on sample A1213 (only two analyses). These are the best estimates for the age of magmatic zircon of the Pitkäperä volcanic rocks.

The TIMS data on the two samples do not plot exactly on the same chord (Fig. 29). In particular, the two CA-TIMS data points fairly close to concordia are slightly distinct in terms of the Pb/Pb age, which calls for some explana-tion. It is conceivable that some metamorphic effects are responsible for this scatter, involving different discordia patterns for different samples. This interpretation receives some support from a TIMS analysis carried out on zircon from a third sample N5, giving results clearly distinct from the other data (Appendix 2, Fig. 29). Another possibility could be that A1213 contains a mi-nor inherited component or some unconstrained fractionation took place during the CA treat-ment. The third potential explanation appeared after MC-ICPMS analyses, since two Protero-zoic magmatic grains with an age of ca. 1.75 Ga were observed in sample A1254 during the first analytical session (data not shown in Appendix 2). It is very likely that their presence is due to contamination during sample crushing, which fits well with the laboratory log book records, showing that the previous sample in the crushing line was a 1.75 Ga granite.

A120 & A1000 Ruokojärvi felsic volcanic rocks

The Ruokojärvi samples A120 and A1000 repre-sent a small felsic volcanic unit in the northern part of the Kuhmo belt (Fig. 13). These rocks are situated in a small, granitoid-surrounded enclave ca. 1 km east of the main schist belt and consist of tuffs and pyroclastic breccias, which are strongly tectonized and cataclasized (Luukkonen 1988).

A large amount of fine-grained zircon is avail-able from sample A120. For the most part, it is prismatic (l:w ~3-4), brownish and transparent to translucent. In the density fraction 3.8–4.0 g/cm3, zircon grains tend to be more turbid, have a tint of brown colour and occur as shorter grains than in other fractions. In BSE images, many zircon crystals show clear oscillatory zoning with strong zone-controlled alteration patterns (Fig. 14K). Distinct cores are also common.

The previous multi-grain zircon U-Pb TIMS data from A120 are discordant, and the low-den-sity, turbid zircon grains have a very high amount of common lead (Appendix 2). The data are clearly scattered but suggest an age of ca. 3 Ga (Fig. 30).

To improve our basis for interpretation, a to-tal of 40 zircon domains were analysed from the Ruokojärvi sample A120 using SIMS (Appendix 1). Nine analyses mainly from the clearly zoned grains had to be rejected from further evaluation

A1753 Arola quartzite

3400

3000

2600

2200

0.35

0.45

0.55

0.65

0.75

6 10 14 18 22 26 30 34207Pb/235U

206 Pb

/238 U


A175311 analyses ca. 2.7 Ga

(of total 22)

Fig. 28. Concordia diagram of zircon SIMS analyses from the Arola quartzite A1753.

106


Pitkäperä andesites A1254 & A1213

3000

2900

2800

2700

2600

N5A (low Th/U)

0.42

0.46

0.50

0.54

0.58

0.62

0.66

11 13 15 17 19207Pb/235U

206Pb238U


A1254 LA-MC-ICPMSConcordia Age = 2847 ±8 Ma (n=8)

A1213 TIMS Intercepts at 722 ± 59 & 2842 ± 5 Ma n=2

Fig. 29. Concordia diagram of zircon U-Pb analyses from the Pitkäperä andesites: Error ellipses - LA-MC-ICPMS on A1254, red triangles – TIMS on A1254, black diamonds – TIMS on A1213, black square – TIMS on N5. The inset shows a BSE image of zircon from A1254.

Ruokojärvi felsic volcanic rocks

3000

2600

2200

1800

0.2

0.4

0.6

4 8 12 16 20 24207Pb/235U

206 Pb

/238 U


A1000 TIMS Intercepts at -19 ± 180 & 2818 ± 11 Ma

MSWD = 19 (n=8)

A120 SIMS16 grains

ca. 3.13 Ga

A1000bD Pb/Pb age2816 ± 2 Ma

(nearly concordant CA-TIMS)

Fig. 30. Concordia diagram of zircon analyses from the Ruokojärvi felsic volcanics. Error ellipses – SIMS data on A120, red diamonds – TIMS data on A120, squares – TIMS data on A1000.

107


due to an unusually high amount of common lead. The remaining SIMS data scatter consider-ably, but most analyses from both zoned and ho-mogeneous zircon domains plot at around 3.13 Ga (Fig. 30). Some weakly zoned grains give ages close to 2.99 Ga. The youngest ages of ca. 2.8 Ga were measured from structurally homo-geneous zircon domains. The data also reveal a wide range in Th/U ratios from 0.03 to 1.4 (Ap-pendix 1), but there seems to be no correlation with age and Th/U.

The other sample, A1000, collected later from the same rock unit as A120 seems to represent a more homogeneous variety, but evaluation of the primary nature of the rocks in the area is difficult due to strong tectonic strain. Zircon in sample A1000 consists of euhedral, brown to reddish and

translucent crystals. Seven multi-grain TIMS analyses yield discord-

ant results, and mostly contain abundant com-mon lead (Appendix 2). Instead, the CA-TIMS analysis carried out on the highest density zircon fraction gives a nearly concordant result with a 207Pb/206Pb age of 2816 ± 2 Ma, which should be the minimum age for the material analysed. Re-gression of all TIMS data gives an upper intercept age of 2818 ± 11 Ma, but the scatter is consider-able and the lower intercept is set to the origin.

The results allow us to conclude that the Ruokojärvi felsic volcanic rocks are ca. 2.82 Ga in age and some samples, like the breccia A120, con-tain abundant xenocrystic zircon mostly derived from 3.13 Ga crustal sources.

U-Pb geochronology of the Tipasjärvi greenstone belt

A few kilometres SSW of the southern end of the Kuhmo greenstone belt, Archaean supracrustal rocks form an approximately 25-km-long, NE–SW-trending Tipasjärvi greenstone belt (Figs. 1 and 31). An age of ca. 2.79 Ga was reported for felsic volcanic rock A1174 by Vaasjoki et al. (1999). In conjunction with subsequent mapping and research, three additional samples were col-lected from felsic volcanic rocks.

A1922 Tipasjärvi intermediate volcanic rock

Sample A1922 collected from a drill core (4322-2006-R337/138.55-139.75) represents the inter-mediate, pyroclastic volcanic unit along the west-ern margin of the Tipasjärvi belt. These volcanic rocks are considered older than the associated ultramafic volcanism.

Sample A1922 yielded a small number of light-coloured, euhedral, fairly transparent zircon grains. The population looks homogeneous and magmatic in origin. Only two U-Pb TIMS analy-ses were carried out on this sample, one using a lengthy air-abrasion treatment (analysis A) and the other with chemical abrasion (CA, analysis B, Appendix 2). They show that the common-lead content is low and provide nearly concord-ant data, with an average Pb/Pb age of 2828 ± 3 Ma (Fig. 32). Analyses by LA-MC-ICPMS were carried out in two stages, but here only the data from the last session (August 2010) utilizing the Archaean in-house standard are included in cal-culations (Appendix 3). Isotopic results for zircon A1922 are concordant and provide an age of 2826 ± 8 Ma (Fig. 32). Including the analytical results

from the first session, no significant heterogeneity is observed in the data on 30 zircons, which sug-gests that the date of the nearly concordant TIMS analyses is the best age estimate for magmatic zir-con of this intermediate volcanic rock.

A1921 Tipasjärvi felsic volcanic rock

Sample A1921 collected from a drill core (4322-2006-R324/16.25-17.40) represents a felsic vol-canic unit at the eastern margin of the Tipasjärvi belt. These felsic rocks are thought to postdate the main ultramafic magmatic phase.

Only a small number of zircon grains were ob-tained from sample A1921 consisting of small, euhedral, transparent crystals. A U-Pb analysis using the chemical abrasion technique gave a con-cordant result and an age of 2781 ± 3 Ma (Appen-dix 2, Fig. 32). However, concordant analyses by LA-MC-ICPMS yielded an older age of 2810 ± 10 Ma (Appendix 3). In addition to these 11 anal-yses, this sample was also analysed in an earlier session, but due to some uncertainties with the calibration, these data are excluded from the final age calculations. Nevertheless, all analyses on 31 zircon grains give the same age within error, sug-gesting that zircon is of magmatic origin without significant inherited domains. It appears that few grains in the zircon mount prepared of sample A1921 are actually monazite, which is optically very similar to zircon. According to an LA-MC-ICPMS analysis, this monazite is ca. 1.9 Ga in age (A1921-18a, Appendix 3). It is very likely that a minor amount of such monazite could have been included in the multi-grain TIMS analysis, which

108


Fig. 31. Geological map of the Tipasjärvi greenstone belt showing sample sites (red star – this study, other samples – Vaasjoki et al. 1999, Käpyaho et al. 2006; see also http://geomaps2.gtk.fi/activemap/). Igneous ages with 2-sigma errors are given in Ma after the sample number. The map is based on the 1:1 000 000 geological map (Korsman et al. 1997), where the greenstone belt consists of four main rock types: mafic metavolcanic rocks (brown), ultramafic metavolcanic rocks (green), intermediate-felsic metavolcanic rocks (yellow) and metasediments (blue). Granitoids surrounding the greenstone belts are divided into TTGs and intrusive rocks (stippled), and (Nurmes) paragneisses are shown in grey.

109


Tipasjärvi volcanic rocks A1921 & A1922

29002860

28202780

27402700

0.46

0.48

0.50

0.52

0.54

0.56

0.58

0.60

0.62

13 14 15 16 17207Pb/235U

206Pb238U A1922 LA-MC-ICPMS

Concordia Age 2826 ±8 Ma, n=11

TIMS average Pb/Pb2828 ±3 Ma


A1921 LA-MC-ICPMS Concordia Age

2810 ±10 Ma, n=10

(TIMS 2781 ±3 Ma)

Fig. 32. Concordia diagram of zircon U-Pb TIMS (solid error ellipses) and LA-MC-ICPMS analyses from the Tipasjärvi volcanic rocks (A1922-red, A1921-blue). The length of zircon grains is approximately 100 µm.

thus would explain the younger age. This is sup-ported by the elevated 208Pb/206Pb ratio measured by the TIMS analysis.

Although the error ellipses in the laser MC-ICPMS analyses on A1921 and A1922 are over-lapping, there is a clear tendency of A1922 giving slightly older ages than A1921. These data were obtained during the same session using the same calibration.

A1174 Taivaljärvi rhyolite

Sample A1174 represents the felsic volcanic rocks hosting the Taivaljärvi Ag-Zn deposit and was collected from the mine incline (Vaasjoki et al. 1999). Abundant zircon available at the GTK storage consists of clear, euhedral, mostly elon-gate crystals. A U-Pb analysis using the chemi-cal abrasion technique gave a concordant result and an age of 2798 ± 2 Ma (Appendix 2, Fig. 33). This age is slightly older than the date (2790 ± 3 Ma) published by Vaasjoki et al. (1999), who also reported some analytical problems with their data. Compared to our new result (A1174E), the old data show much higher levels of common lead and were also obtained using separate U and Pb spikes, which may yield accidental Pb/U

errors during weighing. The CA-TIMS age of 2798 ± 2 Ma obtained

in this work is strongly supported by the LA-MC-ICPMS results. Excluding two analyses, the amount of common lead is negligible in all other 26 analyses, which give an average 207Pb/206Pb age of 2800 ± 6 Ma (Appendix 3, Fig. 33). It seems evident that there is no xenocrystic zircon in sam-ple A1174, and thus the age of 2798 ± 2 Ma can be considered as a reliable estimate for the timing of the felsic volcanism.

A1886 Tipasjärvi felsic tuff

Sample A1886 represents a large, fairly homo-geneous felsic unit, which occurs in the middle part of the Tipasjärvi belt (Fig. 31). According to the geological map, it may correlate with sample A1174 discussed above. Sample A1886, collected from a drill core (4322-2005-R305/235-239), is a rhyolitic tuff mainly consisting of quartz and sericite.

Sample A1886 yielded a good amount of light-coloured, euhedral, fairly transparent zircon. The zircon population looks quite homogeneous and magmatic in origin. Some rutile was also observed in the heavy fraction.

110


The five U-Pb TIMS analyses yield intercepts with the concordia at 2792 ± 5 and 1191 ± 150 Ma (MSWD = 1.6, Appendix 2). The upper intercept age is consistent with analysis #A1886I, which was carried out using the CA-TIMS method and gave a concordant age of 2794 ± 2 Ma.

All ten LA-MC-ICPMS analyses yielded con-cordant results and an age of 2796 ± 8 Ma (Ap-pendix 3, Fig. 34). The date of 2796 ± 8 Ma may be considered as the crystallization age of zircon and felsic tuff A1886.

A1748 Aarreniemi greywacke

The metagreywacke-dominated Kokkoniemi Formation is considered to be the uppermost unit in the volcanic-metasedimentary succession pre-served in the Tipasjärvi greenstone belt (Taipale 1983). The sampled outcrop (A1748 Aarrenie-mi) at the SE corner of Tipasjärvi Lake consists mainly of schistose, medium-grained, grey-col-oured metawacke with a few bands of slightly fin-er-grained, darker grey metawacke that contains some graphite and iron sulphide. Although dis-tinctly schistose, the Aarreniemi metawacke still shows clear remains of a clastic texture with flat-tened sand-size clasts up to 0.5 mm in their long-est dimension. The larger, still identifiable clasts consist either of mono- or polycrystalline quartz

A1174 Taivaljärvi rhyolite

2900

2800

2700

2600

2500

0.38

0.42

0.46

0.50

0.54

0.58

0.62

10 12 14 16 18207Pb/235U

206 Pb

/238 U

A1174 LA-MC-ICPMS average Pb/Pb age 2800 ± 6 Ma

MSWD = 0.83, n=26


A1174E CA-TIMSconcordant at2798 ± 2 Ma

Fig. 33. Concordia diagram of zircon U-Pb analyses from the Tipasjärvi volcanic rock A1174 collected from the Taivaljärvi mine. Small red error ellipse – CA-TIMS analysis A1174E, large error ellipses – LA-MC-ICPMS analyses.

or granoblastic plagioclase plus quartz, presum-ably from felsic volcanic or subvolcanic sources. The matrix between the sand-size clasts is recrys-tallised to a granoblastic-lepidoblastic mass of plagioclase, quartz and biotite with minor sul-phide, and zircon. The separation yielded a fair amount of predominantly distinctly euhedral, long-prismatic oscillatory zoned zircon grains, for the most part without signs of abrasion.

Thirteen domains of 12 different zircon grains were analysed using SHRIMP II at VSEGEI, St. Petersburg (Appendix 4). Excluding one analysis, the data define an upper intercept age of 2746 ± 8 Ma (Fig. 35). Although the number of analy-ses is small and calculation assumes a common origin, and is thus not fully justified for detrital zircon, the data nevertheless strongly suggest that zircon grains in A1748 were predominantly from a source approximately 2.75 Ga in age. This is supported by one multi-grain TIMS analysis car-ried out at GTK (Appendix 2, Fig. 35) and the uniform appearance of the zircon population.

The results suggest that the maximum age of deposition of the Kokkoniemi Formation is ca. 2.75 Ga. A minimum age for the deposition is pro-vided by the leucogranites cross-cutting the Kok-koniemi Formation along its NE border, dated at 2697 ± 7 Ma at Katajavaara 10 km N of Tipas-järvi (A1703, Fig. 31, Käpyaho et al. 2006).

111


Fig. 34. Concordia diagram of zircon U-Pb analyses from the Tipasjärvi felsic tuff A1886 (TIMS data – small red error ellipses, MC-ICPMS data – open error ellipses). Length of zircon is 150 µm.

A1886 Tipasjärvi felsic tuff

2850

2750

2650

2550

0.40

0.44

0.48

0.52

0.56

0.60

10.5 11.5 12.5 13.5 14.5 15.5 16.5207Pb/235U

206 Pb

/238 U

LA-MC-ICPMS average Pb/Pb age2796 ± 8 Ma, MSWD = 0.36, n=9


A1886F CA-TIMS concordant at 2794 ± 2 Ma


MSWD = 1.6 n=5

A1748 Tipasjärvi greywacke

2900

2800

2700

2600

2500

2400

0.36

0.40

0.44

0.48

0.52

0.56

0.60

9 11 13 15 17207Pb/235U

206Pb238U

SHRIMP Intercepts at 412 ± 240 & 2746 ± 8 Ma

MSWD = 0.85 n=12


Fig. 35. Concordia diagram of zircon U-Pb analyses from the Aarreniemi, Tipasjärvi greywacke A1748 (SIMS/SHRIMP data – open error ellipses, TIMS analysis – filled diamond). Only one grain is clearly older than 2.75 Ga.

112


The results presented in this paper provide an im-proved basis for constraining the evolution of the Kuhmo and Tipasjärvi greenstone belts. Accord-ing to the stratigraphic scheme of the Kuhmo greenstone belt, komatiites, most voluminous in the Siivikko Formation, are younger than the tholeiitic basalts of the Pahakangas Formation, for which an age of 2790 ± 18 Ma has previously been applied. This age was based on discordant TIMS zircon data from the Moisiovaara mafic-ultramafic sill considered to intrude and be co-eval with the Pahakangas tholeiites (Luukkonen 1992, Papunen et al. 2009). The new data on the Moisiovaara sample (A976) suggest a slightly older age of 2823 ± 6 Ma, which, according to the stratigraphy, should give the upper age limit for the komatiites.

The age of dated igneous rocks in the Kello-järvi area, in the central part of the Kuhmo belt, is close to 2800 Ma (Fig. 36). Four of these sam-ples are felsic rocks belonging to the Mäkisensuo Formation and give an average age of 2798 ± 2 Ma. According to the geological field relations, some of these rocks are considered intruding the komatiites of the Siivikko Formation and should thus provide the minimum age for the associated

mafic-ultramafic magmatism. Particularly strong evidence is provided by the felsic porphyry dyke A2027 with an age of 2795 ± 3 Ma, which clearly intrudes the komatiites in the Siivikkovaara area. The results call for a revision of the stratigraphic position of the Mäkisensuo Formation, which was previously thought to be located below the Pahakangas Formation (Papunen et al. 2009).

The igneous ages obtained from the four sam-ples of the felsic volcanic units in the Tipasjärvi greenstone belt range from 2828 ± 3 Ma to 2796 ± 8 Ma and thus resemble those measured from the Kuhmo belt. The revised age of 2798 ± 2 Ma from the felsic volcanic host rock of the Taivaljärvi ore deposit is equal to that obtained for the felsic rocks in the Kellojärvi area. In terms of age con-straints, the komatiitic volcanism in the Tipasjärvi belt resembles that in the Kuhmo belt.

A major adjustment concerns the age of the Ruokojärvi Formation, which has been thought to be as old as ca. 3 Ga (Papunen et al. 2009). This was based on multi-grain TIMS data and the position of these rocks in the marginal zone of the greenstone belt. The new U-Pb data on two felsic volcanic rocks suggest that the magmatic age ac-tually is ca. 2.82 Ga, but the presence of abundant

Discussion on the Kuhmo-Tipasjärvi greenstone belt

A14

18

A13

77 A20

27A

1886

Tip

asjä

rvi

A15

60

A17

71

A13

46

A11

74 T

ipas

järv

iA

0511

Kat

erm

a

A07

88 P

olvi

lam

pi

A19

21 T

ipas

järv

i

A10

00 R

uoko

järv

i

A09

76 M

oisi

ovaa

ra

A19

22 T

ipas

järv

i

A17

73 H

ette

ilä/ V

uosa

nka

A12

13 P

itkäp

erä

A12

54 P

itkäp

erä

2760

2780

2800

2820

2840

2860

Age

(Ma)

Kuhmo - Tipasjärvi belt U-Pb ages

data-point error symbols are 2σ

Fig. 36. Summary of the U-Pb ages (Ma) of the Kuhmo and Tipasjärvi greenstone belts. Red labels in italics refer to samples from the Kellojärvi area.

113


xenocrystic zircon up to 3.13 Ga in age is also evi-dent. Rocks with ages of ca. 2.84 Ga observed in the Vuosanka (Hetteilä) and Pitkäperä areas (Fig. 13) on the eastern side of the main Kuhmo belt seem to represent volcanic activity preceding the main magmatic phases of volcanism recorded in the Kuhmo belt (Fig. 36).

Both the Kuhmo and Tipasjärvi belts contain sedimentary rocks that were deposited after 2.75 Ga and thus at least 50 Ma after the associated volcanism. These rocks have been assigned to the Ronkaperä and Kokkoniemi Formations. Still younger sediments have been found at Arola, in the Kuhmo belt, where a quartzite sliver contains detrital zircon as young as 2.7 Ga.

The new ages from the greenstone belts also im-ply that many felsic plutons, including the 2785 ± 7 Ma Viitavaara tonalite close to Kellojärvi, are clearly younger than the volcanic rocks within the

belt. However, the 2830 ± 2 Ma Haasiavaara and 2814 ± 3 Ma Huuskonvaara tonalites flanking the Tipasjärvi belt are coeval with the oldest volcanic rocks in this belt.

One of the main conclusions from the Sm-Nd (Huhma et al. this volume) and U-Pb results is that the bulk of the Kuhmo and Tipasjärvi belt igneous rocks represent juvenile, 2.8 Ga materials from mantle, and the contribution of older crust is very limited. This is consistent with Patchett et al. (1981), who reported an εHf(2800) of +6 for zircon in the rhyolite A511 (Katerma), and is also seen in trace element compositions of the mafic vol-canic rocks of these greenstone belts, as they are systematically characterized by low Th/Yb and LREE/Yb coupled with low Nb/Yb (ref). Many granitoids surrounding the belt, e.g. those at Viita- vaara and Haasiavaara, also represent juvenile additions to the crust (Huhma et al. this volume).

The geology of the Ilomantsi area and the Ilo-mantsi (Hattu) schist belt, in particular, was dealt with in great detail in the Ilomantsi gold project (Nurmi & Sorjonen-Ward 1993). The region con-sists of an Archaean plutonic dominated terrain, in which mostly tonalitic and granodioritic intru-sions penetrated and deformed a sediment-dom-inated supracrustal sequence. No depositional basement for the volcano-sedimentary rock suc-cessions has been found or any obvious uncon-formities within the successions. All contacts between the granitoid and volcanic-sedimentary rocks are intrusive or tectonic. Primary deposi-tional features such as graded and cross-bedding are commonly preserved and have enabled a fair-ly confident assessment of the regional structural

framework (Sorjonen-Ward 1993).The Ilomantsi (Hattu) schist belt proper (Fig.

37) was formed ~2.75 Ga ago (Vaasjoki et al. 1993), and granitoids intruded immediately after or during the volcanic activity. Some conglomer-ate clasts in flanking sediments exhibit ages close to those of the greenstone belt volcanics and the intruding granitoid rocks. Multi-grain TIMS U-Pb data available on some greywackes also sug-gest relatively rapidly evolving crustal generation (Vaasjoki et al. 1993). In order to obtain a bet-ter picture of the geochronological relationships, zircons from a sedimentary rock (A221) and por-phyry dyke (A282, A301) were analysed using the ion microprobe (Nordsim).

ILOMANTSI AND KOVERO SCHIST BELTS

A221 Hattuvaara greywacke in Ilomantsi

Sample A221 represents a fine-grained, schistose, lower-amphibolite-facies greywacke from Hattu-vaara, on which multi-grain U-Pb TIMS analyses were published by Vaasjoki et al. (1993, Fig. 37). Abundant zircon available at GTK storage con-sists of a light-coloured, fairly homogeneous pop-ulation. Many grains are stubby and translucent prisms showing oscillatory zoning typical for zir-con of felsic plutonic rocks. The signs of sedimen-tary abrasion are evident but relatively minor.

SIMS U-Pb analyses were carried out on 35 zir-con grains, mostly from inner, oscillatory-zoned

domains (Appendix 1). The bulk of the data plots in a cluster, which suggests an age of ca. 2.75 Ga (Fig. 38). Only two dates are significantly older and two slightly younger at ca. 2.7 Ga. Consider-ing only the concordant data, the youngest Pb/Pb ages are 2700 ± 6 Ma (n2494-15, 2-sigma error) and 2711 ± 14 Ma (n2494-24). Several analyses yield ages of ca. 2.75 Ga, which can be considered as a reliable upper age limit for the deposition. The ages of the granitoids and dykes that intrude the Ilomantsi schists represented by sample A221 are also close to 2.75 Ga (samples A1094 Tasanvaara,

114


U-Pb geochronology of the Vehkavaara dykes in Ilomantsi

The age data from the Vehkavaara porphyritic dykes presented a vexing problem (Vaasjoki et al. 1993). Based on well-exposed field relations, there is no doubt that these dykes cut across mafic host rocks, which closely resemble those of the Ilo-mantsi schist belt exposed to the north and east of the Silvevaara granodiorite. Within the frame-work of the Ilomantsi data discussed above, an age of around 2.75 Ga or less would thus be an-ticipated. However, results of conventional bulk analyses suggested an upper intercept age of ca. 3 Ga for zircons in sample A282, and the least discordant, air-abraded zircon fractions from two other samples (A301 and A338) registered 207Pb/206Pb ages of 2.93 and 3.01 Ga, respectively (Vaasjoki et al. 1993). Although the convention-al data were heterogeneous, the option that the mafic volcanic rocks in this western part of the Ilomantsi belt were as old as 3 Ga was considered a possibility. Thus, an ion-probe investigation of zircon from the Vehkavaara dykes seemed war-ranted and was carried out in 2000 at the NOR-DSIM laboratory.

Plagioclase-phyric dykes at Vehkavaara intrude a NE-trending zone of mafic volcanic rocks ex-posed near the western margin of the Silvevaara granodiorite (Fig. 37, Vaasjoki et al. 1993). Con-tacts against the host greenstones are sharp. The

dykes range in width from 0.2 to 60 m and are strongly deformed and metamorphosed. The exist-ing zircon separates from samples A282 and A301 were used for the isotopic analyses. The zircon grains from both samples are rather similar, euhe-dral or subhedral, with simple prismatic and pyr-amidic faces dominant. A striking feature is the frequent occurrence of a thin, darker, crack-filled layer within the crystals, which seems to define an interface between cores and outer domains. The latter often display oscillatory zoning, while zonation in the cores is less frequent but wider (Fig. 39).

The U-Pb data from both samples are similar. Analyses from the zircon cores yield, with one ex-ception, significantly older ages than the outer do-mains (Appendix 1). Four nearly concordant data points from the outer domains of A301 define an average 207Pb/206Pb age of 2755 ± 8 Ma, and the results of three further analyses from the outer zircon domains in A282 are consistent with this age (Fig. 40). Seven analyses of cores from A282 provide ages close to 3.0 Ga, while the 207Pb/206Pb ages of other core analyses range from 2.9 to 3.3 Ga. The few nearly concordant TIMS data points from both samples plot within the field deter-mined by the ion probe analyses.

A1095 Kivisuo, A285 Kuittila, A284 Lehtovaara, Vaasjoki et al. 1993, Sorjonen-Ward & Claoué-Long 1993, Heilimo et al. 2011). These ages are based on both TIMS and SIMS U-Pb analyses and thus confirm the rapid crustal generation and uni-form sedimentary source. Consequently, the two younger dates obtained in A221 cannot represent crystallization ages of the source rocks, but are ei-ther due to metamorphic disturbance or contami-

nation during sample processing. In fact, analysis n2494-15 shows distinctly higher Th/U and total Th+U, making a case for metamorphic lead loss very plausible. In the available BSE images, these two grains are not distinct from the other zircons. The Sm-Nd model age TDM for this sample is 2.82 Ga (O’Brien et al. 1993), which is also consistent with a relatively juvenile provenance.

The ion-microprobe results from the Vehkavaara porphyry samples record, beyond any doubt, a complex history for these rocks. The oscillatory-zoned zircon domains surrounding distinct cores are considered to represent growth within felsic magma. Thus, the age of 2755 ± 8 Ma obtained from these outer domains should also record the emplacement of the Vehkavaara dykes. Although some grains are nearly devoid of such envelop-ing zircon, in several grains from sample A301, in particular, these domains make up a signifi-cant proportion of the zircon grain volumes (Fig.

39). One analysis (n760-08a) suggests a slightly younger age (Fig. 40), which is probable due to a post-magmatic open-system behaviour of this high-U zircon.

The analyses from the cores do not record any specific older event, as the ages range from 2.9 to 3.3 Ga (Fig. 40). It is conceivable that some of the scatter could be due to partial resetting of the U-Pb system, but it more likely originates from a heterogeneous protolith.

An origin predominantly from a much older (e.g. 3.3 Ga) crustal source is not supported by the Sm-Nd

Discussion on the Vehkavaara dykes

115


Fig. 37. Geological map of the Ilomantsi-Kovero area showing sample sites (red star – this study, other samples – Vaasjoki et al. 1993, Heilimo et al. 2011). Igneous ages with 2-sigma errors are given in Ma after the sample number. The map is based on the 1:1 000 000 geological map (Korsman et al. 1997), where the greenstone belt consists of three main rock types: mafic (and minor ultramafic) metavolcanic rocks (brown), intermediate-felsic metavolcanic rocks (yellow) and metasediments (blue). Granitoids surrounding the greenstone belts are divided into TTGs and intrusive rocks (stippled).

116


A221 Hattuvaara mica gneiss

3000

2800

2600

2400

0.34

0.38

0.42

0.46

0.50

0.54

0.58

0.62

8 10 12 14 16 18207Pb/235U

206Pb238U


A221 SIMS analyses ca. 2.75 Ga

31 analyses (of total 35)(reference line intercepts at

2750 and 250 Ma)

Fig. 38. Concordia diagram of zircon U-Pb SIMS analyses from the Hattuvaara greywacke A221 (error ellipses). The multi-grain TIMS analyses on A221 (solid diamonds) and another greywacke A543 (open diamonds) are shown for reference (Vaas-joki et al. 1993).

Fig. 39. Scanning electron microscope (SEM) backscatter electron (BSE) images of grain 4 from sample A301 (left) and grain 6 from sample A282 (right) showing analysis spots and 207Pb/206Pb ages with 1-sigma errors. Note the darker, fractured zone between the old cores and ca. 2.75 Ga oscillatory zoned outer domains.

117


Fig 40. U-Pb concordia plot of zircon data from the Vehkavaara porphyry dyke samples A282 and A301. The black squares denote TIMS data points by Vaasjoki et al. (1993).

118


Depleted Mantle (DePaolo)

CHUR A282#3 Vehkavaara dike

A301#3 Vehkavaara dike

A1095 Kivisuo dike

A285 Kuittilatonalite

A1094 Tasanvaara tonalite

A284#2 Lehtovaara granodiorite

A339 Silvevaara granodiorite

A1602 Siurua gneiss

-8

-6

-4

-2

0

2

4

2500 2700 2900 3100

Age (Ma)

Eps-

Nd

Fig. 41. Epsilon-Nd vs. age diagram of Vehkavaara porphyries and selected samples from the Ilomantsi area (data from Huh-ma et al. this volume, O’Brien et al. 1993). In addition to evolution lines, initial ratios are shown for Vehkavaara (diamonds) and Kivisuo porphyries (triangle). The evolution of chondritic uniform reservoir (CHUR, DePaolo & Wasserburg 1976), depleted mantle (DePaolo 1981) and the 3.5 Ga Siurua gneiss (Mutanen & Huhma 2003) are shown for reference.

data, which provide slightly negative εNd(2750) val-ues and TDM model ages slightly exceeding 3.0 Ga (Fig. 41). In any case, the Vehkavaara porphyry contains abundant inherited zircon, which sur-vived well through the melting process that formed the felsic magma, and typically acted as nuclei for new zircon growth at 2.75 Ga.

Accepting the age of ca. 2.75 Ga as the timing of emplacement of the dykes also removes strati-graphic difficulties, as this age is practically iden-tical to the intrusion ages of the granitoid domes deforming the Hattu schist belt. Moreover, this interpretation agrees with the titanite U-Pb data from the Vehkavaara samples A301 and A338 (Vaasjoki et al. 1993). The ages of the plutons intruding the belt include 2748 ± 8 Ma (A1094-Tasanvaara) and 2741 ± 9 Ma (A285-Kuittila), which are also indistinguishable from the age of volcanism dated at 2754 ± 6 Ma in the Hattu schist belt (A1038-Poikapää, Vaasjoki et al. 1993).

These conventional results are supported by the U-Pb zircon age of 2757 ± 4 Ma determined by SIMS (SHRIMP) for the Silvevaara granodiorite (A284, Sorjonen-Ward & Claoué-Long 1993). In addition to this magmatic population, the grano-diorite sample also contains few older grains up to 3.19 Ga in age. This heterogeneity was expected based on the scattered conventional data (Vaas-joki et al. 1993).

The conventional U-Pb zircon ages available for other felsic dykes dated from the Ilomantsi area are also close to 2.75 Ga (Vaasjoki et al. 1993). These include 2756 ± 6 Ma from the por-phyry (A1095-Kivisuo) near Kuittila on the east-ern side of the Silvevaara pluton and 2733 ± 10 Ma from a dyke (A223-Iknonvaara) on the south-ern margin of the Silvevaara pluton (Fig. 37). Al-though the data from A223 are slightly scattered, there is no evidence for major old inheritance in either of these dykes.

119


A1624 Hämäläniemi felsic volcanic rock

2900

2800

2700

2600

2500

A1624I CA-TIMS

A1624H

A1624G

A1624F

A1624E

A1624DA1624C

A1624B

A1624A

0.40

0.44

0.48

0.52

0.56

0.60

10 12 14 16207Pb/235U

206Pb238U

Intercepts at841 ± 120 & 2875 ± 9 Ma

MSWD = 8.6 n=9


A1624I CA-TIMSConcordant age = 2877 ± 2 Ma

The Sm-Nd data support the pattern observed from the U-Pb zircon studies (Fig. 41). The results from the Vehkavaara porphyries (initial epsilon of -1.5 and -1.9) are similar to that from the 2.75 Ga Silvevaara granodiorite (A284 and A339, O’Brien et al. 1993), which also contains some older (3.1–3.2 Ga) zircon crystals (Sorjonen-Ward & Claoué-Long 1993), suggesting a significant contribution from old crustal sources. In contrast, the Sm-Nd data from the Kivisuo dyke and Kuittila tonalite provide clearly positive initial epsilon values, sug-gesting a short crustal prehistory for the source material of these rocks.

U-Pb geochronology of the Kovero greenstone belt

From the Vehkavaara area discussed above, the Ilomantsi (Hattu) schist belt continues to the southwest and at a distance of ca. 30 km, joins a wider domain of volcanic rocks called the Kovero greenstone belt (Fig. 37). The Kovero greenstone belt has been subdivided into three stratigraphic sections: 1) Keskijärvi (western part), 2) Kuusi-järvi (middle part) and 3) Sonkaja (eastern part) (Tuukki 1991). The belt mostly consists of th-oleiitic volcanic rocks, komatiites, komatiitic ba-salts, felsic volcanic rocks and sedimentary rocks

(Tuukki 1991, Konnunaho 1999). The research carried out on the ore potential and related map-ping of the area has provided the framework and goals for the isotope studies (Konnunaho 1999). Eight samples were collected from representa-tive felsic and mafic lithologies, and four of these have yielded zircon for U-Pb analyses. Zircon from three previously studied samples was also included in this study and analysed using the CA-TIMS method.

A1624 Hämäläniemi felsic volcanic rock

The Hämäläniemi sample A1624 is a fine-grained, felsic volcanic rock. The rock seems to form a thin tuffaceous interlayer within the tholeiitic Kontio-kangas Formation of the Kuusijärvi section. Fel-sic volcanic interlayers and banded iron forma-tions within mafic units at the Kovero greenstone belt are quite common manifestations of the bi-modal volcanism in the area (Tuukki 1991, Kon-nunaho 1999).

Mineral separation yielded a fair number of zircon grains, which are small (<70 µm), fairly turbid, subhedral and slightly rounded due to resorption. The colour of the grains ranges from reddish to pale or colourless. The U-Pb zircon

Fig. 42. Concordia diagram of zircon U-Pb TIMS analyses from the Hämäläniemi felsic rock (A1624), which is considered as a tuffaceous interlayer within tholeiitic volcanic rocks of the Kovero greenstone belt.

120


data including one CA-TIMS analysis define a chord with intercepts on the concordia at 2875 ± 9 and 841 ± 120 Ma (MSWD = 8.6, Appendix 2, Fig. 42). Some scatter is evident, but no dis-tinction in the isotopic composition was observed between the analysed red and pale zircon grains. The analytical result obtained using chemical abrasion (A1624I) is concordant at 2877 ± 2 Ma and is considered the age of zircon and the host felsic rock as well.

A1627 Rasisuo felsic tuff

A 30-metre-thick zone of felsic pyroclastic rock occurs in the upper part of the Kuuspuro For-mation in the Kuusijärvi section of the Rasisuo area. The felsic rock occurs between mafic and ultramafic volcanics. Some primary textures are also visible on the outcrops of felsic tuffaceous rocks in the Rasisuo area. Sample A1627 from this exposure is very fine-grained and mainly con-sists of plagioclase, quartz and biotite and minor amounts of chlorite and amphibole.

A fair number of zircon grains were obtained from this sample. They consist of euhedral, short prismatic (l:w ~2) to more equant, brownish and translucent crystals. The population is homoge-neous, and the grain-size is predominantly fine

to medium (~100 μm). In BSE images, the grains commonly show weak oscillatory, magmatic zon-ing (Fig. 14I). A few grains have distinct core and mantle domains, and thin, obviously metamor-phic rims are common (Fig. 14I, zircon 13).

Both TIMS and SIMS analyses on zircon are available from the Rasisuo felsic tuff. A total of 18 zircon domains were analysed by SIMS from the sample (Appendix 1). Two of these have high common-lead content and are useless for age cal-culations. Two data points are marginally above concordia, but as a whole, the data are concord-ant and yield an age of 2875 ± 4 Ma (Fig. 43). There are no age differences between various zir-con domains.

Before access to the SIMS facility, TIMS U-Pb analyses yielded a chord with concordia inter-cepts at 2868 ± 22 and 1232 ± 250 Ma (Fig. 43). The data are, however, slightly scattered along the line (MSWD = 17), very likely due to metamor-phic effects, which are pronounced in Archaean terrains in Finland.

A CA-TIMS analysis carried out on the high density zircon fraction provides a concordant result at 2878 ± 2 Ma. As no heterogeneity was observed in the SIMS data and the Th/U ratio (deduced from the radiogenic 208Pb/206Pb ratio, Appendix 2) in chemically abraded zircon is the

A1627 Rasisuo felsic tuff

2900

2800

2700

2600

A1627E

A1627DA1627C

A1627B

A1627A

A1627F CA-TIMS

0.44

0.48

0.52

0.56

0.60

11 13 15 17207Pb/235U

206 Pb

/238 U

A1627 SIMS2875 ± 4 Ma n=16

CA-TIMS A1627FConcordant at 2878 ± 2 Ma

A1627 TIMS Intercepts at1232 ± 250 & 2868 ± 22 Ma

MSWD = 17, n=6

Fig. 43. Concordia diagram of zircon U-Pb SIMS (error ellipses) and TIMS (diamonds) analyses from the Rasisuo felsic tuff (A1627), Kovero greenstone belt.

121


same as in untreated material, the age of 2878 ± 2 Ma is considered to date the felsic volcanism of the Rasinsuo area.

A1625 Rasisuo plagioclase porphyry dyke

Dykes of andesitic to dacitic compositions are common in the Kovero greenstone belt. Sample A1625 was collected from a plagioclase porphyry dyke approximately 1 km south of the sampling site of the felsic tuff A1627 discussed above. The dyke crosscuts tholeiitic volcanic rocks of the Kuuspuro Formation in the Kuusijärvi section. The groundmass consists of fine-grained plagio-clase, quartz and biotite and minor amounts of titanite, ilmenite, chlorite, sericite, apatite and zircon. The phenocrysts are mainly oligoclase and also hornblende in some andesitic dykes (Tuukki 1991, Konnunaho 1999).

Sample A1625 yielded abundant subhedral zircon grains, which are translucent, brown and mostly larger than 75 µm (+200 mesh). Crystal edges are commonly sharp, and the population looks homogeneous. The five U-Pb TIMS analy-ses carried out on zircon define a chord, which has intercepts at 2757 ± 12 Ma and 921 ± 260 Ma (Ap-pendix 2, Fig. 44). Some scatter presumably due to metamorphic effects is evident (MSWD = 5),

but the nearly concordant CA-TIMS analysis #A1625F and the homogeneity of the zircon population strongly suggest that the upper inter-cept age can be considered a good estimate for the crystallization time of zircon and the dyke as well. In fact, the 207Pb/206Pb age of 2756 ± 2 Ma should provide the minimum age, constraining the lower error limit of the regression calculation.

A1626 Rasisuo gabbro

Sample A1626 represents the most evolved vari-ety of gabbroic amphibolites in the Rasisuo area. These amphibolites comprise a series of vari-able fractionated mafic to intermediate, coarse-grained gabbroic rocks. Sample (A1626) is a variety of intermediate, coarse-grained, plagio-clace- and quartz-rich rock. Tuukki (1991) sug-gested that the gabbroic rocks are stratigraphi-cally associated with the Kuuspuro Formation of the Kuusijärvi section. However, the stratigraphi-cal situation and genesis of the gabbroic amphi-bolites are still open.

Zircon separated from the Rasisuo gabbro A1626 consists of dark brown, transparent to translucent, coarse grained (<75 μm grain-size fraction largely comprises zircon fragments), mainly subhedral, long to more equant crystals.

A1625 Rasisuo porphyry dike

2640

2680

2720

2760

A1625A +4.3/>75 a16h long

A1625B +4.3/>75 long

A1625C +4.3/<75 a1h longA1625D +4.3/<75 long

A1625E +4.3/>75 a16h clear

A1625F +4.3/>75 CA

0.46

0.48

0.50

0.52

0.54

12.0 12.4 12.8 13.2 13.6 14.0 14.4207Pb/235U

206Pb238U

Intercepts at 921 ± 260 & 2757 ± 12 Ma

MSWD = 5.3 n=6


Fig. 44. Concordia diagram of zircon U-Pb TIMS analyses from the Rasisuo porphyry dyke (A1625), which crosscuts mafic volcanic rocks in the Kovero greenstone belt.

122


A1626 Rasisuo gabbro

2500

2600

2700

2800

2900

A1626B

A1626C

A1626D

A1626F

A1626A

0.44

0.48

0.52

0.56

0.60

10 12 14 16207Pb/235U

206 Pb

/238 U


A1626 SIMS average Pb/Pb age2756 ± 4 Ma, MSWD =2,n=16

Fig. 45. Concordia diagram of zircon U-Pb SIMS (error ellipses) and TIMS (diamonds) analyses from the Rasisuo gabbro (A1626), Kovero greenstone belt.

The fraction 4.0–4.2 g/cm3 also contains pale and smaller grains with varying, mostly subhedral to anhedral forms. Generally, the zircon population is rather homogeneous and typical for gabbroic rocks.

In BSE images (Fig. 14H), the zircon grains commonly show either weak, longitudinal com-positional zoning or homogeneous internal struc-tures. Few grains show separate core and rim structures, and some grains have suffered from a varying degree of alteration.

A total of 18 zircon domains were analysed by ion microprobe from the Rasisuo gabbro. Two of these analyses were rejected due to high com-mon-lead contents (Appendix 1). All other U-Pb data plot in a tight cluster and define a concor-dia age of 2756 ± 4 Ma (Fig. 45). The previous multi-grain TIMS U-Pb determinations on zircon produced discordant and heterogeneous data, but are roughly compatible with the age obtained by SIMS (Appendix 2, Fig. 45). It is clear from the BSE images that many zircon grains contain metamict domains, which are the major source for discordance in the TIMS analyses. As Archaean rocks, especially near the Proterozoic boundary, have undergone a complex metamorphic history, lead loss may have had taken place in several stag-es and with a variable intensity depending on the

zircon domains and fractions, resulting in hetero-geneous U-Pb data.

A1520 Kiukoinvaara felsic dyke

A granodioritic dyke crosscuts andalusite-bear-ing mica schist at Kiukoinvaara (Luukkonen et al. 2002). The dyke is deformed, and on the geo-logical map this location (A1520) is clearly west of the main Kovero volcanic belt discussed above.

Zircon separated from sample A1520 consists of euhedral, brown, short and resorbed grains.

Five previously performed TIMS analyses on zircon revealed a large amount of common lead and yielded discordant U-Pb data (Appendix 2) plotting along a chord with concordia intercepts at 2724 ± 6 and 423 ± 48 Ma (MSWD=1.6; not shown in Fig. 46). In contrast, the composition obtained by CA-TIMS analysis has very high 206Pb/204Pb (28500) and yields a nearly concordant date of 2750 ± 2 Ma, significantly older than the upper intercept obtained from the discordant data (Fig. 46). Six data points yield intercepts at 2748 ± 16 and 585 ± 150 Ma, and an obviously large MSWD of 16. It is clear that discordant analy-ses with high common lead should have a minor weight in determining the real age of magmatic zircon. The CA-TIMS analysis together with two

123


A1520 Kiukoinvaara felsic dike

2800

2700

2600

25002400

2300

A1520F +4.3/>75/ CA

A1520E 4.2-4.3/>75

A1520D 4.2-4.3/>75/abr 6 hA1520C +4.3/<75

A1520B +4.3/abr 2 h

A1520A +4.3/abr 6 h

0.32

0.36

0.40

0.44

0.48

0.52

0.56

8 10 12 14207Pb/235U

206Pb238U

Intercepts at585 ± 150 & 2748 ± 16 Ma

MSWD = 16, n=6


TIMS Intercepts at 804 ± 79 & 2754 ± 4 MaMSWD = 0.2, n=3 (A,B,F)

Fig. 46. Concordia diagram of zircon U-Pb TIMS analyses from the Kiukoinvaara felsic dyke (A1520), Kovero greenstone belt (analyses A1520A-E from Vaasjoki et al. 1993).

Fig. 47. Concordia diagram of zircon U-Pb TIMS analyses from the Linnansuo felsic dyke (A1155), Kovero belt (analyses A1155A-F from Vaasjoki et al. 1993).

A1155 Linnansuo felsic dike

2800

2700

2600

2500

2400

2300

A1155G +4.3 CA

A1155F 3.6-4.0

A1155E 4.2-4.3

A1155D +4.3 a2hA1155C +4.2

A1155B 4.0-4.2

A1155A +4.3

0.36

0.40

0.44

0.48

0.52

0.56

8 10 12 14 16207Pb/235U

206Pb238U

Intercepts at1177 ± 200 & 2767 ± 26 Ma

MSWD = 15 n=7


A1155G CA-TIMSConcordia Age = 2762 ± 2 Ma

A1155 TIMS Intercepts at 933 ± 280 & 2758 ± 17 Ma

MSWD = 7.0 n=5

124


Two Archaean age groups are evident in the Ko-vero greenstone belt: 1) the felsic volcanic rocks at 2878 ± 2 Ma and 2) felsic dykes and gabbroic rocks at 2.75–2.76 Ga. The relative abundance of rocks in each age group is, however, impossible to evaluate from the information available.

Sample A1624 (felsic volcanic rock) represents a thin interlayer within tholeiitic basalts, which would suggest that the associated mafic volcanic rocks are also ca. 2.88 Ga old.

Unfortunately, the samples north along the strike (A1622 Otravaara and A1623) were devoid of separable zircon and the extent of these old rocks, as well as the age of one of the main strati-graphic horizons with the Kovero belt (Otravaara formation), remains open.

If the age of the dated gabbro A1626 represents significant volumes of the mafic volcanics, then

the rocks of the Kovero greenstone belt would be predominantly 2.75–2.76 Ga in age, which is also the age of the volcanism recorded in the Ilomantsi schist belt. However, the correlation between the Kovero and the Ilomantsi belt is not obvious, since there are differences in their lithologies and geochemistry (O’Brien et al. 1993, Tuukki 1991, Hölttä et al. this volume).

The Ipatti belt ca. 75 km NNW of Kovero con-tains felsic volcanic rock, which has yielded an age of 2811 ± 4 Ma (Appendix 2, Pekkarinen et al. 2006), and therefore is not directly related to the Kovero belt. The age of 2.88 Ga is unique within the Archaean bedrock in Finland. In Russian Ka-relia, similar zircon ages have been measured from the Sumozero-Kenozero greenstone belt (2875 ± 2 Ma, Puchtel et al. 1999).

Discussion on the Kovero greenstone belt

other TIMS analyses on high density, air-abraded zircon fractions yield an upper intercept age of 2754 ± 4 Ma, which we consider to be the best es-timate for the crystallization age of the Kiukoin-vaara dyke.

A1155 Linnansuo felsic dyke

The Linnansuo plagioclase-phyric, tonalitic dyke crosscuts sedimentary rocks of the Kovero belt. On the aeromagnetic map, the location is at the southern edge of a magnetic high, which seems to follow the mafic rocks. Discordant and slightly het-erogeneous U-Pb data were reported by Vaasjoki

et al. (1993). The CA-TIMS analysis on high den-sity zircon gives a concordant result at 2762 ± 2 Ma (Appendix 2, Fig. 47). Including all analyses on high density zircon, an upper intercept age of 2758 ± 17 Ma can be calculated. The homogeneous nature of the zircon population in the high densi-ty fraction, consisting of euhedral, brown, fairly transparent and short grains, implies that the age obtained can be considered the magmatic age of the dyke. The slight scatter in the data is likely to be due to metamorphic effects. The dyke is de-formed and probably predates the major defor-mations in the area.

125


The Oijärvi greenstone belt is located in the cen-tral part of the Archaean Pudasjärvi area (Fig. 48). Due to limited outcrop, the area is relatively poorly known, and much of the current under-standing of the geology is based on aeromag-netic data. The few published age results avail-able from the Pudasjärvi area reveal that the oldest rocks in the Fennoscandian Shield, i.e. the 3.5 Ga Siurua gneisses, are found in this re-gion (Mutanen & Huhma 2003). However, the

greenstone belt (Fig. 48). Sample A1782 repre-sents a medium-grained, fairly homogeneous gabbro surrounded by mafic volcanic rocks and may be part of a subvolcanic sill. The main min-erals are amphibole and plagioclase.

Only a small amount of zircon was obtained from this sample with all grains found in the density fraction d > 4.2 gcm-3. They are mostly medium- to fine-grained (75–150 μm), weakly yellowish and transparent to translucent. The morphology varies from short subhedral to long prismatic (l:w >3). In BSE images (Fig. 17), al-most all zircon grains are pale and show a vary-ing degree of fluid corrosion (“holes”) with oc-casional phase separation (white, dense spots. Only a few grains show clear variation in internal composition (grain 05 in Fig. 14L). Some have pale, quite homogeneous or corroded core do-mains surrounded by thin dark BSE rims.

Only ten zircon domains were analysed by SIMS (Nordsim, Appendix 1). Most data are marginally above concordia, which is obviously related to the U/Pb calibration. In SIMS analy-ses, this calibration has no effect on the lead iso-tope ratios, and thus ages based on Pb isotopic composition on nearly concordant data are reli-able. Seven of the ten data points cluster around 2.8 Ga and the corresponding weighted average 207Pb/206Pb age is 2802 ± 5 Ma (Fig. 50). Analysis #09a from a dark BSE core of a tiny, presumably metamorphic grain yields an age of 2.70 Ga, #03a from a darker BSE domain has an age of 1.85 Ga, and the youngest grain (#10a) is dated at 0.86 Ga. The Th/U ratio for the 2.8 Ga zircon grains is high, which is common for zircon in mafic rocks. Although the data are relatively sparse, the age of 2802 ± 5 Ma is considered a reliable crystalliza-tion age for magmatic zircon and the Käärme-vaara gabbro.

OIJÄRVI GREENSTONE BELT AND PUDASJÄRVI AREA

geographical extent of these old gneisses seems to be quite limited. The N–S-trending Oijärvi greenstone belt consists of typical components of Archaean greenstone belts, including mafic, ultramafic, intermediate and minor felsic vol-canic rocks and sediments. No age determina-tions have previously been published from the greenstone belt. The belt is surrounded by grani-toids, which are also the subject of the isotope studies reported here.

U-Pb geochronology of the Oijärvi greenstone belt and adjacent areas

This paper presents U-Pb data on 13 samples from the Pudasjärvi area (Fig. 48). Most of these samples are granitoids collected from exploration drill-cores and only two samples are from the su-pracrustal rocks of the greenstone belt. Results on two paragneisses outside the Oijärvi belt are given in a separate chapter below, and Sm-Nd analyses for most samples are given in Huhma et al. (this volume).

A1783 Puljunlehto dacite

The Puljunlehto sample A1783 was collected from a small outcrop in the northern part of the belt (Fig. 48), where felsic rocks occur among mafic volcanic rocks. The sampled dacitic rock is pale and fine-grained. Mineral separation yielded only a small number of zircon grains, which were all (appr. 50) mounted in epoxy for ion micro-probe measurements. The population is slightly heterogeneous in terms of size and morphology. Some grains are prismatic (l:w ~2.5), but more rounded forms also occur. In BSE images, both magmatic, oscillatory-zoned (grains 04, 05) and homogeneous crystals without a distinct internal structure (grain 07) are available (Fig. 14M).

Ten zircon domains were analysed by ion mi-croprobe (Nordsim) from sample A1783 (Appen-dix 1). The U-Pb data are mostly concordant, low in U and plot in a cluster on a concordia diagram (Fig. 49). Using all data, an average 207Pb/206Pb age of 2820 ± 11 Ma can be calculated. The slight scatter may result from metamorphic effects, al-though the age differences are quite marginal.

A1782 Käärmevaara gabbro

The sampled outcrop of the Käärmevaara gab-bro is located at the northern edge of the Oijärvi

126


Fig. 48. Geological map of the Pudasjärvi area showing sampling sites (red star – this study, other samples – Mutanen & Huhma 2003, Lauri et al. 2011, Perttunen & Vaasjoki 2001).Igneous ages with 2-sigma errors are given in Ma after sample number. The map is based on the 1:1 000 000 geological map (Korsman et al. 1997), where the main units are the Oijärvi greenstone belt (brownish) and granitoid areas.

127


2860

2820

2780

2740

0.51

0.53

0.55

0.57

13.4 13.8 14.2 14.6 15.0 15.4 15.8 16.2207Pb/235U

206 Pb

/238 U

A1783 Puljunlehto daciteAverage 207Pb/206Pb age

2820 ± 11 Ma, n=10


29202880

28402800

27602720

26802640

0.48

0.50

0.52

0.54

0.56

0.58

0.60

0.62

12 13 14 15 16 17207Pb/235U

206 Pb

/238 U


A1782 Käärmevaara gabbroAverage 207Pb/206Pb age

2802 ± 5 Ma, n=7

Fig. 49. Concordia diagram showing zircon SIMS U-Pb isotopic data from A1783 Puljunlehto dacite, Oijärvi greenstone belt.

Fig. 50. Concordia diagram showing zircon SIMS U-Pb isotopic data from the Käärmevaara gabbro (A1782), Oijärvi green-stone belt.

128


A1533 Surmakumpu porphyry dyke

The Surmakumpu-type porphyries occur as crosscutting or conformable dykes within the mafic and ultramafic volcanic rocks in central part of the Oijärvi greenstone belt (Fig. 48). Sam-ple A1533 (TPT-96-80), which was collected from a 20-m-thick dyke, is a reddish and sheared rock containing phenocrysts of quartz and altered pla-gioclase. The matrix minerals include quartz, pla-gioclase, K-feldspar, carbonate, sericite, biotite, opaque and zircon.

Mineral separation yielded abundant zircon, which consists of euhedral prisms with well-devel-oped pyramids and typically sharp crystal edges. Zircon is generally dark reddish, and many crys-tals, especially in the low-density fraction, have distinct, turbid inner domains. The isotopic data reveal a very wide range in Pb/U ratios consist-ent with microscopic observations on the pres-ence of metamict domains (Appendix 2, Fig. 51). The common-lead content is high in the domains, producing discordant data. In contrast, the CA-TIMS analysis #A1533F shows very low common lead and provides a nearly concordant result with a 207Pb/206Pb age of 2690 ± 2 Ma.

Recently, a few analyses were carried out us-ing LA-MC-ICPMS. The data on fresh zircon are concordant and yield an age of 2670 ± 9 Ma, but turbid cores are strongly discordant (e.g. #8a, Appendix 3, Fig. 51). Both methods give roughly consistent results, although the age obtained by CA-TIMS is slightly older than the age obtained by ICPMS. As the ICPMS session was stable and analyses were carried out using the in-house Ar-chaean standard, we consider the age of 2670 ± 9 Ma the best estimate for the crystallization time of magmatic zircon and the dyke. It is conceivable that some older inherited zircon was included in the CA-TIMS analysis.

A1553 Pitkäkumpu tonalite

Sample A1553 collected from a drill core (3521/97/R590/33.60–56.10) is from a reddish, medium-grained and homogeneous tonalite in-trusion crosscutting volcanic rocks in the central part of the Oijärvi belt (Fig. 48). The main min-erals are fairly coarse, euhedral plagioclase and more fine-grained quartz and biotite. The acces-sory minerals include apatite, zircon and pyrite, and sericite, carbonate and chlorite as alteration

A1533 Surmakumpu porphyry dike

2600

2200

1800

1400

1000

600

0.0

0.2

0.4

0.6

0 4 8 12 16207Pb/235U

206Pb238U


A1533 LA-MC-ICPMSConcordia Age = 2670 ± 9 Ma, n=7


MSWD = 82, n=6

Fig. 51. Concordia diagram of zircon U-Pb TIMS (diamonds) and LA-MC-ICPMS (error ellipses) analyses from the Surma- kumpu porphyry dyke (A1533), which crosscuts volcanic rocks of the Oijärvi greenstone belt.

129


products of plagioclase and biotite. Inclusions of volcanic rocks are observed near the margin of the intrusion.

Zircon obtained from the Pitkäkumpu to-nalite consists of euhedral, long prisms, which are mostly pale and fairly clear. The six U-Pb TIMS analyses on zircon show a range of Pb/U ratios and are scattered along a chord, which gives in-tercepts with the concordia at 2728 ± 14 and 48 ± 92 Ma (MSWD = 42, Appendix 2 and Fig. 52). The CA-TIMS analysis #A1553F has a very low common-lead content and gives a nearly concord-ant result with a 207Pb/206Pb age of 2735 ± 2 Ma. Although there are no detailed images of zircon or spot analyses at hand, the morphology of the zircon grains suggests that this result is close to the age of zircon and magmatic crystallization of the Pitkäkumpu tonalite.

A1490 Tuore Ristisuonpalo granodiorite

Sample A1490 represents granodioritic gneiss close to the western margin of the Oijärvi green-stone belt (Fig. 48). The sample was collected from an exploration drill core (M52/3521/96/R511, depth 65.50-75.20). Based on drill-core observations, the rock is strongly deformed and seems to cross cut a mica schist of the Oijärvi

belt. The main minerals of the sample are al-tered plagioclase, K-feldspar, quartz and biotite. The accessory minerals include titanite, apatite, opaque and zircon. Mineral separation yielded a relatively small number of zircon grains, which are euhedral and prismatic but in transmitted light are fairly turbid.

The four conventional U-Pb TIMS analyses provide discordant results and define a chord with an upper intercept at 2699 ± 22 Ma (Appendix 2, Fig. 53). However, the analysis #A1490E us-ing chemical abrasion is closer to concordia and yields a 207Pb/206Pb age of 2801 ± 2 Ma, which is the minimum age for the material analysed. The data as a whole are thus scattered, which is due to zircon inheritance and/or multistage meta-morphic effects resulting in variable discordia patterns. As the Th/U ratio (calculated from ra-diogenic 208Pb/206Pb) in the CA-treated zircon fraction #A1490E and the other heavy (>4.2 g/cm3) zircon fractions are similar, it is likely that the CA-TIMS analysis registers the composition of the same magmatic domains. Using these two analyses, an upper intercept age of 2815 ± 5 Ma can be calculated. Without further studies, the precise age of this sample remains unclear but may well be close to 2.8 Ga.

A1553 Pitkäkumpu tonalite

2700

2500

2300

2100

A1553F +4.0 >75 CA***

A1553E +4.0 <75 a20h

A1553D +4.0 <75

A1553C +4.0 <75 a4h

A1553B +4.0 >75

A1553A +4.0 >75 a18h

0.25

0.35

0.45

0.55

6 8 10 12 14207Pb/235U

206 Pb

/238 U

Intercepts at 248 ± 92 & 2728 ± 14 Ma

MSWD = 42 n=6

CA-TIMS A1553F nearly concordant

Pb/Pb age 2735 ± 2 Ma

Fig. 52. Concordia diagram of zircon analyses from the Pit-käkumpu tonalite (A1553), which crosscuts volcanic rocks in the Oijärvi greenstone belt.

A1490 Tuore Ristisuonpalo granodiorite

2100

2300

2500

2700

A1490A +4.2

A1490B +4.2 a6h

A1490C 4.0-4.2

A1490D 4.0-4.2 a6h

A1490E +4.2 CA

0.26

0.30

0.34

0.38

0.42

0.46

0.50

0.54

0.58

6 8 10 12 14 16207Pb/235U

206 Pb

/238 U

A1490E&A: Intercepts at988 ± 25 & 2815 ± 5 Ma

Fig. 53. Concordia diagram of zircon analyses from the Tuo-re Ristisuonpalo granodiorite (A1490) occurring close to the western margin of the Oijärvi greenstone belt.

130


A1534 Keväpalo tonalite

Sample A1534 (TPT-96-61) from Keväpalo rep-resents tonalites occurring on the eastern side of the Oijärvi greenstone belt (Fig. 48). The rock is medium grained and light-coloured and mostly consists of altered plagioclase, quartz and biotite. Titanite, apatite, opaque and zircon are the main accessory minerals. Zircon forms euhedral, long magmatic crystals, which are pale in colour and typically fairly transparent.

The U-Pb data on zircon, including one CA-TIMS analysis define a chord and intercepts at 2781 ± 6 and 330 ± 100 Ma (MSWD = 3; Appen-dix 2, Fig. 54). The upper intercept age is younger than the age of 2830 ± 20 Ma interpreted from laser MC-ICPMS analyses carried out in Oslo (Lauri et al. 2011). The U-Pb analysis on sphene gives an age of 2717 ± 3 Ma, which probably reg-isters the timing of a metamorphic event.

A1739 Veskanmaa granodiorite

The Veskanmaa granodiorite represents felsic plutonic rocks occurring west of the Oijärvi greenstone belt (Fig. 48). Sample A1739 col-lected from a drill core (3521/00/R677/ 170.70–

192.90) is fine-grained, only slightly deformed and has plagioclase, quartz and K-feldspar as the main minerals. Plagioclase is partly altered to epidote, sericite and carbonate. Other minor minerals are biotite, apatite, titanite and opaque. Only a small number of zircon grains was ob-tained from this sample. They are mostly clear, euhedral and slightly rounded on edges due to resorption.

The U-Pb data are discordant and do not yield a coherent chord on the concordia diagram (Appendix 2, Fig. 55). The CA-TIMS analysis #A1739E is also somewhat discordant, but the Pb/Pb age of 2.76 Ga can be taken as a mini-mum age for the analysed material. As the Th/U ratios (based on radiogenic 208Pb/206Pb) are the same in all analysed fractions, it is likely that the CA-TIMS analysis registers the composition of the primary magmatic domains. The scatter of the data is due to zircon inheritance and/or mul-tiple metamorphic effects, which are pronounced in many Archaean rocks in Finland. In this sample, these effects are also shown by the U-Pb analysis on titanite, which gives a Pb/Pb age of 2.63 Ga. Without further studies, the exact age of this rock remains unclear, but may well be close to 2.77 Ga.

A1534 Keväpalo tonalite

25002540

25802620

26602700

27402780

A1534A +4.2/>75/abr18h

A1534B +4.2/>75

A1534C +4.2/<75/abr20h

A1534D +4.2/<75

A1534E +4.2/>75/ CA

A1534 titanite

0.41

0.43

0.45

0.47

0.49

0.51

0.53

0.55

10.5 11.5 12.5 13.5 14.5207Pb/235U

206 Pb

/238 U

TIMS Intercepts at330 ± 100 & 2781± 6 Ma

MSWD = 3, n=5

A1534 titanite 2717 ± 3 Ma

A1739 Veskanmaa granodiorite

25002540

25802620

26602700

27402780

A1739A

A1739B

A1739CA1739D titanite

A1739E +4.2 CA

0.42

0.44

0.46

0.48

0.50

0.52

0.54

10.5 11.5 12.5 13.5 14.5207Pb/235U

206 Pb

/238 U

A1739D titanitePb/Pb age

2628 ± 2 Ma


Intercepts at 84 ± 84 & 2687 ± 4 Ma

MSWD = 0.70 n=3 (A,B,C)

A1739E&BIntercepts at

945 ± 55 & 2772 ± 5 Ma

Fig. 54. Concordia diagram of zircon and titanite analy-ses from the Keväpalo tonalite (A1534), east of the Oijärvi greenstone belt.

Fig. 55. Concordia diagram of zircon and titanite analyses from the Veskanmaa granodiorite (A1739) occurring on the western side of the Oijärvi greenstone belt.

131


A1731 Palomaa granite

The Palomaa sample A1731 was collected from a drill core (3514/01/R410/41.55–51.50) recov-ered ca. 12 km west of the 3.5 Ga Siurua gneisses (Fig. 48). The main minerals are plagioclase, K-feldspar and quartz, and the accessory minerals include biotite, titanite and opaque phases. Al-though the rock is now chemically and miner-alogically granite, it is possible that it has been granitized and was originally a tonalite.

Zircon in sample A1731 consists of euhedral, brownish and fairly long, translucent prisms. Five U-Pb TIMS analyses are slightly scattered along a chord, which has an upper intercept at 2702 ± 16 Ma (MSWD = 8.9; Appendix 2, Fig. 56). The scatter is likely to be due to complex metamorphic effects, which have taken place in several stages during Archaean and Proterozoic times or even later. Compared to the CA-TIMS data #A1731E, the three most discordant fractions have a fairly high amount of common lead and should be weighted less in determining the zircon age. Re-jecting them, the remaining two analyses indicate an upper intercept age of 2708 ± 6 Ma.

A1740 Palomaa monzonite

The Palomaa monzonite sample A1740 was col-lected from a drill core (3514/01/R406/ 146.00–151.10) approximately 600 m west of the site of the previous sample. The rock is medium-grained and homogeneous with plagioclase and K-feld-spar as the main minerals. The accessory miner-als include biotite, brown amphibole, orthopy-

roxene, clinopyroxene, quartz, apatite, zircon and opaque phases. Pyroxenes are partly altered to light-coloured amphibole. The Palomaa monzo-nite shows up on the aeromagnetic maps as a pro-nounced positive anomaly.

Mineral separation yielded abundant zircon grains, which are mainly euhedral, brown and fair-ly transparent. Crystal surfaces are shiny probably due to resorption. Most grains are larger than 75 µm. In spite of the relatively high content of U in zircon, the TIMS U-Pb data are only mildly dis-cordant (Appendix 2, Fig. 57). The effects of air abrasion are negligible, consistent with the mor-phology of zircon. All seven data points includ-ing the concordant CA-TIMS analysis #A1740G define a chord with concordia intercepts at 2682 ± 15 Ma and 970 ± 380 Ma (MSWD = 5.7). Analysis A1740G gives a concordant result at 2672 ± 2 Ma, but has a clearly lower Th/U ratio (deduced from radiogenic 208Pb/206Pb) than in the other data. It is thus feasible that, compared to the other data, the latter contained a larger meta-morphic zircon component distinct from the main magmatic population.

A1741 Pahkakoski granodiorite

Sample A1741 was collected from a drill core (3512/02/R339/ 20.20-27.70), which was drilled in Pahkakoski on the southern margin of the Pudas-järvi area close to the Proterozoic Kiiminki schist belt (Fig. 48). On the geological map, the rock unit is named as Tannila granodiorite. The rock is massive, medium-grained granodiorite, which has altered plagioclase, quartz and K-feldspar as the

A1731 Palomaa granite

27402700

26602620

25802540

25002460

2420

A1731E CA-TIMS

A1731D

A1731C

A1731B

A1731A

0.40

0.42

0.44

0.46

0.48

0.50

0.52

0.54

9.5 10.5 11.5 12.5 13.5207Pb/235U

206 Pb

/238 U

Intercepts at 643 ± 190 & 2702 ± 16 Ma

MSWD = 8.9 n=5


A1731E&A Intercepts at 839 ± 120 & 2708 ± 6 Ma

Fig. 56. Concordia diagram of zircon analyses from the Palomaa granite (A1731).

A1740 Palomaa monzonite

25702590

26102630

26502670

2690

A1740A +4.0 >75 a16h

A1740B +4.0 >75 a5h

A1740C +4.0 <75 a5h

A1740D +4.0 <75 a16h

A1740E +4.0 >75

A1740F +4.0 <75 a17h

A1740G +4.0>75 CA

0.47

0.48

0.49

0.50

0.51

0.52

11.4 11.8 12.2 12.6 13.0207Pb/235U

206 Pb

/238 U

Intercepts at970 ± 380 & 2682 ± 15 Ma

MSWD = 5.7 n=7 (all data)


>75µm zirconIntercepts at

832±120 & 2674 ± 4 MaMSWD = 1.2 n=4

<75µm zircon & A1740G

Intercepts at285±180 & 2672 ± 3 Ma

MSWD = 1.4 n=4

A1740G Concordia Age2672 ±2 Ma

Fig. 57. Concordia diagram of zircon analyses from the Palomaa monzonite (A1740).

132


main minerals. Among the accessory minerals are biotite, epidote, apatite and opaque.

Sample A1741 yielded only a small number of zircon grains, which are mostly reddish and tur-bid. The conventional U-Pb data reveal that the common-lead content is very high, and the results are strongly discordant. In contrast, the CA-TIMS analysis #A1741E shows only a small amount of common lead and provides Pb/U ratios reasonably close to the concordia curve (Appendix 2, Fig. 58). All data define a chord with concordia intercepts at 2758 ± 13 and 140 ± 35 Ma. The data do not fit perfectly with the regression line (MSWD =18), which may partly be due to an underestimate of analytical errors for the low 206Pb/204Pb analyses. Nevertheless, due to the CA-TIMS analysis, the date of 2758 ± 13 Ma may be considered a rea-sonable estimate for the crystallization age of the Pahkakoski (Tannila) granodiorite.

A1742 Viitakangas granite

The Viitakangas granite is also located on the southern margin of the Pudasjärvi area ca. 20 km west of the Pahkakoski locality discussed above (Fig. 48). Sample A1742 was collected from an outcrop (SIR-02-1.1) and has K-feldspar, plagio-clase and quartz as the main minerals. The rock is fairly coarse-grained, grey and sheared, and pla-gioclase is partly altered.

Zircon grains obtained from sample A1742 are short, grey and turbid prisms. Only two U-Pb TIMS analyses were carried out on this sample, resulting in very discordant data with high con-centrations of uranium and common lead (Ap-pendix 2, Fig. 58). Consequently, no age estimate can be made from these data.

A1741 Pahkakoski granodiorite& A1742 Viitakangas granite

2600

2200

1800

1400

1000

A1741E +4.2 CA

A1741D +4.2 a17h

A1741C 4.0-4.2

A1741B +4.2

A1741A +4.2 a5h

A1742B

A1742A

0.05

0.15

0.25

0.35

0.45

0.55

0.65

1 3 5 7 9 11 13 15 17207Pb/235U

206 Pb

/238 U


MSWD = 18 n=5(low 206Pb/204Pb in A-D)

Fig. 58. Concordia diagram of zircon analyses from the Pahkakoski granodiorite (A1741) and Viitakangas granite (A1742).

SIMS U-Pb analyses on two samples, A1782 and A1783, suggest that the age of the Oijärvi greenstone belt is ca. 2.82–2.80 Ga. Provided that the gabbroic rock A1782 represents a primary, undisturbed composition, an origin from time-integrated depleted mantle with clearly positive initial εNd (+2.7) is indicated for the mafic litholo-gies (Huhma et al. this volume).

Many of the granitoids and dykes in close as-sociation with the greenstone belt provide dis-cordant and heterogeneous U-Pb zircon data. The age estimates for these samples presented above are largely based on concordant or nearly concordant isotopic compositions obtained by CA-TIMS analysis, but some of these may still represent mixtures of various age components.

Discussion on the age of the Oijärvi greenstone belt and adjacent areas

Nevertheless, most of these estimates suggest that the surrounding granitoids are younger than the greenstone belt, which is consistent with the crosscutting relationship whenever the contact is observed. The Sm-Nd model ages (TDM) for these felsic rocks range from 2.7 to 3.0 Ga and suggest that many lithologies are relatively juvenile and thus do not represent much older reworked crust, in contrast to the 3.5 Ga Siurua gneisses east of the greenstone belt (Fig. 48, Huhma et al. this volume). The Sm-Nd model ages from the Siurua gneisses are mostly ca. 3.5–3.7 Ga, and distinctly old crustal signatures are also evident from Lu-Hf results on zircon from these rocks (Lauri et al. 2011).

133


In addition to metasediments within the green-stone belts discussed above, ion microprobe dat-ings have been performed on four samples taken from sedimentary rocks in Archaean paragneiss belts. In their previous study on the Archaean Nurmes paragneisses in eastern Finland, Kontin-en et al. (2007) concluded that the deposition of the protolith wackes took place close to 2.7 Ga. Their trace element and U–Pb data suggest that the source terrains mainly comprised 2.75–2.70 Ga TTG gneisses and sanukitoid-type plutons and mafic volcanic rocks. Most zircon grains in the few studied metasediment samples from the Central Puolanka Group of the Kainuu belt (Fig. 1) are also ca. 2.73 Ga (Huhma et al. 2000).

A1814 Pitkäpalo mica gneiss in the Pudasjärvi area

Sample A1814 (56-PSH-04) represents a slightly migmatized sedimentary rock occurring ca. 15 km west-northwest of the Oijärvi greenstone belt (Fig. 48). The zircon grains obtained from this sample are mostly euhedral with slightly rounded edges, typical for zircon in many paragneisses.

SIMS U-Pb analyses were carried out on 26 zir-con grains, but many analyses provided discord-ant age results (Appendix 1). However, most data

SIMS AGES ON ZIRCON IN PARAGNEISSES

A1814 Pitkäpalo mica gneiss

3200

2800

2400

2000

0.2

0.3

0.4

0.5

0.6

0.7

4 8 12 16 20 24207Pb/235U

206 Pb

/238 U


A1814 SIMSca. 2.74 Ga

20 analyses (of total 26)Reference line intercepts

203 & 2737 Ma

Fig. 59. Concordia diagram of zircon SIMS analyses from the Pitkäpalo (Ranua) mica gneiss A1814.

plot on a chord which intercepts the concordia at ca. 2.74 Ga and 0.2 Ga (Fig. 59). The rest of the analyses suggest older ages up to 3.17 Ga. The re-sults imply that the deposition of this sediment took place after 2.73–2.74 Ga. The relatively young average provenance is consistent with the Sm-Nd TDM model age of 2.81 Ga (Huhma et al. this volume).

A1842 Jäkälämaa mica gneiss in the Pudasjärvi area

Sample A1842 (PSH$-2004-79) was collected 7 km NE of the 3.5 Ga Siurua gneiss (Fig. 48). The rock is medium-grained, grey, mica-rich banded gneiss containing ca. 5–10% granitic leucosome. Zircon grains obtained from this sample are mostly light grey and rounded, showing internal oscillatory zoning. In addition to zircon, separa-tion yielded abundant garnet and monazite.

SIMS U-Pb analyses were carried out on 32 zircon grains from inner, mostly oscillatory-zoned domains (Appendix 1). One-third of the data provide discordant ages and as a whole, the ages range from ca. 2.7 up to ca. 3 Ga (Fig. 60). Considering only concordant data, most ages are between 2.70 and 2.76 Ga. The key ques-tion also here is whether these ages represent real

134


magmatic ages from the source rocks or whether there are any metamorphic effects that might produce younger ages. Some constraint for the timing of metamorphism in the case of sample A1842 is provided by the U-Pb TIMS analysis on monazite, which is concordant at 2632 ± 2 Ma (Appendix 2, Fig. 60). In terms of the mor-phology and Th/U ratio, the youngest zircons do not notably differ from the other grains. For ex-ample, zircon n2497-29 is a large (200 µm), oscil-latory zoned grain, and the analysis carried out on the core yielded a date of 2701 ± 10 Ma. Al-though there are no obvious reasons to interpret the several dates between 2.70 and 2.73 Ga as representing metamorphic events, one may still speculate whether the zircon grains have been partly affected by metamorphism, since the rock is migmatitic.

In any case, the results obtained from sample A1842 are similar to those reported by Kontinen et al. (2007) for Archaean paragneisses in eastern Finland. It is also evident that no 3.5 Ga zircons were found in the sample, even though the sam-pling site is located only 6.7 km from the 3.5 Ga Siurua gneisses (Mutanen & Huhma 2003). This indicates that either the Siurua gneiss was not exposed at the time of sedimentation or that the paragneiss and the Siurua gneiss were later jux-taposed by tectonic movements. The relatively

young average provenance of the mica gneiss is consistent with the Sm-Nd TDM model age of 2.74 Ga (Huhma et al. this volume).

A1840 Riihivaara mica gneiss

Sample A1840 (PIM$-2003-497-N7) represents migmatitic mica gneisses located ca. 40 km WSW of the Suomussalmi greenstone belt and ca. 20 km east of the Palaeoproterozoic Kainuu schist belt. The rock is a medium-grained, pale to dark grey and banded gneiss containing 10–15% gra-nitic leucosome. Zircon grains are moderately rounded, fairly dark and oscillatory-zoned.

SIMS U-Pb analyses were carried out on 32 zircon grains from inner, mostly oscillatory-zoned domains (Appendix 1). Due to a high content of common lead, three analyses were rejected. Most data are concordant and give dates from 2.72 up to 2.97 Ga (Fig. 61). Provided that these register the ages of igneous protoliths, several analyses suggest that the deposition took place after 2.72-2.73 Ga. This is consistent with the results ob-tained from a tonalitic vein crosscutting the mica gneiss, which has yielded a U-Pb zircon age of 2702 ± 14 Ma (Mikkola et al. 2011a). The Sm-Nd TDM model age for this sample is 2.87 Ga (Huhma et al. this volume).

A1842 Jäkälämaa mica gneiss

3000

2900

2800

2700

2600

2500

2400

A1842B Zircon TIMS

A1842A monazite

0.38

0.42

0.46

0.50

0.54

0.58

0.62

9 11 13 15 17 19207Pb/235U

206 Pb

/238 U


A1842Zircon 2.7- 3 Ga

Monazite 2632 ± 2 Ma

Fig. 60. Concordia diagram showing U-Pb analyses from the Jäkälämaa mica gneiss A1842 from Pudasjärvi. Error ellipses – SIMS analyses, diamonds – multi-grain TIMS analyses on zircon and monazite.

135


A1243 Susi-Kervinen mica gneiss in the Iisalmi complex

Sample A1243 is a migmatitic mica gneiss from Rautavaara, belonging to the Iisalmi complex (Fig. 1). The rocks in the Susi-Kervinen area

comprise mica gneisses, amphibolites and strong-ly altered lithologies including garnet-cordierite-rocks and migmatites (Paavola 1999). Zircon grains in sample A1243 are grey, turbid, rounded and shiny on surfaces.

SIMS U-Pb analyses were carried out on 30 zir-

A1840 Riihivaara mica gneiss

3000

2800

2600

2400

0.3

0.4

0.5

0.6

8 10 12 14 16 18 20207Pb/235U

206 Pb

/238 U


A1840 zircon2.72 - 2.97 Ga

Fig. 61. Concordia diagram showing U-Pb zircon analyses from the Riihivaara mica gneiss (A1840) from Suomussalmi. Error ellipses – SIMS analyses, diamond – multi-grain TIMS analysis.

A1243 Susi-Kervinen mica gneiss

2800

27002600

25002400

23002200

0.30

0.34

0.38

0.42

0.46

0.50

0.54

0.58

7 9 11 13 15

207Pb/235U

206 Pb

/238 U


A1243 Zirconfew grains ca. 2.74 Ga,

many analyses high U/Thmetamorphic ca. 2.63 Ga

Fig. 62. Concordia diagram showing U-Pb zircon analyses from the Susi-Kervinen mica gneiss (A1243) from Rautavaara, Iisalmi complex. Error ellipses – SIMS analyses, diamonds – multi-grain TIMS analyses.

136


Fig. 63. Concordia diagram showing U-Pb zircon analyses from the Ansosuo diorite A1926. Error ellipses – LA-MC-ICPMS analyses, diamonds – multi-grain TIMS analyses.

con grains (Appendix 1). The data reveal that the U content in most analyses is high and the com-positions tend to be discordant (Fig. 62). Most analyses suggest ages of ca. 2.6–2.7 Ga with a cluster around 2.63–2.64 Ga, which is the age of the granulite facies metamorphism in the Iisalmi complex (Hölttä et al. 2000, Mänttäri & Hölttä 2002). A few analyses with a moderate U content are concordant at ca. 2.74 Ga and are thought to represent the ages of the source rocks. The young-est zircon grains in sample A1243 are evidently metamorphic, which is also indicated by their high U concentrations and low Th/U ratios compared with the other, older zircon grains (Appendix 1).

A1926 Ansosuo diorite (Loso)

Important age constraints for the deposition of Archaean paragneisses are provided by crosscut-ting granitoids. One of these rocks is the Loso quartz diorite of sanukitoid affinity, for which an age of 2719 ± 19 Ma was reported by Kontinen et al. (2007). The relatively large error was due to slight heterogeneity in the SIMS (SHRIMP) U-Pb data on zircon (sample A331). In order to improve this result, a new sample was taken from the most mafic variety of the Loso intrusion. Sample A1926 from Ansosuo is a homogeneous gneissic diorite with the main minerals being pla-

gioclase, hornblende and biotite. Other minerals include quartz, titanite, apatite and zircon. Pla-gioclase and biotite are relatively fresh, indicating only mild Proterozoic effects. Abundant zircon grains obtained from this sample are mostly eu-hedral, 100–200-µm-long crystals showing inter-nal oscillatory zoning.

Both TIMS and LA-MC-ICPM analyses were carried out on zircon. The two conventional TIMS analyses yield discordant results and have an unusually high amount of common lead (Ap-pendix 2). However, after chemical abrasion the amount of common lead became negligible and the result concordant at 2715 ± 2 Ma (Fig. 63). All data obtained by laser MC-ICPMS are con-sistent with this age and give an average Pb/Pb age of 2712 ± 6 Ma (Appendix 3, Fig. 63).

We have also carried out additional U-Pb analyses on zircon from the original Loso quartz diorite sample A331 (Fig. 64). Again, the CA-TIMS analysis gives concordant results, but the age of 2703 ± 3 Ma is younger than that obtained from sample A1926. In contrast to A1926, it also appears that the LA-MC-ICPMS data from sam-ple A331 are heterogeneous. Most analyses yield dates close to 2.7 Ga, but one is older at ca. 2.8 Ga and a few analyses are clearly younger than 2.7 Ga. It seems likely that metamorphic effects have disturbed the U-Pb system in zircon, which

137


also explains the slightly younger CA-TIMS re-sult. It should be noted that 90% of zircon was lost in the CA pretreatment, and the analysis may well represent zircon, which contains a significant proportion of the annealed material. The hetero-geneity obtained is consistent with previous re-sults by Kontinen et al. (2007), and it remains im-

possible to precisely determine the age of sample A331.

It can be concluded that the emplacement age of the Loso sanukoid intrusion is 2715 ± 2 Ma, the age of sample A1926. This gives the minimum age for the deposition of the sedimentary rocks within the Nurmes paragneisses.

Fig. 64. Concordia diagram showing U-Pb zircon analyses from the Loso quartz diorite A331. Error ellipses – LA-MC-ICPMS analyses, diamonds – multi-grain TIMS analyses from Kontinen et al. (2007), except A331I.

Discussion on Archaean paragneisses

The results of this study are similar to those of Kontinen et al. (2007) and Huhma et al. (2000). The majority of zircon grains in most samples have an age of ca. 2.73–2.75 Ga, which sug-gests that Neoarchaean granitoid intrusions of this age probably produced most of the detritus of the sediments (Fig. 65). The relatively young provenance is also supported by the Sm-Nd re-sults obtained on whole-rock samples (Kontinen et al. 2007, Huhma et al. this volume) and average U-Pb TIMS analyses from some other localities (Vaasjoki et al. 1993, 1999, 2001).

The U-Pb results also provide important con-straints on the age of deposition. However, as was discussed above, there are serious problems in reliably determining the age of the youngest detrital zircon population due to common post-depositional metamorphic reworking of these mostly migmatite-grade rocks. Figure 65 shows

zircon dates from 13 sedimentary samples col-lected both from greenstone and paragneiss belts. Sample A1243 from the Iisalmi complex is dis-tinct, since it contains many 2.6–2.7 Ga zircon grains clustering around 2.63–2.64 Ga, which is the age of the granulite facies metamorphism in that area (Hölttä et al. 2000, Mänttäri & Hölt-tä 2002). The youngest zircon grains in sample A1243 are evidently metamorphic, which is also indicated by their high U contents and low Th/U ratios compared to the other zircon grains (Table 1). As was discussed above, the 2.7 Ga zircons in the Arola quartzite (A1753) are all considered de-trital and thus constrain the time of deposition to be younger than that of other sediments in the Kuhmo greenstone belt.

In all mica gneisses analysed from the Kuhmo, Tipasjärvi and Ilomantsi greenstone belts, the youngest grains seem to be close to 2.74 Ga in age.

138


2500

2700

2900

3100

3300

3500

207 Pb

/206 Pb

age

Ages of 243 concordant U-Pb zirconanalyses on 13 samples

Mean = 2753 Ma


A1243 A1840 A1842 A1814 1-KUH 1-NUR A1081 A221 A1774 A1746 83-PGN A1748 A1753

Fig. 65. U-Pb ages of concordant SIMS or LA-MC-ICPMS (83-PGN) analyses on zircon grains in seven Archaean parag-neisses (left) and six metasedimentary rocks from the Kuhmo, Tipasjärvi and Ilomantsi greenstone belts. Data for each sample are organized according to nominal age, increasing from left to right. Data on paragneisses 1-KUH, 1-NUR and A1081 are from Kontinen et al. (2007).

In contrast, most samples in the paragneiss belts contain a small population of slightly younger zir-con grains in the range 2.72–2.73 Ga, which we be-lieve constrains the time of deposition. This is sup-ported by the new U-Pb zircon age of 2715 ± 2 Ma obtained from the Loso sanukitoid (sample A1926 Ansosuo), which crosscuts the paragneisses.

The minimum age of 2715 ± 2 Ma for the depo-sition of paragneisses requires that the few dates of ca. 2.70 Ga obtained from mica gneisses in this

terrain (Kontinen et al. 2007) do not solely repre-sent detrital zircon grains but rather post-depo-sitional metamorphic effects. It is also likely that the deposition of greywackes in the paragneiss belts took place slightly later than the deposition of greywackes in the greenstone belts. There also seems to be a slight difference in the average prov-enance, although the effects of metamorphism may have had some contribution to the age distri-bution obtained (Fig. 66).

CONCLUSIONS

This paper reports U-Pb analyses on 60 samples from the Archaean schist belts and associated granitoids in Finland. The data were obtained using TIMS, SIMS and LA-MC-ICPMS tech-niques. When samples were characterised by a single age population, consistent results were obtained using all the different methods applied during this study. For LA-MC-ICPMS analyses, we have utilized the Archaean in-house standard A1772, which has yielded relatively concordant multi-grain TIMS Pb/U results and an age of 2711 ± 3 Ma. The analyses by ion probe (Nord-

sim) show that in terms of age, the zircon stand-ard is homogeneous and gives an age 2712 ± 1 Ma.

The U-Pb ages for igneous supracrustal and closely related rocks dated so far from the Ar-chaean schist belts in central Finland are summa-rized in Table 1 and Figure 67.

In Figures 68A–D, the ages of volcanic rocks are compared with ages from surrounding grani-toids in each belt, and a summary of the Sm-Nd results from the Tipasjärvi-Kuhmo-Suomussalmi greenstone complex is given in Figure 69.

139


Concordant ages on zircon in micaceous metasediments in Kuhmo-Tipasjärvi & Ilomantsi greenstone belts (n=96/ 5 samples)

and paragneisses (n=116/ 6 samples)

2600 2700 2800 2900 3000 3100 3200 3300 3400

Pb/Pb age

Rel

ativ

e pr

obab

ility

A1243 (strongly metamorphic) and A1753 (Arola quartzite) not includedFig. 66. Distribution of concordant zircon U-Pb ages in Archaean mica gneisses from paragneiss belts (blue) and greenstone

belts (red). The data are the same as in Fig. 70, except that samples A1243 (abundant metamorphic zircon) and A1753 (quartz-ite) are excluded. Age population distributions of the two groups are similar but differ in detail.

A16

27 K

over

oA

1624

Kov

ero

A17

49 K

oli

A16

25 K

over

oA

1626

Kov

ero

Kiv

isuo

Ilom

ants

iVe

hkav

aara

Ilom

ants

iPo

ikap

ää Il

oman

tsi

A19

22 T

ipas

järv

iA

1921

Tip

asjä

rvi

A11

74 T

ipas

järv

iA

1886

Tip

asjä

rviPitk

äper

ä K

uhm

oPi

tkäp

erä

Kuh

mo

Het

teilä

Kuh

mo

Moi

siov

aara

Kuh

mo

Ruo

kojä

rvi K

uhm

oPo

lvila

mpi

Kuh

mo

Kat

erm

a K

uhm

oLa

mpe

la K

uhm

oK

ello

järv

i Kuh

mo

Huu

hilo

nkyl

ä K

uhm

oSi

ivik

ko K

uhm

oN

iitty

laht

i Kuh

mo

Saar

ikyl

ä Su

omus

salm

iSa

arik

ylä

Suom

ussa

lmi

Torm

ua S

uom

ussa

lmi

Kilp

asuo

Suo

mus

salm

iM

esa-

Aho

Suo

mus

salm

i

A17

83 O

ijärv

i dac

iteA

1782

Oijä

rvi g

abbr

o

2700

2750

2800

2850

2900

2950

3000

Age

(Ma)

U-Pb zircon ages of Archean volcanic rocksfrom Oijärvi, Suomussalmi, Kuhmo-Tipasjärvi

and Ilomantsi-Kovero greenstone belts


Fig. 67. U-Pb zircon ages of Archaean volcanic rocks in Finland.

140

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H

ölttä, Heikki Juopperi, Jukka K

onnunaho et al.

Table 1. Summary of U-Pb ages of Archaean schist belts with remarks on stratigraphy.

Tipasjärvi Kuhmo Suomussalmi Ilomantsi-Kovero (& Ipatti) Oijärvi

Sample Age Rock type Sample Age Rock type Sample Age Rock type Sample Age Rock type Sample Age Rock type (Ma) stratigraphy (Ma) stratigraphy (Ma) stratigraphy (Ma) stratigraphy (Ma)

A1753 <2700 quartzite (Arola)

A1553 2728±14 tonalite, crosscut volc. rocks

A221 ca. 2750 mica gneiss Hattuvaara A1814 <2740 mica gneiss

A1038 2754±6 andesite Poikapää

A1748 <2750 mica gneiss, Kokkoniemi Fm

83-PGN <2750 mica gneiss, Ronkaperä Fm

A1520 2754±4 dyke cutting mica gneiss, Kovero

A1746 <2750 mica gneiss, Ronkaperä Fm

A1625 2757±12 dyke cutting mica gneiss, Kovero

A1774 <2750 mica gneiss, Ronkaperä Fm

A1626 2756±4 gabbro, Kovero

A1418 2788±4 gabbro intruding Kellojärvi cplx/Siivikko Fm

A1771 2798±8 gabbro intruding Kellojärvi cplx/Siivikko Fm

A2027 2795±3 porphyry dyke intruding komatiites of Siivikko Fm

A1886 2796±8 felsic tuff, Koivumäki Fm?

A1377 2795±7 felsic fragment (dike?) in Kellojärvi cplx

A1174 2798±2 rhyolite, Koivumäki Fm

A1346 2798±4 andesite, Mäkisensuo Fm

A1560 2798±2 porphyry, Mäkisensuo Fm, intr. Kellojärvi cplx?

A1921 2810±10 rhyolite, Koivumäki Fm?

A511 2799±5 rhyolite, Mäkisensuo Fm

A788 2799±5 rhyolite, Mäkisensuo Fm A1782 2802±5 gabbro

2798 ±2 <komatiites < 2823 ±6A1749 2811±4 Ipatti belt felsic

volcanic rockA1000 2818±11 rhyolite, Ruokojärvi Fm A1701 2815±4 volc, Kiannanniemi A1490 2815±20 granodiorite,

crosscut volc. rocks

A1428 2817±4 porphyry, Mesa-aho A1783 2820±11 dacite

A1922 2828±3 dacite A976 2823±6 gabbro, Moisiovaara, Pahakangas Fm

A1429 2822±7 andesite, Tormua

A1773 2836±6 dacite?, Vuosanka belt

A1213 2842±5 andesite, Pitkäperä belt

A1254 2847±8 andesite, Pitkäperä belt

A1821 2866±4 gabbro, Tormua

A1624 2877±2 felsic volc. rock, Kovero

A1627 2878±2 felsic volc. rock, Kovero

A1467 2940±12 felsic volc. rock

A1593 2942±3 felsic porphyry

A1191 <2950 sediment, Luoma

141


A185

6

Saar

ikyl

ä A

1593

Saar

ikyl

ä A

1467

Torm

ua A

1821

A007

9

A190

6

Kilp

asuo

A14

29

A185

7

A190

1

Mes

a-ah

o A

1428

Kia

nnan

niem

i A17

01x

A190

4

A190

8

A191

5

A191

2

A004

4

A190

2

A002

8

A191

0

A190

7

A185

8

A190

3

A190

5

2600

2700

2800

2900

3000

Age

(Ma)

SuomussalmiU-Pb ages


A04

04Pi

tkäp

erä

A12

54Pi

tkäp

erä

A12

13Vu

osan

ka A

1773

A10

86A

1922

Moi

siov

aara

A09

76R

uoko

järv

i A10

00A

1089

A19

21A

0788

A05

11A

1174

A13

46A

1771

A15

60A

1886

A20

27A

1377

A14

18A

1705

A01

85A

1183

A17

02A

1085

A04

02A

0572

A11

46A

0331

A03

37A

1926

A17

07A

0027

A11

47A

1704

A17

03A

1719

A17

06A

0329

A04

03

2600

2700

2800

2900

3000

Age

(Ma)

Kuhmo-TipasjärviU-Pb ages

Volcanic rocks:red - Kuhmo belt

green - Tipasjärvi belt


Fig. 68A. U-Pb ages on six volcanic rocks from the Suomussalmi greenstone belt (blue bold labels) compared with the ages of surrounding granitoids. Data from this study, Mikkola et al. (2011a, b), Käpyaho et al. (2007) and Heilimo et al. (2011).

Fig. 68B. U-Pb ages on 16 volcanic rocks from the Kuhmo (red labels) and Tipasjärvi (green labels) greenstone belts compared with the ages of surrounding granitoids. Data from this study, Hyppönen (1983), Käpyaho et al. (2006, 2007), Luukkonen (1985, 2001), Vaasjoki et al. (1999) and Heilimo et al. (2011).

142


Kov

ero

A16

27K

over

o A

1624

Kol

i A17

49

Kov

ero

dyke

A11

55K

over

o dy

ke A

1625

Kov

ero

gabb

ro A

1626

Kiv

isuo

por

phyr

y A

1095

Vehk

avaa

ra d

yke

A03

01K

over

o dy

ke A

1520

Poik

apää

and

esite

A10

38A0

284

A109

4A0

338

A028

5A1

078

A095

0A0

299

A022

3A0

140

A095

1A0

050

A133

9A1

336

A177

2A1

340

A009

12600

2700

2800

2900

3000

Age

(Ma)

Ilomantsi - KoveroU-Pb ages


Fig. 68C. U-Pb ages on nine volcanic or dyke rocks from the Ilomantsi-Kovero greenstone belt (bold coloured labels) com-pared with the ages of surrounding granitoids. Data from this study, Vaasjoki et al. (1993), Sorjonen-Ward and Claoué-Long (1993) and Halla (2002). The age of 2811 ± 4 Ma for the volcanic rock A1749 from the Ipatti belt is also shown (Pekkarinen et al. 2006; the age is updated utilizing the CA-TIMS analysis given in Appendix 2).

Fig. 68D. U-Pb ages on two volcanic rocks from the Oijärvi greenstone belt (green labels) compared with the ages of surround-ing granitoids. Data from this study, Perttunen and Vaasjoki (2001), Mutanen and Huhma (2003) and Lauri et al. (2011). The age of Siurua gneisses is ca. 3500 Ma (Mutanen & Huhma 2003).

A005

2

A009

4

A153

3

A181

0

A174

0 A173

1

A161

1 A155

3 A174

1 A173

9

Oijär

vi ga

bbro

A17

82

A149

0

A153

4

Oijär

vi da

cite A

1783

A160

3

2600

2700

2800

2900

3000

Age

(Ma)

Pudasjärvi U-Pb ages

data-point error symbols are 2s

Siur

ua

143


Fig. 69. Epsilon-Nd vs. age diagram showing evolution lines for mostly felsic samples from the Tipasjärvi-Kuhmo-Suomus-salmi greenstone complex (data from Huhma et al. this volume). Initial values using filled symbols are shown for samples for which the age is based on U-Pb zircon dating. Suomussalmi: blue squares and dotted blue evolution lines. Kuhmo-Tipasjärvi: red dots and solid red evolution lines. Komatiites and komatiitic basalts from the Pahakangas-Siivikkovaara area in Kuhmo: red x at 2810 Ma, basalts from other sites in Kuhmo belt: red +. Depleted mantle evolution is according to DePaolo (1981).

Kuhmo-Tipasjärvi & Suomussalmi greenstone belt

Depleted Mantle

CHUR

A1428

A1429

A1821 gabbro

A1000

A976 gabbro

A1213

A1593

-8

-6

-4

-2

0

2

4

2700 2800 2900 3000

Age (Ma)

Nd-

eps

ilon

"old crust, >>3 Ga"

The results obtained call for the revision of some traditional views on these belts and allow the fol-lowing conclusions to be made:

1. Mafic rocks of the Kuhmo belt represented by the Moisiovaara gabbro are 2823 ± 6 Ma old, which according to the stratigraphic scheme (e.g. Papunen et al. 2009) should give the upper age limit for komatiites.

2. Felsic rocks in the Kellojärvi area, the central part of the Kuhmo belt, formed 2798 ± 2 Ma ago and provide the minimum age for the local mafic-ultramafic magmatism, including komatiites.

3. The igneous ages obtained for the four volcanic rocks from the Tipasjärvi belt range from 2828 ± 3 Ma to 2796 ± 8 Ma and thus resemble the ge-ochronological data from the Kuhmo belt. The revised age of 2798 ± 2 Ma determined for the host rock of the Taivaljärvi Ag-Zn ore deposit is exactly the same as the age obtained for the felsic rocks in the Kellojärvi area.

4. Felsic rocks in the Kuhmo and Tipasjärvi belts represent new crustal materials ultimately derived from depleted mantle-type sources with εNd(2.8 Ga) about +2. The bulk of the surrounding granitoids postdate the volcanism, and the isotope results as a whole suggest that the contribution of older crustal material is negligible and do not support the concept of formation of the Kuhmo belt in a rift basin on an ancient sialic basement.

5. Volcanic rocks with ages of ca. 2.84 Ga, oc-curring in the Vuosanka (Hetteilä) and Pitkäperä areas on the eastern side of the main Kuhmo belt, represent an event of volcanic activity preceding the major magmatic phase in the Kuhmo belt.

6. A major re-appraisal concerns the age of the Ruokojärvi Formation east of the main Kuhmo belt, which has previously been regarded to be as old as ca. 3 Ga (Papunen et al. 2009). The new U-Pb data on two felsic volcanic rocks suggest that the magmatic age is ca. 2.82 Ga, but abun-dant xenocrystic zircon suggests the involvement of ca. 3.1 Ga crust in the genesis of these rocks.

144


7. Both the Kuhmo and Tipasjärvi greenstone belts contain sedimentary rocks that were depos-ited after 2.75 Ga and thus at least 50 Ma after the recorded volcanism. Still younger sediments have been found in the Arola area, the Kuhmo belt, where a deformed quartzite contains detrital zircon grains as young as 2.7 Ga.

8. The Suomussalmi belt contains at least three age groups of volcanic rocks erupted at 2.94, 2.87 and 2.82 Ga, but the relative proportions of these units remain unclear. Compared to the Kuhmo and Tipasjärvi belts, the Sm-Nd crustal residence ages in the Suomussalmi belt are significantly older, mostly exceeding 3 Ga.

9. The supracrustal rocks in the Ilomantsi belt and many surrounding/intruding granitoids formed within a short period of time at ca. 2.75 Ga ago, but signs of older crustal contribution are evi-dent in the form of xenocrystic zircon up to 3.3 Ga in age. In the Kovero belt SW of Ilomantsi, two age groups are evident at 2.75 and 2.88 Ga,

but the relative proportions of these units remain unclear. Involvement of older crustal material is consistent with models suggesting a continental arc setting for the Ilomantsi belt (O’Brien et al. 1993).

10. The age of the supracrustal rocks exposed in the Oijärvi belt in the Pudasjärvi area is ca. 2.80–2.82 Ga. No contribution from such old sources as the nearby 3.5 Ga Siurua gneisses was found in igneous rocks within or surrounding the belt.

11. The sediments in the paragneiss belts were de-posited ca. 2.72 Ga ago, which in the case of the Nurmes belt, according to Kontinen et al. (2007), took place in a back arc or intra-arc setting.

Altogether, the isotope results suggest that the greenstone belts store a long-lived (>200 Ma), fragmentary record of geological evolution. The interpretation and modelling of the tectonic framework of this evolution remains a major challenge.

ACKNOWLEDGEMENTS

The Nordic geological ion-microprobe facil-ity (Nordsim) is operated and funded under an agreement between the respective research fund-ing agencies of Denmark, Norway and Sweden, the Geological Survey of Finland, and the Swed-ish Museum of Natural History. This paper is NORDSIM contribution No. 313. The staff of the NORDSIM laboratory, and the separation laboratory at GTK are acknowledged for skilled technical assistance. We thank the staff of CIR,

VSEGEI, St. Petersburg for SHRIMP analyses of three samples, and are deeply grateful to Tom Andersen for providing his excellent program to handle the ICPMS data. Discussions and com-ments by Perttu Mikkola and review comments by Hugh O’Brien are greatly acknowledged. We want to express our gratitude to Olavi Kouvo for initiating the isotope research in Finland and the Geological Survey of Finland for providing fa-cilities and support for these studies.

REFERENCES

Andersen T., Griffin W. L., Jackson S. E., Knudsen T.-L. & Pearson N. J. 2004. Mid-Proterozoic magmatic arc evolu-tion at the southwest margin of the Baltic Shield. Lithos 73, 289–318.

Belousova E. A., Griffin W. L. & O’Reilly S. Y. 2006. Zir-con crystal morphology, trace element signatures and Hf isotope composition as a tool for petrogenetic modeling: examples from Eastern Australian granitoids. J Petrol 47, 329–353.

DePaolo, D. J. 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Protero-zoic. Nature 291, 684−687.

DePaolo, D. J. & Wassenburg, G. J. 1976. Nd isotopic vari-

ations and petrogenetic models. Geophys. Res. Lett. 3, 249−252.

Engel, W. & Dietz, G.-J. 1989. A modified stratigraphic and tectonomagmatic model for the Suomussalmi greenstone belt, eastern Finland, based on the remapping of the Ala-Luoma area. Bulletin of the Geological Society of Fin-land 61, 143−160.

Gruau, G., Tourpin, S., Fourcade, S. & Blais, S. 1992. Loss of isotopic(Nd, O) and chemical (REE) memory during metamorphism of komatiites: new evidence from eastern Finland. Contributions to Mineralogy and Petrology 112, 66–82.

Halla, J. 2002. Origin and Paleoproterozoic reactivation of

145


Neoarchean high-K granitoid rocks in eastern Finland. Annales Academiae Scientiarum Fennicae. Geologica - Geographica 163. Helsinki: Suomalainen Tiedeakatemia. 103 p.

Hanski, E. J. 1980. Komatiitic and tholeiitic metavolcanic rocks of the Kellojärvi group in the Siivikkovaara area of the Archaean Kuhmo greenstone belt, eastern Finland. Bulletin of the Geological Society of Finland 52, 67–100.

Hanski, E., Walker, R.J., Huhma, H. & Suominen I. 2001. The Os and Nd isotopic systematics of c. 2.44 Ga Akan-vaara and Koitelainen mafic layered intrusions in north-ern Finland. Precambrian Research 109, 73–102.

Hanski, E., Huhma, H. & Vuollo, J. 2010. SIMS zircon ages and Nd isotope systematics of the 2.2 Ga mafic intru-sions in northern and eastern Finland. Bulletin of the Geological Society of Finland 82, 31−62.

Heilimo, E., Halla, J. & Huhma, H. 2011. Single-grain zircon U-Pb age constraints of the western and eastern sanuki-toid zones in the Finnish part of the Karelian Province. Lithos 121, 87−99.

Hölttä, P., Huhma, H., Mänttäri, I. & Paavola J. 2000. P-T-t development of Archaean granulites in Varpaisjärvi, Central Finland II. Dating of high-grade metamorphism with the U-Pb and Sm-Nd methods. Lithos 50, 121−136.

Hölttä, P., Heilimo, E., Huhma, H., Kontinen, A., Mertanen, S., Mikkola, P., Paavola, J., Peltonen, P., Semprich, J., Slabunov, A. & Sorjonen-Ward, P. 2012. The Archean of the Karelia Province in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Horstwood, M. S. A., Foster, G. L., Parrish, R. R., Noble, S. R. & Nowell, G. M. 2003. Common-Pb corrected in situ U–Pb accessory mineral geochronology by LA-MC-ICP-MS. Journal of Analytical Atomic Spectrometry 18, 837–846.

Huhma, H., Kontinen, A. & Laajoki, K. 2000. Age of the metavolcanic-sedimentary units of the Central Puolanka Group, Kainuu schist belt, Finland. In: 24. Nordiske Geologiske Vintermøte, Trondheim 6.−9. januar 2000. Geonytt (1), 87−88.

Huhma, H., Kontinen, A., Mikkola, P., Halkoaho, T., Hokka-nen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Luukko-nen, E., Mutanen, T. Peltonen, P., Pietikäinen, K. & Pulk-kinen, A. 2012. Nd isotopic evidence for Archean crustal growth in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.


Jackson S. E., Pearson N. J., Griffin W. L. & Belousova E. A. 2004. The application of laser ablation-inductively cou-pled plasma-mass spectrometry to in-situ U–Pb zircon geochronology. Chemical Geology 211, 47–69.

Jahn, B.-M., Vidal, P. & Kröner, A. 1984. Multi-chronometric ages and origin of Archaean tonalitic gneisses in Finnish Lapland: a case for long crustal residence time. Contribu-tions to Mineralogy and Petrology 86, 398−408.

Käpyaho, A., Mänttäri, I. & Huhma, H. 2006. Growth of Archaean crust in the Kuhmo district, eastern Finland: U-Pb and Sm-Nd isotope constraints on plutonic rocks. Precambrian Research 146, 95−119.

Käpyaho, A. Hölttä, P. & Whitehouse, M. J. 2007. U-Pb zir-

con geochronology of selected Archaean migmatites in eastern Finland. Bulletin of the Geological Society of Finland 79 (1), 95−115.

Konnunaho, J. 1999. Kuusijärven jakson komatiitit ja niiden malmipotentiaali Koveron arkeeisella vihreäkivivyöhyk-keellä. M.Sc. thesis, University of Oulu, Department of Geology, 73 p. (in Finnish)

Kontinen, A., Käpyaho, A., Huhma, H., Karhu, J., Matukov, D., Larionov, A. & Sergeev, S. 2007. Nurmes paragneisses in eastern Finland, Karelian craton: Provenance, tectonic setting and implications for Neoarchaean craton correla-tion Precambrian Research 152, 119–148.

Kopperoinen, T. & Tuokko, I. 1988. The Ala-Luoma and Taivaljärvi Zn-Pb-Ag-Au deposits, eastern Finland. In: Marttila, E. (ed.) Archaean geology of the Fennoscan-dian Shield. Geological Survey of Finland, Special Paper 4, 131−144.

Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman, H. & Pekkala, Y. (eds.)1997. Suomen kallioperäkartta – Berggundskarta över Finland – Bedrock map of Finland 1:000 000. Es-poo: Geological Survey of Finland.

Kouvo, O. 1958. Radioactive age of some Finnish Precam-brian minerals. Bulletin de la Commission Géologique de Finlande 182.

Kouvo, O. & Tilton, G. 1966. Mineral ages from the Finnish Precambrian. Journal of Geology 74, 421−442.

Krogh, T. E. 1973. A low-contamination method for hydro-thermal decomposition of U and Pb for isotopic age de-terminations. Geochim. Cosmochim. Acta 37, 485−494.

Krogh, T. E. 1982. Improved accuracy of U–Pb zircon ages by the creation of more concordant systems using an air abrasion technique. Geochim. Cosmochim. Acta 46, 637–649.

Larionov, A. N., Andreichev, V. A. & Gee, D. G. 2004. The Vendian alkaline igneous suite of northern Timan: ion microprobe U–Pb zircon ages of gabbros and syenite. In: Gee, D. G. & Pease, V. L. (eds.) The Neoproterozoic Timanide Orogen of Eastern Baltica, vol. 30. Geol. Soc., London Mem, 69–74.

Lauri, L. S., Rämo, O. T., Huhma, H., Mänttäri, I. & Rä-sänen, J. 2006. Petrogenesis of silicic magmatism related to the ~ 2.44 Ga rifting of Archean crust in Koillismaa, eastern Finland. Lithos 86, 137−166.

Lauri, L. S., Andersen, T., Hölttä, P., Huhma, H. & Graham, S. 2011. Evolution of the Archaean Karelian province in the Fennoscandian Shield in the light of U–Pb zircon ages and Sm–Nd and Lu–Hf isotope systematics. Jour-nal of the Geological Society 168, 201–218.

Ludwig, K. R. 1991. PbDat 1.21 for MS-dos: A computer program for IBM-PC Compatibles for processing raw Pb-U-Th isotope data. Version 1.07. U.S. Geological Sur-vey. Open File Report, 88−542. 35 p.

Ludwig, K. R. 2003. User’s manual for Isoplot/Ex, Version 3.00. A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication No.4.

Luukkonen, E. 1985. Structural and U-Pb isotopic study of late Archaean migmatitic gneisses of the Presvecokare-lides, Lylyvaara, eastern Finland. Transactions of the Royal Society at Edinburgh, Earth Sciences 76, 401−410.

Luukkonen, E. 1988. Moisiovaaran ja Ala-Vuokin kartta-alueiden kallioperä. Summary: Pre-Quaternary Rocks of the Moisiovaara and Ala-Vuokki Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps of Pre-Quaternary Rocks, Sheets 4421 and

146


4423+4441. Geological Survey of Finland. 90 p.Luukkonen, E. J. 1992. Late Archaean and early Proterozoic

structural evolution Kuhmo–Suomussalmi terrain, east-ern Finland. Ann. Univ. Turkuensis, Ser. A. Biol. Geogr. Geol. 78.

Luukkonen, E. J. 2001. Lentiiran kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Lentiira Map-Sheet area. Geological Map of Finland 1:100 000,Expla-nation to the Maps of Pre-Quaternary Rocks, Sheet 4414 + 4432. Geological Survey of Finland. 51 p., 1 app.

Luukkonen, E., Halkoaho, T., Hartikainen, A., Heino, T., Nis-kanen, M., Pietikäinen, K. & Tenhola, M. 2002. Itä-suo-men arkeeiset alueet–hankkeen (12201 ja 210 5000) toi-minta vuosina 1992–2001 Suomussalmen, Hyrynsalmen, Kuhmon, Nurmeksen, Rautavaaran, Valtimon, Lieksan, Ilomantsin, Kiihtelysvaaran, Enon, Kontiolahden, Toh-majärven ja Tuupovaaran alueella. Geological Survey of Finland, archive report M19/4513/2002/1. (in Finnish)

Mänttäri, I. & Hölttä, P. 2002. U-Pb dating of zircons and monazites from Archean granulites in Varpaisjärvi, Cen-tral Finland: - Evidence for multiple metamorphism and Neoarchean terrane accretion. Precambrian Research 118(1−2), 101−131.

Martin, H. & Querré, G. 1984. A 2.5 Ga reworked sialic crust: Rb-Sr ages and isotopic geochemistry of late Archaean volcanic and plutonic rocks from E. Finland. Contribu-tions to Mineralogy and Petrology 85, 292−299.

Mattinson, J. M. 2005. Zircon U-Pb chemical abrasion (“CA-TIMS”) method: Combined annealing and multi-step partial dissolution analysis for improved precision and accuracy of zircon ages. Chemical Geology 220, 47−66.

Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011a. Archean crustal evolution of the Suomussalmi district as part of the Kianta Complex, Karelia: Con-straints from geochemistry and isotopes of granitoids. Lithos 125, 287−307.

Mikkola, P., Salminen, P., Torppa, A. & Huhma H. 2011b. The 2.74 Ga Likamännikkö complex in Suomussalmi, East Finland: Lost between sanukitoids and truly alka-line rocks? Lithos 125, 716−728.

Miller, R. G., O’Nions, R. K., Hamilton, P. J. & Welin, E. 1986. Crustal residence ages of clastic sediments, orogeny and continental evolution. Chemical Geology 57, 87−99.

Mutanen, T. & Huhma, H. 2003. The 3.5 Ga Siurua trond-hjemite gneiss in the Archaean Pudasjärvi Granulite Belt, northern Finland. Bull. Geol. Soc. Finland 75, 51−68.

O’Brien, H., Huhma, H. & Sorjonen-Ward, P. 1993. Petro-genesis of the late Archean Hattu schist belt, Ilomantsi, eastern Finland : geochemistry and Sr, Nd isotopic com-position. In: Nurmi, P. & Sorjonen-Ward, P. (eds.) Geo-logical development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 147−184.

Paavola, J. 1999. Rautavaaran kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Rautavaara Map-Sheet area. Geological Map of Finland 1:100 000, Explanation to the Map of Pre-Quaternary Rocks, Sheet 3343. Geological Survey of Finland. 53 p.

Papunen, H., Halkoaho, T., Tulenheimo, T. & Liimatainen, J. 1998. Excursion to the Kuhmo greenstone belt. In: Hans-ki, E. & Vuollo, J. (eds.) International Ophiolite Symposi-um and Field Excursion: Generation and Emplacement of Ophiolites Through Time, August 10 15, 1998, University of Oulu, Oulu, Finland. Abstracts and Excursion Guide. Geological Survey of Finland, Special Paper 26, 91–106.

Papunen, H., Halkoaho, T. & Luukkonen, E. 2009. Archaean evolution of the Tipasjärvi-Kuhmo-Suomussalmi Green-stone Complex, Finland. Geological Survey of Finland, Bulletin 403. 68 p.

Patchett, J., Kouvo, O., Hedge, C. & Tatsumoto, M. 1981. Evolution of continental crust and mantle heterogeneity: evidence from Hf isotopes. Contributions to Mineralogy and Petrology 78, 279−297.

Patchett, J. & Kouvo, O. 1986. Origin of continental crust of 1.9-1.7 Ga age: Nd isotopes and U-Pb zircon ages in the Svecokarelian terrain of south Finland. Contributions to Mineralogy and Petrology 92, 1−12.

Pekkarinen, L., Kohonen, J., Vuollo, J. & Äikäs, O. 2006. Ko-lin kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Koli Map-Sheet area. Geological Map of Finland 1:100 000, Explanation to the Map of Pre-Qua-ternary Rocks, Sheet 4313. Geological Survey of Fin-land. 116 p. + 3 app. maps.

Peltonen, P., Mänttäri, I., Huhma, H. & Whitehouse, M. J. 2006. Multi-stage origin of the lower crust of the Kare-lian craton from 3.5 to 1.7 Ga based on isotopic ages of kimberlite-derived mafic granulite xenoliths. Precambri-an Research 147, 107−123.

Perttunen, V. & Vaasjoki, M. 2001. U-Pb geochronology of the Peräpohja Schist Belt, northwestern Finland. In: Vaasjoki, M. (ed.) Radiometric age determinations from Finnish Lapland and their bearing on the timing of Pre-cambrian volcano-sedimentary sequences. Geological Survey of Finland, Special Paper 33, 45−84.

Piirainen, T. 1988. The geology of the Archaean greenstone - granitoid terrain in Kuhmo, eastern Finland. In: Mar-ttila, E. (ed.) Archean geology of the Fennoscandian Shield. Geological Survey Finland, Special Paper 4, 39−51.

Puchtel, I. S., Hofmann, A. W., Amelin, Yu, V., Garbe-Schon-berg, C. D., Samsonov, A. V. & Shchipansky, A. A. 1999. Combined mantle plume-island arc model for the forma-tion of the 2.9 Ga Sumozero-Kenozero greenstone belt, SE Baltic Shield: isotope and trace element constraints. Geochimica et Cosmochimica Acta 63(21), 3579−3595.

Rosa D. R. N., Finch A. A., Andersen T. & Inverno C. M. C. 2009. U-Pb geochronology and Hf isotope ratios of mag-matic zircons from the Iberian pyrite belt. Miner. Petrol. 95, 47−69.

Schoene B., Crowley J. L., Condon D. J., Schmitz M. D. & Bowring, S. A. 2006. Reassessing the uranium decay con-stants for geochronology using ID-TIMS U–Pb data. Geochimica et Cosmochimica Acta 70, 426–445.

Sorjonen-Ward, P. 1993. An overview of structural evolution and lithic units within and intruding the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. & Sorjonen-Ward, P. (eds.) Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 9−102.

Sorjonen-Ward, P. & Claoué-Long, J. 1993. Preliminary note on ion probe results for zircons from the Silvevaara granodiorite, Ilomantsi, eastern Finland. In: Autio, S. (ed.) Geological Survey of Finland, Current Research 1991−1992. Geological Survey of Finland, Special Paper 18, 25−29.

Sorjonen-Ward, P. & Luukkonen, E. J. 2005. Archean rocks. In: Lehtinen, M., Nurmi, P. A., & Rämö, O. T. (eds.) Pre-cambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier B.V., 19−99.

147


Stacey, J. S. & Kramers, J. D. 1975. Approximation of terres-trial lead isotope evolution by a two-stage model. Earth and Planetary Science Letters 26, 207−221.

Taipale, K. 1983. The geology and geochemistry of the Ar-chaean Kuhmo greenstone-granite terrain in the Tipas-järvi area, eastern Finland. Acta Univ. Oul., Ser. A 151.

Tuukki, P. 1991. Arkeeinen Koveron liuskejakso ja sen ma-fisten ja ultramafisten kivien geokemia ja petrogenesis. Pohjois-Karjalan malmiprojekti. University of Oulu. Re-port 28. 129 p.

Vaasjoki, M. 1981. The lead isotopic composition of some Finnish galenas. Geological Survey of Finland Bulletin 316. 32 p.

Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen, S. 1993. U-Pb age determinations and sulfide Pb-Pb characteris-tics from the late Archean Hattu schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. & Sorjonen-Ward, P. (eds.) Geological development, gold mineralization and explo-ration methods in the late Archean Hattu schist belt, Ilo-mantsi, eastern Finland. Geological Survey of Finland. Special Paper 17, 103−131.

Vaasjoki, M., Taipale, K. & Tuokko, I. 1999. Radiometric ages and other isotopic data bearing on the evolution of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland. Bulletin of the Geological Society of Finland 71, 155−176.

Vaasjoki, M., Kärki, A, & Laajoki, K. 2001. Timing of Pale-aeoproterozoic crustal shearing in the central Fennos-candian Shield according to U-Pb data from associated granitoids, Finland. Bulletin of the Geological Society of Finland 73, 87−101.

Vidal, P., Blais, S., Jahn, B.-M., Capdevila, R. & Tilton, G. 1980. U-Pb and Rb-Sr systematics of the Suomussalmi Archaean greenstone belt (eastern Finland). Geochimica et Cosmochimica Acta 44, 2033−2044.

Wetherill, G., Kouvo, O., Tilton, G. & Gast, P. 1962. Age measurements of rocks from the Finnish Precambrian. Journal of Geology 70, 74−88.

Whitehouse, M. J., Kamber, B. & Moorbath, S. 1999. Age sig-nificance of U-Th-Pb zircon data from early Archaean rocks of west Greenland – a reassessment based on com-bined ion-microprobe and imaging studies. Chemical Geology 160, 201−224.

Whitehouse, M. J. & Kamber, B. S. 2005. Assigning dates to thin gneissic veins in high-grade metamorphic terranes – a cautionary tale from Akilia, southwest Greenland. Journal of Petrology, 46, 291−318.

Wiedenbeck, M., Allé, P., Corfu, F., Griffin, W. L., Meier, M., Oberli, F., Von Quadt, A., Roddick, J. C. & Spiegel, W. 1995. Three natural zircon standards for U–Th–Pb, Lu–Hf, trace elements and REE analyses. Geostandards Newsletter 19, 1–23.

Williams, I. S. 1998. U–Th–Pb geochronology by ion micro-probe. In: McKibben, M. A., Shanks III, W. C. & Ridley, W. I. (eds.) Applications of Microanalytical Techniques to Understanding Mineralizing Processes, vol. 7. Rev. Econ. Geol., 1–35.

Zartman, R. E & Doe, B. R. 1981. Pumbotectonics – the model. Tectonophysics 75, 135−162.

148

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 1. Ion microprobe U-Pb data on zircons (NORDSIM). Derived ages Corrected ratios Elemental data

Sample/ Zircon domain

207Pb ±s 207Pb ±s 206Pb ±s 207Pb ±s 206Pb ±s r 1) Disc. % 2)

[U] [Pb] Th/U f206 % 3)

spot # 206Pb 235U 238U 235U % 238U % ppm ppm measSuomussalmi greenstone beltA1191 Ala-Luoma metasediment. Suomussalmi (n759)n759-01a zoned inner 2810 5 2704 30 2565 66 13.34 3.1 0.4886 3.1 1.00 -4.9 161 104 0.41 0.19n759-01a2 zoned inner 2810 10 2725 20 2613 43 13.64 2.1 0.4998 2.0 0.96 -4.1 184 121 0.48 0.27n759-02a zoned inner 2953 3 2931 30 2900 73 16.94 3.1 0.5682 3.1 1.00 622 453 0.22 0.07n759-03a zoned inner 2967 2 2949 30 2923 74 17.25 3.1 0.5736 3.1 1.00 649 644 1.69 0.02n759-04a zoned inner 2948 4 2876 30 2774 71 15.98 3.1 0.5378 3.1 1.00 -1.4 340 258 0.75 0.20n759-05a zoned inner 2945 4 2969 30 3005 75 17.62 3.1 0.5939 3.1 1.00 512 406 0.44 0.15n759-06b zoned inner 2887 13 2566 35 2179 67 11.51 3.7 0.4021 3.6 0.98 -22.9 523 284 0.71 0.92n759-08a zoned inner 2960 4 2999 30 3056 76 18.17 3.1 0.6065 3.1 1.00 385 383 1.48 0.04n759-09a homog. inner 2955 3 2924 30 2879 73 16.80 3.1 0.5630 3.1 1.00 408 362 1.62 0.07n759-10a zoned inner 2816 3 2759 30 2680 69 14.13 3.1 0.5155 3.1 1.00 -0.0 316 224 0.60 0.16n759-10a2 zoned inner 2820 8 2732 20 2614 43 13.74 2.1 0.5001 2.0 0.97 -4.7 390 271 0.66 0.38A1428 Mesa-aho porphyry. Suomussalmi (n762)n762-01a zoned inner 2820 15 2679 21 2497 41 13.00 2.2 0.4730 2.0 0.90 -8.8 45 36 1.94 * 0.06n762-02a zoned inner 2814 15 2711 21 2575 42 13.44 2.2 0.4910 2.0 0.90 -5.3 59 42 0.96 0.17n762-03a zoned inner 2811 9 2783 19 2745 44 14.51 2.0 0.5309 2.0 0.96 91 73 1.17 0.13n762-04a zoned inner 2801 9 2765 21 2715 47 14.23 2.2 0.5238 2.1 0.97 85 71 1.42 0.12n762-05a zoned inner 2811 13 2752 20 2673 43 14.04 2.1 0.5139 2.0 0.93 -1.2 58 48 1.48 0.21n762-06a zoned inner 2787 10 2683 20 2548 41 13.05 2.0 0.4847 2.0 0.95 -6.1 79 56 1.14 0.19n762-07a zoned inner 2818 7 2802 19 2780 44 14.79 2.0 0.5391 2.0 0.97 116 92 1.05 * 0.04n762-08a zoned inner 2816 9 2795 19 2767 44 14.69 2.0 0.5360 1.9 0.96 66 59 1.77 0.11A1467 Saarikylä felsic volcanic rock. Suomussalmi (n761)n761-01a zoned core 2847 12 2119 19 1453 26 7.061 2.1 0.2528 2.0 0.94 -51.0 657 224 0.91 9.92n761-02a zoned inner 3188 2 3112 19 2996 47 20.44 2.0 0.5917 2.0 1.00 -3.8 845 679 0.45 0.13n761-03a zoned inner 2918 5 2863 19 2785 44 15.77 2.0 0.5405 2.0 0.99 -1.7 830 581 0.32 0.07n761-04a zoned core 2933 7 2899 19 2851 45 16.38 2.0 0.5561 1.9 0.98 146 108 0.45 0.28n761-04b zoned inner 2950 4 2954 19 2959 46 17.34 2.0 0.5825 2.0 0.99 733 540 0.19 0.02n761-05a zoned inner 2937 10 2881 20 2802 44 16.07 2.0 0.5444 1.9 0.95 -1.2 656 480 0.45 1.14n761-05b zoned inner 2926 5 2824 19 2684 43 15.15 2.0 0.5165 1.9 0.99 -6.4 349 240 0.45 0.13n761-06a zoned inner 2934 7 2855 19 2744 44 15.63 2.0 0.5306 1.9 0.98 -4.0 322 228 0.50 0.11n761-07a zoned inner 2943 8 2754 20 2503 42 14.06 2.1 0.4744 2.0 0.97 -14.3 202 125 0.33 0.37A1821Tormua gabbro. Suomussalmin2252-01a pale homog. 2618 846 2551 1085 2468 342 11.33 71.4 0.4664 16.3 0.23 261 384 6.40 54.53n2252-02a pale homog. 2863 2 2889 14 2926 33 16.20 1.4 0.5744 1.4 1.00 810 865 2.47 0.01n2252-03a pale homog. 2867 3 2857 13 2843 32 15.67 1.4 0.5543 1.4 0.99 842 983 3.42 0.01n2252-04a striped zoning 2867 5 2896 14 2938 33 16.32 1.4 0.5773 1.4 0.98 165 176 2.38 0.05n2252-05a dark homog. rim 2800 17 2731 16 2640 30 13.73 1.7 0.5061 1.4 0.79 -2.1 113 123 3.43 5.83n2252-05b pale homog. inner 2866 5 2872 13 2881 32 15.92 1.4 0.5634 1.4 0.97 190 262 4.51 0.10n2252-07a dark quite homog. 2853 8 2860 14 2870 33 15.72 1.5 0.5609 1.4 0.95 67 84 3.77 0.21n2252-08a pale homog. 2869 4 2871 13 2874 31 15.90 1.4 0.5618 1.3 0.99 308 358 3.17 0.02n2252-09a 2876 4 2880 14 2886 34 16.05 1.5 0.5646 1.4 0.99 264 351 4.31 0.02n2252-10a dark homog. 2884 11 2892 15 2903 32 16.25 1.5 0.5688 1.4 0.90 42 45 2.45 0.57

149

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A

rchaean greenstone belts in F

inland

Appendix 1. cont.Derived ages Corrected ratios Elemental data



[U] [Pb] Th/U f206 % 3)

spot # 206Pb 235U 238U 235U % 238U % ppm ppm meas

A1821Tormua gabbro. Suomussalmin2252-11a dark homog. rim 2588 87 2620 53 2662 31 12.20 5.5 0.5112 1.4 0.26 5 3 0.23 13.53n2252-11b pale homog. inner 2864 3 2866 13 2868 32 15.82 1.4 0.5604 1.4 0.99 516 567 2.84 0.01n2252-13a dark homog. rim 2687 36 2692 46 2699 95 13.17 4.8 0.5198 4.3 0.89 21 14 0.50 7.36n2252-14a quite homog 2858 5 2843 13 2822 31 15.45 1.4 0.5493 1.4 0.98 213 312 5.48 0.03n2252-15a pale homog. inner 2847 4 2847 13 2847 32 15.50 1.4 0.5552 1.4 0.99 715 916 4.18 0.02n2252-15b dark homog. rim 2789 4 2623 13 2415 27 12.24 1.4 0.4544 1.3 0.98 -13.6 367 301 3.20 0.34A1701x Kuikkapuro. Kiannanniemi SuomussalmiHost rock #1/ n2523 (4511/98/R361/44.40-45.40)n2523-01a weakly zoned. long 2828 4 2794 20 2748 46 14.67 2.1 0.5316 2.1 0.99 688 507 0.66 0.01n2523-02a weakly zoned. long 2821 4 2797 19 2765 44 14.72 2.0 0.5355 1.9 0.99 497 375 0.75 0.02n2523-03a weakly zoned 2812 4 2795 19 2771 44 14.68 2.0 0.5371 1.9 0.99 331 234 0.43 0.05n2523-04a quite homog stubby 2807 3 2808 19 2809 44 14.88 2.0 0.5462 1.9 0.99 489 350 0.41 0.01n2523-05a weakly zoned. long 2819 3 2827 19 2840 45 15.19 2.0 0.5535 2.0 1.00 804 637 0.86 0.01n2523-06a weakly zoned stubby 2811 3 2821 19 2834 45 15.08 2.0 0.5521 1.9 1.00 874 664 0.66 0.05n2523-07a weakly zoned stubby 2813 3 2831 19 2857 46 15.25 2.0 0.5577 2.0 1.00 676 493 0.41 0.03n2523-08a weakly zoned. long 2849 9 2845 20 2840 45 15.48 2.0 0.5537 2.0 0.96 132 93 0.25 0.02n2523-09a weakly zoned 2850 8 2842 19 2831 45 15.43 2.0 0.5514 2.0 0.97 133 93 0.27 0.05n2523- weakly zoned 2814 3 2845 19 2889 46 15.48 2.0 0.5653 2.0 0.99 426 329 0.64 0.03n2523-11a weakly zoned 2852 6 2864 19 2881 45 15.78 2.0 0.5634 1.9 0.98 165 120 0.35 0.14Host rock #2/ n2524 (4511/98/R361/97.00-99.70)n2524-01a weakly zoned 2948 6 2849 14 2710 31 15.54 1.4 0.5225 1.4 0.96 -7.0 253 175 0.36 0.09n2524-02a quite homog 2807 6 2776 14 2734 31 14.39 1.4 0.5282 1.4 0.97 -0.2 165 118 0.56 0.02n2524-03a weakly zoned 2957 6 2952 14 2944 33 17.30 1.4 0.5789 1.4 0.96 178 141 0.54 0.03n2524-04a weakly zoned 2915 6 2900 14 2879 33 16.40 1.5 0.5630 1.4 0.96 107 79 0.38 0.06n2524-05a quite homog rounded 3528 4 3518 14 3499 37 30.95 1.4 0.7207 1.4 0.99 230 225 0.17 0.03n2524-06a weakly zoned 2957 4 2935 14 2903 33 17.01 1.4 0.5689 1.4 0.98 260 188 0.22 0.04Kuhmo greenstone beltA1346 Lampela andesite. Kuhmon2250-01a zoned darker rim 2799 8 2795 14 2790 31 14.68 1.4 0.5416 1.3 0.94 77 54 0.32 0.19n2250-01b (=02a) homog pale core 2799 9 2809 14 2822 32 14.90 1.5 0.5493 1.4 0.92 143 102 0.38 0.25n2250-03a weakly zoned 2798 7 2819 14 2850 31 15.07 1.4 0.5560 1.3 0.95 88 63 0.32 0.04n2250-04a weakly zoned 2814 8 2796 14 2771 30 14.70 1.4 0.5370 1.3 0.94 73 52 0.48 0.19n2250-05a weakly zoned 2800 7 2801 14 2802 31 14.78 1.4 0.5445 1.4 0.96 96 68 0.41 0.17n2250-06a zoned 2793 6 2815 14 2847 32 15.00 1.4 0.5553 1.4 0.97 132 96 0.41 0.13n2250-07a pale inner 2770 3 2787 13 2810 31 14.55 1.4 0.5463 1.3 0.99 899 745 1.19 0.07n2250-07b (=08a) darker rim 2784 12 2796 15 2813 31 14.70 1.6 0.5471 1.4 0.87 47 32 0.27 0.09n2250-09a weakly zoned 2787 8 2809 14 2839 32 14.90 1.5 0.5533 1.4 0.95 69 50 0.37 0.07n2250-10a weakly zoned dark rim 2800 6 2787 13 2769 30 14.56 1.4 0.5365 1.3 0.96 150 105 0.46 0.57n2250-10b (=11a) weakly zoned pale center 2795 4 2823 14 2863 33 15.13 1.4 0.5592 1.4 0.99 280 210 0.53 0.03n2250-12 quite homog. 2760 7 2737 14 2705 31 13.81 1.5 0.5215 1.4 0.96 142 95 0.37 0.47n2250-13 weakly zoned 2653 94 2625 63 2589 63 12.27 6.5 0.4942 2.9 0.45 700 459 0.62 2.98

150

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)


A1418 Niittylahti gabbro. Kuhmon2251-01a quite homog. pale corroded 2795 4 2819 13 2853 32 15.06 1.4 0.5568 1.4 0.99 282 232 1.01 0.11n2251-02a quite homog. pale (corroded) 2789 4 2812 13 2845 32 14.95 1.4 0.5548 1.4 0.98 251 202 0.97 0.02n2251-03a quite homog. pale (corroded) 2785 6 2786 14 2787 32 14.54 1.5 0.5409 1.4 0.97 234 181 0.89 0.66n2251-04a quite homog. pale (corroded) 2788 4 2799 13 2814 31 14.75 1.4 0.5473 1.4 0.98 239 191 0.98 0.22n2251-05a quite homog. pale (corroded) 2793 4 2812 13 2839 31 14.96 1.4 0.5534 1.3 0.99 324 267 1.08 0.06n2251-06a homog. pale 2787 3 2802 13 2823 31 14.80 1.4 0.5495 1.4 0.99 421 350 1.15 0.05n2251-07a homog. pale 2790 4 2808 13 2833 31 14.89 1.4 0.5519 1.3 0.99 418 347 1.14 0.02n2251-08a weak zoning (corroded) 2774 12 2760 15 2740 30 14.15 1.5 0.5297 1.3 0.88 227 180 1.16 0.74n2251-09a quite homog. pale (corroded) 2781 4 2753 15 2715 34 14.04 1.6 0.5236 1.5 0.99 465 363 1.09 0.48n2251-10a quite homog. pale (corroded) 2603 6 2565 13 2517 28 11.50 1.4 0.4777 1.4 0.97 -1.0 803 602 1.38 0.52n2251-11a quite homog. pale (corroded) 2770 3 2768 13 2765 31 14.27 1.4 0.5356 1.4 0.99 404 301 0.71 0.14n2251-12a quite homog. pale 2743 4 2733 13 2718 30 13.75 1.4 0.5246 1.4 0.98 277 211 0.95 0.43n2251-13a quite homog. pale 2789 5 2803 14 2822 32 14.80 1.4 0.5493 1.4 0.98 177 130 0.53 0.08n2251-14a dark. weak zoning 2788 6 2771 8 2747 18 14.31 0.9 0.5314 0.8 0.91 69 49 0.48 {0.03}n2251-15a dark. weak zoning 2771 20 2747 15 2715 22 13.96 1.6 0.5238 1.0 0.62 221 170 0.99 2.98n2251-16a pale weakly zoned inner 2785 4 2781 8 2775 18 14.46 0.8 0.5379 0.8 0.96 192 145 0.78 0.08n2251-17a weakly zoned 2866 162 2920 113 2998 89 16.73 11.2 0.5922 3.7 0.33 202 183 2.62 7.83n2251-18a quite homog 2772 17 2684 13 2569 17 13.06 1.3 0.4897 0.8 0.60 -4.4 139 95 0.69 1.33n2251-19a weakly zoned 1907 4 1810 7 1727 12 4.946 0.8 0.3073 0.8 0.96 -9.0 510 260 1.95 0.12n2251-20a quite homog dark inner 2788 4 2778 8 2764 18 14.42 0.8 0.5355 0.8 0.96 159 117 0.63 0.03n2251-21a dark quite homog 2796 10 2784 10 2768 19 14.52 1.1 0.5364 0.9 0.80 73 52 0.48 0.53

A1771 Kellojärvi gabbronorite. Kuhmon2249-01 homog. pale. long 2776 3 2763 14 2745 33 14.20 1.5 0.5309 1.5 0.99 513 406 1.10 0.06n2249-02 homog. dark inner . short 1090 38 1083 16 1080 14 1.906 2.4 0.1824 1.4 0.59 26 7 1.39 {0.34}n2249-03 homog. dark. short 970 69 1012 24 1031 13 1.709 3.7 0.1735 1.4 0.37 23 6 1.41 1.11n2249-04 weakly zoned pale. long 2749 4 2752 14 2755 32 14.03 1.4 0.5333 1.4 0.99 384 283 0.69 0.56n2249-05 quite homog. pale 2802 4 2828 14 2864 33 15.20 1.4 0.5594 1.4 0.98 199 153 0.69 0.03n2249-06 weakly zoned pale 2774 4 2789 13 2810 32 14.59 1.4 0.5463 1.4 0.98 264 212 1.03 0.01n2249-07 weakly zoned pale. long 2793 8 2815 14 2846 31 15.00 1.4 0.5549 1.4 0.94 419 345 1.08 1.61n2249-08 weakly zoned. long 2758 4 2762 13 2767 30 14.18 1.4 0.5361 1.3 0.99 311 240 0.94 0.07n2249-09 weakly zoned. long 2785 6 2777 14 2766 31 14.41 1.4 0.5359 1.4 0.97 117 88 0.74 0.04n2249-10 weakly zoned. dark 3229 4 3244 14 3268 35 23.40 1.4 0.6602 1.4 0.98 166 159 0.74 0.02n2249-11 weakly zoned. short 2795 5 2808 13 2826 31 14.89 1.4 0.5502 1.4 0.98 209 165 0.90 {0.01}n2249-12 homog. pale. long (luid holes....) 2742 6 2741 13 2738 30 13.87 1.4 0.5293 1.3 0.97 720 549 0.93 0.02n2249-13 weakly zoned dark. long 2806 7 2819 14 2837 32 15.06 1.5 0.5529 1.4 0.96 95 74 0.81 0.09A1377 Siivikko felsic fragment in komatiite. Kuhmon2248-01a zoned dark inner 2786 5 2846 14 2931 34 15.49 1.5 0.5756 1.4 0.98 3.2 163 135 0.90 0.03n2248-02a zoned dark inner 2794 7 2806 14 2822 31 14.86 1.4 0.5493 1.4 0.95 82 60 0.57 0.17n2248-03a pale 2800 3 2783 14 2760 32 14.50 1.4 0.5343 1.4 0.99 572 448 1.01 0.11n2248-03b (=04a) dark 2803 7 2844 14 2902 32 15.46 1.4 0.5687 1.4 0.95 1.0 76 58 0.57 0.06n2248-05a pale homog rim 2775 3 2791 15 2813 35 14.62 1.6 0.5470 1.5 0.99 602 479 0.97 0.03n2248-06a dark inner 2780 8 2829 15 2898 34 15.21 1.5 0.5676 1.5 0.94 1.6 77 58 0.48 0.09n2248-06b (=07a) pale outer 2769 5 2760 14 2748 33 14.16 1.5 0.5315 1.5 0.98 227 169 0.78 0.41

151

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


A1377 Siivikko felsic fragment in komatiite. Kuhmon2248-08a pale rim 2793 4 2844 14 2916 34 15.46 1.5 0.5720 1.5 0.99 2.3 299 243 0.85 0.03n2248-08b (=9a) weakly zoned dark inner 2806 10 2817 15 2834 32 15.03 1.5 0.5520 1.4 0.92 85 64 0.61 0.17n2248-10a zoned 2790 4 2808 14 2834 33 14.89 1.5 0.5520 1.4 0.98 249 193 0.80 0.04n2248-11a pale homog. tip 2645 5 2587 6 2513 11 11.77 0.6 0.4766 0.5 0.86 -4.4 796 570 1.33 0.05n2248-12a pale homog. rim 2764 5 2754 6 2740 12 14.06 0.6 0.5298 0.5 0.88 462 359 1.18 0.09n2248-13a pale homog. rim 2734 4 2697 6 2648 11 13.24 0.6 0.5080 0.5 0.89 -2.4 781 597 1.37 0.03n2248-14a pale homog. rim 2490 4 2284 5 2062 9 8.486 0.6 0.3770 0.5 0.90 -18.7 1554 973 2.09 0.30n2248-15a pale homog. rim 2775 7 2784 6 2798 12 14.52 0.7 0.5434 0.5 0.78 519 412 1.09 0.02A120 Ruokojärvi dacite. Suomussalmin2554-01a quite homog core 3127 4 3097 6 3052 13 20.13 0.6 0.6056 0.5 0.92 -1.7 513 364 0.01 0.04n2554-01b quite homog rim 2883 2 2921 8 2975 20 16.75 0.9 0.5864 0.8 0.99 2.1 553 454 0.70 0.32n2554-02a weakly zoned 3012 3 2972 5 2913 12 17.67 0.6 0.5713 0.5 0.95 -2.9 393 329 0.47 0.16n2554-02b zoned dark rim 2794 18 2458 12 2073 11 10.25 1.2 0.3792 0.6 0.49 -25.9 397 318 0.47 5.41n2554-03a dark core 3127 3 3105 6 3070 14 20.28 0.6 0.6100 0.6 0.96 -1.1 597 445 0.26 0.02n2554-03b weakly zoned pale rim 2978 2 2960 5 2933 13 17.45 0.6 0.5762 0.5 0.96 -0.7 391 306 0.31 0.11n2554-04a weakly zoned rim 3073 4 3044 6 3000 13 19.04 0.6 0.5925 0.5 0.92 -1.6 284 196 0.03 0.08n2554-05a zoned 2981 4 2938 6 2874 12 17.05 0.6 0.5619 0.5 0.92 -3.1 248 114 0.24 0.17n2554-07a zoned 3099 2 3046 5 2968 13 19.09 0.6 0.5847 0.5 0.97 -4.1 370 302 0.16 0.13n2554-07a#2 zoned 2924 9 3057 27 3263 69 19.30 2.7 0.6589 2.7 0.98 8.2 213 [ 123] 0.48 0.71n2554-08a zoned 2753 22 2279 13 1789 9 8.436 1.5 0.3199 0.6 0.39 -34.7 155 [ 107] 0.25 32.51n2554-08a#2 zoned 2665 278 2454 192 2208 71 10.21 18.9 0.4085 3.8 0.20 194 95 0.41 29.48n2554-09a zoned unaltered core 2802 174 2467 113 2081 36 10.35 11.5 0.3810 2.0 0.18 466 367 0.47 19.82n2554-10a weakly zoned 2992 5 2997 6 3006 12 18.15 0.6 0.5940 0.5 0.85 271 253 1.11 0.08n2554-11a quite homog-weakly zoned 3131 6 3141 7 3157 15 21.06 0.7 0.6320 0.6 0.84 127 115 0.89 0.12n2554-12a weakly zoned core 3135 10 3141 8 3151 13 21.06 0.8 0.6303 0.5 0.65 219 204 1.23 0.08n2554-13a weakly zoned 3115 7 3114 7 3112 15 20.47 0.7 0.6206 0.6 0.81 373 359 1.01 0.09n2554-14a weakly zoned 3104 8 3158 7 3244 13 21.43 0.7 0.6541 0.5 0.71 3.4 336 276 0.54 0.30n2554-15a weakly zoned 3112 7 3091 7 3059 13 19.99 0.7 0.6072 0.5 0.78 -0.2 107 91 0.77 0.14n2554-16a weakly zoned 3123 13 3103 10 3071 13 20.23 1.0 0.6102 0.5 0.55 860 647 0.90 0.30n2554-17a homog pale inner 2902 4 2853 6 2785 14 15.61 0.7 0.5404 0.6 0.93 -3.4 524 191 0.86 0.18n2554-18a zoned 2745 24 2129 14 1551 7 7.136 1.6 0.2720 0.5 0.33 -42.9 912 526 0.34 15.55n2554-19a homog pale inner 2837 13 2695 9 2511 11 13.22 1.0 0.4762 0.5 0.54 -10.6 386 245 0.03 2.74n2554-20a quite homog pale inner 2776 8 2763 7 2744 12 14.19 0.7 0.5306 0.5 0.72 356 233 0.03 0.81n2554-21a quite homog inner 2822 5 2810 8 2793 19 14.92 0.9 0.5424 0.8 0.93 373 207 1.03 0.48n2554-22a zoned 2844 85 2601 54 2301 26 11.96 5.6 0.4289 1.4 0.24 -2.4 453 382 0.64 21.48n2554-23a quite homog pale core 3111 4 3067 9 3000 21 19.49 0.9 0.5926 0.9 0.97 -2.5 586 [ 308] 0.68 0.63n2554-24a zoned 2840 200 2049 125 1358 29 6.524 13.4 0.2346 2.4 0.18 -8.0 174 124 0.91 55.33n2554-25a darker inner 2561 90 2715 58 2928 53 13.50 6.0 0.5748 2.3 0.38 445 172 0.96 11.39n2554-26a darker inner 2918 83 2228 49 1557 11 7.973 5.3 0.2733 0.8 0.15 -32.1 345 236 0.46 17.89n2554-27a quite homog 3017 6 2875 9 2678 19 15.98 1.0 0.5150 0.9 0.92 -11.6 630 318 1.42 0.52n2554-28a darker rim 2666 11 2337 34 1980 61 8.993 3.6 0.3595 3.6 0.98 -24.2 197 182 0.97 1.18n2554-29a zoned 3120 3 3102 8 3073 19 20.22 0.8 0.6108 0.8 0.98 -0.2 67 58 0.73 0.01n2554-30a dark homog core 3132 5 3083 8 3010 19 19.84 0.8 0.5950 0.8 0.94 -3.0 218 189 0.61 0.03

152

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)

spot # 206Pb 235U 238U 235U % 238U % ppm ppm measA120 Ruokojärvi dacite. Suomussalmin2554-31a weakly zoned tiny grain 3124 5 3115 11 3101 28 20.49 1.2 0.6177 1.1 0.97 216 185 0.62 0.18n2554-32a weakly zoned tiny grain 3125 5 3108 11 3082 25 20.35 1.1 0.6130 1.0 0.96 288 260 1.03 0.05n2554-33a weakly zoned tiny grain 3115 3 3080 8 3028 19 19.77 0.8 0.5996 0.8 0.97 -1.8 325 297 0.94 0.09n2554-34a weakly zoned tiny grain 3129 2 3106 8 3071 19 20.31 0.8 0.6102 0.8 0.99 -0.7 134 105 0.17 0.10n2554-35a quite homo. dark inner 3127 5 3101 8 3060 19 20.19 0.8 0.6075 0.8 0.93 -0.8 627 439 0.35 0.03n2554-35b pale weakly zoned 3047 5 2918 9 2736 19 16.71 0.9 0.5288 0.9 0.95 -10.6 0.07A1773 Hetteilä#1 intermediate volcanic rock. Kuhmon2556-01a pale homog rim 522 13 530 7 532 8 0.686 1.7 0.0860 1.6 0.94 6645 607 0.02 0.03n2556-02a dark core 2839 12 2820 18 2793 38 15.07 1.8 0.5423 1.7 0.91 152 117 1.02 0.07n2556-02b pale rim 2668 8 2667 16 2665 35 12.83 1.7 0.5120 1.6 0.96 1244 756 0.03 0.08n2556-03a zoned grain 2830 12 2802 17 2765 36 14.80 1.8 0.5356 1.6 0.90 118 90 1.08 0.13n2556-04a zoned grain 2853 15 2828 18 2792 37 15.20 1.9 0.5420 1.6 0.87 148 115 1.11 0.17n2556-06a quite homog tiny grain 2832 12 2797 17 2749 37 14.72 1.8 0.5318 1.6 0.91 158 116 0.85 0.28n2556-07a dark core 2853 17 2811 18 2752 36 14.93 1.9 0.5326 1.6 0.84 110 80 0.82 {0.13}n2556-07b pale rim 2683 7 2664 16 2640 35 12.79 1.6 0.5062 1.6 0.97 641 385 0.02 0.18n2556-08a dark quite homog 2809 21 2769 20 2713 36 14.28 2.1 0.5232 1.6 0.77 146 102 0.75 0.76n2556-09a dark hazy 2848 15 2792 18 2714 37 14.63 1.9 0.5234 1.7 0.88 -1.0 164 120 1.00 0.23n2556-10a weakly zoned grain 2797 19 2738 19 2658 36 13.83 2.0 0.5104 1.6 0.81 -0.5 91 65 1.06 0.68n2556-11a dark core 2836 3 2817 8 2791 18 15.03 0.8 0.5418 0.8 0.97 -0.2 207 156 0.64 0.07n2556-11b pale rim 2677 7 2658 8 2632 17 12.70 0.9 0.5042 0.8 0.89 1144 688 0.05 1.38n2556-12a hazy 2820 3 2999 31 3275 81 18.18 3.1 0.6619 3.1 1.00 13.0 352 315 0.58 0.05n2556-13a pale rim 2679 2 2666 8 2648 18 12.81 0.8 0.5079 0.8 0.99 1568 948 0.03 0.02A1774 Hetteilä#2 mica schist. Kuhmon2557-01a#2 zoned 2745 5 2711 16 2665 36 13.44 1.7 0.5119 1.7 0.99 -0.2 262 196 1.02 {0.01}n2557-02#2 zoned 2720 9 2761 9 2816 18 14.16 1.0 0.5479 0.8 0.81 1.5 114 86 0.67 {0.02}n2557-03a#2 zoned 2724 14 2612 16 2470 30 12.10 1.7 0.4669 1.5 0.87 -7.1 217 132 0.36 0.51n2557-04a#2 quite homogeneous core 2787 7 2755 11 2712 23 14.08 1.1 0.5230 1.0 0.92 -0.7 190 130 0.41 0.18n2557-05a#2 zoned 2735 7 2774 10 2828 22 14.36 1.1 0.5506 1.0 0.92 1.6 307 229 0.64 0.02n2557-06#2 zoned 2749 8 2758 10 2771 21 14.13 1.1 0.5371 0.9 0.90 97 71 0.65 {0.02}n2557-07a#2 zoned 2745 5 2754 9 2767 20 14.07 0.9 0.5362 0.9 0.95 179 126 0.45 0.03n2557-08a#2 zoned 2732 4 2713 8 2688 17 13.47 0.8 0.5175 0.8 0.96 -0.1 226 160 0.65 0.07n2557-09a#2 zoned 2742 4 2785 8 2845 18 14.54 0.8 0.5549 0.8 0.96 2.8 211 163 0.75 {0.01}n2557-10a#2 dark zoned 2793 7 2796 8 2802 18 14.71 0.9 0.5443 0.8 0.89 130 102 0.94 0.02A1746 Petäjäniemi metasediment. Kuhmon2246-01a weakly zoned unfractured

(=metamorphic?)2867 10 2904 15 2958 33 16.47 1.5 0.5824 1.4 0.91 0.1 47 34 0.20 {0.03}

n2246-02a pale homog (healed?) core 2856 3 2909 14 2987 33 16.55 1.4 0.5894 1.4 0.99 2.7 356 272 0.34 0.02n2246-03a weakly zoned dark rim 2806 12 2684 15 2526 29 13.06 1.6 0.4796 1.4 0.89 -8.3 54 33 0.34 0.56n2246-03b homog. pale core 2855 5 2799 13 2721 30 14.74 1.4 0.5251 1.3 0.98 -3.0 248 177 0.70 0.20n2246-04a homog. core 2847 7 2898 16 2973 39 16.36 1.7 0.5858 1.6 0.97 1.7 123 97 0.54 {0.01}n2246-05a zoned 2821 5 2792 15 2752 35 14.63 1.6 0.5325 1.5 0.98 174 116 0.19 0.12n2246-06a weakly zoned 2879 12 2941 16 3033 35 17.12 1.6 0.6009 1.4 0.89 2.4 32 25 0.43 {0.06}n2246-07a dark weakly zoned rim 2849 7 2908 14 2993 33 16.52 1.4 0.5909 1.4 0.95 2.9 78 61 0.41 0.04

153

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


A1746 Petäjäniemi metasediment. Kuhmon2246-08a homogenized core 2850 3 2895 13 2961 32 16.31 1.4 0.5830 1.4 0.99 1.9 419 341 0.74 0.02n2246-09a dark quite homog rim 2737 7 2778 14 2834 31 14.42 1.4 0.5520 1.4 0.95 1.0 85 61 0.41 0.04n2246-09b pale homog. core 2855 6 2896 13 2954 32 16.32 1.4 0.5813 1.3 0.96 1.2 126 99 0.58 {0.02}n2246-10a weak hazy zoning 2848 6 2881 14 2929 32 16.07 1.4 0.5752 1.4 0.97 0.4 177 140 0.64 0.02n2246-11a dark weakly zoned inner

(thin pale zones around)2865 5 2884 14 2913 34 16.13 1.5 0.5712 1.4 0.98 170 127 0.37 0.02

n2246-12a weakly zoned 2744 11 2752 15 2763 32 14.04 1.6 0.5351 1.4 0.90 39 27 0.35 0.09n2246-13a zoned 2856 5 2840 13 2818 31 15.39 1.4 0.5482 1.4 0.98 221 158 0.42 0.05n2246-14a weakly zoned core 2833 5 2810 13 2778 30 14.92 1.4 0.5387 1.3 0.98 225 160 0.44 0.03n2246-14b (=15a) weakly zoned rim 2696 6 2179 13 1674 20 7.553 1.4 0.2965 1.3 0.96 -40.8 240 95 1.29 0.12n2246-16 dark homog. outer 2826 54 2239 34 1656 21 8.072 3.7 0.2928 1.4 0.39 -33.6 11 4 0.82 7.82

Ilomantsi greenstone beltA221 Hattuvaara Ilomantsi mica gneiss (= n2494). all analyses on mostly oscillatory zoned inner domainsn2494-01 2740 5 2657 20 2549 45 12.69 2.1 0.4850 2.1 0.99 -4.4 265 183 0.81 0.83n2494-02 2736 3 2706 18 2666 42 13.37 1.9 0.5122 1.9 0.99 264 196 0.85 0.54n2494-03 2749 2 2711 16 2660 36 13.44 1.7 0.5107 1.7 1.00 -0.7 679 502 0.85 0.09n2494-04 2743 4 2635 21 2496 46 12.39 2.2 0.4728 2.2 0.99 -6.8 201 132 0.67 0.61n2494-05 2740 4 2696 17 2638 38 13.23 1.8 0.5055 1.7 0.99 -1.1 278 194 0.65 0.53n2494-06 2747 5 2680 19 2591 43 13.00 2.0 0.4947 2.0 0.99 -3.0 149 102 0.70 0.74n2494-07 2745 3 2714 18 2672 42 13.48 1.9 0.5135 1.9 0.99 391 294 0.98 0.14n2494-08 2743 3 2732 18 2716 41 13.73 1.8 0.5239 1.8 1.00 485 360 0.80 0.02n2494-09 2749 4 2723 17 2689 39 13.62 1.8 0.5176 1.8 0.99 246 182 0.83 0.04n2494-10 2757 7 2737 15 2711 34 13.82 1.6 0.5228 1.5 0.96 83 62 0.81 0.04n2494-11 2729 6 2664 18 2580 40 12.79 1.9 0.4921 1.9 0.98 -2.8 247 171 0.80 0.40n2494-12 2743 4 2708 20 2662 45 13.40 2.1 0.5112 2.1 0.99 313 226 0.78 0.04n2494-13 2742 6 2599 16 2420 33 11.93 1.7 0.4556 1.7 0.98 -10.9 206 127 0.63 0.91n2494-14 2852 13 3071 37 3417 98 19.58 3.7 0.6990 3.7 0.98 15.8 2025 2105 0.88 1.16n2494-15 2700 3 2683 15 2660 34 13.04 1.5 0.5107 1.5 0.99 591 466 1.34 0.16n2494-16 2737 7 2681 16 2608 36 13.02 1.7 0.4986 1.7 0.97 -2.1 324 221 0.76 1.93n2494-17 2742 4 2697 16 2637 37 13.24 1.7 0.5055 1.7 0.99 -1.3 327 232 0.90 0.12n2494-18 2750 3 2737 15 2719 34 13.81 1.6 0.5246 1.5 0.99 545 416 0.98 0.18n2494-19 2749 6 2712 15 2662 34 13.45 1.6 0.5112 1.5 0.97 -0.6 209 146 0.71 0.05n2494-20 2748 8 2726 15 2697 34 13.66 1.6 0.5194 1.5 0.96 223 165 0.91 0.06n2494-21 2746 5 2709 15 2659 34 13.40 1.6 0.5105 1.5 0.98 -0.7 382 275 0.82 0.19n2494-22 2749 7 2744 17 2738 38 13.92 1.8 0.5291 1.7 0.97 107 79 0.77 {0.02}n2494-23 2740 5 2734 16 2726 38 13.77 1.7 0.5262 1.7 0.98 220 164 0.82 0.02n2494-24 2711 7 2698 15 2681 34 13.26 1.6 0.5157 1.6 0.96 124 89 0.73 0.07n2494-25 2757 6 2729 15 2692 34 13.70 1.6 0.5183 1.6 0.98 212 158 0.93 0.04n2494-26 2743 7 2748 17 2754 38 13.97 1.7 0.5331 1.7 0.97 180 130 0.63 0.05n2494-27 2710 9 2534 16 2320 31 11.13 1.7 0.4333 1.6 0.95 -13.7 101 61 0.96 0.29n2494-28 2721 7 2629 16 2511 34 12.32 1.7 0.4762 1.6 0.97 -5.9 151 97 0.66 0.09n2494-29 2751 4 2757 15 2765 35 14.11 1.6 0.5355 1.6 0.99 336 255 0.87 0.02

154

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)


Ilomantsi greenstone beltA221 Hattuvaara Ilomantsi mica gneiss (= n2494). all analyses on mostly oscillatory zoned inner domainsn2494-30 2734 3 2664 15 2574 33 12.79 1.6 0.4907 1.5 0.99 -4.1 601 445 1.35 0.06n2494-31 2749 6 2726 15 2695 34 13.65 1.6 0.5190 1.5 0.97 211 150 0.73 0.02n2494-32 2730 9 2652 18 2550 37 12.62 1.9 0.4853 1.8 0.95 -4.0 434 296 1.16 0.23n2494-33 2763 8 2739 16 2707 35 13.84 1.6 0.5219 1.6 0.96 169 119 0.60 {0.01}n2494-34 2887 10 2890 16 2895 37 16.23 1.7 0.5668 1.6 0.93 64 52 0.95 {0.03}n2494-35 2735 6 2484 15 2189 29 10.55 1.6 0.4044 1.6 0.97 -20.7 287 159 1.00 0.62A282-Vehkavaara porphyry dike. Ilomantsin763-01a core 3006 4 3024 19 3051 48 18.65 2.0 0.6053 2.0 0.99 500 393 0.29 0.04n763-02a core 2971 9 2948 20 2915 47 17.24 2.1 0.5718 2.0 0.96 68 51 0.39 0.34n763-02b zoned core 3018 6 2986 19 2938 46 17.93 2.0 0.5773 2.0 0.98 179 138 0.42 0.1n763-03a zoned outer 2738 3 2690 19 2625 42 13.14 2.0 0.5027 1.9 0.99 -1.3 571 348 0.08 0.03n763-04a core 3237 9 3200 20 3141 49 22.37 2.0 0.6279 2.0 0.96 91 80 0.49 0.22n763-05a core 2999 3 2986 19 2966 47 17.92 2.0 0.5843 2.0 0.99 490 390 0.52 0.11n763-06a core 3005 5 2943 19 2853 45 17.14 2.0 0.5566 1.9 0.99 -2.4 314 237 0.48 0.2n763-06b zoned outer 2751 5 2706 19 2647 43 13.37 2.0 0.5076 2.0 0.99 -0.7 687 416 0.01 0.12n763-07a zoned outer 2764 4 2685 19 2581 42 13.07 2.0 0.4925 2.0 0.99 -4.3 643 382 0.05 0.11n763-08a zoned core 2978 6 2922 19 2841 46 16.78 2.0 0.5538 2.0 0.98 -1.7 244 180 0.42 0.18n763-09a core 2984 3 2896 19 2773 44 16.33 2.0 0.5374 1.9 1.00 -5.1 1068 716 0.10 0.02n763-10a core 2986 9 2883 20 2737 44 16.10 2.0 0.5289 2.0 0.96 -6.1 77 55 0.51 0.14n763-11a zoned core 3091 8 3005 20 2878 45 18.29 2.0 0.5627 2.0 0.97 -4.5 616 530 1.25 0.05n763-12a core 2908 10 2823 21 2704 45 15.12 2.1 0.5212 2.0 0.95 -4.1 151 105 0.47 0.97A301-Vehkavaara porphyry dike. Ilomantsin760-01a core 3100 3 3097 20 3093 50 20.12 2.0 0.6157 2.0 0.99 462 375 0.31 0.03n760-02b core 3300 4 3228 20 3115 50 23.04 2.0 0.6214 2.0 0.99 -3.2 577 495 0.44 0.03n760-03a zoned core 3103 3 3096 20 3085 50 20.10 2.1 0.6137 2.0 0.99 410 340 0.45 0.05n760-04a core 2899 5 2838 20 2753 45 15.37 2.0 0.5328 2.0 0.99 -2.3 262 172 0.09 0.02n760-04b zoned outer 2754 3 2857 20 3004 49 15.67 2.0 0.5937 2.0 1.00 6.8 728 522 0.06 0.22n760-05a zoned outer 2762 5 2707 20 2634 44 13.38 2.0 0.5047 2.0 0.99 -1.7 612 373 0.05 0.04n760-05b core 2996 4 2966 20 2922 49 17.57 2.1 0.5736 2.1 0.99 372 279 0.31 0.05n760-06a zoned outer 2753 3 2703 19 2636 44 13.33 2.0 0.5053 2.0 1.00 -1.3 804 489 0.05 0.01n760-06b core 3077 3 3023 20 2942 48 18.63 2.0 0.5782 2.0 1.00 -1.6 589 428 0.08 0.05n760-07a core 3224 6 3012 20 2706 44 18.43 2.0 0.5216 2.0 0.98 -16.1 660 448 0.19 0.81n760-07b zoned outer 2743 7 2750 20 2758 46 14.00 2.1 0.5340 2.0 0.98 653 419 0.04 0.08n760-08a zoned outer 2614 4 2550 19 2470 41 11.32 2.0 0.4669 2.0 0.99 -2.7 1624 912 0.09 0.66n760-8b core 2702 3 2533 19 2327 39 11.11 2.0 0.4347 2.0 0.99 -13.1 785 411 0.06 0.02Kovero greenstone beltA1626 Rasisuo#1 gabbro. Ilomantsin2247-01a quite homog stubby 2752 6 2759 14 2769 31 14.14 1.4 0.5365 1.4 0.96 129 95 0.66 0.06n2247-02a weakly zoned 2759 4 2772 13 2791 31 14.34 1.4 0.5418 1.4 0.98 261 210 1.09 0.04n2247-03a weakly zoned 2757 4 2778 13 2807 32 14.42 1.4 0.5455 1.4 0.99 378 312 1.17 0.05n2247-04a weakly zoned pale 2747 5 2771 14 2805 33 14.32 1.5 0.5451 1.4 0.98 242 195 1.08 0.03

155

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


Kovero greenstone beltA1626 Rasisuo#1 gabbro. Ilomantsin2247-05a dark zoned inner 2749 6 2764 14 2783 32 14.21 1.5 0.5399 1.4 0.97 133 103 0.92 0.14n2247-06a quite homog stubby 2760 6 2778 14 2802 31 14.42 1.4 0.5444 1.4 0.97 144 112 0.88 0.04n2247-07a weakly zoned 2759 16 2764 17 2771 33 14.22 1.7 0.5370 1.5 0.83 177 136 0.93 2.01n2247-08a quite homog. 2759 4 2776 14 2800 34 14.40 1.5 0.5440 1.5 0.99 429 354 1.23 0.01n2247-09a core. altered mantle 2759 3 2788 14 2829 34 14.58 1.5 0.5508 1.5 0.99 393 320 1.09 0.02n2247-10a weakly zoned 2757 3 2776 14 2801 33 14.39 1.5 0.5442 1.5 0.99 580 485 1.28 0.02

n2247-11a weakly zoned 2735 5 2707 13 2671 30 13.39 1.4 0.5134 1.3 0.98 257 190 0.93 0.39n2247-12a dark inner zoned 2765 5 2704 13 2622 29 13.33 1.4 0.5020 1.3 0.97 -3.5 203 145 0.82 0.14n2247-13a pale core 2764 10 2750 14 2731 31 14.00 1.5 0.5276 1.4 0.91 654 523 1.24 1.46n2247-13b dark rim 2768 42 2698 28 2606 31 13.26 3.0 0.4982 1.4 0.48 147 100 0.68 13.98n2247-14a quite homog. 2757 4 2757 14 2758 32 14.11 1.4 0.5340 1.4 0.98 224 165 0.73 0.03n2247-15a quite homog. 2759 4 2772 13 2791 31 14.34 1.4 0.5418 1.4 0.99 539 438 1.18 0.02n2247-16a weakly zoned pale 2749 35 2777 25 2816 32 14.41 2.6 0.5477 1.4 0.54 545 469 1.44 2.52n2247-16b dark weakly zoned 2762 5 2733 14 2693 31 13.75 1.4 0.5187 1.4 0.98 -0.1 217 159 0.80 0.10A1627 Rasisuo#2 felsic tuff. Ilomantsin2555-01a weakly zoned 2877 4 2857 8 2830 18 15.68 0.8 0.5510 0.8 0.96 -0.3 222 166 0.55 0.02n2555-02a weakly zoned 2832 10 2791 10 2734 19 14.62 1.1 0.5282 0.9 0.80 -1.3 503 354 0.51 2.62n2555-03a weakly zoned 2877 5 2876 8 2875 18 15.99 0.8 0.5620 0.8 0.94 174 145 1.05 0.31n2555-04a weakly zoned 2874 4 2919 8 2984 19 16.72 0.8 0.5887 0.8 0.94 2.8 390 312 0.61 0.42n2555-05a weakly zoned 2879 3 2900 8 2932 19 16.40 0.8 0.5759 0.8 0.97 0.5 382 283 0.31 0.29n2555-06a weakly zoned 2878 6 2913 9 2964 19 16.62 0.9 0.5836 0.8 0.90 1.4 186 148 0.59 0.74n2555-07a weakly zoned 2855 6 2874 9 2901 19 15.96 0.9 0.5684 0.8 0.90 345 263 0.53 0.13n2555-08a weakly zoned 2866 8 2861 9 2854 18 15.73 0.9 0.5569 0.8 0.84 96 75 0.80 0.02n2555-09a zoned 2863 5 2878 9 2899 20 16.02 0.9 0.5679 0.9 0.95 243 188 0.64 0.05n2555-10a dark inner 2880 4 2872 8 2861 19 15.92 0.9 0.5586 0.8 0.96 242 183 0.57 0.02n2555-10b pale rim 2870 3 2881 8 2897 18 16.08 0.8 0.5674 0.8 0.97 460 364 0.75 0.01n2555-11a quite homog 2882 6 2886 9 2892 20 16.15 0.9 0.5661 0.9 0.92 121 91 0.44 {0.01}n2555-12a quite homog 2870 4 2879 8 2892 19 16.04 0.9 0.5662 0.8 0.95 140 106 0.49 {0.02}n2555-13a quite homog 2865 4 2865 8 2865 18 15.81 0.8 0.5597 0.8 0.96 159 118 0.45 0.03n2555-14a weakly zoned 2878 3 2892 8 2911 19 16.25 0.8 0.5709 0.8 0.98 246 186 0.42 {0.01}n2555-15a dark homog 2882 4 2887 8 2894 19 16.17 0.8 0.5667 0.8 0.95 122 92 0.45 {0.01}n2555-16a zoned 2891 7 2876 10 2855 22 15.99 1.1 0.5571 1.0 0.92 389 295 0.59 0.40n2555-17a dark homog rim 2866 23 2871 16 2878 20 15.90 1.7 0.5628 0.9 0.52 110 83 0.52 3.93

Pudasjärvi greenstone beltA1782 Käärmevaara gabbro. Ranuan2558-01a#2 pale quite homog

(partly corroded)2791 3 2810 10 2838 25 14.93 1.1 0.5530 1.1 0.98 979 856 1.33 0.01

n2558-02a#2 pale homog (partly corroded) 2798 2 2834 11 2884 28 15.30 1.2 0.5642 1.2 0.99 1.3 525 692 4.16 0.05n2558-03a#2 darker homog 1845 6 1869 8 1891 15 5.30 0.9 0.3410 0.9 0.94 0.6 275 118 0.51 0.03n2558-04a#2 pale homog 2803 3 2870 11 2966 26 15.88 1.1 0.5842 1.1 0.99 4.8 492 451 1.38 0.03n2558-05a#2 darker quite homog 2798 16 2778 18 2750 36 14.42 1.9 0.5321 1.6 0.86 115 117 2.74 0.31n2558-06a darker quite homog 2811 7 2830 9 2858 19 15.24 0.9 0.5579 0.8 0.88 123 98 0.80 0.02

156

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)


Pudasjärvi greenstone beltA1782 Käärmevaara gabbro. Ranuan2558-07a pale homog 2806 2 2842 10 2893 24 15.43 1.0 0.5664 1.0 0.99 1.6 430 455 2.55 0.02n2558-08a pale homog 2806 2 2842 9 2894 21 15.43 0.9 0.5666 0.9 0.99 2.0 629 576 1.55 0.02n2558-09a dark inner . tiny grain 2704 6 2683 9 2654 20 13.04 1.0 0.5094 0.9 0.93 76 59 1.15 0.04n2558-10a hazy small grain 855 9 850 6 848 8 1.309 1.1 0.1405 0.9 0.90 569 90 0.19 0.06A1783 Puljunlehto dacite. Ranuan2559-01a homog metam grain 2811 14 2803 11 2792 18 14.81 1.2 0.5420 0.8 0.67 19 13 0.27 0.18n2559-02a smoothly zoned (metam?) 2840 12 2837 10 2832 18 15.34 1.1 0.5515 0.8 0.72 22 16 0.60 0.14n2559-03a weakly zoned euhedral 2783 11 2808 10 2842 20 14.88 1.1 0.5540 0.9 0.79 24 17 0.25 0.11n2559-04a weakly zoned euhedral 2820 6 2818 9 2815 19 15.04 0.9 0.5475 0.8 0.90 98 75 0.71 0.03n2559-05a weakly zoned euhedral 2826 11 2841 10 2862 18 15.41 1.0 0.5589 0.8 0.76 31 23 0.50 0.15n2559-06a weakly zoned euhedral 2825 8 2797 11 2758 23 14.71 1.1 0.5338 1.0 0.90 -0.2 64 44 0.34 0.07n2559-07a homog metam grain 2788 20 2765 14 2735 18 14.23 1.4 0.5284 0.8 0.55 11 8 0.21 0.27n2559-08a dark quite homog 2816 9 2786 9 2745 18 14.54 1.0 0.5308 0.8 0.83 -0.4 38 28 0.73 0.13n2559-09a weakly zoned/wague euhedral 2832 4 2827 12 2820 28 15.18 1.2 0.5487 1.2 0.98 128 95 0.54 0.04n2559-10a dark quite homog 2798 8 2804 9 2811 19 14.82 1.0 0.5467 0.8 0.86 37 27 0.41 0.09ParagneissesA1814 Pitkäpalo Ranua mica gneiss (= n2129) n2129-03 2847 5 2832 10 2811 24 15.27 1.1 0.5467 1.0 0.96 130 94 0.42 {0.01}n2129-05 2742 3 2732 10 2718 23 13.74 1.0 0.5245 1.0 0.98 286 202 0.61 {0.01}n2129-06 2703 6 2229 28 1750 46 7.980 3.0 0.3119 3.0 0.99 -36.3 399 170 1.83 0.73n2129-07 2745 28 2741 19 2735 23 13.87 2.0 0.5284 1.0 0.52 7 5 0.80 {0.00}n2129-08 2735 5 2699 10 2652 23 13.27 1.1 0.5089 1.0 0.96 -1.3 207 149 0.96 0.21n2129-10 2746 2 2744 10 2741 23 13.92 1.0 0.5299 1.0 0.99 662 497 0.82 {0.01}n2129-11 2730 4 2705 10 2671 22 13.35 1.0 0.5133 1.0 0.97 -0.5 271 200 0.90 0.09n2129-13 2728 4 2651 10 2550 22 12.61 1.1 0.4853 1.0 0.97 -5.7 366 261 1.16 0.21n2129-14 2835 5 2837 10 2839 23 15.34 1.0 0.5533 1.0 0.96 173 132 0.64 {0.02}n2129-15 2846 9 2785 11 2702 23 14.53 1.2 0.5207 1.1 0.89 -3.3 539 382 0.60 {0.02}n2129-16 2693 10 2377 25 2026 46 9.391 2.7 0.3693 2.6 0.97 -24.4 339 165 1.02 1.22n2129-17 3166 7 3149 11 3122 25 21.23 1.1 0.6232 1.0 0.92 228 195 0.72 {0.02}n2129-18 2733 4 2747 10 2766 23 13.96 1.0 0.5358 1.0 0.97 220 157 0.51 {0.01}n2129-19 2731 5 2686 10 2628 22 13.09 1.1 0.5032 1.0 0.95 -2.3 281 191 0.85 {0.02}n2129-20 2732 5 2694 11 2643 24 13.20 1.1 0.5068 1.1 0.96 -1.5 157 107 0.70 {0.09}n2129-21 2784 7 2781 10 2778 23 14.48 1.1 0.5388 1.0 0.92 456 324 0.49 {0.02}n2129-22 2701 8 2591 10 2452 21 11.82 1.1 0.4629 1.0 0.91 -8.5 218 139 0.74 0.24n2129-23 2940 6 2845 10 2712 22 15.47 1.1 0.5230 1.0 0.93 -7.1 239 168 0.82 0.05n2129-24 2719 7 2473 16 2186 32 10.43 1.8 0.4037 1.7 0.97 -19.9 268 145 1.33 0.11n2129-25 2733 6 2755 10 2784 23 14.07 1.1 0.5402 1.0 0.94 155 112 0.60 0.07n2129-26 2735 7 2706 11 2668 24 13.37 1.2 0.5127 1.1 0.93 -0.3 171 114 0.45 0.12n2129-27 2703 5 2615 10 2503 21 12.14 1.1 0.4745 1.0 0.96 -6.7 695 398 0.23 0.28n2129-29 2725 7 2625 10 2498 21 12.27 1.1 0.4733 1.0 0.93 -7.6 232 141 0.49 0.02n2129-30 2722 6 2630 10 2512 21 12.33 1.1 0.4764 1.0 0.93 -6.9 287 190 1.18 0.06n2129-31 2715 7 2603 10 2461 21 11.98 1.1 0.4649 1.0 0.93 -8.8 652 388 0.50 0.01n2129-33 2694 8 2408 11 2084 19 9.712 1.2 0.3817 1.1 0.90 -23.9 320 162 0.85 0.40

157

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


A1842 Jäkälämaa Pudasjärvi mica gneiss (= n2497). all analyses on mostly oscillatory zoned inner domainsn2497-01 2714 6 2688 16 2653 35 13.12 1.7 0.5092 1.6 0.98 230 155 0.49 0.23n2497-02 2798 5 2723 16 2622 34 13.60 1.6 0.5020 1.6 0.98 -4.4 325 206 0.24 0.60n2497-03 2691 4 2560 15 2398 31 11.44 1.6 0.4505 1.5 0.99 -10.2 362 223 0.65 0.23n2497-04 2723 3 2726 15 2730 35 13.65 1.6 0.5273 1.6 0.99 1205 986 1.31 0.07n2497-05 2748 6 2723 16 2689 35 13.60 1.6 0.5175 1.6 0.97 175 127 0.77 0.05n2497-06 2744 8 2750 17 2757 38 14.00 1.8 0.5337 1.7 0.96 207 146 0.47 0.61n2497-07 2741 4 2703 15 2653 34 13.33 1.6 0.5092 1.5 0.99 -0.8 365 261 0.75 0.11n2497-08 2732 6 2745 15 2763 35 13.93 1.6 0.5352 1.5 0.98 218 160 0.63 0.05n2497-09 2720 4 2708 16 2693 38 13.40 1.7 0.5185 1.7 0.99 681 565 1.43 0.07n2497-10 2706 6 2701 16 2694 36 13.29 1.6 0.5188 1.6 0.98 334 235 0.60 0.08n2497-11 2743 6 2724 16 2699 36 13.63 1.6 0.5199 1.6 0.98 219 158 0.71 0.04n2497-12 2728 6 2571 16 2376 33 11.57 1.7 0.4457 1.7 0.98 -12.3 230 135 0.49 0.41n2497-13 2705 6 2595 15 2457 32 11.89 1.6 0.4640 1.5 0.97 -7.9 1107 612 0.02 0.10n2497-14 2748 6 2703 17 2644 38 13.33 1.8 0.5072 1.7 0.98 -1.0 304 232 1.09 0.24n2497-15 2701 6 2594 16 2459 34 11.86 1.7 0.4643 1.7 0.98 -7.5 644 422 0.79 0.49n2497-16 2712 13 1877 15 1218 17 5.351 1.7 0.2081 1.5 0.88 -56.7 4059 1216 1.11 0.25n2497-17 2764 7 2749 17 2728 38 13.98 1.7 0.5267 1.7 0.97 933 685 0.72 0.02n2497-18 2742 8 2751 15 2765 35 14.03 1.6 0.5355 1.5 0.96 249 206 1.29 0.04n2497-19 2805 8 2729 16 2627 34 13.69 1.6 0.5032 1.6 0.95 -4.2 357 223 0.16 0.25n2497-20 2736 4 2755 16 2780 38 14.08 1.7 0.5392 1.7 0.99 412 308 0.71 0.01n2497-21 2741 6 2731 15 2718 35 13.73 1.6 0.5243 1.6 0.98 271 211 1.06 0.07n2497-22 2857 3 2831 20 2794 48 15.24 2.1 0.5426 2.1 1.00 684 482 0.35 0.03n2497-23 2877 29 2886 24 2899 41 16.15 2.5 0.5678 1.7 0.69 253 191 0.48 1.21n2497-24 2788 4 2652 15 2477 32 12.62 1.6 0.4686 1.6 0.99 -10.5 958 598 0.57 0.05n2497-25 2967 4 2894 20 2791 47 16.29 2.1 0.5418 2.1 0.99 -3.3 431 332 0.76 0.32n2497-26 2812 3 2723 15 2605 33 13.61 1.5 0.4979 1.5 0.99 -6.0 1651 1152 0.73 0.08n2497-27 2765 8 2585 15 2361 30 11.75 1.6 0.4423 1.5 0.96 -14.3 611 344 0.31 1.65n2497-28 2759 7 2773 16 2791 38 14.34 1.7 0.5418 1.7 0.97 126 92 0.55 0.19n2497-29 2701 5 2695 15 2688 35 13.22 1.6 0.5174 1.6 0.98 238 158 0.36 {0.01}n2497-30 2734 10 2574 16 2376 31 11.62 1.7 0.4457 1.5 0.93 -12.1 433 239 0.18 0.50n2497-31 2892 3 2886 15 2877 36 16.15 1.6 0.5626 1.6 0.99 877 659 0.47 0.07n2497-32 2888 3 2906 16 2932 38 16.49 1.6 0.5758 1.6 0.99 304 226 0.31 0.01A1840 Riihivaara Suomussalmi mica gneiss (= n2496). all analyses on mostly oscillatory zoned inner domainsn2496-01 2684 7 2621 16 2540 36 12.21 1.7 0.4829 1.7 0.97 -2.9 219 149 0.80 0.55n2496-02 2797 9 2805 16 2817 37 14.84 1.7 0.5479 1.6 0.95 84 60 0.45 {0.02}n2496-03 2785 13 2795 23 2808 51 14.68 2.4 0.5459 2.2 0.94 408 301 0.60 0.06n2496-04 2749 8 2769 16 2797 35 14.29 1.6 0.5433 1.5 0.95 137 116 1.40 {0.01}n2496-05 2726 3 2752 15 2787 36 14.03 1.6 0.5408 1.6 0.99 546 379 0.36 0.03n2496-06 2724 5 2724 15 2725 34 13.63 1.6 0.5261 1.5 0.98 560 389 0.52 0.02n2496-07 2724 7 2608 16 2463 33 12.05 1.7 0.4653 1.6 0.96 -8.2 944 629 0.90 0.76n2496-08 2970 5 2963 15 2954 37 17.51 1.6 0.5813 1.5 0.98 225 181 0.65 0.35n2496-09 2950 6 2948 16 2946 37 17.24 1.6 0.5792 1.6 0.97 141 119 0.97 0.05n2496-10 2742 6 2734 15 2725 34 13.78 1.6 0.5260 1.5 0.97 122 91 0.90 0.16

158

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)


A1840 Riihivaara Suomussalmi mica gneiss (= n2496). all analyses on mostly oscillatory zoned inner domainsn2496-11 2730 4 2702 16 2665 36 13.31 1.6 0.5119 1.6 0.99 702 477 0.50 0.06n2496-12 2702 7 2448 15 2153 28 10.14 1.6 0.3966 1.5 0.97 -21.0 1214 595 0.14 0.04n2496-13 2717 2 2711 16 2702 37 13.43 1.7 0.5207 1.7 1.00 869 625 0.71 0.02n2496-14 2637 74 2674 47 2724 37 12.93 4.8 0.5259 1.7 0.34 765 549 0.60 10.94n2496-15 2684 20 2439 18 2157 28 10.05 2.0 0.3974 1.5 0.78 -17.7 1069 543 0.45 8.48n2496-16 2807 4 2769 17 2717 38 14.29 1.7 0.5242 1.7 0.99 -0.5 599 413 0.44 0.01n2496-17 2655 15 2271 20 1870 33 8.365 2.2 0.3366 2.0 0.91 -29.5 170 77 0.77 2.44n2496-17_8 2753 4 2646 20 2509 45 12.55 2.2 0.4758 2.1 0.99 -6.8 1041 689 0.72 0.08n2496-18 2737 4 2756 15 2781 36 14.09 1.6 0.5395 1.6 0.99 283 216 0.83 0.02

n2496-19 2840 4 2851 18 2866 43 15.57 1.8 0.5599 1.8 0.99 245 197 0.89 0.04n2496-20 2771 6 2752 15 2727 34 14.04 1.6 0.5266 1.5 0.97 167 123 0.71 1.67n2496-21 2724 8 2702 16 2672 35 13.31 1.7 0.5136 1.6 0.95 135 87 0.26 0.47n2496-22 2759 21 2758 19 2757 35 14.12 2.0 0.5337 1.5 0.77 105 77 0.68 0.51n2496-23 2805 10 2794 16 2779 36 14.67 1.7 0.5389 1.6 0.93 71 51 0.45 0.06n2496-24 2733 4 2735 16 2737 37 13.78 1.7 0.5289 1.7 0.99 634 433 0.37 0.30n2496-25 2835 8 2801 16 2755 36 14.78 1.7 0.5331 1.6 0.96 154 102 0.22 0.10n2496-26 2729 5 2633 16 2509 34 12.37 1.6 0.4758 1.6 0.99 -6.6 202 130 0.57 0.60n2496-27 2795 8 2817 16 2848 36 15.03 1.6 0.5555 1.6 0.96 52 40 0.67 0.05n2496-28 2753 18 2687 21 2600 41 13.10 2.2 0.4968 1.9 0.86 -1.1 84 54 0.32 1.03n2496-29 2960 4 2884 15 2777 35 16.13 1.6 0.5385 1.5 0.99 -4.6 257 192 0.61 0.14n2496-30 2780 6 2776 17 2770 38 14.39 1.7 0.5369 1.7 0.98 90 63 0.44 0.05n2496-31 2763 7 2742 16 2714 36 13.89 1.7 0.5236 1.6 0.97 199 140 0.58 0.33n2496-32 2726 4 2708 16 2683 37 13.40 1.7 0.5163 1.7 0.99 356 239 0.39 0.05A1243 Susi-Kervinen Rautavaara mica gneiss (= n2495). all analyses on inner zircon domainsn2495-01 2619 6 2320 18 1997 33 8.829 2.0 0.3631 1.9 0.98 -24.4 2862 1241 0.07 0.16n2495-02 2612 27 2458 22 2277 32 10.26 2.3 0.4236 1.6 0.71 -8.2 1944 980 0.04 1.73n2495-03 2724 4 2673 15 2605 33 12.90 1.6 0.4980 1.5 0.99 -2.2 506 340 0.57 0.37n2495-04 2692 6 2621 15 2530 32 12.22 1.6 0.4807 1.5 0.98 -4.1 688 423 0.32 1.32n2495-05 2613 19 2473 20 2306 34 10.42 2.1 0.4301 1.7 0.83 -8.5 1727 886 0.08 1.57n2495-06 2661 5 2623 15 2575 33 12.24 1.6 0.4909 1.6 0.98 -0.8 1156 691 0.16 0.01n2495-07 2630 4 2390 15 2119 28 9.525 1.6 0.3892 1.5 0.99 -20.1 908 431 0.15 0.22n2495-08 2748 3 2727 15 2698 35 13.66 1.6 0.5197 1.6 0.99 770 535 0.57 0.02n2495-09 2622 3 2583 15 2533 32 11.72 1.5 0.4812 1.5 0.99 -1.1 928 536 0.10 0.01n2495-10 2685 3 2642 15 2587 33 12.50 1.5 0.4939 1.5 0.99 -1.4 1497 934 0.33 0.01n2495-11 2731 5 2501 15 2229 29 10.75 1.6 0.4130 1.5 0.98 -19.0 342 187 0.47 0.14n2495-12 2741 4 2742 15 2743 34 13.89 1.6 0.5304 1.5 0.98 667 477 0.63 0.02n2495-13 2595 3 2558 15 2513 32 11.42 1.5 0.4767 1.5 0.99 -0.8 1006 572 0.08 0.05n2495-14 2778 89 2603 56 2383 32 11.98 5.8 0.4472 1.6 0.27 351 213 0.59 11.68n2495-15 2675 4 2499 15 2289 30 10.72 1.6 0.4263 1.5 0.99 -14.4 720 387 0.36 0.02n2495-16 2579 3 2516 15 2439 32 10.92 1.6 0.4599 1.6 0.99 -3.5 1420 773 0.05 0.40n2495-17 2639 4 2543 15 2425 31 11.24 1.6 0.4567 1.5 0.99 -6.8 1337 742 0.16 0.02n2495-18 2632 2 2613 15 2590 33 12.11 1.5 0.4944 1.5 1.00 1469 858 0.01 0.01n2495-19 2624 3 2559 15 2478 32 11.44 1.6 0.4688 1.5 0.99 -3.7 1723 988 0.19 0.14

159

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


A1243 Susi-Kervinen Rautavaara mica gneiss (= n2495). all analyses on inner zircon domainsn2495-20 2627 11 2497 18 2341 36 10.70 1.9 0.4378 1.8 0.94 -8.9 1398 733 0.07 0.68n2495-21 2628 2 2610 15 2588 33 12.07 1.6 0.4940 1.6 1.00 2600 1528 0.05 0.01n2495-22 2623 2 2591 15 2550 33 11.82 1.5 0.4852 1.5 1.00 -0.4 2597 1494 0.03 0.04n2495-23 2583 4 2498 15 2396 31 10.71 1.6 0.4501 1.5 0.99 -5.7 1137 607 0.05 0.32n2495-24 2604 4 2531 17 2440 36 11.09 1.8 0.4601 1.7 0.99 -4.2 2229 1220 0.05 0.21n2495-25 2634 3 2623 16 2608 36 12.24 1.7 0.4987 1.7 1.00 1329 794 0.08 0.02n2495-26 2736 4 2723 15 2705 35 13.60 1.6 0.5214 1.6 0.99 415 290 0.63 0.05n2495-27 2577 4 2413 14 2223 29 9.763 1.6 0.4118 1.5 0.99 -13.4 1992 971 0.03 0.58n2495-28 2695 4 2627 15 2540 34 12.30 1.6 0.4830 1.6 0.99 -3.8 505 308 0.29 0.77n2495-29 2603 3 2505 15 2385 32 10.79 1.6 0.4478 1.6 0.99 -7.0 902 482 0.09 0.75n2495-30 2738 5 2724 15 2706 34 13.63 1.6 0.5216 1.5 0.98 752 516 0.49 0.83In house zircon standardsA382 (n3563) Voinsalmi graniten3563-01 1888 6 1869 7 1852 11 5.301 0.8 0.3327 0.7 0.90 -0.15 198 78 0.21 0.04n3563-01b 1873 5 1866 8 1860 15 5.282 1.0 0.3344 0.9 0.95 280 112 0.28 0.04n3563-02 core 1887 2 1942 7 1994 13 5.771 0.8 0.3625 0.8 0.99 4.89 5396 2263 0.13 0.01n3563-02b rim 1887 4 1849 7 1815 12 5.177 0.8 0.3252 0.8 0.96 -2.61 524 200 0.20 0.03n3563-04 core 1875 10 1920 34 1962 65 5.626 3.9 0.3557 3.8 0.99 10162 4498 0.36 0.01n3563-04b rim 1874 6 1872 7 1871 11 5.322 0.8 0.3367 0.7 0.91 263 105 0.23 {0.02}n3563-06 core 1881 1 1948 6 2012 12 5.811 0.7 0.3663 0.7 1.00 6.56 6678 2933 0.29 0.00n3563-06b rim 1877 7 1817 7 1766 11 4.988 0.8 0.3151 0.7 0.90 -4.62 205 75 0.19 0.05n3563-08 1889 7 1876 7 1863 11 5.342 0.8 0.3351 0.7 0.88 148 60 0.33 {0.02}n3563-09 1870 7 1864 7 1858 12 5.269 0.8 0.3341 0.7 0.87 128 52 0.40 {0.01}n3563-10 1894 10 1850 8 1811 11 5.183 0.9 0.3244 0.7 0.79 -2.13 71 28 0.41 {0.03}n3563-11 1879 7 1874 7 1870 12 5.334 0.8 0.3365 0.7 0.88 238 98 0.34 {0.01}n3563-12 1879 6 1871 7 1863 12 5.310 0.8 0.3351 0.7 0.89 197 79 0.27 0.03n3563-13 1871 6 1883 7 1894 13 5.388 0.9 0.3415 0.8 0.91 206 87 0.43 0.03n3563-14 1878 8 1868 7 1859 11 5.296 0.8 0.3343 0.7 0.85 119 50 0.45 {0.05}n3563-15 1889 8 1865 7 1843 11 5.274 0.8 0.3310 0.7 0.86 -0.41 128 52 0.36 {0.03}n3563-16 1876 6 1875 7 1875 11 5.341 0.8 0.3376 0.7 0.91 318 122 0.09 0.02n3563-17 1871 8 1882 7 1891 12 5.380 0.9 0.3409 0.7 0.84 111 48 0.49 {0.04}n3563-17b 1870 9 1977 10 2080 18 6.007 1.1 0.3809 1.0 0.90 9.96 148 70 0.48 0.12n3563-18 1871 4 1867 7 1863 12 5.288 0.8 0.3351 0.7 0.95 387 157 0.33 {0.01}n3563-18b 1884 6 1871 7 1859 11 5.313 0.8 0.3343 0.7 0.91 247 97 0.21 0.04n3563-20 1884 8 1876 7 1870 11 5.345 0.8 0.3364 0.7 0.85 121 51 0.46 {0.02}n3563-21 1889 7 1874 9 1860 15 5.333 1.0 0.3345 0.9 0.92 154 62 0.31 {0.03}n3563-22 1877 5 1890 8 1901 15 5.431 1.0 0.3430 0.9 0.96 351 141 0.20 0.02n3563-23 1871 7 1878 9 1884 15 5.355 1.0 0.3393 0.9 0.91 140 60 0.48 {0.01}n3563-24 1871 9 1882 9 1893 15 5.382 1.1 0.3412 0.9 0.88 99 42 0.48 0.06n3563-25 1873 5 1873 8 1873 15 5.327 1.0 0.3372 0.9 0.96 309 126 0.30 0.03n3563-26 1877 8 1885 9 1893 15 5.401 1.0 0.3412 0.9 0.89 107 44 0.33 {0.02}n3563-27 1872 7 1877 9 1882 16 5.350 1.0 0.3390 1.0 0.92 221 91 0.33 0.03n3563-29 1884 5 1879 8 1875 15 5.365 1.0 0.3376 0.9 0.96 327 134 0.34 0.02

160

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.




[U] [Pb] Th/U f206 % 3)

spot # 206Pb 235U 238U 235U % 238U % ppm ppm measIn house zircon standards

A382 (n3563) Voinsalmi graniten3563-30 1859 9 1891 9 1920 15 5.438 1.0 0.3470 0.9 0.89 0.86 248 108 0.49 0.03n3563-31 1869 5 1889 8 1907 15 5.425 1.0 0.3442 0.9 0.95 282 119 0.40 0.02n3563-32 1880 6 1870 9 1861 15 5.308 1.0 0.3347 0.9 0.94 211 87 0.40 {0.02}n3563-33 1878 7 1888 9 1896 15 5.417 1.0 0.3420 0.9 0.92 191 79 0.33 0.04n3563-34 1883 7 1883 9 1884 15 5.391 1.0 0.3394 0.9 0.92 178 74 0.37 0.04n3563-35 1877 6 1873 9 1869 15 5.324 1.0 0.3363 1.0 0.95 302 123 0.32 0.02n3563-36 1880 8 1876 9 1873 15 5.344 1.0 0.3371 0.9 0.91 143 58 0.33 {0.03}n3563-37 1869 7 1863 9 1858 15 5.266 1.0 0.3340 0.9 0.93 201 84 0.49 {0.02}n3563-38 1872 6 1885 9 1896 16 5.400 1.0 0.3420 1.0 0.95 244 101 0.34 {0.01}n3563-39 1877 7 1869 9 1863 16 5.303 1.0 0.3351 1.0 0.94 219 90 0.37 0.03n3563-40 1871 7 1892 9 1911 16 5.442 1.0 0.3450 0.9 0.92 170 71 0.32 0.05n3563-41 1886 6 1877 9 1869 15 5.352 1.0 0.3363 0.9 0.93 195 79 0.32 {0.03}n3563-42 1880 5 1874 8 1868 15 5.330 1.0 0.3361 0.9 0.96 376 156 0.41 0.02n3563-43 1887 7 1881 9 1876 15 5.377 1.0 0.3377 0.9 0.93 200 81 0.29 {0.02}n3563-44 1884 7 1887 9 1890 15 5.416 1.0 0.3408 0.9 0.92 172 71 0.30 {0.02}n3563-45 1881 6 1889 8 1896 15 5.425 1.0 0.3419 0.9 0.94 247 105 0.45 0.03n3563-46 rim 1875 11 1883 9 1891 15 5.389 1.1 0.3409 0.9 0.84 76 31 0.33 {0.03}n3563-46b core 1869 9 1860 9 1852 15 5.245 1.1 0.3328 0.9 0.88 113 45 0.26 0.07n3563-48 1879 5 1882 8 1884 15 5.381 1.0 0.3395 0.9 0.95 293 116 0.17 0.03n3563-49 1886 10 1878 9 1871 15 5.357 1.1 0.3367 0.9 0.87 102 42 0.34 0.07n3563-50 1857 8 1845 9 1835 15 5.156 1.0 0.3294 0.9 0.91 177 71 0.34 0.04n3563-51 1877 7 1882 9 1886 15 5.379 1.0 0.3398 0.9 0.92 162 67 0.33 {0.03}n3563-52 1870 5 1871 8 1873 15 5.315 1.0 0.3371 0.9 0.95 298 124 0.41 0.02n3563-53 1867 8 1831 10 1799 18 5.070 1.2 0.3219 1.1 0.93 -1.25 158 62 0.35 {0.03}n3563-54 1883 5 1864 8 1847 15 5.270 1.0 0.3319 0.9 0.96 327 134 0.41 0.02n3563-55 1878 6 1872 9 1865 16 5.317 1.0 0.3356 1.0 0.95 275 109 0.24 0.03A1772 (n3565) Änäkäinen gabbro

n3565-01 2713 6 2714 8 2716 16 13.49 0.8 0.5240 0.7 0.89 221 138 0.01 {0.01}n3565-01b 2712 2 2736 9 2767 21 13.79 0.9 0.5362 0.9 0.99 0.53 624 489 0.98 {0.01}n3565-02 2715 2 2701 7 2684 16 13.30 0.7 0.5164 0.7 0.98 591 437 0.92 0.01n3565-02b 2713 2 2691 10 2661 22 13.15 1.0 0.5110 1.0 0.99 -0.30 833 640 1.15 {0.00}n3565-03 2713 3 2692 7 2664 16 13.17 0.7 0.5116 0.7 0.97 -0.67 572 428 1.03 {0.00}n3565-03b 2713 4 2694 8 2669 17 13.20 0.8 0.5129 0.8 0.95 -0.18 499 368 0.97 {0.00}n3565-03c 2711 2 2691 9 2665 20 13.16 0.9 0.5119 0.9 0.99 -0.17 542 402 0.95 0.01n3565-05 2711 1 2709 7 2707 16 13.42 0.7 0.5218 0.7 1.00 2300 1435 0.03 0n3565-05b 2715 2 2679 9 2632 20 13.00 0.9 0.5043 0.9 0.99 -1.85 664 478 0.85 0.01n3565-06 2711 3 2693 7 2669 15 13.18 0.7 0.5129 0.7 0.97 -0.34 413 279 0.48 {0.00}n3565-07 2714 3 2697 7 2673 15 13.23 0.7 0.5138 0.7 0.96 -0.29 480 331 0.57 {0.01}n3565-08 2713 2 2697 7 2675 16 13.24 0.7 0.5144 0.7 0.99 -0.18 795 622 1.24 {0.00}n3565-09 2711 3 2691 7 2664 15 13.16 0.7 0.5116 0.7 0.98 -0.64 500 346 0.61 0.01n3565-10 2712 2 2708 7 2703 16 13.40 0.7 0.5210 0.7 0.99 939 641 0.46 {0.00}n3565-10b 2714 2 2720 9 2727 21 13.56 0.9 0.5266 0.9 0.99 636 462 0.68 {0.01}

161

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland




[U] [Pb] Th/U f206 % 3)


A1772 (n3565) Änäkäinen gabbron3565-11 2711 3 2705 7 2697 16 13.35 0.7 0.5195 0.7 0.97 444 327 0.83 {0.01}n3565-12 2714 1 2714 7 2714 16 13.48 0.7 0.5235 0.7 0.99 1824 1173 0.16 {0.00}n3565-13 2715 3 2697 7 2674 15 13.24 0.7 0.5141 0.7 0.98 -0.30 440 330 1.00 {0.00}n3565-14 2714 2 2701 7 2685 16 13.30 0.7 0.5167 0.7 0.98 616 461 0.96 {0.00}n3565-15 2704 3 2672 7 2630 15 12.90 0.7 0.5038 0.7 0.97 -1.81 372 239 0.33 0.05n3565-16 2714 1 2717 7 2722 16 13.53 0.7 0.5254 0.7 0.99 1818 1136 0.01 {0.00}n3565-16b 2709 2 2713 9 2717 21 13.46 0.9 0.5243 0.9 0.99 1083 719 0.28 0n3565-17 core 2715 2 2702 7 2684 16 13.31 0.7 0.5164 0.7 0.99 805 548 0.48 0.01n3565-17b rim 2711 2 2658 7 2588 15 12.70 0.7 0.4939 0.7 0.99 -4.13 1396 823 0.03 0.03n3565-19 2713 3 2690 7 2660 15 13.15 0.7 0.5108 0.7 0.97 -0.85 421 301 0.79 0.03n3565-20 2710 2 2672 7 2623 15 12.90 0.7 0.5021 0.7 0.98 -2.42 542 375 0.70 0.01n3565-21 2711 4 2708 9 2703 20 13.40 1.0 0.5210 0.9 0.97 535 392 0.78 {0.01}n3565-22 2706 2 2684 9 2655 20 13.06 0.9 0.5096 0.9 0.99 -0.41 482 324 0.47 0.05n3565-23 2712 2 2700 9 2683 20 13.28 0.9 0.5161 0.9 0.99 555 382 0.53 {0.00}n3565-24 2714 2 2707 9 2697 21 13.38 1.0 0.5194 0.9 0.99 460 339 0.84 {0.01}n3565-25 2707 3 2704 9 2700 21 13.34 1.0 0.5203 1.0 0.99 417 303 0.74 0.01n3565-26 2711 3 2706 9 2699 20 13.36 0.9 0.5199 0.9 0.98 497 375 0.95 0.01n3565-27 2713 2 2709 9 2704 22 13.42 1.0 0.5212 1.0 0.99 1841 1247 0.41 {0.00}n3565-28 2717 2 2709 9 2700 20 13.42 0.9 0.5202 0.9 0.99 729 551 0.95 {0.00}n3565-29 2712 2 2700 9 2684 21 13.28 0.9 0.5165 0.9 0.99 828 552 0.38 0.01n3565-30 2711 2 2700 10 2686 22 13.29 1.0 0.5169 1.0 0.99 624 460 0.86 0.01n3565-31 2708 3 2691 9 2667 20 13.15 0.9 0.5125 0.9 0.98 386 271 0.68 {0.01}n3565-32 2699 3 2684 9 2664 21 13.06 1.0 0.5117 0.9 0.99 416 257 0.08 0.01n3565-33 2702 3 2685 9 2661 20 13.07 0.9 0.5111 0.9 0.99 449 281 0.14 0.01n3565-34 2713 2 2691 9 2661 20 13.15 0.9 0.5111 0.9 0.99 -0.43 530 391 0.92 0.01n3565-35 2711 2 2698 9 2679 21 13.25 0.9 0.5153 0.9 0.99 795 603 1.02 0.1n3565-36 2712 3 2684 9 2646 21 13.05 1.0 0.5074 1.0 0.98 -1.01 438 319 0.88 0.04n3565-37 2707 2 2688 9 2663 21 13.12 1.0 0.5115 1.0 0.99 -0.03 455 282 0.10 0.01n3565-38 2708 3 2676 9 2634 20 12.95 0.9 0.5046 0.9 0.98 -1.45 392 236 0.06 0.03n3565-39 2708 2 2693 9 2673 21 13.19 1.0 0.5138 1.0 0.99 558 367 0.34 0.01n3565-40 2712 2 2698 9 2678 21 13.25 1.0 0.5151 0.9 0.99 593 447 0.98 {0.00}n3565-41 2715 1 2710 9 2704 21 13.43 0.9 0.5211 0.9 1.00 2363 1508 0.14 0n3565-42 2710 3 2677 9 2633 20 12.96 0.9 0.5045 0.9 0.98 -1.52 266 159 0.01 0.02n3565-43 2707 2 2684 9 2655 20 13.06 0.9 0.5095 0.9 0.99 -0.46 518 373 0.81 0.01n3565-44 2654 2 2630 9 2599 20 12.33 0.9 0.4966 0.9 0.99 -0.62 982 603 0.20 0.01n3565-47 2714 3 2694 9 2667 21 13.19 1.0 0.5124 0.9 0.99 -0.15 412 292 0.70 {0.01}n3565-48 2691 2 2686 9 2680 21 13.09 1.0 0.5154 0.9 0.99 483 314 0.29 0.01n3565-49 2710 2 2701 9 2688 20 13.29 0.9 0.5174 0.9 0.99 813 577 0.67 0.01n3565-50 2717 2 2698 9 2674 21 13.26 1.0 0.5140 1.0 0.99 -0.02 703 507 0.77 {0.00}n3565-54 2703 3 2698 9 2693 20 13.26 0.9 0.5185 0.9 0.98 388 245 0.11 0.01n3565-55 2713 3 2692 9 2664 20 13.17 1.0 0.5116 0.9 0.98 -0.25 487 361 0.94 0.02

All errors are in 1 sigma level. 1) Error correlation in conventional concordia space. 2) Age discordance at closest approach of error ellipse to concordia (2s level). 3) Percentage of common 206Pb in measured 206Pb. calculated from the 204Pb signal assuming a present-day Stacey and Kramers (1975) model terrestrial Pb-isotope composition. Figures in parentheses are given when no correction has been applied. Some analyses with high common lead are not used in evaluation (strikethrough).A5homog = homogeneous

162

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 2. U-Pb TIMS data on zircon. monazite and titanite.Sample information Sample U Pb 206Pb/204Pb 208Pb/206Pb ISOTOPIC RATIOS* r ** APPARENT AGES / Madensity/size (µm)/abraded x hours weight / mg ppm ppm measured radiogenic 206Pb/238U 207Pb/235U 207Pb/206Pb 2s% 206Pb/238U 207Pb/235U 207Pb/206PbSuomussalmi greenstone beltA260 Haaponen metagreywackeA260A +4.6/>75 20.1 299 169 6314 0.20 0.4658 13.131 0.2045 0.15 0.98 2465 2689 2862A260B 4.2-4.6/>75 15.1 496 284 5079 0.20 0.4726 13.052 0.2003 0.15 0.98 2494 2683 2828A1428 Mesa-aho quartz porphyryA1428A +4.3 8.2 161 105 3383 0.28 0.5094 13.850 0.1972 0.15 0.98 2654 2739 2803A1428B +4.3/abr 5 h 7.5 152 104 4611 0.28 0.5328 14.565 0.1983 0.15 0.98 2753 2787 2812A1428C +4.3/abr 16 h 7.5 157 108 4854 0.28 0.5351 14.630 0.1983 0.15 0.98 2762 2791 2812A1429 Kilpasuo meta-andesiteA1429A +4.0 1.2 501 316 1041 0.26 0.4860 12.834 0.1915 0.15 0.98 2553 2667 2755A1429B +4.0/abr 5 h 0.5 542 358 2818 0.31 0.5074 13.453 0.1923 0.15 0.98 2645 2712 2762A1429D +4.0/abr 5 h/tabular 0.3 653 435 2299 0.30 0.5087 13.515 0.1927 0.15 0.98 2651 2716 2765A1467 Saarikylä felsic volcanic rockA1467A +4.3/brownish 0.7 441 210 994 0.15 0.3870 11.582 0.2170 0.16 0.97 2109 2571 2959A1467B +4.3/pale 0.3 355 143 641 0.21 0.3099 8.705 0.2037 0.15 0.98 1740 2307 2856A1467C 4.2-4.3/brown/abr 2 h 0.3 514 292 1079 0.13 0.4693 13.920 0.2151 0.15 0.98 2481 2744 2944A1467D 3.8-4.2/abr 2 h 0.6 812 395 429 0.14 0.3767 11.004 0.2119 0.23 0.95 2061 2524 2920A1467E +4.2/abr 7 h 0.3 325 201 2383 0.18 0.5061 14.802 0.2121 0.15 0.98 2640 2803 2922A1593 Saarikylä quartz porphyryA1593A Monazite 0.1 2851 13402 2359 8.23 0.5728 16.963 0.2148 0.15 0.98 2920 2933 2942A1840Palovaara Suomussalmi mica gneiss (west from the greenstone belt)A1840A +4.2 >75 a18h 0.49 250 150 18161 0.15 0.5191 13.695 0.1913 0.15 0.98 2695 2729 2754Kuhmo greenstone beltA120 Ruokojärvi daciteA120A. +4.6 20 221 59 317 0.29 0.3067 8.355 0.1976 0.30 0.89 1724 2270 2806A120C 4.2-4.6/<75/abr 1 h 10 443 194 6004 0.08 0.5070 15.238 0.2180 0.15 0.97 2672 2830 2966A120D 4.2-4.6/>75/abr 3 h 13 458 204 6083 0.09 0.5137 15.574 0.2199 0.15 0.97 2672 2851 2980A120E 4.2-4.6/<75/abr 5 h 11 439 198 5461 0.09 0.5204 15.737 0.2194 0.15 0.97 2700 2860 2976A120F 4.0-4.2 <75 a3h 10 488 181 162 0.13 0.2473 6.692 0.1963 0.30 0.93 1424 2071 2796A120G 3.6-3.8 +150 a 4.0 927 336 109 0.09 0.2187 5.931 0.1967 0.30 0.93 1274 1965 2799A120I 4.2-4.6 a11h 1.7 459 278 5260 0.09 0.5329 16.230 0.2209 0.15 0.98 2753 2890 2987A1000 Ruokojärvi daciteA1000aA +4.3 dark 3.5 236 135 2168 0.12 0.4951 13.711 0.2008 0.20 0.96 2592 2729 2833A1000aB +4.3 microgems 8.7 151 89 2397 0.12 0.5121 13.985 0.1981 0.20 0.96 2665 2748 2711A1000aC +4.2 long 3 294 165 351 0.12 0.4324 11.859 0.1989 0.30 0.91 2316 2593 2817A1000aD 4.2-4.3 +150 a2h 4 399 220 369 0.10 0.4364 11.942 0.1985 0.30 0.91 2334 2599 2814A1000bA +4.2 >75 a2h 4.5 290 153 241 0.12 0.3934 10.804 0.1992 0.30 0.91 2138 2506 2820A1000bB +4.2 +100 a5h 3.5 205 121 392 0.13 0.4561 12.573 0.1999 0.30 0.91 2422 2648 2826A1000bC +4.2 <75 a5h 2.1 312 179 632 0.12 0.4712 12.945 0.1993 0.30 0.91 2488 2675 2820A1000bD +4.3 +150 CA** 17679 0.13 0.5396 14.790 0.1988 0.15 0.98 2782 2802 2816A1346 Lampela andesiteA1346A +4.5/abr 1 h 4.4 157 86 977 0.12 0.4646 12.205 0.1906 0.20 0.96 2459 2620 2747A1346B 4.3-4.5/>75/abr 1 h 4.9 208 108 1023 0.13 0.4376 11.300 0.1873 0.20 0.96 2339 2548 2719A1346C 4.3-4.5/<75/abr 1 h 5.1 266 130 1004 0.14 0.4124 10.461 0.1840 0.20 0.96 2225 2476 2689A1346D 4.3-4.5/>75/pink 0.6 222 120 1353 0.13 0.4590 11.956 0.1889 0.20 0.96 2435 2601 2733A1346E 4.3-4.5/<75/pink 0.7 275 136 927 0.14 0.4132 10.513 0.1845 0.30 0.91 2230 2481 2694A1346F 4.3-4.5 <75 CA*** 19630 0.13 0.5377 14.562 0.1964 0.15 0.98 2774 2787 2797

163

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland

Appendix 2. cont.Sample information Sample U Pb 206Pb/204Pb 208Pb/206Pb ISOTOPIC RATIOS* r ** APPARENT AGES / Madensity/size (µm)/abraded x hours weight / mg ppm ppm measured radiogenic 206Pb/238U 207Pb/235U 207Pb/206Pb 2s% 206Pb/238U 207Pb/235U 207Pb/206PbA1377 Siivikko felsic fragment in komatiiteA1377A +4.5/abr 3 h 4.0 325 123 2556 0.19 0.3147 7.835 0.1806 0.15 0.98 1763 2212 2658A1377B 4.3-4.5/abr 3 h 4.8 351 141 2617 0.21 0.3302 8.249 0.1812 0.15 0.98 1839 2258 2664A1377C 4.3-4.5 4.5 303 115 2419 0.20 0.3151 7.821 0.1801 0.20 0.96 1765 2210 2654A1418 Niittylahti gabbroA1418A +4.3/>75 6.2 164 101 1027 0.27 0.4717 11.754 0.1807 0.15 0.98 2491 2585 2659A1418B1 +4.3/>75/abr 6.3 245 154 1177 0.27 0.4843 12.217 0.1830 0.15 0.98 2545 2621 2680A1418B2 +4.3/>75/abr 6.3 245 154 1215 0.28 0.4846 12.249 0.1834 0.15 0.98 2547 2623 2684A1418C 4.2-4.3/>75 5.5 356 201 659 0.32 0.4147 9.517 0.1665 0.20 0.96 2236 2389 2523A1418D 4.0-4.2/>75 6.2 394 202 746 0.34 0.3778 8.169 0.1568 0.20 0.96 2066 2249 2421A1418E +4.3/>75/abr 16 h 4.8 239 148 1444 0.27 0.4816 12.094 0.1822 0.15 0.98 2534 2611 2673A1418F 4.2-4.3 turbid CA*** 1110 0.28 0.7570 19.170 0.1837 0.20 0.98 3633 3050 2686A1771 Kellojärvi Kuhmo gabbronorite pegmatoid A1771A +4.0 >75 a3h turbid 0.59 260 163 4593 0.23 0.5080 13.248 0.1891 0.15 0.98 2648 2698 2735A511 Katerma metarhyoliteA511H +4.2 CA*** 23748 0.12 0.5361 14.524 0.1965 0.15 0.98 2767 2785 2797A788 Polvilampi quartz-feldspar schistA788E +4.2 >75 CA*** 6292 0.10 0.5284 14.296 0.1962 0.15 0.99 2735 2770 2795A976 Moisiovaara amphibolite (metavolcanic rock)A976J 4.2-4.6 >75 CA*** 10368 0.51 0.5342 14.594 0.1982 0.15 0.98 2759 2789 2811A976K 4.2-4.6 >75 CA*** 18807 0.54 0.5407 14.730 0.1976 0.15 0.98 2786 2798 2806A1213, A1254, N5A Pitkäperä meta-andesiteA1213A. +3.6 2.2 328.6 173.9 2515 0.11 0.4631 12.424 0.1945 0.15 0.98 2453 2636 2781A1213B +3.6 CA*** 17536 0.10 0.5423 15.041 0.2012 0.15 0.98 2793 2818 2835A1254A. +4.0/clear 0.3 349.8 182.5 5730 0.10 0.4630 12.512 0.1960 0.15 0.98 2453 2644 2793A1254B +4.0 CA*** 25328 0.11 0.5415 14.934 0.2000 0.15 0.98 2790 2811 2827N5A. +4.2/abr 1 h/turbid 0.2 373.0 186.3 19511 0.005 0.4886 12.418 0.1843 0.15 0.97 2565 2637 2692A1560 Huuhilonkylä porphyry A1560A +4.3 >75 clear a16h 0.3 131 76.9 2662 0.13 0.5086 13.647 0.1946 0.15 0.98 2651 2726 2782A1560B +4.3 >75 clear 0.48 169 89.6 5374 0.13 0.4623 12.354 0.1938 0.15 0.98 2450 2632 2775A1560C 4.2-4.3 a16h 0.37 301 149 3586 0.14 0.4311 11.047 0.1859 0.15 0.98 2311 2527 2706A1560D 4.0-4.2 <75 a6h 0.55 427 204 3050 0.14 0.4135 10.537 0.1848 0.15 0.98 2231 2483 2697A1560E +4.3 >75 clear a24h 0.24 134 78.1 6020 0.13 0.5098 13.670 0.1945 0.15 0.98 2656 1727 2781A1560F +4.3 <75 water-clear a16h 0.07 238 111 9043 0.14 0.4137 9.4426 0.1655 0.15 0.98 2232 2382 2513A1560G +4.3 >75 CA*** 19828 0.11 0.5418 14.683 0.1966 0.15 0.98 2791 2795 2798A2027 Siivikkovaara porphyry dikeA2027A +4.2 >75 0.44 147 87 1636 0.14 0.4988 13.137 0.1910 0.15 0.98 2609 2690 2751A2027B +4.2 >75 a17h 0.56 142 87 7273 0.14 0.5288 14.203 0.1948 0.15 0.98 2736 2763 2783A2027C +4.2 CA*** 17258 0.15 0.5402 14.609 0.1961 0.15 0.98 2785 2790 2794Naavala 7, amphibolite, metamorphic zirconNaa 7 zr +3.6 a2h 0.32 145.0 83.7 22782 0.11 0.5162 13.174 0.1851 0.15 0.98 2683 2692 2699Tipasjärvi greenstone beltA1174 Taivaljärvi felsic volcanic rock (Vaasjoki et al 1999, anal A-D)A1174E +4.5 CA*** 31736 0.11 0.5417 14.684 0.1966 0.15 0.98 2791 2795 2798A1886 Tipasjärvi felsic volcanic rock (4322-2005-R305/235-239)A1886E +4.3 >75 a17h 0.52 319 200 5200 0.16 0.5334 14.283 0.1942 0.2 0.96 2756 2769 2778A1886F +4.3 <75 a17h 0.38 288 177 14191 0.13 0.5300 14.200 0.1943 0.15 0.98 2741 2763 2779A1886G +4.3 >75 0.4 288 170 5262 0.14 0.5101 13.470 0.1915 0.15 0.98 2657 2713 2755A1886H +4.3 >75 a17h 0.37 242 146 16449 0.13 0.5254 14.060 0.1941 0.15 0.98 2722 2754 2777A1886I +4.3 >75 CA*** 47164 0.12 0.5435 14.699 0.1961 0.15 0.98 2798 2796 2794

164

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 2. cont.Sample information Sample U Pb 206Pb/204Pb 208Pb/206Pb ISOTOPIC RATIOS* r ** APPARENT AGES / Madensity/size (µm)/abraded x hours weight / mg ppm ppm measured radiogenic 206Pb/238U 207Pb/235U 207Pb/206Pb 2s% 206Pb/238U 207Pb/235U 207Pb/206PbA1377 Siivikko felsic fragment in komatiiteA1921A +3.3 CA*** 7146 0.3 0.5375 14.416 0.1945 0.15 0.98 2773 2778 2781A1922 Tipasjärvi volcanic rock, agglomerate (4322-2006-R337/138.55-139.75)A1922A +4.0 a17h 0.21 62.9 40.1 12216 0.16 0.5429 15.007 0.2005 0.15 0.98 2796 2816 2830A1922B +4.0 CA*** 38708 0.16 0.5446 15.023 0.2001 0.15 0.98 2802 2817 2827A1748 Aarreniemi Tipasjärvi greywackeA1748A +4.2 a4h 0.58 333 198 3473 0.19 0.4938 12.965 0.1904 0.15 0.98 2587 2677 2746Kovero greenstone beltA1624 Hämälänniemi felsic volc.A1624A +4.3 >75 a4h pale 0.59 248 157 4264 0.19 0.5244 14.701 0.2033 0.3 0.91 2718 2796 2853A1624B +4.3 >75 a5h red 0.36 315 201 6874 0.19 0.5287 14.756 0.2024 0.15 0.98 2736 2800 2846A1624C +4.3 <75 pale 0.46 301 189 1220 0.19 0.5043 14.014 0.2016 0.15 0.98 2632 2751 2839A1624D +4.3 <75 red 0.3 288 179 1276 0.19 0.5023 13.963 0.2016 0.3 0.91 2624 2747 2839A1624E +4.3 <75 a4h pale 0.42 197 124 1418 0.19 0.5072 14.104 0.2017 0.15 0.98 2645 2757 2840A1624F +4.3 >75 a16h 0.57 223 145 5770 0.18 0.5388 15.083 0.2030 0.15 0.98 2779 2821 2851A1624G 4.2-4.3 “bulk” 0.51 515 291 699 0.21 0.4413 11.762 0.1933 0.15 0.98 2356 2586 2771A1624H +4.3 >75 a16h 0.44 307 194 5283 0.18 0.5260 14.687 0.2025 0.15 0.98 2725 2795 2847A1624I +4.3 >75 CA*** (“69”) 10689 0.16 0.5604 15.939 0.2063 0.12 0.99 2868 2873 2877A1625 Rasisuo pl-porphyry dykeA1625A +4.3 >75 a16h long 0.45 262 159 5095 0.18 0.5118 13.343 0.1891 0.15 0.98 2665 2704 2734A1625B +4.3 >75 long 0.3 291 171 1932 0.16 0.4940 12.791 0.1878 0.15 0.98 2588 2664 2723A1625C +4.3 <75 a1h long 0.3 343 201 1261 0.17 0.4826 12.445 0.1871 0.2 0.96 2538 2639 2716A1625D +4.3 <75 long 0.28 354 205 2750 0.18 0.4854 12.498 0.1867 0.15 0.98 2551 2643 2714A1625E +4.3 >75 a16h clear 0.42 177 111 6730 0.20 0.5204 13.623 0.1899 0.15 0.98 2701 2724 2741A1625F +4.3 >75 CA*** (“100”) 26367 0.19 0.5274 13.936 0.1916 0.15 0.98 2731 2745 2756A1626 Rasisuo gabbroA1626A +4.3 >75 a16h 0.46 488 285 2884 0.28 0.4566 11.408 0.1812 0.15 0.98 2424 2557 2664A1626B +4.3 >75 0.46 385 233 1374 0.27 0.4673 12 0.1863 0.15 0.98 2472 2604 2709A1626C +4.3 <75 a1h 0.24 321 200 1380 0.27 0.4809 12.457 0.1879 0.15 0.98 2531 2640 2723A1626D +4.3 <75 0.17 331 200 1178 0.27 0.4647 12.002 0.1873 0.25 0.99 2460 2605 2719A1626F +4.3 >75 a21h 0.46 398 254 3822 0.27 0.5032 13.007 0.1875 0.15 0.98 2628 2680 2720A1627 Rasisuo felsic tuffA1627A +4.3 >75 a4h dark euh 0.43 360 218 6309 0.13 0.5237 14.469 0.2004 0.15 0.98 2715 2781 2829A1627B +4.3 <75 0.54 381 196 2674 0.11 0.4524 11.749 0.1884 0.15 0.98 2406 2585 2728A1627C +4.3 <75 a16h 0.52 221 138 10519 0.15 0.5380 14.891 0.2007 0.15 0.98 2775 2808 2832A1627D +4.3 >75 a16h 0.48 283 174 8717 0.14 0.5301 14.62 0.2000 0.15 0.98 2742 2791 2826A1627E +4.3 >75 a32h 0.55 243 152 10090 0.14 0.5389 14.967 0.2014 0.15 0.98 2779 2813 2838A1627F +4.3 >75 CA*** (“97”) 36972 0.14 0.5584 15.898 0.2065 0.15 0.98 2860 2871 2878A1520 Kiukoinvaara (granitic-granodioritic vein)A1520A +4.3/stubby/abr 6 h 0.44 363 287 122 0.15 0.4805 12.365 0.1867 0.43 0.84 2529 2633 2713A1520B +4.3/longish/abr 2 h 0.46 466 301 230 0.14 0.463 11.820 0.1852 0.3 0.92 2453 2590 2700A1520C +4.3/<75/euhedral 0.15 503 327 158 0.14 0.4302 10.891 0.1836 0.33 0.91 2307 2514 2686A1520D 4.2-4.3/>75/abr 6 h 0.49 496 339 146 0.15 0.4409 11.161 0.1836 0.36 0.89 2355 2537 2686A1520E 4.2-4.3/>75/long 0.23 766 429 159 0.14 0.3723 9.235 0.1799 0.34 0.91 2040 2362 2652A1520F +4.3 >75 CA** (“97”) 28504 0.16 0.5273 13.881 0.1909 0.12 0.99 2730 2742 2750A1155 Linnasuo porphyryA1155G +4.3 >75 CA*** (“67”) 25584 0.13 0.5376 14.2560 0.1923 0.12 0.99 2774 2767 2762

165

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland

Appendix 2. cont.Sample information Sample U Pb 206Pb/204Pb 208Pb/206Pb ISOTOPIC RATIOS* r ** APPARENT AGES / Madensity/size (µm)/abraded x hours weight / mg ppm ppm measured radiogenic 206Pb/238U 207Pb/235U 207Pb/206Pb 2s% 206Pb/238U 207Pb/235U 207Pb/206PbA1377 Siivikko felsic fragment in komatiiteA1749D +4.2 >75 CA*** (“98”) 26695 0.12 0.5415 14.765 0.1978 0.12 0.99 2790 2800 2808Pudasjärvi complexA1490 Tuore Ristisuonpalo granodioriteA1490A +4.2 0.49 453 197 5714 0.15 0.3803 9.150 0.1745 0.15 0.98 2078 2353 2601A1490B +4.2 a6h 0.19 284 151 7347 0.13 0.4693 11.791 0.1822 0.15 0.98 2480 2588 2673A1490C 4.0-4.2 0.25 601 220 2096 0.12 0.3241 7.503 0.1679 0.15 0.98 1810 2173 2537A1490D 4.0-4.2 a6h 0.22 281 257 5084 0.11 0.3959 9.578 0.1755 0.15 0.98 2150 2395 2610A1490E +4.2 CA*** (“87”) 17350 0.15 0.5313 14.429 0.1970 0.12 0.99 2747 2778 2801A1533 Surmakumpu porphyryA1533A +4.3 a18h 0.22 222 101 2368 0.23 0.3692 9.070 0.1782 0.15 0.98 2026 2345 2636A1533B +4.3 0.48 422 114 233 0.46 0.1641 3.635 0.1607 0.3 0.93 979 1557 2463A1533C 4.2-4.3 a18h 0.27 396 113 1619 0.29 0.2223 5.237 0.1709 0.15 0.98 1294 1859 2566A1533D 4.0-4.2 0.53 784 114 339 0.49 0.0925 1.836 0.1439 0.3 0.91 570 1058 2275A1533E +4.3 a23h 0.15 125 64 6496 0.2 0.4336 10.768 0.1801 0.15 0.98 2322 2503 2654A1533F +4.3 CA*** (“99”) 43514 0.19 0.5127 13.015 0.1841 0.15 0.98 2668 2681 2690A1534 Keväpalo tonaliteA1534A +4.2 >75 a18h 0.46 204 119 5987 0.11 0.5173 13.847 0.1941 0.15 0.98 2688 2739 2778A1534B +4.2 >75 0.45 238 120 1162 0.08 0.4412 11.610 0.1909 0.15 0.98 2356 2573 2750A1534C +4.2 <75 a20h 0.06 366 213 3161 0.11 0.515 13.742 0.1935 0.15 0.98 2678 2732 2773A1534D +4.2 <75 0.35 244 127 792 0.09 0.4512 11.933 0.1918 0.2 0.96 2400 2599 2758A1534E +4.2 >75 CA*** (“58”) 11208 0.08 0.5304 14.200 0.1942 0.15 0.98 2743 2763 2778A1534sphene 9.52 31 20 791 0.17 0.5205 13.427 0.1871 0.2 0.96 2701 2710 2717A1553 Pitkäkumpu tonaliteA1553A +4.0>75 a18h 0.42 244 120 4633 0.1 0.4397 11.287 0.1862 0.15 0.98 2357 2551 2709A1553B +4.0 >75 0.45 405 144 1297 0.09 0.3134 7.855 0.1818 0.15 0.98 1758 2215 2669A1553C +4.0 <75 a4h 0.25 214 106 4495 0.1 0.4448 11.351 0.1851 0.15 0.98 2372 2552 2699A1553D +4.0 <75 0.52 322 123 2052 0.1 0.3399 8.523 0.1819 0.15 0.98 1886 2288 2670A1553E +4.0 <75 a20h 0.17 217 116 2729 0.11 0.4723 12.160 0.1867 0.15 0.98 2494 2617 2714A1553F +4.0 >75 CA*** (“68”) 26356 0.09 0.5242 13.672 0.1892 0.15 0.98 2717 2727 2735A1731 Palomaa graniteA1731A +4.2 <75 a15h 0.09 1172 622 2313 0.1 0.4726 11.832 0.1816 0.15 0.98 2495 2591 2667A1731B +4.2 <75 0.56 657 338 589 0.11 0.4271 10.552 0.1792 0.15 0.98 2293 2485 2645A1731C +4.2 >75 a14h 0.53 1067 544 1380 0.09 0.4521 11.252 0.1805 0.15 0.98 2404 2544 2658A1731D +4.2 >75 a2h 0.41 856 433 1161 0.09 0.4451 11.048 0.18 0.15 0.98 2374 2527 2653A1731E +4.0 CA*** (“51”) 19927 0.08 0.5112 13.051 0.1852 0.15 0.98 2662 2683 2700A1739 Veskanmaa granodioriteA1739A +4.2 a3h long clear euhedral 0.57 871 464 10559 0.09 0.4845 12.266 0.1836 0.15 0.98 2547 2625 2686A1739B +4.2 >75 euhedral turbid 0.45 788 394 3355 0.10 0.4472 11.298 0.1832 0.15 0.98 2383 2548 2682A1739C +4.2 <75 a17h euh 0.52 908 487 10196 0.09 0.4873 12.327 0.1835 0.15 0.98 2559 2630 2685A1739D titanite 3.3-3.6 abr 1.5 259 167 2725 0.32 0.4910 12.001 0.1773 0.15 0.98 2575 2605 2628A1739E +4.2 CA*** (“54”) 13444 0.09 0.5237 13.877 0.1922 0.15 0.98 2715 2741 2761A1740 Palomaa monzoniteA1740A +4.0 >75 a16h long euh 0.46 2441 1429 22497 0.23 0.4816 11.901 0.1792 0.15 0.98 2534 2597 2646A1740B +4.0 >75 a5h long euh 0.44 1886 1097 19323 0.22 0.4824 11.937 0.1795 0.15 0.98 2538 2600 2648A1740C +4.0 <75 a5h long euh 0.43 675 384 8408 0.16 0.4915 12.311 0.1817 0.15 0.99 2577 2628 2668A1740D +4.0 <75 a16h 0.35 444 259 12085 0.17 0.4992 12.495 0.1815 0.15 0.98 2610 2642 2667A1740E +4.0 >75 0.47 1162 682 11893 0.22 0.4851 12.042 0.1800 0.15 0.98 2550 2608 2653A1740F +4.0 <75 a17h 0.44 862 502 21403 0.17 0.4979 12.479 0.1818 0.15 0.98 2605 2641 2669A1740G +4.0 >75 CA*** (“63”) 26707 0.12 0.5128 12.876 0.1821 0.15 0.98 2668 2671 2672

166

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 2. cont.Sample information Sample U Pb 206Pb/204Pb 208Pb/206Pb ISOTOPIC RATIOS* r ** APPARENT AGES / Madensity/size (µm)/abraded x hours weight / mg ppm ppm measured radiogenic 206Pb/238U 207Pb/235U 207Pb/206Pb 2s% 206Pb/238U 207Pb/235U 207Pb/206PbA1377 Siivikko felsic fragment in komatiiteA1741A +4.2 a5h 0.54 226 110 232.2 0.14 0.3492 9.1559 0.1902 0.4 0.90 1931 2354 2744A1741B +4.2 0.47 511 133 243.9 0.15 0.1893 4.7372 0.1815 0.4 0.90 1117 1774 2667A1741C 4.0-4.2 0.39 838 179 193.3 0.16 0.1480 3.5822 0.1756 0.4 0.90 890 1546 2611A1741D +4.2 a17h 0.4 145 58.2 1002 0.13 0.3395 8.7446 0.1868 0.3 0.93 1884 2312 2714A1741E +4.2 CA*** (“49”) 17571 0.10 0.5235 13.841 0.1918 0.15 0.98 2714 2739 2757A1742 Viitakangas graniteA1742A 3.6-4.0 a2h turbid 0.49 2260 517 204.1 0.33 0.1493 2.532 0.123 0.4 0.90 897 1281 2000A1742B +4.0 a2h 0.56 1386 430 215.2 0.33 0.2016 3.7896 0.1363 0.4 0.90 1184 1591 2181A1842 Jäkälämaa Pudasjärvi mica gneissA1842A monazite +4.3 magn a20min 0.26 2981 4580 91080 2.33 0.5073 12.431 0.1777 0.15 0.98 2645 2637 2632A1842B Zr +4.3 a17h 0.44 174 104 8241 0.14 0.5216 13.704 0.1906 0.15 0.98 2706 2729 2747Iisalmi complex, A1243 Susi-Kervinen mica gneissA1243A +4.3 5.0 529 276 3927 0.06 0.4811 11.929 0.1798 0.15 0.98 2532 2598 2651A1243B 4.2-4.3 5.1 702 351 3732 0.05 0.4679 11.508 0.1784 0.15 0.98 2474 2565 2638A1243C 4.0-4.2 5.3 932 459 2956 0.04 0.4631 11.315 0.1772 0.15 0.98 2453 2549 2627A1243D 3.8-4.0 5.0 1262 554 1654 0.03 0.4110 9.941 0.1755 0.15 0.98 2219 2429 2610JVP-II +3.3 5.3 749 348 4493 0.07 0.4293 10.460 0.1767 0.15 0.98 2302 2476 2622Loso sanukitoidsA331I Loso 4.2-4.3 <75 CA*** 12409 0.17 0.5194 13.292 0.1856 0.15 0.98 2697 2701 2703A1926 Ansosuo dioriteA1926A +4.2 >75 0.52 325 191 271 0.21 0.4163 10.561 0.1840 0.3 0.94 2244 2485 2689A1926B +4.2 >75 a17h 0.47 307 190 265 0.21 0.4362 10.991 0.1827 0.3 0.94 2334 2522 2678A1926C +4.2 >75 CA*** 32628 0.19 0.5213 13.43 0.1869 0.15 0.98 2705 2710 2715In house zircon standards:A382 Voinsalmi granite (for A382F-I concordia age 1877±2 Ma)A382F +4.6 >75 a17h 0.45 172 61 6867 0.10 0.3375 5.3366 0.1147 0.15 0.98 1874 1875 1875A382G +4.6 >75 a5h 0.49 167 59.1 8642 0.10 0.3377 5.3467 0.1148 0.15 0.98 1876 1876 1877A382H +4.6 <75 a17h 0.52 165 58.2 9801 0.10 0.3368 5.3326 0.1148 0.15 0.98 1871 1874 1877A382I +4.6 >75 0.57 189 66.1 8579 0.09 0.3363 5.3284 0.1149 0.15 0.98 1869 1874 1879A382J +4.6 >75 CA*** (“85”) 16502 0.09 0.3363 5.3521 0.1154 0.15 0.98 1869 1877 1886A382K +4.6 >75 CA*** (“97”) 75302 0.09 0.3365 5.3522 0.1154 0.15 0.98 1870 1877 1885A382L +4.6 <75 CA*** (“105”) 13697 0.08 0.3356 5.3196 0.1150 0.15 0.98 1866 1872 1879A1772 Änäkäinen gabbro (upper intercept age 2711±3 Ma)A1772A +4.0 >75 a17h 0.58 567 342 11241 0.17 0.5146 13.2140 0.1862 0.15 0.98 2676 2695 2709A1772B +4.0 >75 a9h 0.53 655 401 18816 0.19 0.5149 13.2135 0.1861 0.15 0.98 2678 2695 2708A1772C +4.0 <75 a3h 0.4 522 310 6372 0.19 0.4959 12.6781 0.1854 0.15 0.98 2596 2656 2702

*) Isotopic ratios corrected for fractionation, blank and age related common lead (Stacey & Kramers 1975).For most analyses 2-sigma errors in Pb/U ratios are estimated at 0.7%.Pb-blank 10-50 pg except 100 pg for A1428 and A120 and 500 pg for A260.**) Error correlation for 207Pb/235U vs. 206Pb/238U ratios.***) Pre-treated using chemical abrasion (CA, Mattinson 2005), final sample weight in analysis was not obtained. For CA analyses number in “U ppm” calculated using original sample wt (ca. 0.4 mg), thus not real concentration, but a signal of the amount of material in the analysisMost zircons were hand-picked and chemically processed by Tuula Hokkanen. Mass-spectrometry mostly by Arto Pulkkinen.Sample locations are given by Huhma et al. (this volume)

167

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland

Appendix 3. LA-MC-ICPMS analyses on zirconppm Ratios Discordance Ages (Ma)

Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1sA1429 Kilpasuo, Tormua andesite (analyzed 20100812)A1429-3b 105 79 0.38 3783 0.2022 0.0015 14.57 0.47 0.5227 0.0165 0.98 -6 2844 12 2788 31 2711 70A1429-4b 491 370 0.16 9500 0.2005 0.0013 14.97 0.44 0.5415 0.0156 0.98 -2 2830 10 2813 28 2790 65A1429-5b 505 385 2.30 621 0.2003 0.0014 15.07 0.43 0.5458 0.0151 0.97 -1 2828 11 2820 27 2808 63A1429-21a 568 436 0.00 37394 0.1998 0.0013 15.27 0.44 0.5543 0.0156 0.98 1 2824 10 2832 28 2843 65A1429-7b 533 415 0.00 21148 0.2001 0.0013 15.39 0.45 0.5578 0.0161 0.98 1 2827 10 2839 28 2857 67A1429-22a 162 123 3.50 386 0.2068 0.0020 15.37 0.45 0.5389 0.0149 0.95 -4 2881 15 2838 28 2779 63A1429-23a 258 207 0.61 10091 0.1984 0.0013 15.70 0.45 0.5739 0.0161 0.97 5 2813 11 2858 28 2924 66A1429-24a 737 548 0.12 15507 0.1970 0.0012 14.64 0.41 0.5390 0.0147 0.98 -1 2802 10 2792 27 2779 62A1429-25a 404 305 0.00 31484 0.1991 0.0013 14.80 0.45 0.5391 0.0161 0.98 -2 2819 10 2803 29 2780 67A1429-26a 311 247 0.00 16987 0.1991 0.0013 15.51 0.56 0.5650 0.0202 0.98 3 2818 10 2847 35 2887 83A1429-27a 144 115 0.00 8207 0.1982 0.0013 15.92 0.47 0.5824 0.0168 0.98 7 2812 10 2872 28 2959 69A1191 Ala-Luoma Suomussalmi metasediment (20101220, 35µm spot, GJ1 and A1772 standards)A382-1 control 131 63 0.00 4260 0.1143 0.0013 5.432 0.28 0.3447 0.0170 0.98 3 1869 20 1890 43 1909 82A382-2 control 119 57 0.00 2796 0.1142 0.0011 5.429 0.39 0.3447 0.0248 0.99 3 1868 17 1889 62 1909 119A382-3 control 176 83 0.00 6440 0.1130 0.0011 5.245 0.38 0.3367 0.0243 0.99 1 1848 18 1860 62 1871 117A1191-1a (=n759-01) 223 174 0.40 9439 0.1975 0.0023 15.87 0.93 0.5828 0.0336 0.98 7 2806 18 2869 56 2960 137A1191-2a (=n759-02) 596 447 0.20 7846 0.2133 0.0025 17.39 1.02 0.5913 0.0338 0.98 3 2931 19 2957 56 2995 137A1191-3a 647 543 0.00 14803 0.2220 0.0031 20.16 1.25 0.6586 0.0398 0.97 11 2995 22 3099 60 3262 155A1191-4a 338 269 0.68 2410 0.2187 0.0026 18.36 1.11 0.6090 0.0361 0.98 4 2971 18 3009 58 3066 145A1191-5a 392 338 0.20 13599 0.2161 0.0029 20.38 1.17 0.6840 0.0382 0.97 18 2952 21 3109 56 3359 146A1191-6a 284 222 0.16 7518 0.2190 0.0030 19.47 1.06 0.6448 0.0340 0.97 10 2973 22 3065 53 3208 133A1191-7a 198 133 0.55 3984 0.2202 0.0031 17.39 0.86 0.5726 0.0272 0.96 -3 2982 22 2956 47 2919 111A1191-8a 326 258 0.14 10850 0.2198 0.0031 20.29 1.09 0.6693 0.0349 0.97 14 2979 22 3105 52 3303 135A1191-9a 199 154 0.36 4171 0.2099 0.0029 19.14 1.05 0.6614 0.0350 0.97 16 2905 22 3049 53 3272 136A1191-10a 550 410 0.13 9735 0.2107 0.0029 18.29 0.96 0.6296 0.0318 0.97 10 2911 22 3005 50 3148 126A1191-11a 167 126 0.08 19887 0.2194 0.0031 20.12 1.04 0.6648 0.0331 0.96 13 2977 22 3097 50 3286 128A1191-12a 782 536 0.09 17144 0.2102 0.0029 17.92 0.91 0.6182 0.0301 0.96 9 2907 22 2985 49 3103 120A1191-13a 475 279 1.60 1027 0.2056 0.0037 14.81 0.74 0.5224 0.0244 0.93 -7 2871 29 2803 48 2709 103A1191-14a 358 260 0.34 5950 0.2119 0.0026 18.37 1.03 0.6287 0.0344 0.98 10 2920 19 3009 54 3144 136A1191-15a 471 342 0.35 9638 0.2165 0.0033 19.45 1.05 0.6518 0.0338 0.96 12 2955 24 3064 52 3235 132A1191-16a 464 323 0.31 7470 0.2080 0.0031 18.08 0.91 0.6306 0.0304 0.96 12 2890 23 2994 49 3152 120A1191 Ala-Luoma Suomussalmi metasediment (sessio #2, 20101220, GJ1 and A1772 standards)A1191-17a 199 266 0.21 8976 0.2162 0.0025 18.57 0.62 0.6228 0.0195 0.94 7 2953 18 3020 32 3121 78A1191-18a 329 445 0.25 6649 0.2146 0.0025 18.44 0.63 0.6235 0.0203 0.94 8 2940 17 3013 33 3124 80A1191-19a (=n759-10) 264 339 0.29 5086 0.1971 0.0022 16.32 0.59 0.6005 0.0207 0.95 10 2803 17 2896 35 3032 83A1191-20a 304 360 0.48 76733 0.2085 0.0024 15.99 0.50 0.5561 0.0163 0.93 -2 2894 19 2876 30 2851 68A1191-21a 330 439 0.55 5964 0.2186 0.0033 18.59 0.95 0.6168 0.0302 0.96 5 2971 25 3021 49 3097 120A1191-22a 421 568 0.00 17023 0.2184 0.0030 19.10 0.97 0.6343 0.0310 0.96 8 2969 23 3047 49 3166 122A1191-23a 121 156 0.36 12027 0.2127 0.0026 17.56 0.91 0.5989 0.0304 0.97 4 2926 20 2966 50 3026 122A1191-24a 238 308 0.26 4480 0.2168 0.0026 17.89 0.95 0.5984 0.0310 0.97 3 2957 19 2984 51 3024 125A1191-25a 58 74 0.92 1309 0.2101 0.0026 16.91 0.91 0.5836 0.0307 0.97 3 2906 20 2930 52 2964 125A1191-26a 503 653 0.15 10760 0.2169 0.0026 18.23 0.63 0.6097 0.0199 0.94 5 2958 18 3002 33 3069 80

168

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 3. cont.ppm Ratios Discordance Ages (Ma)

Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1sA1429 Kilpasuo, Tormua andesite (analyzed 20100812)A976-1 435 244 0.04 81060 0.2004 0.0014 14.91 0.72 0.5395 0.0259 0.99 -2 2830 11 2810 46 2782 108A976-2a 246 136 0.08 30257 0.1996 0.0014 14.68 0.70 0.5332 0.0252 0.99 -3 2823 11 2794 45 2755 106A976-3a 252 142 0.15 38587 0.1998 0.0014 14.93 0.72 0.5422 0.0260 0.99 -1 2824 11 2811 46 2793 109A976-4a 232 127 0.00 43591 0.1992 0.0014 14.63 0.69 0.5328 0.0247 0.99 -3 2819 12 2792 45 2753 104A976-4b 288 159 0.29 5333 0.1995 0.0014 14.61 0.69 0.5314 0.0250 0.99 -3 2822 11 2790 45 2747 105A976-6a 229 117 0.24 14933 0.1983 0.0014 13.71 0.62 0.5014 0.0222 0.99 -8 2812 11 2730 42 2620 95A976-7a 394 213 0.00 114942 0.2011 0.0014 14.67 0.65 0.5289 0.0233 0.99 -4 2836 11 2794 42 2737 98A976-8a 327 182 0.83 2431 0.1997 0.0015 14.81 0.67 0.5378 0.0240 0.99 -2 2824 12 2803 43 2774 101A976-9a 286 154 0.00 108612 0.1995 0.0014 14.47 0.66 0.5261 0.0238 0.99 -4 2822 12 2781 44 2725 101A976-11a 328 176 0.00 52564 0.1999 0.0015 14.47 0.66 0.5250 0.0237 0.99 -5 2826 12 2781 43 2720 100A976-12a 398 210 0.00 991859 0.1999 0.0015 14.26 0.66 0.5176 0.0236 0.99 -6 2825 12 2767 44 2689 100A976-15a 338 173 0.27 38742 0.1994 0.0015 13.89 0.63 0.5055 0.0225 0.99 -8 2821 12 2742 43 2637 96A976-5a 235 127 0.22 8701 0.1961 0.0013 14.16 0.66 0.5238 0.0242 0.99 -4 2794 11 2761 44 2715 102A976-1b 429 232 0.00 2474 0.2039 0.0015 14.73 0.68 0.5241 0.0239 0.99 -6 2858 12 2798 44 2717 101A976-10a 369 185 0.41 3809 0.1895 0.0014 12.87 0.54 0.4928 0.0202 0.98 -7 2737 12 2670 39 2583 87A976-13a 341 184 0.57 2675 0.1997 0.0015 14.49 0.68 0.5263 0.0245 0.99 -4 2823 12 2782 45 2726 103A1346 Lampela, Kuhmo, andesite (anal. 20091218)A1346-1a 194 96 0.43 2784 0.1959 0.0015 13.39 0.52 0.4957 0.0188 0.98 -9 2793 13 2708 36 2595 81A1346-2a 178 91 0.42 4565 0.1961 0.0014 13.70 0.59 0.5066 0.0216 0.99 -7 2794 12 2729 41 2642 92A1346-3a 128 65 0.28 6304 0.1951 0.0014 13.55 0.58 0.5036 0.0213 0.99 -7 2786 12 2719 41 2629 91A1346-4a 155 78 0.39 4503 0.1965 0.0015 13.50 0.57 0.4982 0.0208 0.99 -8 2798 11 2715 40 2606 89A1346-5a 350 182 0.10 19749 0.1993 0.0015 14.25 0.62 0.5186 0.0223 0.99 -6 2820 11 2766 41 2693 95A1346-6a 284 134 2.40 453 0.1975 0.0021 12.73 0.52 0.4677 0.0183 0.97 -14 2805 17 2660 38 2473 80A1346-7a 173 87 0.38 3433 0.1977 0.0022 13.74 0.62 0.5043 0.0219 0.97 -8 2807 18 2732 42 2632 94A1346-8a 127 64 0.04 36935 0.1942 0.0015 13.41 0.59 0.5008 0.0216 0.99 -7 2778 12 2709 41 2617 93A1346-9a 149 76 0.27 33300 0.1965 0.0015 13.67 0.61 0.5049 0.0221 0.99 -7 2797 12 2727 42 2635 95A1346-10a 121 59 0.48 7553 0.1939 0.0015 13.08 0.56 0.4892 0.0208 0.98 -9 2776 12 2685 41 2567 90A2027 Siivikkovaara, Kuhmo, porphyry dike (20100820)A2027-1a 119 119 0.00 12881 0.1961 0.0014 14.47 0.44 0.5352 0.0160 0.97 -1 2794 12 2781 29 2763 67A2027-2a 56 53 0.00 7472 0.1974 0.0015 14.50 0.56 0.5328 0.0202 0.98 -2 2805 12 2783 37 2753 85A2027-3a 99 98 0.00 15478 0.1961 0.0015 14.36 0.43 0.5312 0.0154 0.97 -2 2794 12 2774 28 2747 65A2027-4a 147 147 0.00 20915 0.1977 0.0015 14.42 0.41 0.5292 0.0147 0.97 -3 2807 12 2778 27 2738 62A2027-5a 209 205 0.00 25355 0.1964 0.0014 14.27 0.52 0.5272 0.0187 0.98 -3 2796 11 2768 34 2729 79A2027-6a 99 98 0.00 11463 0.1978 0.0015 14.31 0.41 0.5246 0.0147 0.97 -4 2808 12 2770 28 2719 62A2027-6b 112 111 0.00 12643 0.1968 0.0015 14.20 0.41 0.5231 0.0144 0.97 -4 2800 12 2763 27 2712 61A2027-7a 160 159 0.00 27251 0.1971 0.0015 14.25 0.43 0.5242 0.0153 0.97 -4 2802 12 2766 29 2717 65A2027-7b 103 103 0.00 16505 0.1979 0.0015 14.49 0.45 0.5312 0.0161 0.97 -3 2809 12 2783 30 2747 68A2027-8a 93 95 0.10 10520 0.2012 0.0015 15.13 0.56 0.5453 0.0199 0.98 -1 2836 12 2823 35 2805 83A2027-9a 141 141 0.00 16750 0.1973 0.0015 14.24 0.43 0.5236 0.0152 0.97 -4 2804 12 2766 28 2714 64A2027-10a 131 131 0.00 22100 0.1963 0.0015 14.16 0.41 0.5234 0.0145 0.97 -4 2795 12 2761 27 2713 61A2027-11a 133 135 0.00 21964 0.1961 0.0015 14.34 0.42 0.5304 0.0150 0.97 -2 2794 12 2773 28 2743 63A2027-12a 95 93 0.00 13561 0.1972 0.0015 14.19 0.44 0.5219 0.0156 0.97 -4 2803 12 2763 29 2707 66A2027-13a 50 48 0.00 5098 0.2005 0.0016 13.98 0.46 0.5055 0.0160 0.97 -8 2830 13 2748 31 2637 68

169

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland


Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1sA2027 Siivikkovaara, Kuhmo, porphyry dike (20100820)A2027-14a 117 117 0.00 17914 0.1954 0.0015 14.17 0.44 0.5260 0.0158 0.97 -3 2788 13 2761 29 2725 67A2027-15a 103 101 0.00 15936 0.1959 0.0015 14.04 0.47 0.5196 0.0168 0.97 -4 2792 13 2752 32 2697 71A2027 Siivikkovaara, Kuhmo, porphyry dike (20100820)A2027-16a 65 65 0.00 7398 0.1958 0.0015 14.18 0.48 0.5254 0.0172 0.97 -3 2791 12 2762 32 2722 73A2027-17a 76 75 0.10 7174 0.1949 0.0015 13.84 0.41 0.5153 0.0146 0.96 -5 2784 12 2739 28 2679 62A2027-18a 107 106 0.00 12125 0.1965 0.0015 14.26 0.42 0.5264 0.0151 0.97 -3 2797 12 2767 28 2726 64A2027-19a 236 232 0.00 30601 0.1959 0.0015 14.11 0.46 0.5225 0.0165 0.97 -4 2792 12 2757 31 2710 70A2027-20a 106 105 0.00 11259 0.1958 0.0015 14.08 0.41 0.5217 0.0148 0.96 -4 2791 12 2755 28 2706 63A1254 Pitkäperä, Kuhmo, andesite (anal. 20100812)A1254-3b 161 107 0.08 5036 0.1969 0.0013 13.35 0.34 0.4916 0.0122 0.97 -10 2801 11 2705 24 2577 53A1254-9b 90 71 0.18 4101 0.2009 0.0013 15.69 0.45 0.5664 0.0159 0.97 3 2834 11 2858 28 2893 66A1254-41a 354 284 0.00 19762 0.2037 0.0013 16.33 0.47 0.5814 0.0163 0.98 4 2856 10 2896 27 2955 66A1254-8b 385 298 0.06 11692 0.2032 0.0013 15.81 0.44 0.5643 0.0152 0.97 1 2852 10 2865 26 2884 63A1254-5b 222 175 0.00 10186 0.2028 0.0013 15.84 0.46 0.5667 0.0160 0.98 2 2849 11 2867 28 2894 66A1254-42a 155 124 0.00 11138 0.2027 0.0013 16.26 0.46 0.5817 0.0161 0.97 5 2848 11 2892 27 2956 66A1254-11b 103 82 0.00 12703 0.2016 0.0014 15.96 0.47 0.5741 0.0163 0.97 4 2839 11 2874 28 2925 67A1254-12b 289 233 0.00 14730 0.2022 0.0013 16.06 0.47 0.5764 0.0165 0.98 4 2844 10 2881 28 2934 68A1254-15b 248 188 0.01 9094 0.2030 0.0013 15.30 0.44 0.5465 0.0155 0.98 -2 2851 10 2834 28 2811 64A1174 Tipasjärvi (Taivaljärvi) felsic volcanic rock (anal. 20091217)A1174-02-1a 239 121 2.00 766 0.1929 0.0026 13.41 0.94 0.5043 0.0348 0.98 -6 2767 22 2709 66 2632 149A1174-02-2a 102 52 0.00 36931 0.1962 0.0027 13.95 1.00 0.5156 0.0365 0.98 -5 2795 22 2746 68 2680 155A1174-02-3a 59 29 0.00 19243 0.1956 0.0027 13.32 0.98 0.4938 0.0356 0.98 -9 2790 22 2703 69 2587 154A1174-02-3b 48 24 0.00 14626 0.1958 0.0027 13.60 0.90 0.5035 0.0325 0.98 -7 2792 22 2722 62 2629 139A1174-02-3c 137 68 0.00 44188 0.1978 0.0027 13.67 0.94 0.5013 0.0339 0.98 -8 2808 22 2727 65 2619 146A1174-02-4a 204 102 0.00 81869 0.1972 0.0027 13.88 0.93 0.5105 0.0333 0.98 -6 2803 22 2742 63 2659 142A1174-02-5a 64 32 0.00 34986 0.2008 0.0028 14.19 0.95 0.5124 0.0336 0.98 -7 2833 22 2762 64 2667 143A1174-02-6a 84 43 0.04 25268 0.2008 0.0028 14.30 0.96 0.5166 0.0340 0.98 -6 2833 23 2770 64 2685 144A1174-02-7a 51 25 0.09 18842 0.1946 0.0027 13.46 0.88 0.5016 0.0322 0.98 -7 2782 23 2713 62 2621 138A1174-02-8a 42 20 0.00 24455 0.1953 0.0027 13.55 0.89 0.5032 0.0324 0.98 -7 2787 21 2719 62 2628 139A1174-02-9a 85 43 0.00 31549 0.1957 0.0027 13.93 0.94 0.5165 0.0341 0.98 -5 2790 21 2745 64 2684 145A1174-02-10a 66 32 0.01 24093 0.1954 0.0027 13.49 0.88 0.5007 0.0320 0.98 -8 2788 22 2715 62 2617 137A1174-02-11a 78 44 0.00 13284 0.2008 0.0012 14.62 0.25 0.5281 0.0086 0.94 -4 2833 10 2791 17 2734 36A1174-02-12a 103 57 0.00 34585 0.1965 0.0012 14.05 0.23 0.5187 0.0081 0.93 -5 2797 10 2753 16 2694 34A1174-02-7b 44 24 0.00 8030 0.1965 0.0013 13.93 0.24 0.5142 0.0082 0.93 -5 2797 10 2745 16 2674 35A1174-02-13a 72 40 0.00 10295 0.1963 0.0013 14.09 0.24 0.5207 0.0084 0.93 -4 2795 10 2756 16 2702 36A1174-02-14a 88 50 0.00 14709 0.1963 0.0013 14.39 0.27 0.5319 0.0092 0.93 -2 2795 11 2776 18 2749 39A1174-02-14b 269 152 0.00 32782 0.1987 0.0014 14.58 0.29 0.5323 0.0100 0.94 -3 2815 11 2788 19 2751 42A1174-02-15a 48 29 0.00 14515 0.1957 0.0019 14.69 0.30 0.5443 0.0099 0.88 1 2790 15 2795 20 2802 41A1174-02-15b 40 24 0.00 12085 0.1957 0.0019 14.54 0.30 0.5389 0.0097 0.88 -1 2790 16 2786 20 2779 41A1174-02-15c 85 52 0.21 18887 0.1960 0.0019 14.80 0.30 0.5478 0.0099 0.88 1 2793 16 2803 20 2816 41A1174-02-16a 64 38 0.20 12707 0.1954 0.0019 14.41 0.29 0.5349 0.0096 0.88 -1 2788 16 2777 19 2762 40A1174-02-16b 56 33 0.00 16537 0.1966 0.0020 14.25 0.30 0.5257 0.0096 0.88 -3 2798 16 2766 20 2723 41A1174-02-17a 79 43 0.07 19103 0.1959 0.0020 13.32 0.27 0.4929 0.0087 0.87 -9 2792 16 2702 19 2583 37

170

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.


Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1sA1174 Tipasjärvi (Taivaljärvi) felsic volcanic rock (anal. 20091217)A1174-02-18a 80 48 0.00 23646 0.1966 0.0020 14.57 0.30 0.5374 0.0096 0.87 -1 2798 16 2787 20 2772 40A1174-02-19a 48 31 7.70 194 0.1820 0.0026 13.40 0.30 0.5343 0.0094 0.78 4 2671 23 2709 21 2759 39A1174-02-20a 116 68 0.00 51844 0.1964 0.0020 14.28 0.30 0.5276 0.0096 0.88 -3 2796 16 2769 20 2731 40A1174-02-21a 46 28 0.00 12352 0.1956 0.0020 14.45 0.29 0.5359 0.0093 0.86 -1 2790 16 2780 19 2766 39A1886 Tipasjärvi felsic volcanic rock (anal. 20091218)A1886-1a 192 99 0.46 2965 0.1957 0.0014 14.08 0.61 0.5220 0.0225 0.99 -4 2790 11 2755 41 2708 95A1886-3a 363 184 0.00 79887 0.1981 0.0014 14.20 0.61 0.5200 0.0220 0.99 -5 2810 11 2763 41 2699 93A1886-5a 173 86 0.08 24619 0.1962 0.0014 13.80 0.59 0.5102 0.0214 0.99 -6 2794 11 2736 40 2658 92A1886-6a 139 69 0.14 21233 0.1953 0.0014 13.79 0.60 0.5122 0.0219 0.99 -5 2787 11 2736 41 2666 93A1886-7a 149 77 0.00 54562 0.1960 0.0014 14.35 0.64 0.5311 0.0235 0.99 -2 2794 12 2773 43 2746 99A1886-9a 166 82 0.28 9039 0.1962 0.0014 13.84 0.59 0.5116 0.0215 0.99 -6 2795 11 2739 40 2663 92A1886-10a 172 86 0.02 30776 0.1968 0.0014 13.99 0.60 0.5157 0.0218 0.99 -5 2800 11 2749 41 2681 93A1886-11a 239 121 0.06 40690 0.1970 0.0014 14.19 0.62 0.5224 0.0224 0.99 -4 2802 11 2763 41 2710 95A1886-2a 114 52 0.01 27092 0.1935 0.0014 12.65 0.51 0.4741 0.0189 0.99 -12 2772 11 2654 38 2501 83A1886-8a 104 50 0.00 32563 0.1957 0.0014 13.54 0.57 0.5018 0.0208 0.99 -7 2790 12 2718 40 2622 89A1921 Tipasjärvi felsic volcanic rock (anal. 20100816)A1921-3c 513 435 0.01 19153 0.1999 0.0018 15.33 0.41 0.5562 0.0139 0.94 1 2825 14 2836 25 2851 58A1921-12b 196 161 0.05 9753 0.1973 0.0018 14.48 0.44 0.5323 0.0153 0.96 -2 2804 14 2781 29 2751 65A1921-20b 292 239 0.00 12322 0.1986 0.0018 14.86 0.41 0.5429 0.0143 0.95 -1 2814 14 2806 27 2795 60A1921-23b 283 255 0.00 18054 0.1982 0.0018 16.42 0.45 0.6009 0.0154 0.94 10 2812 14 2902 26 3034 62A1921-26c 252 207 0.00 9533 0.1985 0.0018 14.88 0.41 0.5437 0.0140 0.95 -1 2814 15 2808 26 2799 58A1921-27b 398 345 0.00 22948 0.1974 0.0018 15.57 0.43 0.5719 0.0149 0.95 5 2805 14 2851 26 2916 61A1921-30a 318 268 0.00 13195 0.1971 0.0017 14.91 0.39 0.5488 0.0137 0.94 1 2802 14 2810 25 2820 57A1921-31a 404 335 0.00 19253 0.1957 0.0017 14.67 0.39 0.5437 0.0135 0.94 0 2791 13 2794 25 2799 57A1921-32a 487 369 0.00 16286 0.1984 0.0018 13.50 0.37 0.4935 0.0129 0.95 -10 2813 14 2715 26 2586 56A1921-33c 267 228 0.00 17460 0.1984 0.0018 15.17 0.43 0.5547 0.0148 0.95 1 2813 14 2826 27 2845 61A1921-34c 239 196 0.00 18436 0.1987 0.0018 14.54 0.42 0.5306 0.0147 0.95 -3 2815 14 2785 28 2744 62A1921-18a monazite 512 198 0.01 52944 0.1121 0.0008 5.309 0.17 0.3434 0.0109 0.97 4 1834 13 1870 28 1903 52A1922 Tipasjärvi felsic volcanic rock (anal. 20100816)A1922-7c 139 121 0.12 5028 0.2000 0.0018 15.46 0.43 0.5606 0.0148 0.95 2 2826 14 2844 27 2869 61A1922-8b 100 85 0.00 29147 0.2009 0.0018 15.18 0.42 0.5481 0.0144 0.95 -1 2833 14 2826 26 2817 60A1922-12b 406 343 0.00 29487 0.2015 0.0017 15.01 0.41 0.5402 0.0142 0.95 -2 2838 13 2816 26 2784 59A1922-13b 133 108 0.22 5636 0.2039 0.0018 14.42 0.41 0.5129 0.0139 0.95 -8 2858 14 2778 27 2669 59A1922-14c 45 38 0.00 2351 0.2000 0.0019 14.62 0.42 0.5299 0.0145 0.95 -4 2827 15 2791 28 2741 61A1922-15c 120 102 0.07 4333 0.1999 0.0017 14.48 0.44 0.5255 0.0152 0.96 -5 2825 14 2782 29 2722 64A1922-20b 80 69 0.00 6709 0.2000 0.0018 15.41 0.44 0.5587 0.0151 0.95 2 2826 14 2841 27 2861 62A1922-23b 152 126 0.00 6921 0.1999 0.0017 14.63 0.41 0.5308 0.0142 0.95 -4 2825 14 2791 27 2745 60A1922-28a 160 134 0.00 14099 0.1997 0.0017 14.55 0.41 0.5285 0.0144 0.95 -4 2824 14 2786 27 2735 61A1922-29a 64 54 0.00 2627 0.1995 0.0018 14.59 0.41 0.5304 0.0143 0.95 -3 2822 14 2789 27 2743 60A1922-30a 116 98 0.00 8588 0.1991 0.0018 15.07 0.41 0.5487 0.0143 0.95 . 2819 14 2819 26 2820 5983-PGN-90 Rakennuslahti, Kuhmo, metagreywacke (anal. 20100816)83-PGN-90-1b 301 262 0.00 13978 0.1914 0.0012 13.73 0.52 0.5201 0.0196 0.99 -2 2755 10 2731 36 2699 8383-PGN-90-2b 109 97 0.00 4587 0.1914 0.0013 14.05 0.53 0.5324 0.0196 0.98 -0 2754 11 2753 35 2752 82

171

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland


Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1s83-PGN-90 Rakennuslahti, Kuhmo, metagreywacke (anal. 20100816)83-PGN-90-5b 196 176 0.00 9982 0.1921 0.0013 14.39 0.54 0.5433 0.0200 0.99 2 2760 10 2776 36 2797 8483-PGN-90-3b 163 163 0.00 10171 0.1891 0.0013 15.75 0.60 0.6041 0.0227 0.99 14 2734 11 2862 36 3046 9183-PGN-90-4b 615 557 0.00 32502 0.1935 0.0012 14.51 0.54 0.5441 0.0200 0.99 1 2772 10 2784 35 2801 8383-PGN-90-6b 306 301 0.00 20989 0.1917 0.0012 15.81 0.61 0.5981 0.0227 0.99 12 2757 10 2865 37 3022 9183-PGN-90-7b 114 101 0.00 39762 0.1920 0.0013 14.17 0.52 0.5355 0.0194 0.98 0 2759 11 2761 35 2764 8183-PGN-90-10b 245 224 0.00 13915 0.1910 0.0012 14.73 0.54 0.5594 0.0201 0.98 5 2751 10 2798 35 2864 8383-PGN-90-11b 288 250 0.01 11409 0.1920 0.0013 13.81 0.52 0.5216 0.0194 0.99 -2 2760 10 2737 36 2706 8283-PGN-90 Rakennuslahti metagreywacke (anal. 20100312)83-PGN-90-1a 163 106 0.00 27230 0.1905 0.0021 14.11 0.60 0.5373 0.0223 0.97 1 2747 17 2757 41 2772 9383-PGN-90-2a 143 94 0.07 12549 0.1901 0.0021 14.31 0.61 0.5457 0.0224 0.97 3 2743 18 2770 40 2807 9383-PGN-90-3a 346 219 0.07 25432 0.1853 0.0018 13.71 0.51 0.5368 0.0194 0.97 3 2701 15 2730 35 2770 8183-PGN-90-4a 218 148 0.00 18002 0.1933 0.0020 15.03 0.67 0.5638 0.0245 0.97 5 2770 16 2817 42 2882 10183-PGN-90-5a 127 83 0.00 13600 0.1905 0.0019 14.30 0.61 0.5446 0.0227 0.97 3 2746 16 2770 41 2803 9583-PGN-90-6a 273 189 0.00 20472 0.1947 0.0020 15.33 0.69 0.5712 0.0250 0.97 6 2782 17 2836 43 2913 10383-PGN-90-7a 163 112 0.00 18522 0.1908 0.0023 14.64 0.71 0.5566 0.0263 0.97 5 2749 19 2792 46 2852 10983-PGN-90-8a 326 224 0.00 38472 0.2030 0.0025 15.65 0.69 0.5594 0.0237 0.96 1 2850 19 2856 42 2864 9883-PGN-90-9a 223 169 0.00 24617 0.2308 0.0031 19.45 0.95 0.6113 0.0286 0.96 1 3057 21 3064 47 3075 11483-PGN-90-10a 185 122 0.00 15079 0.1900 0.0022 14.35 0.61 0.5479 0.0225 0.96 3 2742 18 2773 40 2816 9383-PGN-90-11a 47 30 0.00 4268 0.1906 0.0023 14.14 0.59 0.5380 0.0215 0.96 1 2747 19 2759 40 2775 9083-PGN-90-12a 252 166 0.15 13184 0.2020 0.0025 15.23 0.65 0.5471 0.0225 0.96 -1 2842 20 2830 41 2813 9483-PGN-90-13a 120 64 0.00 10789 0.1911 0.0022 12.19 0.46 0.4627 0.0164 0.95 -13 2752 19 2619 35 2451 7283-PGN-90-14a 163 109 0.00 11234 0.1904 0.0022 14.51 0.63 0.5527 0.0230 0.96 4 2746 18 2784 41 2836 9683-PGN-90-15a 133 87 0.00 11494 0.1905 0.0022 14.30 0.60 0.5447 0.0220 0.96 3 2746 19 2770 40 2803 9283-PGN-90-16a 84 55 0.00 6540 0.1913 0.0023 14.50 0.61 0.5497 0.0223 0.96 3 2753 19 2783 40 2824 9383-PGN-90-17a 176 115 0.00 16729 0.1902 0.0022 14.17 0.60 0.5404 0.0221 0.96 2 2744 19 2761 40 2785 9283-PGN-90-18a 288 178 0.00 19904 0.1900 0.0022 13.52 0.56 0.5160 0.0205 0.96 -3 2742 18 2717 39 2682 8783-PGN-90-19a 86 60 0.00 7707 0.2059 0.0026 16.41 0.73 0.5783 0.0247 0.96 3 2873 20 2901 43 2942 10183-PGN-90-20a 83 67 0.00 7672 0.2560 0.0038 22.95 1.18 0.6503 0.0319 0.96 0 3222 22 3225 50 3229 12583-PGN-90-21a 82 66 0.16 5784 0.2604 0.0039 23.29 1.20 0.6489 0.0320 0.96 -1 3249 24 3239 50 3224 12583-PGN-90-22a 178 124 0.00 12956 0.2068 0.0026 16.34 0.72 0.5733 0.0244 0.96 2 2881 19 2897 42 2921 10083-PGN-90-23a 161 116 0.00 14275 0.2158 0.0028 17.69 0.81 0.5946 0.0261 0.96 3 2950 20 2973 44 3008 10683-PGN-90-24a 42 26 0.00 3231 0.1844 0.0021 13.13 0.52 0.5165 0.0197 0.96 -0 2693 18 2689 38 2684 8483-PGN-90-24b 66 42 0.08 4727 0.1899 0.0023 13.98 0.57 0.5338 0.0210 0.96 1 2741 19 2748 39 2758 8883-PGN-90-25a 68 45 0.00 6660 0.2268 0.0031 17.27 0.75 0.5524 0.0228 0.95 -8 3029 21 2950 42 2835 9583-PGN-90-26a 206 133 0.00 14420 0.1892 0.0022 14.15 0.60 0.5424 0.0219 0.96 3 2736 19 2760 40 2794 9283-PGN-90-27a 101 65 0.00 8713 0.1910 0.0023 14.32 0.60 0.5437 0.0217 0.96 2 2751 19 2771 40 2799 9183-PGN-90-28a 60 40 0.00 63602 0.2060 0.0024 16.08 0.72 0.5662 0.0244 0.97 1 2874 18 2882 43 2892 10083-PGN-90-29a 156 104 0.00 11858 0.2133 0.0026 16.48 0.73 0.5604 0.0238 0.96 -3 2931 18 2905 42 2868 9883-PGN-90-30a 102 62 0.24 5194 0.1894 0.0021 13.50 0.56 0.5171 0.0205 0.96 -2 2737 18 2715 39 2687 8783-PGN-90-31a 101 73 0.21 7257 0.2154 0.0024 17.74 0.84 0.5974 0.0275 0.97 3 2947 18 2976 46 3019 11183-PGN-90-32a 76 58 0.00 7634 0.2518 0.0032 21.91 1.12 0.6309 0.0314 0.97 -2 3196 21 3180 50 3153 12483-PGN-90-33a 155 102 0.00 12761 0.2038 0.0022 15.63 0.69 0.5563 0.0238 0.97 -0 2857 17 2854 42 2851 9983-PGN-90-34a 110 73 0.00 8369 0.2034 0.0022 15.81 0.70 0.5639 0.0244 0.97 1 2854 17 2866 43 2883 100

172

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.


Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1s83-PGN-90 Rakennuslahti metagreywacke (anal. 20100312)83-PGN-90-35a 103 67 0.02 7383 0.1900 0.0020 14.38 0.63 0.5491 0.0232 0.97 4 2742 16 2775 41 2822 9783-PGN-90-36a 128 83 0.00 19525 0.1895 0.0020 14.30 0.63 0.5475 0.0233 0.97 4 2738 16 2770 42 2815 9783-PGN-90-37a 156 100 0.01 21636 0.1893 0.0019 14.27 0.62 0.5468 0.0230 0.97 3 2736 16 2768 41 2812 9683-PGN-90-38a 117 83 0.00 12578 0.2151 0.0024 17.42 0.81 0.5875 0.0266 0.97 2 2944 17 2958 45 2979 10883-PGN-90-39a 64 41 0.00 5489 0.1903 0.0020 14.25 0.61 0.5429 0.0226 0.97 2 2745 17 2766 41 2796 9483-PGN-90-40a 78 53 0.00 7705 0.2050 0.0022 16.13 0.73 0.5706 0.0249 0.97 2 2866 17 2884 43 2910 10283-PGN-90-41a 237 172 0.05 18111 0.2200 0.0025 18.24 0.88 0.6014 0.0281 0.97 2 2980 18 3002 46 3035 11383-PGN-90-42a 211 135 0.07 44542 0.1897 0.0020 14.32 0.63 0.5477 0.0233 0.97 3 2739 16 2771 42 2816 9783-PGN-90-43a 169 111 0.07 13189 0.1892 0.0019 14.57 0.64 0.5587 0.0238 0.97 6 2735 16 2788 42 2861 9983-PGN-90-44a 171 123 0.00 16501 0.2155 0.0025 17.85 0.85 0.6005 0.0279 0.97 4 2948 19 2982 46 3032 11283-PGN-90-45a 67 45 0.04 4904 0.2038 0.0022 15.96 0.72 0.5681 0.0248 0.97 2 2857 17 2875 43 2900 102A1533 Surmakumpu porphyry dike, Pudasjärvi complex (anal. 20100812&16)A1533-1a 85 61 0.20 4978 0.1810 0.0012 12.82 0.34 0.5138 0.0134 0.97 1 2662 11 2667 25 2673 57A1533-1b 71 61 0.00 5082 0.1818 0.0013 11.97 0.45 0.4774 0.0175 0.98 -7 2670 12 2602 35 2516 76A1533-2a 74 55 0.00 71713 0.1821 0.0012 13.30 0.36 0.5297 0.0138 0.97 3 2672 11 2701 25 2740 58A1533-2b 79 75 0.00 4087 0.1821 0.0013 13.33 0.51 0.5308 0.0199 0.98 3 2672 11 2703 36 2745 84A1533-3a 165 121 0.15 12029 0.1817 0.0012 13.12 0.36 0.5239 0.0138 0.97 2 2668 10 2689 26 2716 58A1533-4a 84 61 0.13 5853 0.1818 0.0012 13.05 0.37 0.5207 0.0142 0.97 2 2669 10 2683 26 2702 60A1533-5a 73 51 0.21 4205 0.1819 0.0012 12.64 0.34 0.5042 0.0133 0.97 -2 2670 11 2654 26 2632 57A1533-6a 89 63 0.00 4166 0.1822 0.0012 12.62 0.35 0.5025 0.0134 0.97 -2 2673 11 2652 26 2624 58A1533-7a 1473 114 2.10 1286 0.0620 0.0011 0.378 0.02 0.0442 0.0017 0.91 -60 675 39 325 12 279 11A1533-8a 759 49 5.20 628 0.0688 0.0014 0.336 0.01 0.0354 0.0012 0.85 -76 892 43 294 10 224 7A1533-9a 1593 65 0.30 12161 0.0521 0.0004 0.180 0.01 0.0250 0.0007 0.97 -46 290 17 168 5 159 5A1533-10a 605 88 16.00 92 0.1291 0.0020 1.242 0.07 0.0697 0.0040 0.97 -82 2086 26 820 33 435 24A331 Loso quartz diorite (sanukitoid) (20100824)A331-6a 665 510 0.06 23417 0.1599 0.0006 9.468 0.65 0.4295 0.0297 1.00 -7.3 2454 6 2384 63 2303 134A331-21a 453 383 0.75 7725 0.1626 0.0008 10.24 0.84 0.4566 0.0373 1.00 -2.8 2483 8 2456 76 2425 165A331-6b 138 111 0.78 3396 0.1661 0.0018 10.76 0.76 0.4698 0.0329 0.99 -1.7 2519 18 2503 66 2483 144A331-8a 483 392 0.00 26653 0.1716 0.0012 11.02 0.82 0.4658 0.0343 1.00 -5 2573 11 2525 69 2465 151A331-24a 319 279 1.20 8806 0.1722 0.0008 11.67 0.89 0.4917 0.0373 1.00 . 2579 8 2578 71 2578 161A331-9a 324 291 0.00 13059 0.1791 0.0007 12.26 0.90 0.4964 0.0364 1.00 -2.1 2644 6 2624 69 2598 157A331-22a 417 370 0.00 15463 0.1803 0.0007 12.30 0.95 0.4949 0.0382 1.00 -2.9 2655 6 2628 73 2592 165A331-13a 437 402 0.00 11647 0.1811 0.0007 12.83 0.94 0.5138 0.0376 1.00 0.4 2663 6 2667 69 2673 160A331-7a 336 300 0.00 15695 0.1823 0.0007 12.55 0.93 0.4994 0.0370 1.00 -2.9 2674 6 2647 70 2611 159A331-10b 275 233 0.47 4560 0.1823 0.0009 11.88 0.87 0.4725 0.0344 1.00 -8.1 2674 8 2595 68 2495 151A331-1a 146 135 0.69 2331 0.1825 0.0009 12.11 0.93 0.4815 0.0368 1.00 -6.4 2675 8 2613 72 2534 160A331-10a 343 317 0.03 18503 0.1834 0.0007 12.92 0.97 0.5111 0.0383 1.00 -1 2683 6 2674 71 2661 163A331-15a 282 253 0.76 1815 0.1837 0.0007 12.56 0.91 0.4960 0.0358 1.00 -4.1 2686 6 2647 68 2596 154A331-16a 522 465 0.10 9519 0.1842 0.0008 12.64 0.95 0.4978 0.0374 1.00 -3.9 2691 7 2653 71 2604 161A331-14a 373 357 0.00 18424 0.1849 0.0007 13.56 1.02 0.5320 0.0398 1.00 2.4 2697 6 2720 71 2750 168A331-2a 169 152 0.00 14558 0.1852 0.0007 12.47 0.93 0.4885 0.0364 1.00 -6.1 2700 6 2641 70 2564 158A331-23a 143 134 0.00 16806 0.1853 0.0011 13.60 0.83 0.5323 0.0322 1.00 2.3 2700 9 2722 57 2751 135A331-25a 606 565 0.18 13906 0.1855 0.0007 13.29 1.06 0.5199 0.0413 1.00 -0.2 2702 6 2701 75 2699 175

173

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland


Name U 206Pb 206Pbc(%) 206Pb/204Pb 207Pb/206Pb* 1s 207Pb/235U* 1s 206Pb/238U* 1s Rho Central (%) 207Pb/206Pb 1s 207Pb/235U 1s 206Pb/238U 1sA331 Loso quartz diorite (sanukitoid) (20100824)A331-17a 208 194 0.23 9860 0.1856 0.0011 13.21 1.02 0.5164 0.0399 1.00 -0.9 2703 9 2695 73 2684 170A331-4a 178 173 0.04 6991 0.1856 0.0016 13.78 1.04 0.5382 0.0405 0.99 3.3 2704 14 2734 72 2776 170A331-19a 255 237 0.00 10790 0.1860 0.0009 13.25 1.02 0.5167 0.0399 1.00 -1 2707 8 2697 73 2685 170A331-11a 222 210 0.00 8907 0.1861 0.0007 13.45 1.01 0.5244 0.0393 1.00 0.5 2708 6 2712 71 2718 166A331-5a 430 423 0.00 14522 0.1866 0.0007 13.78 1.04 0.5358 0.0403 1.00 2.4 2712 6 2735 71 2766 169A331-12a 256 238 0.00 15372 0.1876 0.0007 13.46 1.00 0.5206 0.0386 1.00 -0.9 2721 6 2713 70 2702 163A331-18a 191 186 0.00 12294 0.1881 0.0009 14.09 1.12 0.5433 0.0432 1.00 3.2 2726 8 2756 75 2797 180A331-20a 131 122 0.00 5262 0.1897 0.0010 13.62 1.05 0.5209 0.0402 1.00 -1.6 2739 8 2724 73 2703 171A331-3a 197 195 0.00 5228 0.1985 0.0009 15.26 1.27 0.5576 0.0464 1.00 1.9 2814 7 2832 79 2857 192A1926 Ansosuo diorite (Loso sanukitoid) (20100824)A1926-5b 87 73 0.16 2034 0.1803 0.0011 11.62 0.87 0.4674 0.0347 1.00 -8.3 2655 10 2574 70 2472 152A1926-5a 269 248 0.00 8251 0.1821 0.0008 12.92 1.00 0.5148 0.0396 1.00 0.3 2672 7 2674 73 2677 169A1926-20a 391 365 0.12 8026 0.1840 0.0009 13.30 1.08 0.5242 0.0427 1.00 1.3 2689 7 2701 77 2717 181A1926-9a 109 105 0.52 2333 0.1845 0.0009 13.54 1.07 0.5320 0.0420 1.00 2.5 2694 8 2718 75 2750 177A1926-11a 270 231 0.00 8924 0.1848 0.0008 12.08 0.91 0.4744 0.0356 1.00 -8.6 2696 7 2611 70 2503 155A1926-13a 280 269 0.00 10232 0.1851 0.0008 13.64 1.08 0.5343 0.0422 1.00 2.7 2700 7 2725 75 2759 177A1926-15a 402 401 0.00 32352 0.1855 0.0007 14.05 1.13 0.5493 0.0443 1.00 5.5 2703 6 2753 77 2822 184A1926-1a 42 39 0.00 1966 0.1856 0.0012 13.29 1.08 0.5191 0.0421 1.00 -0.4 2704 10 2700 77 2696 179A1926-16a 474 448 0.00 17166 0.1860 0.0008 13.48 1.06 0.5258 0.0414 1.00 0.8 2707 7 2714 74 2724 175A1926-6a 151 146 0.00 6994 0.1861 0.0008 13.67 1.08 0.5329 0.0420 1.00 2.1 2708 7 2727 75 2754 177A1926-19a 211 213 0.77 2297 0.1863 0.0009 14.32 1.17 0.5573 0.0454 1.00 6.6 2710 8 2771 77 2855 188A1926-3a 117 114 0.00 7069 0.1871 0.0009 13.77 1.09 0.5340 0.0422 1.00 1.9 2716 7 2734 75 2758 177A1926-12b 184 182 0.00 5532 0.1871 0.0009 14.11 1.14 0.5471 0.0440 1.00 4.4 2717 8 2757 76 2813 183A1926-8a 189 182 0.00 10990 0.1872 0.0008 13.85 1.09 0.5365 0.0424 1.00 2.3 2718 7 2739 75 2769 178A1926-12a 118 118 0.00 4754 0.1874 0.0009 14.28 1.16 0.5528 0.0448 1.00 5.3 2719 7 2769 77 2837 186A1926-16b 100 100 0.00 3008 0.1874 0.0009 14.43 1.18 0.5584 0.0454 1.00 6.4 2719 8 2778 77 2860 188A1926-12c 195 199 0.00 7650 0.1874 0.0007 14.51 1.18 0.5613 0.0456 1.00 6.9 2720 6 2783 77 2872 188A1926-7a 238 223 0.09 6464 0.1877 0.0009 13.34 1.04 0.5152 0.0403 1.00 -2 2722 7 2704 74 2679 171A1926-4a 262 247 0.01 6395 0.1878 0.0009 13.63 1.07 0.5265 0.0412 1.00 0.2 2723 7 2724 74 2727 174A1926-18a 416 417 0.00 15644 0.1878 0.0008 14.43 1.18 0.5574 0.0454 1.00 6.1 2723 7 2779 77 2856 188A1926-2a 180 173 0.00 6551 0.1880 0.0009 13.81 1.08 0.5329 0.0418 1.00 1.3 2724 7 2737 74 2754 176A1926-17a 105 108 0.00 6052 0.1880 0.0009 14.78 1.22 0.5704 0.0470 1.00 8.5 2724 8 2801 78 2910 193A1926-10a 382 399 0.00 14307 0.1885 0.0008 15.06 1.24 0.5796 0.0476 1.00 10 2729 7 2819 78 2947 194A1926-14a 189 183 0.00 6382 0.1887 0.0009 14.00 1.12 0.5383 0.0428 1.00 2.1 2730 7 2750 76 2776 179

LA-MCICPMS measurements were made using 35µm laser spot and GJ1 (609 Ma) and A382 (1877 Ma) standards (before June 2010) or 25µm spot and GJ1 and A1772 (2712 Ma) standards (after June 2010)206Pbc(%): percentage of common 206Pb in measured 206Pb calculated from the 204Pb signal using age-related common lead after model by Stacey&Kramers (1975)Errors are 1-sigma absoluteRho: Correlation of Pb/U errorsSome analyses with high common lead are not used in evaluation (strikethrough).

174

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 4. SIMS U-Th-Pb data.Sample Spot %

206Pbc

ppm U

ppm Th

232Th /238U

ppm 206Pb*

(1) 206Pb/238U

Age

(1) 207Pb/206Pb

Age

% Dis-

cordant

(1) 207Pb* /206Pb*

±% (1) 207Pb* /235U

±% (1) 206Pb*/238U

±% err corr

A788 Polvilampi felsic rockA788.1.1 0.14 231 103 0.46 103 2686 25 2791 7 4 0.1957 0.45 13.95 1.2 0.5169 1.1 0.93A788.2.1 0.27 217 85 0.41 94 2632 22 2786 8 6 0.1951 0.48 13.57 1.1 0.5043 1 0.91A788.3.1 0.41 192 68 0.37 80 2550 22 2770 9 8 0.1933 0.53 12.93 1.2 0.4852 1.1 0.89A788.4.1 0.24 235 81 0.36 101 2604 22 2800 7 7 0.1969 0.45 13.51 1.1 0.4977 1 0.92A788.5.1 0.30 165 83 0.52 74 2702 24 2801 9 4 0.1970 0.54 14.14 1.2 0.5205 1.1 0.89A788.6.1 0.30 95 28 0.30 44 2776 26 2779 11 0 0.1944 0.7 14.42 1.4 0.5383 1.2 0.86A788.7.1 0.07 483 186 0.40 213 2667 22 2786 5 4 0.1952 0.29 13.79 1 0.5124 1 0.96A788.8.1 0.17 215 93 0.45 97 2728 23 2767 8 1 0.1929 0.46 14.01 1.1 0.5268 1 0.92A788.9.1 0.18 259 177 0.71 110 2591 22 2791 9 7 0.1957 0.56 13.35 1.2 0.4947 1.1 0.88A788.10.1 0.57 153 55 0.38 67 2649 25 2772 12 4 0.1935 0.75 13.56 1.4 0.5083 1.1 0.83A788.11.1 0.31 122 43 0.37 55 2700 25 2803 10 4 0.1972 0.63 14.15 1.3 0.5203 1.1 0.87A788.12.1 0.77 181 115 0.65 80 2649 24 2783 10 5 0.1948 0.6 13.65 1.2 0.5082 1.1 0.88A788.13.1 0.29 198 82 0.43 89 2698 24 2788 8 3 0.1953 0.48 14.00 1.2 0.5196 1.1 0.91A788.14.1 0.24 250 106 0.44 109 2629 22 2786 7 6 0.1952 0.43 13.55 1.1 0.5036 1 0.92A788.15.1 0.17 140 47 0.35 62 2699 24 2801 9 4 0.1969 0.56 14.11 1.2 0.5199 1.1 0.89A788.16.1 0.15 108 32 0.30 50 2773 26 2790 10 1 0.1956 0.64 14.49 1.3 0.5374 1.1 0.87

A1748 Aarreniemi. Tipasjärvi metagreywackeA1748.1.1 0.02 121 112 0.95 55 2737 30 2752 9 1 0.1911 0.6 13.94 1.4 0.529 1.3 0.92A1748.2.1 0.03 514 151 0.30 233 2730 26 2746 5 1 0.1905 0.3 13.85 1.2 0.527 1.2 0.97A1748.3.1 0.34 171 127 0.76 72 2559 29 2744 14 7 0.1903 0.9 12.78 1.6 0.487 1.4 0.85A1748.4.1 1.30 191 176 0.95 87 2701 44 2741 21 1 0.1899 1.3 13.62 2.4 0.520 2.0 0.85A1748.5.1 0.56 301 155 0.53 132 2642 28 2827 12 7 0.2001 0.7 13.98 1.5 0.507 1.3 0.87A1748.6.1 -0.00 63 40 0.66 30 2847 40 2746 18 -4 0.1905 1.1 14.58 2.1 0.555 1.7 0.84A1748.7.1 1.35 188 175 0.96 82 2613 30 2737 22 5 0.1894 1.3 13.05 1.9 0.500 1.4 0.73A1748.8.1 1.21 216 172 0.83 92 2560 28 2750 15 7 0.1909 0.9 12.84 1.6 0.488 1.3 0.84A1748.9.1 0.95 209 116 0.57 92 2633 30 2747 25 4 0.1906 1.5 13.26 2.1 0.505 1.4 0.67A1748.10.1 0.37 346 177 0.53 141 2496 27 2707 12 8 0.1860 0.7 12.12 1.5 0.473 1.3 0.87A1748.11.1 0.46 380 296 0.81 171 2703 28 2728 10 1 0.1883 0.6 13.53 1.4 0.521 1.3 0.90A1748.12.1 1.46 177 94 0.55 79 2655 31 2726 19 3 0.1882 1.1 13.22 1.8 0.510 1.4 0.79A1748.12.2 2.09 293 256 0.90 110 2278 26 2710 17 19 0.1863 1.0 10.89 1.7 0.424 1.4 0.81

A1753 Arola quartzite (55-PTP-03)55.11.1 0.17 408 341 0.86 170 2550 43 2680 6 5 0.1830 0.38 12.25 2.1 0.485 2 0.9855.13.1 0.53 100 72 0.74 45 2694 45 2683 16 -0 0.1833 0.98 13.11 2.3 0.519 2.1 0.9055.21.1 0.28 286 213 0.77 115 2462 40 2686 8 8 0.1836 0.47 11.77 2 0.465 2 0.9755.4.1 0.49 127 92 0.74 57 2674 44 2693 13 1 0.1845 0.8 13.08 2.2 0.514 2 0.9355.16.1 0.18 260 145 0.58 114 2663 43 2697 8 1 0.1849 0.49 13.04 2 0.511 2 0.9755.3.1 0.37 283 217 0.79 113 2457 40 2699 9 9 0.1850 0.52 11.83 2 0.464 2 0.9755.2.1 0.20 178 49 0.29 80 2714 44 2700 10 -1 0.1852 0.58 13.37 2.1 0.523 2 0.9655.8.1 0.65 161 113 0.73 64 2433 41 2701 12 10 0.1853 0.72 11.71 2.1 0.459 2 0.9455.7.1 0.19 208 109 0.54 93 2699 44 2707 9 0 0.1860 0.51 13.33 2 0.520 2 0.9755.18.1 0.66 68 26 0.40 31 2743 47 2716 18 -1 0.1870 1.1 13.67 2.4 0.530 2.1 0.8955.12.1 0.48 103 58 0.58 47 2732 46 2729 14 -0 0.1885 0.83 13.72 2.2 0.528 2 0.9355.5.1 0.69 40 40 1.01 18 2730 50 2748 26 1 0.1906 1.6 13.86 2.7 0.527 2.3 0.82

175

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland

Appendix 4. cont.Sample Spot %

206Pbc

ppm U

ppm Th

232Th /238U

ppm 206Pb*

(1) 206Pb/238U

Age

(1) 207Pb/206Pb

Age

% Dis-

cordant

(1) 207Pb* /206Pb*

±% (1) 207Pb* /235U

±% (1) 206Pb*/238U

±% err corr

A1753 Arola quartzite (55-PTP-03)55.17.1 0.21 200 54 0.28 92 2774 45 2795 8 1 0.1962 0.5 14.54 2 0.538 2 0.9755.20.1 0.27 177 140 0.82 85 2849 46 2807 9 -1 0.1977 0.55 15.15 2.1 0.556 2 0.9655.6.1 0.17 529 422 0.82 239 2720 43 2809 5 3 0.1980 0.31 14.32 2 0.525 1.9 0.9955.9.1 0.56 84 116 1.42 41 2877 54 2932 14 2 0.2135 0.86 16.55 2.5 0.562 2.3 0.9455.15.1 0.14 397 113 0.29 201 2982 46 2952 5 -1 0.2161 0.32 17.52 2 0.588 1.9 0.9955.22.1 0.34 161 217 1.39 85 3079 52 3195 7 4 0.2517 0.46 21.25 2.2 0.612 2.1 0.9855.19.1 0.20 164 90 0.57 89 3160 50 3196 7 1 0.2518 0.45 21.96 2.1 0.633 2 0.9855.1.1 0.11 275 234 0.88 146 3105 49 3200 6 3 0.2525 0.36 21.54 2 0.619 2 0.9855.10.1 0.16 130 150 1.19 72 3175 51 3211 8 1 0.2541 0.52 22.30 2.1 0.636 2 0.9755.14.1 0.10 315 153 0.50 189 3414 52 3450 4 1 0.2960 0.29 28.50 2 0.698 2 0.99

Errors are 1-sigma; Pbc and Pb* indicate the common and radiogenic portions. respectively.Error in Standard calibration was 0.5-0.9%( not included in above errors but required when comparing data from different mounts).(1) Common Pb corrected using measured 204Pb.Analysed at VSEGEI. St. Petersburg

176

Huhma, H., Kontinen, A., Mikkola, P., Halkoaho, T., Hokkanen, T., Hölttä, P., Juopperi, H., Konnunaho, J., Luukkonen, E., Mutanen, T., Peltonen, P., Pietikäinen, K. & Pulkkinen, A. 2012. Nd isotopic evidence for Archaean crustal growth in Finland. Geological Survey of Finland, Special Paper 54, 176−213, 20 figures and 1 appendix.

Sm-Nd isotopic data from 400 samples provide a view of the formation of the Ar-chaean crust in Finland and the Fennoscandian Shield. Despite problems related to secondary REE mobility, the Sm-Nd results show that a mantle reservoir with time-integrated depletion in LREE was an important source of magmas already during the Archaean. The data show that most Archaean felsic rocks in Finland have depleted mantle model ages of ca. 2.8-3.0 Ga, suggesting, together with the U-Pb zircon ages, that much of the Archaean consists of relatively juvenile crust. This is particularly true for the Kuhmo area, whereas in Suomussalmi area, the recycling of older crustal material is more pronounced. Throughout the Finnish Archaean rocks with model ages in excess of 3.3 Ga are few. The 3.5 Ga Siurua gneisses in Pudasjärvi, which are the oldest rocks recognized so far in the Fen-noscandian Shield, have yielded the oldest reliable Sm-Nd model ages, up to ca. 3.7 Ga.

Keywords (GeoRef Thesaurus, AGI): absolute age, Sm/Nd, crust, mantle, Archean, Finland

1) Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland2) Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland3) Geological Survey of Finland, P.O. Box 77, FI-96101 Rovaniemi, Finland4) Present address: First Quantum Minerals Ltd, Kaikukuja 1, FI-99600 Sodankylä,

Finland



ND ISOTOPIC EVIDENCE FOR ARCHAEAN CRUSTAL GROWTH IN FINLAND

byHannu Huhma1), Asko Kontinen2), Perttu Mikkola 2), Tapio Halkoaho2),

Tuula Hokkanen1), Pentti Hölttä1), Heikki Juopperi3), Jukka Konnunaho3), Erkki Luukkonen 2), Tapani Mutanen3), Petri Peltonen1,4),

Kimmo Pietikäinen2) and Arto Pulkkinen1)

177

Geological Survey of Finland, Special Paper 54Nd isotopic evidence for Archaean crustal growth in Finland

INTRODUCTION

One of the applications of Sm-Nd isotope analy-sis of rocks is that the results give constraints on the average crustal residence time of the rocks and their provenances. This is based on the as-sumption that REE fractionation associated with the crust generating processes are large compared to fractionation during later processes within the crust (McCulloch & Wasserburg 1978). A gen-eral problem related to this approach, especially with Archaean rocks, is the question whether the Sm-Nd system has remained closed since their formation. If metamorphic Sm/Nd fractiona-tion has occurred, the results are obviously er-roneous. Examples of clearly anomalous results are often related to samples which have relatively low abundance of REE and elevated Sm/Nd ra-tio (147Sm/144Nd > 0.13). The calculated model ages for such samples tend to be too old and do not characterize true crustal residence ages. Most of these problematic samples are relatively fine-grained volcanogenic rocks and often related to shear zones with associated high fluid flow. The opposite case is also seen where some rocks have very low Sm/Nd due to fractionation related to partial melting, providing calculated model-ages that are “too young” compared to the true pro-tolith age.

This paper reports the Sm-Nd isotope results from the Archaean crust in central Finland. The

main features of the Archaean bedrock in Fin-land and the Fennoscandian Shield are provid-ed by Sorjonen-Ward & Luukkonen (2005) and Slabunov et al. (2006). The Archaean area can be divided into a few main domains, which in this paper are simply geographic areas: Pudasjärvi, Suomussalmi/Koillismaa, Kuhmo, Ilomantsi and Iisalmi (Fig. 1). Archaean rocks occur also in Lapland, particularly in the Eastern Lapland and Inari areas, but are not included here, since this volume deals with the Archaean of central Finland. The Sm-Nd data have been produced at GTK since the early eighties, mostly from samples which have been dated by U-Pb methods (A-series samples), and which have been selected to repre-sent significant lithological units. Some samples reported in the Rock Geochemical Database of Finland (Rasilainen et al. 2007) have also been included. The Sm-Nd database consists of ~ 400 samples, from which ~ 100 have been previously published elsewhere. These papers and the compi-lation by Hölttä et al. (this volume) provide more detailed information of the rock types and their geochemistry, but further studies are needed to better combine the isotope results with the com-prehensive geochemical information that exists. In terms of rock types the samples comprise ~ 250 granitoid, 60 mafic, 50 felsic volcanic and 40 sedimentary rocks (Appendix 1).

Sm-Nd METHODS

For whole-rock Sm-Nd analysis, 120-200 mg of powdered sample was spiked with a 149Sm-150Nd tracer. The sample-spike mixture was dissolved in HF-HNO3 in sealed Teflon bombs in an oven at 180 °C (felsic rocks) or in Savillex screw-cap beakers on a hot plate (mafic rocks) for 48 hours. Prior to dissolving the residue in 6.2 N HCl, the fluorides were gently evaporated using HNO3. Conventional cation exchange chromatography was used for separation of the light rare earth elements and Sm and Nd were separated by a modified Teflon-HDEHP (hydrogen di-ethylhex-yl phosphate) method (Richard et al. 1976). To-tal procedural blank was <0.5 ng for Nd. Isotope ratios were measured on a VG Sector 54 TIMS using Ta-Re triple filaments. Nd isotope ratios

were measured in dynamic mode and Sm iso-topes in static mode. Nd ratios are normalized to 146Nd/144Nd=0.7219. Based on several duplicate analyses (Appendix 1), the error of the 147Sm/144Nd is estimated to be better than 0.4 %. The long-term average 143Nd/144Nd for the La Jolla stand-ard is 0.511850±0.000010 (standard deviation for 220 measurements during the years 1996-2010). Recent analysis on BCR-1 gave Sm=6.63 ppm, Nd=28.88 ppm, 143Nd/144Nd=0.512640±0.000010. The eNd was calculated using λ147Sm=6.54 · 10-12 a-1, 147Sm/144Nd=0.1966, and 143Nd/144Nd=0.512640 for the present CHUR. TDM was calculated after DePaolo (1981). Plotting and calculations of iso-tope data were performed using the Isoplot pro-gram (Ludwig 2003).

178

Geological Survey of Finland, Special Paper 54Hannu Huhma, Asko Kontinen, Perttu Mikkola, Tapio Halkoaho, Tuula Hokkanen, Pentti Hölttä, Heikki Juopperi, Jukka Konnunaho, Erkki Luukkonen, Tapani Mutanen, Petri Peltonen, Kimmo Pietikäinen and Arto Pulkkinen

Fig. 1. (a) Major Archaean tectonic domains of the Fennoscandian Shield. (b) Generalized geological map of central Fin-land (after Kontinen et al. 2007, Korsman et al. 1997) showing the main Archaean units. OGB/SGB/KGB/TGB/IGB/KoGB= Oijärvi/ Suomussalmi/ Kuhmo/ Tipasjärvi/ Ilomantsi/ Kovero greenstone belt.

179


ARCHAEAN MANTLE

Many attempts have been made to characterize the Nd isotopic composition of the Archaean mantle by analyzing mafic-ultramafic rocks (e.g., Dupre et al. 1984, Puchtel et al. 1998, Svetov et al. 2001). However, due to metamorphic REE frac-tionation this has often turned out to be difficult, e.g. the 2.8 Ga komatiites from Siivikkovaara in Kuhmo belt have yielded a Sm-Nd age of ca. 1.8 Ga (Gruau et al. 1992). For those data the cal-culated initial εNd(2800) values range from -9 to +1.

We have also carried out Sm-Nd analyses on samples from the Kuhmo belt, those which are considered least altered. These samples include ten komatiites or komatiitic basalts from the Si-ivikkovaara-Pahakangas area (close to Kellojärvi in Fig. 9), five komatiites/ komatiitic basalts from other sites and four high-Cr basalts (Appendix 1). Our results are also scattered with a range in initial εNd(2800) values from -2.8 to +4.6 (Figs. 2 and 3). It remains difficult to evaluate for which samples, if any, the Sm-Nd system has remained closed since the formation of rocks. However, excluding a few strongly deviating samples, the

data from the Pahakangas-Siivikkovaara area tend to give initial εNd(2800) values clustering close to +0.5, which is particularly evident in the four analyses on komatiitic metalavas from the Paha-kangas profile (red triangles and isochron in Fig. 2). However, komatiitic basalts and two high-Cr basalts from other areas in Kuhmo tend to give higher initial values close to +2.5 (red squares and isochron in Fig. 2). Clearly positive initial values are also provided by three intrusive mafic rocks from the Kuhmo belt, which also have been dated by zircon U-Pb (A976, A1771, A1418, red circles in Fig. 3). A very high εHf(2800) of +14 was reported by Patchett et al. (1981) for zircon of the tholeiitic gabbro A976.

Sm-Nd analyses on the LREE enriched ultra-mafic rocks from the Ilomantsi belt (Fig. 1) are also scattered with a range of εNd(2750) values from -7.6 to +3.4 (green circles in Figs. 2 and 3). In contrast, the analyses on amphibolites associated with the ca. 2.72 Ga Nurmes paragneisses (Fig. 1) give consistently positive initial values at about +1.6 (Fig. 3, Kontinen et al. 2007). There are also

Archaean komatiites and related basalts

0.5110

0.5120

0.5130

0.5140

0.10 0.14 0.18 0.22 0.26 0.30

147Sm/144Nd

143Nd144Nd

Ilomantsi komatiites

Age = 2357 ± 240 Ma

MSWD = 6.2 (n=6,dot)

Gruau et al 1992:

Kuhmo komatiites

Age = 1816 ± 150 Ma

MSWD = 14 n=13 (x)

Tourpin et al 1991:

Tipasjärvi komatiites

Age = 2406 ± 180 Ma

MSWD = 15 n=8 (+)

Kuhmo komatiites & basalts

Age = 2633 ± 240 Ma

MSWD = 66 n=19 (all GTK data)

Komatiitic basalts & high-Cr basalts

Age = 2769 ± 190 Ma

eps = +2.7

MSWD = 4.9 (n=5, square)

Pahakangas profile

(2-PTP-03)

Age = 2827 ± 190 Ma

eps = +0.4

MSWD = 1.2 (n=4)

Fig. 2. Sm-Nd isochron diagram for komatiites and basalts from the Pahakangas-Siivikkovaara area in the Kuhmo belt (red and black triangles, n=13), komatiitic and high-Cr basalts from other areas in Kuhmo belt (red squares, n=5) and LREE en-riched komatiites from the Ilomantsi belt (green circles). Analyses on komatiites from Kuhmo/Siivikkovaara (x) by Gruau et al. (1992) and from Tipasjärvi (+) by Tourpin et al. (1991) are shown for reference.

180


data on intrusive mafic rocks from Ilomantsi, Suomussalmi and Pudasjärvi areas that support clearly positive initial values. These include the 2866 ± 4 Ma gabbro A1821 from the Tormua belt (Suomussalmi), the 2802 ± 5 Ma gabbro A1782 from the Oijärvi belt (Pudasjärvi) and the 2756 ± 4 Ma gabbro from the Kovero belt (Ilomantsi) and several amphibolites from the Iisalmi area (Fig. 3). The newly discovered 2741 ± 2 Ma old Likamännikkö carbonatite and associated mafic rocks in Suomussalmi (A1912 in Fig. 4, Mikkola et al. 2011b) also strongly supports sources with positive initial εNd, since the concentration of REE in these rocks are high and the Sm-Nd sys-tem is thus less sensitive to crustal contamination or later disturbances (Fig. 3).

The results from several felsic rocks, especially from the Kuhmo belt, also provide clearly positive initial-epsilon values. Overall, the Sm-Nd data at-

test to the importance of a depleted mantle source and that the model for the evolution of upper mantle by DePaolo (1981) is a useful reference.

It is tempting to consider that the εNd(2800) val-ues of +0.5 obtained on many komatiitic sam-ples from Kuhmo were primary signatures, which with reference to the rocks with more positive values, would suggest heterogeneity in the Ar-chaean mantle. This speculation is consistent with the conclusion by Maier et al (in prep), who con-sider the geochemistry of the Kuhmo komatiites to indicate their origin in an oceanic plateau set-ting above a plume, derived from primitive upper mantle, rather than in a NMORB-type setting from a depleted, convecting mantle source. Other mantle sources with close to chondritic initial εNd values are evident e.g. for the 2610 ± 4 Ma old Siilinjärvi carbonatite with εNd(2610) = 0 (Figs. 3 and 15, Appendix 1) and the 2712 ± 1 Ma old high

Archaean mafic-ultramafic rocks

Depleted Mantle

CHUR

A1821

A1771

A1418

A976A1782

A1626

Siilinjärvi

-8

-6

-4

-2

0

2

4

2600 2640 2680 2720 2760 2800 2840 2880

Age (Ma)

Nd

-ep

sil

on

A1821 Tormua belt gabbro

Kuhmo belt gabbros

A1782 Oijärvi belt gabbro

Ilomantsi & Kovero gabbros

Likamännikkö carbonatite

Siilinjärvi carbonatite

Kuhmo/Siivikkov. area (n=13)

Kuhmo/'other areas' (n=5)

Ilomantsi (n=10)

Amphibolites (n=7)

A1772

–

Fig. 3. Epsilon-Nd vs. age diagram for 60 Archaean mafic rocks in Finland (GTK data). Calculated initial epsilon values are shown: Kuhmo komatiites/ komatiitic basalts and high-Cr basalts in the Siivikkovaara-Pahakangas-Näätäniemi area (red ×s at 2.81 Ga, n=13), Kuhmo komatiitic and high-Cr basalts in other areas (red +s at 2.81 Ga, n=5), Ilomantsi ultramafic-mafic rocks (green circles at 2.75 Ga, n=10), 2741 ± 2 Ma Likamännikkö carbonatite (light blue diamonds), amphibolites associated with paragneisses (at 2.72 Ga, n=7, six samples at +1.6) and the 2610 ± 4 Ma Siilinjärvi carbonatite (diamonds). Symbols with sample numbers denote gabbroic samples for which the age is based on U-Pb zircon dating (A1782 – Oijärvi belt; A1821 – Suomussalmi/Tormua belt; A976, A1418, A1771 – Kuhmo belt, A1626 – Kovero belt, A1772 – Änäkäinen high REE gabbro). Also shown are the evolution lines for 12 other mafic samples (6 from the Pudasjärvi area, A1180 from the Suomussalmi belt, A1764 from the Ilomantsi area and four amphibolites from the Iisalmi complex). Depleted mantle evolution is according to DePaolo (1981).

181


REE alkali gabbro A1772 from Änäkäinen with εNd(2712) = 0 (Figs. 3 and 11, Appendix 1). Howev-er, the observed clustering of εNd(2800) results from the Siivikkovaara-Pahakangas komatiites may be

accidental, and rocks from other areas in Kuhmo, with positive εNd(2800), may better record the prima-ry signature for the komatiitic magmatism.

KOILLISMAA & SUOMUSSALMI

To evaluate the sources and crustal residence of the felsic rocks, Sm-Nd model ages (TDM) for samples with “typical” upper crustal REE pat-terns (147Sm/144Nd< 0.16) have been calculated using the model of DePaolo (1981). The Sm-Nd data available on the Archaean rocks from the Koillismaa area consist of 24 analyses of grani-toids/gneisses, some of which were published by Lauri et al. (2006) and Heilimo et al. (2013) (Fig. 4). Rocks in the western areas are mostly strongly LREE enriched (low 147Sm/144Nd) and give model ages in the range 2.9-3.1 Ga. In contrast, sam-ples near the Russian border yield systematically younger model ages of ca. 2.8 Ga (Fig. 5). Many of these are included in the 2.72 Ga Kuusamo sa-nukitoids (Heilimo et al. 2013).

In the Suomussalmi area, Sm-Nd analyses have been made on samples from the granitoid areas (32 granitoids and one mica gneiss) and from the Suomussalmi greenstone belt (two mafic and 15 felsic rocks including at least three sedimentary rocks).

Most of the granitoid data are adopted from Mikkola et al. (2011a, b), and generally give TDM ages in the range 2.9-3.1 Ga. Many of these sam-ples have yielded U-Pb zircon ages from 2.70 to 2.82 Ga (Mikkola et al. 2011a, b), and include also the Kaapinsalmi tonalites, which have been denoted as sanukitoids (EPHE samples in Fig. 4, Heilimo et al. 2013). Two gneisses, which have older U-Pb ages, also yield older model ages at 3.28 Ga (A1856 Portinkuru) and 3.56 Ga (A79 Päivärinta). The Sm/Nd ratio in the migmatitic gneiss A79 is, however, slightly higher than in most other samples, possibly due to metamorphic effects, and hence the system likely does not regis-ter primary signatures. Replicate analyses on A79 and many other samples show that variation due to analytical errors is not significant.

Most of the greenstone belt samples are from fine-grained, felsic-intermediate volcanogenic rocks. The Sm-Nd data include also five duplicate analyses, which generally show good reproduc-ibility (within 0.3 epsilon units in calculated initial ratios, Appendix 1). The exception is A1593#2, from which the analytical error is also larger than

in other data, and which also contained some monazite resulting in possible nugget effect. It is evident that some rocks are strongly altered and the Sm-Nd system has been significantly dis-turbed. Results from the Kuhmo greenstone belt discussed above suggested that major REE frac-tionation in the komatiites seems to coincide with the Svecofennian regional metamorphism of the Archaean craton as registered by Rb-Sr and K-Ar isotope data (e.g., Kouvo & Tilton 1966, Kontin-en et al. 1992). There are also investigations sug-gesting late Archaean post-magmatic alteration, including the Rb-Sr study on the Luoma Group volcanic rocks by Martin and Querré (1984), who acquired an age of 2.5 ± 0.1 Ga. Also the Pb-Pb isotope studies on whole-rock samples have pro-vided scattered age results (Vidal et al. 1980, Vaas-joki et al. 1999).

Two mafic volcanic rocks analyzed from the Suomussalmi belt have nearly chondritic REE ra-tios and initial isotopic compositions close to that of coeval depleted mantle (A1180A Saarikylä, A1821 Tormua, Fig. 6). Most of the analyzed fel-sic rock samples are enriched in LREE similar to upper crust (147Sm/144Nd = 0.08-0.12) and should thus be useful samples for crustal residence stud-ies. The felsic samples consistently result in TDM model ages in excess of 3 Ga (Fig. 6). It is also ob-vious that some samples provide meaningless re-sults, particularly the felsic rock A1467, for which the initial epsilon at 2940 Ma is -23 and TDM ca. 7.5 Ga (also checked by duplicate analysis). This sample has low REE contents (Nd<4 ppm) and elevated Sm/Nd, being clearly unrepresentative of the primary chemical composition. In a compari-son with the bulk of the data, also samples A1192 (porphyry) and A1065A (fine-grained felsic rock from drill-core KR-27) provide much lower initial values and old model ages. All three of these sam-ples are strongly altered, sheared, pale schists and are distinct from the other samples in this study. We consider that the Sm-Nd system in these sam-ples has not remained closed since the formation of the rocks.

In light of these observations, one may specu-late whether the other samples have remained

182


Luoma

Koillismaa

Tormua

Suomussalmi

A79

A415

A260

A1905A1908

A1910A1901

A1841

A1903

A1912 A1909

A1831 A1193A1915A1857 A1904

A1907

A1913A1890

A1657A1662

A1661

A1656

A1889

A1888

A1887

A1642A1652

A1644

A1643

A1514

94003728

95001760

95001765

95001741

95001753

95001676

53-PGN-90

TTU$-2004-156

TTU$-2004-148

A80bA80a

A1858

A1902A1962

A28bA

A1856

A1906

A1840

A1821A1429

A1192

A1467

A1191

A1428

A1180AA1179CA1179A

A1593#2

95001798

Soilu TTG

EJL-92-71ASM-94-685ASM-94-684

EPHE-2005-40.1

A1065A EPHE-2004-347.2

EPHE-2004-336.1

EPHE-2004-353.2

EPHE-2004-345.1

EPHE-2004-332.1

L07084729 (193.3)L07084728 (193.2)L07084727 (193.1) A1594

20

Km

TTU$2004-162

TTU$2004-160.1

TTU$2004-167

TTU$2004-154

Koillismaa-Suomussalmi (n=70)

0

5

10

15

20

25

<2.6 2.7-

2.8

2.9-

3.0

3.1-

3.2

3.3-

3.4

>

3.5

T-DM (Ga)

Series1

Fig. 4. Geological map of the Koillismaa-Suomussalmi area showing Sm-Nd sample sites. The size of the symbol denotes the model ages divided in six categories: < 2.7 Ga (small), 2.7-2.85 Ga, 2.85-3.0 Ga, 3.0-3.15 Ga, 3.15-3.3 Ga, >3.3 Ga (large). Model ages are not presented for mafic rocks which have 147Sm/144Nd> 0.16, and symbol for these is small black circle (A1821, A1180A). The map is based on the 1: 1 000 000 geological map of Korsman et al. (1997), with the Suomussalmi greenstone belt divided into three main rock types, mafic metavolcanic rocks (brown), ultramafic metavolcanic rocks (green) and intermediate-felsic metavolcanic rocks (yellow). Rocks outside the greenstone belt consist of TTG’s, intrusive rocks (stippled), amphibolites (brown) and paragneisses (grey).

183


Koillismaa & Suomusssalmi

95001753 Kuusamo

A1856 Portinkuru

A79 Päivärinta

A1191

A260

A1840

A1909 Kuikkavaara

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16

147Sm/

144Nd

T-D

M(M

a)

Koillismaa granitoids

Suomussalmi granitoids

Suomussalmi belt volc

metasediments

Suomussalmi greenstone belt

Depleted Mantle

A1467

A1191 Ala-Luoma

A1065A

A1428A1593

A1192

A260

A1429

A1821

-14

-10

-6

-2

2

2600 2800 3000 3200 3400

Age (Ma)

Ep

s-N

d

Fig. 5. Sm-Nd model ages TDM for Archaean whole rock samples from the Koillismaa-Suomussalmi area. Suomussalmi belt volc= volcanogenic felsic-intermediate rocks.

Fig. 6. Epsilon-Nd vs. age diagram for whole-rock samples from the Suomussalmi greenstone belt. In addition to evolution lines, initial ratios are shown for samples, which have been dated using U-Pb: 2.82 Ga Mesa-aho porphyry (A1428), Kilpasuo andesite (A1429), 2.87 Ga Tormua gabbro (A1821) and 2.94 Ga felsic volcanic rocks (A1593, A1192). The evolution of de-pleted mantle is from DePaolo (1981). Note that samples A1192, A1065A and A1467 (outside the figure) are strongly altered, pale schists and do not register primary isotope signatures.

184


closed. The porphyry sample A1593, which pro-vided a U-Pb monazite age of 2942 ± 3 Ma, is texturally devoid of alteration such as seen in the related, above-mentioned samples, and could thus be assumed to preserve also its primary chemi-cal characteristics. The Sm-Nd analyses of this sample provide εNd(2942) of ~ -3 and a model age TDM of ca. 3.3 Ga. The three fine-grained, volcan-oclastic rocks from the nearby Ala-Luoma site give model ages of 3.2-3.4 Ga (A1191, A1179A, A1179C), and the felsic volcanogenic rocks from Mesa-aho, 2.5 km SSW of Ala-Luoma, yield TDM of 3.1-3.3 Ga (A1428, A1594, EJL-92-71, Figs. 12 and 13). Model ages in excess of 3.0 Ga are also obtained from the three volcanic rocks ana-lyzed from Kiannanniemi located 15 km SW of Ala-Luoma (e.g. A1514 in Fig. 4), as well as from sample A1429 at Tormua (Fig. 4).

The analysis from the Mesa-aho porphyry A1428 shows high REE concentrations (Nd=52 ppm) with a very strong LREE enrichment (147Sm/144Nd = 0.068). Another sample (EJL-92-71) a few meters north of the sampling site of A1428 also has high REE contents but a

less fractionated, “typical crustal” REE pattern (147Sm/144Nd = 0.116). The Sm-Nd analyses from these two samples suggest an age of 2.75 ± 0.05 Ga (epsilon -4), which is close to the U-Pb zir-con age of 2.82 Ga for A1428. Provided that both samples originated from the same chemically and isotopically homogenous source, the result sug-gests that the strong LREE enrichment in A1428 is probably related to the generation of the rock at 2.82 Ga, and thus the model age of 3.08 Ga for A1428 would be “too young” to depict the age of the protolith. The model age of 3.26 Ga cal-culated for sample EJL-92-71 likely reflects more closely the age of the protolith.

In summary, excluding the strongly altered samples, the bulk of the data from the Suomus-salmi greenstone belt yield Sm-Nd crustal resi-dence ages (TDM) of 3.0-3.3 Ga. These old model ages are supported by the inherited ca. 3.2 Ga and 3.53 Ga zircons found in the Saarikylä and Ki-annanniemi samples (Huhma et al. this volume). The results can be compared with the Sm-Nd data available from the Archaean felsic rocks in Fin-land (Fig. 7). Although most of these results come from granitoids, some data from volcanic and

Suomussalmi greenstone belt compared withArchaean rocks in Finland

A260

A1192

A1179C

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16147Sm/144Nd

T-DM

(Ma)

SuomussalmiTojottamanselkäSiurua, PudasjärviIisalmi

Fig. 7. Sm-Nd model age (TDM) vs. 147Sm/144Nd diagram for Archaean felsic rocks in Finland. Blue squares denote samples from the Suomussalmi greenstone belt. The reference data (×) are mostly from granitoids, but include also some volcanic and sedimentary rocks (Jahn et al. 1984, Huhma 1986, O’Brien et al. 1993, Hölttä et al. 2000, Halla 2002, Hanski et al. 2001, Mutanen & Huhma 2003, Käpyaho et al. 2006, Lauri et al. 2006, 2011, Kontinen et al. 2007, Mikkola et al. 2011a, b, Huhma et al. this volume). Red triangles denote the average 147Sm/144Nd ratios for bulk (0.1179) and upper (0.1053) crust by Rudnick and Gao (2004).

185


sedimentary rocks are also included. Although some disturbance in the Sm-Nd system is appar-ent, it is also clear that samples from the Suomus-salmi greenstone belt have older crustal residence ages than most rocks in other areas. Only sam-ples from the ca. 3.5 Ga Siurua gneiss (Mutanen & Huhma 2003, Lauri et al. 2011, Huhma et al. this volume) and the 3.1-3.2 Ga gneisses from Tojottamanselkä, central Lapland (Jahn et al. 1984, Hanski et al. 2001) and the Iisalmi/Lapin-

lahti area (Hölttä et al. 2000) have yielded reliable model ages in excess of 3.2 Ga. The old model ages are consistent with the Pb-Pb and U-Pb re-cord from the Suomussalmi greenstone belt sug-gesting stronger involvement of older crustal ma-terial than in other greenstone belts in Finland (Huhma et al. this volume, Vaasjoki et al. 1999). On the western margin of the Suomussalmi belt relatively old crustal signatures are evident also in the granitoids (A79, A1856, A1909).

KUHMO

The Sm-Nd data produced at GTK from the Kuhmo area consist of 120 samples and cover all three major rock units, i.e., the Kuhmo-Tipas-järvi greenstone belt (47 samples), granitoids (56 samples) and enclaves of Nurmes paragneiss (15 samples). Results from the Nurmes paragneisses and associated amphibolites were published by Kontinen et al. (2007) and half of the analyses on granitoid samples by Käpyaho et al. (2006).

As discussed above, Sm-Nd studies on the komatiites from the Kuhmo-Tipasjärvi green-stone belt have shown major metamorphic dis-turbances (Gruau et al. 1992, Tourpin et al. 1991, this paper). Results from many mafic rocks, how-ever, suggest a mantle source which had time-in-tegrated depletion in LREE with εNd(2800) of +2 (see above), providing a framework for crustal residence studies.

Most granitoids analyzed from the Kuhmo area yield TDM model ages in the range 2.8-2.95 Ga, and only three samples unambiguously sug-gest model ages older than 3 Ga (A404, A1706, A1928, Figs. 8 and 9). Two of these gneissic gran-itoids give U-Pb zircon ages older than the ma-jority of the rocks of the Kuhmo domain, where most granitoids have U-Pb zircon ages at 2.70-2.75 Ga (17 samples) and a few at 2.79-2.83 Ga (3 samples). Most of these granitoids have positive initial epsilon values, which together with the re-sults on felsic volcanic rocks from the greenstone belt (red triangles – Kellojärvi area, green circles – Tipasjärvi in Fig. 8) clearly show that the bulk of the crust in the Kuhmo domain had to be of relatively juvenile nature. Also, most results from the sedimentary rocks within the greenstone belt (solid blue circles in Fig. 8) and Nurmes parag-neisses (open blue circles) typically suggest a rela-tively short crustal prehistory for their sediment sources.

It should be noted that a few samples, for which the calculated model ages are above 3 Ga, were excluded from the discussion above. This is

because these samples have Sm/Nd slightly high-er than typical crustal felsic rocks and thus may not be relevant for TDM calculations (e.g. grani-toids 94003191 and A1183, and metasediments 1-KUH-88, 44-PGN-90, A1746 in Appendix 1). The Naavala migmatitic gneisses provide a related case requiring some special attention. The Naavala gneisses were among the targets for crustal genesis studies by Martin et al. (1983), who dated them, using Rb-Sr whole rock method at 2.62 ± 0.07 Ga. Subsequently GTK reported a much older U-Pb zircon age of 2.75 Ga (Luukkonen 2001) for the same rock. Sm-Nd analyses were also carried out at GTK on nine samples from the Naavala site representing the main rock types observed in the Naavala gneiss domain. These include tonalite-granodiorite mesosomes, different granitic dykes or leucosomes and an amphibolite band (A1183 and Naa samples in Appendix 1 and Fig. 8). The Sm-Nd results on these samples are strongly scat-tered with εNd(2750) values ranging from -3.9 to +2.3 (equivalent to TDM model ages from 3.30 to 2.74 Ga). Duplicate analyses show good reproducibil-ity and hence the reason for the scatter is related to the complex geological history of the Naavala gneiss. A particularly striking aspect is that a large difference in the Sm-Nd isotope composition can be observed even between the whole rock sam-ple A1183 (TDM=3.3 Ga) and a small piece taken from the very same locality (A1183p, TDM=2.74 Ga). The REE abundance in most samples of the Naavala gneiss is fairly low and Sm/Nd high compared to typical granitoids. Thus it is also likely in this case, that metamorphic effects are mainly responsible for the scatter. However, one of the leucosome dykes/bands (Naa4) has quite high REE abundances and a TDM age of 2.74 Ga, which together with the other data, suggests that material from distinct sources have contributed to the Naavala gneisses.

The results from Naavala underscore the level of caution which is needed when applying Sm-Nd

186


data, particularly to rocks which evidently have complex geological histories, such as polymig-matitic rocks or rocks that have been subjected to retrogressive metamorphic-hydrothermal events. On the other hand, there are examples that for even widely spaced samples from a well preserved, non-retrogressed rock unit may yield results all within analytical error. These include the Koitere “sanukitoid” samples in the Ilomantsi area (Halla 2005, Fig. 11), and the Kaapinsalmi and Kuusa-mo “sanukitoids” discussed above (Heilimo et al. 2013, Appendix 1, Fig. 4).

The Sm-Nd results on mafic-ultramafic rocks from the Kuhmo greenstone belt were discussed above. Although the results are scattered due to metamorphic effects, most komatiites and komati-itic basalts from the Kellojärvi area give εNd(2800) values of about +0.5 (red x in Fig. 10), whereas mafic rocks from other locations tend to have more positive εNd(2800) values.

In order to evaluate the crustal residence time and origin of felsic lithologies, whole rock Sm-Nd isotope compositions were measured for some of the samples which have been used for U-Pb dat-ing. These samples were carefully selected to rep-resent the lithological or stratigraphical units in

question. The U-Pb age, if available, is used for calculating the initial εNd values (Fig. 10). As was discussed above, there are some examples also in felsic rocks, where metamorphic effects have se-riously disturbed the Sm-Nd system, rendering it impossible to get information on primary iso-topic compositions. Typically, such samples tend to show LREE depletion and generally have low levels of REE. In our data set of felsic rocks, there are two samples (A788 and A1746) which yield very low apparent initial epsilon values (-22, -11) and are also clearly LREE-depleted compared to common felsic rocks (Nd 3-5 ppm). On the other hand, the calculated initial ratio for the Hetteilä mica schist sample A1774 is anomalously high (+4 at 2.74 Ga). The calculated initial ratios for ancient rocks are very sensitive to even slight changes in Sm/Nd, and in the case of this sample, for example, an increase of Sm/Nd by 6% would drop the epsilon value to +2.

In spite of these problems, the data as a whole provide useful information. The samples analyzed from the Kellojärvi area (A-series felsic volcanics and gabbros) give clearly positive initial εNd val-ues from +1.2 to +2.4 and thus appear to repre-sent largely juvenile crustal material. The Sm-Nd results from the Tipasjärvi felsic volcanic rocks

Kuhmo

A404A1928

A1183

Naa3#2

Naa5

Naa2#2

A1183p#2

Naa1

Naa 4

Naa6A120a

A120b

A1000a

A1213

A1773

A1346A1560 A1771

A1503

A1377A511

A1174cA1174A A1886A1922

A1921

1-KUH-88

44-PGN-90

A1706

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16

147Sm/144Nd

T-D

M(M

a)

granitoids

Naavala gneisses

felsic volc, Kuhmo

felsic volc, Kellojärvi area

felsic volc, Tipasjärvi

metasediments, Kuhmo belt

metasediments, Nurmes belt

Fig. 8. TDM model ages for felsic rock samples from the Kuhmo domain. Red circles: granitoids and gneisses, red +s: Naavala migmatitic gneisses; red triangles: felsic volcanic rocks and gabbro A1771 from Kellojärvi area in Kuhmo greenstone belt; red ×s: felsic volcanic rocks from other Kuhmo greenstone belt; green circles: felsic volcanic rocks from Tipasjärvi greenstone belt; blue solid circles: metasediments from the Kuhmo greenstone belt; blue open circles: metasediments from the Nurmes paragneiss belt.

187


Naavala

Kellojärvi

Tipasjärvi

S4

S22

A790

A331

A402Naa7

Naa5

A511

A788

A976

A1089

A1086

A1703

A1705

A1926

A1928

A1147A1706

A1702

A1704

A1927

A1960A27-4

A1146

A1081

A1921A1922

A1886

A1748

81064

A1747

A1822

A1503

A1346

A1774

A1213

81062A120b

A404b#2

A337 #2

93002713

94002606

53-PTP-03

48-PTP-03

56-PTP-03

AAK-02-21

AAK-02-48

AAK-02-09AAK-02-59

44-PGN-90

AAK-02-166

AAK-02-157

AAK-02-117AAK-02-174

13A-NUR-90

AAK-02-167A

61-1-ATK-86

AAK-02-179A

57-1B-ATK-8

204-2B-ATK-

A1588

A1719 (AAK-02-177)

A572

Naa6

Naa1

A1707

Naa 4

A1183

A27-2A27-1

A1746

A1377A1771

A1418 A1560

A1773

A120a

Naa2#2Naa3#2

A1174AA1174c

A1000a

A790uusi

A1183p#2

1-KUH-88

6-EJH-96

22-PTP-0311-PTP-03

7E-PTP-037F-PTP-03

7B-PTP-037D-PTP-03

2H-PTP-03

2D-PTP-03

7A-PTP-03

52-PTP-03

2C-PTP-03

2E-PTP-03

AAK-02-84

AAK-02-77

AAK-02-87AAK-02-83

AAK-02-81

2B1-PTP-03

AAK-02-100

AAK-02-57B

391-ATK-83

57-1C-ATK-8

17-8-ATK-87

57-1A-ATK-8

204-2A-ATK-

57-3A-ATK-8

R400/73.50-75.50 & 64.80-67.00

94002593

Kuhmo (n=76)

05

1015

20253035

<2.6 2.7-

2.8

2.9-

3.0

3.1-

3.2

3.3-

3.4

>

3.5

T-DM (Ga)

Fig. 9. Geological map of the Kuhmo area showing Sm-Nd sample sites. The size of the symbol denotes the model ages divid-ed into six categories: < 2.7 Ga (small), 2.7-2.85 Ga, 2.85-3.0 Ga, 3.0-3.15 Ga, 3.15-3.3 Ga, >3.3 Ga (large, only one Naavala sample, likely not primary signature, see text). Model ages are not reported for samples which have 147Sm/144Nd> 0.16, and symbols for these mostly mafic rocks are small black circles (e.g. A976). The map is based on the 1: 1 000 000 geological map of Korsman et al. (1997), with the greenstone belts divided into four main rock types, mafic metavolcanic rocks (brown), ul-tramafic metavolcanic rocks (green), intermediate-felsic metavolcanic rocks (yellow) and metasediments (blue). Rocks outside the greenstone belts consist of TTG’s, intrusive rocks (stippled), amphibolites (brown) and paragneisses (grey).

188


are similar. The three samples from the 2.82 Ga Ruokojärvi volcanic unit are low in REE (Nd ~ 6 ppm), but still show normal, LREE-enriched

chondrite-normalized REE patterns. They give a small range of initial values from -0.8 to +0.8 (Fig. 10).

ILOMANTSI

The Ilomantsi area, south from the Kuhmo do-main, covers the southernmost part of the Ar-chaean bedrock in Finland consisting of grani-toid areas and the Ilomantsi (Hattu) and Kovero schist belts (Fig. 11). The Sm-Nd data available on the Archaean rocks from the Ilomantsi area con-sist of roughly 60 samples, which represent grani-toids (27 samples), felsic and mafic-ultramafic volcanic rocks (23) and metasediments. Some of these results have been published in Huhma

(1987), O’Brien et al. (1993), Halla (2005), and Kontinen et al. (2007).

Most of the analysed granitoids have model ages of 2.75-2.9 Ga, and only analyses from the Silvevaara/Lehtovaara pluton give slightly older TDM ages of ca. 3 Ga (A339, A284, Fig. 12). This 2.75 Ga granodiorite also contains inherited zir-cons older than 3 Ga (Sorjonen-Ward & Claoué-Long 1993), and thus both Sm-Nd and U-Pb data suggest involvement of older crustal material in

Kuhmo-Tipasjärvi Greenstone Belt

A1346

A1560A1418#2

A1771

A1503

A1377 A511

A120a

A120b Ruokojärvi

A1000a


A1213 Pitkäperä

A1773 Hetteilä

DM (DePaolo)

A1747 Petäjäniemi

A1748 Aarreniemi

A1922

A1174c

A1174AA1886

A1921

A1588

A1086 Haasiavaara tonalite

A1705 Viitavaara tonalite

A1702 Purnu tonalite

A402 81064 Koitto

Komatiites and komatiitic basalts

-2

-1

0

1

2

3

2740 2760 2780 2800 2820 2840

Age (Ma)

Nd

-ep

sil

on

Fig. 10. Epsilon-Nd vs. age diagram for whole-rock samples from the Kuhmo and Tipasjärvi belt, showing initial values for A-series samples from the Kellojärvi area (filled red circles), komatiites and komatiitic basalts from Pahakangas-Siivikkovaara (10 samples, red ×s), other areas from the Kuhmo (open red circles for A-series, red +s for basalts) and Tipasjärvi belts (green diamonds). An age of 2800 Ma is used for A1503 and A1588, 2810 Ma for komatiites and basalts, and U-Pb zircon age for other samples. Also are shown the evolution lines for three sedimentary rocks and the model depleted mantle (De Paolo 1981). The initial epsilon values for four granitoids (triangles) are shown for reference: A1086-Haasiavaara tonalite, A1705-Viitavaara tonalite, A1702-Purnu tonalite and A402-Härmäjoki felsic dyke intruding the greenstones (Käpyaho et al. 2006).

189


Vehkavaara

Kovero

Koitere

S55A91

R27

S20

S19

S18

S21

A339 A221

A1964

A1963

A1772

A1768A1766

A1764

A1763

A1762

A1336

PK-47

PK-42

PK-50

A1094

A1520

A1155

A1749

A1629

A1039A1038

93002484

94003175

93002466

94003191

9-NUR-90

L05071821

A301#3

A1339 (PK-27)

A285

A1767

A1765PK-49

PK-45

A339b

A1154

A1628A1627A1626A1625A1624

A1623

A1622

A1095

PK-100

A284#2

94003163

L05092835

L05071820

L05071819L05071818

L05071817L05071816

A282#3

A1039b

20

Km

Ilomantsi

Ilomantsi (n=44)

0

5

10

15

20

25

<2.6 2.7-

2.8

2.9-

3.0

3.1-

3.2

3.3-

3.4

>

3.5

T-DM (Ga)

Fig. 11. Geological map of the Ilomantsi area showing Sm-Nd sample sites. The size of the symbol denotes the model ages divided into six categories: < 2.7 Ga (small), 2.7-2.85 Ga, 2.85-3.0 Ga, 3.0-3.15 Ga, 3.15-3.3 Ga two samples, probably neither with primary signatures), >3.3 Ga (large, no reliable data in Ilomantsi area). Model ages are not presented for samples which have 147Sm/144Nd> 0.16, and symbols for these mostly mafic rocks are small black circles. The map is based on the 1: 1 000 000 geological map of Korsman et al. (1997), with the greenstone belts divided into three main rock types, mafic (and minor ultra-mafic) metavolcanic rocks (brown), intermediate-felsic metavolcanic rocks (yellow) and metasediments (blue). Rocks outside the greenstone belts consist of TTG’s, intrusive rocks (stippled), amphibolites (brown) and paragneisses (grey).

190


the genesis of the Silvevaara pluton, as well as in the case of nearby Vehkavaara dykes (A282, A301, see Huhma et al. this volume). Also the 2.88 Ga felsic tuff A1627 from the Kovero schist belt, and sample 93002466 give TDM in excess of 3 Ga, but the latter has high Sm/Nd, and possibly does not provide a relevant TDM age.

As was discussed above, mafic and ultramafic volcanic rocks from the Ilomantsi greenstone belt yield a large range of initial-epsilon εNd(2750) val-ues from -7.6 to +3.4 (Fig. 3), probably because of serious modification in Sm/Nd by metamorphic-hydrothermal fluids. The Sm-Nd results from the felsic volcanic rocks are also scattered due to met-

amorphic effects (Fig. 12). Especially suspect are the old calculated model ages for samples which have relatively high Sm/Nd (A1038 and A1625). A similar tendency towards elevated Sm/Nd and TDM ages is also obvious with the analyses on some metasediments. Based on those felsic sam-ples which have REE patterns close to average crustal values (147Sm/144Nd=0.09-0.12) we may nevertheless estimate that the bulk the Ilomantsi area contains relatively juvenile Neoarchaean crust. This concerns particularly the granidoids denoted as “Koitere sanukitoids” (Fig. 11), which have yielded TDM model ages of ca. 2.8 Ga (Halla 2005, Heilimo et al. 2013).

Ilomantsi

A1627

A1626 gabbro

A1625 ??

A1624 ??

A301#3 A282#3

A1038 ?

A1039 A221

S20

S19

S18

A1520 ??

A339b

A339

A284#293002466

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16

147Sm/144Nd

T-D

M(M

a)

granitoids

schist belt

metasediments

Fig. 12. Sm-Nd model ages for the Archaean rocks in Ilomantsi. Solid triangles denote granitoids and open triangles rocks from the Ilomantsi and Kovero schist belts. Blue circles are metasediments. Some samples have suffered secondary REE mo-bility (at least those marked with “?”).

191


PUDASJÄRVI

The Sm-Nd data available on the Archaean rocks from the Pudasjärvi block consist of analyses on 47 granitoids/gneisses, six mafic rocks, two mica gneisses and a 2.82 Ga metadacite sample (A1783) from the Oijärvi schist belt (Appendix 1). Some of these data have been published by Huhma (1986), Mutanen and Huhma (2003) and Lauri et al. (2011). Mafic rocks analysed include a 2.8 Ga gabbro (A1782) from the Oijärvi belt and amphibolites/ mafic granulites in the granitoid areas. These rocks mostly have relatively flat REE patterns and yield positive initial epsilon values suggesting origin from a depleted mantle source.

The Sm-Nd data on felsic rocks reveal a large range of crustal residence ages with TDM model ages up to 3.7 Ga (Fig. 13). An even older model age (3.86 Ga) was obtained from one sample (TM-04-9.1, Appendix 1, not shown in Fig. 13), but the relatively high Sm/Nd and low REE in this sam-ple probably indicate metamorphic disturbances. The oldest reliable TDM ages (3.67 Ga) were ob-tained from the tonalitic Siurua gneisses relatively devoid of granitic leucosomes. The old ages are

consistent with U-Pb zircon studies, which in ad-dition to abundant 3.5 Ga zircon grains, have rec-ognized a few old cores up to 3.7 Ga (Mutanen & Huhma 2003, Lauri et al. 2011). The presence of such very old material is also evident from the Lu-Hf results (Lauri et al. 2011).

In addition to the classical Siurua outcrops, Sm-Nd model ages above 3.3 Ga were obtained also from migmatitic gneisses in Kolkkoaho, lo-cated 20 km north of the Siurua locality (Fig. 14). Rocks around the Siurua and Kolkkoaho sites have generally yielded model ages between 3.0 and 3.2 Ga, whereas samples from other parts of the Pudasjärvi area yield model ages mostly be-tween 2.7 and 3.0 Ga.

The two Archaean mica gneisses (A1814, A1842) analyzed from the Pudasjärvi area have model ages of 2.81 and 2.74 Ga and thus contain relatively juvenile detritus strongly distinct from the Siurua gneisses. The young model ages of the mica gneisses are consistent with the U-Pb ages of their detrital zircon grains, which are mostly less than 2.75 Ga (Huhma et al. this volume).

Fig. 13. Sm-Nd model ages TDM from the Pudasjärvi area. The Sm/Nd ratios for average bulk and upper crust are from Rud-nick and Gao (2004).

192


Siurua

Oijärvi

R4

A1954

A1611A1717

A1490A1534

A1553A1533

A1739

A1603A1966

A1811A1810A1809

A1740

A1741

A1742

A1601

A1965

A1783

A1782

A1842

A1814

A1686BA1686A

TM-00-13

9300184693001430

L05029441

L05028739

L05028727

TM-04-2.3

TM-04-2.1TM-04-2.2L05028737

L05028797

L05028791

L05028793

L05028786

JON-00-4.1

JON-00-82.1

JON-00-55.3

25

Km

KML-00-77.1TM-04-9.1

TM-04-9.2

TM-04-9.3.1

TM-04-9.3.2JON-00-53.1

KML-00-11.1

TM-04-3.2

A1812A1813TM-04-3.1

A1602A1602b

TM-04-3.3

Pudasjärvi (n=50)

0

5

10

15

20

<2.6 2.7-

2.8

2.9-

3.0

3.1-

3.2

3.3-

3.4

>

3.5

T-DM (Ga)

Fig. 14. Geological map of the Pudasjärvi area showing Sm-Nd sample sites. The size of the symbol denotes the model ages divided into six categories: < 2.7 Ga (small), 2.7-2.85 Ga, 2.85-3.0 Ga, 3.0-3.15 Ga, 3.15-3.3 Ga, >3.3 Ga (large). Model ages are not presented for mafic rocks which have 147Sm/144Nd> 0.16 (A1601, A1782). The map is based on the 1: 1 000 000 geological map of Korsman et al. (1997), where main units are the Oijärvi greenstone belt (brownish), granitoid areas and paragneisses (grey).

193


IISALMI, MANAMANSALO & CENTRAL PUOLANKA GROUP

Most of the 25 Sm-Nd analyses available from the Iisalmi complex have been published by Hölttä et al. (2000), Halla (2005) and Lauri et al. (2011). These results show that the 3.1-3.2 Ga old rocks from the Lapinlahti site also give TDM model ages in the same range (Appendix 1, Figs. 15 and 16). The calculated model age for sample A76 is clearly older, but the high Sm/Nd leaves room for speculation of possible open system be-havior. The Sm–Nd data on samples from other localities in the Iisalmi complex provide TDM ages generally in the range of ca. 2.75–2.82 Ga.

The nine granitoid samples from the Mana-mansalo area, between the Iisalmi and Pudasjärvi terrains, display older average Sm-Nd model ages than the samples from Iisalmi, Ilomantsi and Kuhmo areas. Four analyzed volcanic rocks from the Central Puolanka Group in the Kivesvaara area, east from the Manamansalo granitoid-gneiss complex (e.g. A1292 in Fig. 16), display Sm-Nd characteristics typical for Archaean rocks in Finland, suggesting Archaean ages for these relatively well-preserved intermediate to felsic su-pracrustal rocks.

Iisalmi & Manamansalo

A1515

A76?

A645

A937

A1326

A1145

A1331

A1837

A1291

A1142b

L05028807

94003664A1401

PSH-90-53

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16

147Sm/

144Nd

T-D

M(M

a)

Iisalmi complex

Manamansalo

CPG

Fig. 15. Sm-Nd model ages for the Archaean rocks in the Iisalmi (diamonds) and Manamansalo (triangles) areas, and four volcanic rocks from the Central Puolanka Group (CPG, green squares).

194


Iisalmi

Manamansalo

A76

A187

A279

A979A844

A645A937

A73b

A1959

A1958

A1513

A1332

A1145

A1391

A1925

A1897

A1837

A1291

A1515

A1251

A1235

PK-121

PK-120A

ATK-14B

93002622

93002664

94003664

94003658

L05028811

L05028807

L05028800

A1222#2

A300

A1331A1326

A1401

A1292

A1332b

A1142b

PK-113A

L05029450

PSH-90-53

Siilinjärvi

20Km

Iisalmi-Manamansalo (n=30)

0

5

10

15

20

<2.6 2.7-

2.8

2.9-

3.0

3.1-

3.2

3.3-

3.4

>

3.5T-DM (Ga)

Fig. 16. Geological map of the Iisalmi complex and Manamansalo areas showing Sm-Nd sample sites. The size of the sym-bol denotes the model ages divided into six categories: < 2.7 Ga (small), 2.7-2.85 Ga, 2.85-3.0 Ga, 3.0-3.15 Ga, 3.15-3.3 Ga, >3.3 Ga (large, only sample A76, likely not a primary signature). Model ages are not presented for mafic samples which have 147Sm/144Nd> 0.16. The map is based on the 1: 1 000 000 geological map of Korsman et al. (1997), where the main rock types consist of TTG’s, intrusive granitoids (stippled), and paragneisses (grey).

195


DISCUSSION

The Sm-Nd isotopic data reviewed here provide a general view of the formation of the 2.6-3.5 Ga Archaean crust in Finland representing a large part of the Fennoscandian Shield. However, the picture provided is somewhat blurred as in many places secondary effects on the Sm-Nd system have been strong, resulting in compositions that are virtually useless for evaluating primary signa-tures. The main reason for post-formation open system behaviour has in many cases traced back to CO2-rich metamorphic-hydrothermal fluids, which are able to dissolve and transport REE (Tourpin et al. 1991, Gruau et al. 1992). Altera-tion effects are most common in fine-grained volcanogenic rocks, especially if the sample lo-cations are close to fault/shear zones. Many of the altered samples tend to have relatively low abundances of REE and exhibit depletion in LREE (Appendix 1). On the other hand, several relatively little altered rock associations, e.g. the Koitere granitoids in the Ilomantsi area provide consistent results, which suggests that the Sm-Nd systems have remained closed since the rock forming events.

Despite of the problems introduced by meta-morphic-hydrothermal modification, the Sm-Nd results reviewed here clearly show that a mantle reservoir with time-integrated depletion in LREE and other incompatible elements was an impor-tant source of magmas already during the Ar-chaean time. This observation is supported by the positive initial epsilon values obtained from the Archaean mafic-ultramafic rocks on the Russian side (e.g., Lobach-Zhuchenko et al. 1999, Puch-tel et al. 1998, 1999, Svetov et al. 2001, 2004). It is possible that komatiites in Kuhmo had more primitive mantle plume sources with εNd(2800) values of +0.5 (Fig. 18) than e.g. Kostomuksha komatiites, but the secondary mobility of REE leaves room for speculation. Existence of mantle sources close to chondritic Nd-isotopic composi-tion are supported by the 2609 ± 3 Ma Siilinjärvi carbonatite, whereas Sm-Nd results on the 2741 ± 2 Ma old Likamännikkö carbonatite imply that some mantle source materials had positive εNd-values. Given this strong evidence for depleted mantle sources, we consider that the model of De-Paolo (1981) is a useful reference when evaluating the formation of the Archaean crust.

The Sm-Nd data on samples dated by U-Pb al-low evaluation of the relative importance of crus-tal growth versus crustal recycling. The results provide a basis for comparison between various Archaean provinces in Finland and Fennoscan-

dia (e.g. Lobach-Zhuchenko et al. 2000), and al-low also comparison with other Archaean cratons such as the Superior Province in Canada (Henry et al. 2000). There are more than 200 Archaean samples from Finland for which good-quality U-Pb zircon ages are available, and more than 90 of these have also been analyzed for Sm-Nd iso-topes.

In order to further analyse the petrogenetic significance of the data reviewed above, they are shown in Nd-epsilon versus age diagrams present-ed in Figs. 17A-F. In the diagrams evolution lines are shown for all granitoid samples, and when a U-Pb age is available also an initial Nd-epsilon value is shown by a point on that line. The age considered in the diagrams is restricted between 2.6 to 3.2 Ga since only Siurua gneisses have yielded older U-Pb ages, i.e. ca. 3.5 Ga (Fig. 17A).

Most of the dated Archaean rocks in Finland have ages of 2.68-2.76 Ga (57%) or 2.79-2.84 Ga (25%), and only few samples are older with some clustering seen in ages at ca. 2.86 Ga, 2.95 Ga and 3.1-3.2 Ga (Huhma et al. 2011). Most of the re-sults are from granitoids, and older rocks are typi-cally TTG-gneisses, whereas the youngest group consists of granodiorites and tonalites denoted as sanukitoids (2.74-2.72 Ga), and leucogranitoids and leucosomes in migmatite gneisses (e.g. Käpy- aho et al. 2006). It has become evident that in many areas the 2.7-2.8 Ga rocks give mostly posi-tive initial epsilon values and represent relatively juvenile Neoarchaean crust. The felsic rocks with-in the Kuhmo greenstone belt represent a particu-larly clear example of new crustal growth from depleted mantle at ca. 2.8 Ga (Fig. 17D). This is consistent with Patchett et al. (1981), who report-ed an εHf(2800) of +6 for zircon in the rhyolite A511 (Katerma). Many younger, 2.7-2.75 Ga granitoids in Kuhmo may originate from this newly formed crust. Recycling of significantly older crustal ma-terials seems to be more pronounced in the gener-ation of the 2.7-2.8 Ga rocks in the western Koil-lismaa and Suomussalmi areas, where most initial values are negative (Figs. 17B and C).

The difference between Kuhmo-Tipasjärvi and Suomussalmi belts is emphasized in Fig. 18. The crustal residence ages for the Suomussalmi sam-ples are significantly older exceeding 3 Ga. No-tably this concerns not only the 2.95 Ga rocks, unique to the Suomussalmi belt, but also younger 2.82 Ga rocks.

The Sm-Nd model ages TDM for all samples with “typical” upper crustal REE pattern (147Sm/144Nd< 0.16) have been compiled in a probability

196


Pudasjärvi (54 samples)

DM A1782

A1783

L05028797

A1742

A1602 Siurua

Siurua gneisses

A1740A1533

A1603

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Koillismaa

DM

CHUR

95001753 Kuusamo

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Pudasjärvi (54 samples)

DM A1782

A1783

L05028797

A1742

A1602 Siurua

Siurua gneisses

A1740A1533

A1603

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Koillismaa

DM

CHUR

95001753 Kuusamo

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Fig. 17A. Epsilon-Nd vs. age diagram showing evolution lines (red – granitoids, green dotted – mafics, blue – mica gneisses) for the Archaean rocks from the Pudasjärvi area. Diamonds denote initial values for granitoids (solid symbols) and Oijärvi belt gabbro (A1782) and felsic volcanic rock (A1783, solid symbols) for which the ages are based on U-Pb zircon dating. DM (in Fig. 17A-F) is the depleted mantle evolution according to DePaolo (1981). The TDM model age is the intersection of sample evolution with the DM curve. Samples which have TDM>3.05 Ga are all from the Siurua-Kolkkoaho zone, except A1742 and L05028797.

Fig. 17B. Epsilon-Nd vs. age diagram showing evolution lines for 24 Archaean granitoids from the Koillismaa area (six blue lines represent Kuusamo “sanukitoids”near the Russian border, Heilimo et al. 2013). Solid squares denote initial values for granitoids for which the age is based on U-Pb zircon dating.

197


Suomussalmi

DM

CHUR

A1905

A1856

A79

A1428 A1593

A1429

A1821

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Kuhmo

DM

A1183

A404b#2

A1706

A1928

94003191

A1089

A1086

A1705

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Suomussalmi

DM

CHUR

A1905

A1856

A79

A1428 A1593

A1429

A1821

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Kuhmo

DM

A1183

A404b#2

A1706

A1928

94003191

A1089

A1086

A1705

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Fig. 17D. Epsilon-Nd vs. age diagram showing evolution lines for 47 Archaean granitoid samples from the Kuhmo area. Solid circles denote initial values for granitoids for which the age is based on U-Pb zircon dating. Open circles show initial epsilon values (no evolution lines) for 14 dated volcanic rocks from the Kuhmo-Tipasjärvi greenstone belt.

Fig. 17C. Epsilon-Nd vs. age diagram showing evolution lines for 35 Archaean granitoids from the Suomussalmi area: seven blue lines – Kaapinsalmi tonalites (Heilimo et al. 2013), four green lines – Likamännikkö rocks (Mikkola et al. 2011b). Solid squares denote initial values for granitoids for which the age is based on U-Pb zircon dating. Open squares show initial epsilon values (no evolution lines) for the dated volcanic rocks from the Suomussalmi greenstone belt. Light blue diamonds are 2.74 Ga old carbonatite from Likamännikkö (Mikkola et al. 2011b).

198


Ilomantsi

DM

A339A919300246694003163

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

silo

n

A1625

A1038

A1627

A301

Iisalmi & Manamasalo

A1515A1837

A937

A76

DM

L05029450

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

Fig. 17F. Epsilon-Nd vs. age diagram showing evolution lines for the Archaean rocks from the Iisalmi complex (28 samples, red – granitoids, green dotted – four mafic rocks, blue – two metasediments, pink diamond at 2610 ± 4 Ma – Siilinjärvi car-bonatite) and Manamansalo area (9 samples, dark blue). Solid symbols denote initial values for granitoids for which the age is based on U-Pb zircon dating.

Fig. 17E. Epsilon-Nd vs. age diagram showing evolution lines for the Archaean granitoids from the Ilomantsi area (red, 27 samples). Evolution lines are also shown for two other samples with elevated Sm/Nd (A1038, A1625), which very likely do not represent primary signatures. Solid triangles denote initial values for granitoids for which the age is based on U-Pb zircon dating. Open triangles show initial epsilon values for the dated volcanic rocks from the Ilomantsi-Kovero greenstone belt.

Ilomantsi

DM

A339A919300246694003163

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

silo

n

A1625

A1038

A1627

A301

Iisalmi & Manamasalo

A1515A1837

A937

A76

DM

L05029450

-10

-8

-6

-4

-2

0

2

4

2600 2700 2800 2900 3000 3100 3200

Age (Ma)

Nd

-ep

sil

on

199


density diagram (Fig. 19). These results show that 80 % of the Archaean rocks in Finland have model ages of ca. 2.75-3.15 Ga, suggesting together with the U-Pb zircon ages that much of the Archaean consists of relatively juvenile crust. It should be emphasized that model ages >3.1 Ga, and par-ticularly in excess of 3.3 Ga, are few, and some of these data may derive from samples which have not remained closed since their primary crystal-lization.

The samples with oldest model ages are labeled on the TDM vs. 147Sm/144Nd diagram (Fig. 20). Samples with 147Sm/144Nd higher than 0.16, and thus with possibly questionable model ages, are not shown. For comparison the average crustal 147Sm/144Nd ratios reported by Rudnick and Gao (2004) are 0.1179 (bulk crust) and 0.1053 (upper

crust). The sampling is not random and probably emphasizes the older end of the analyzed spec-trum. Anyway, it is clear that rocks with model ages >3.1 Ga, and especially > 3.3 Ga, must be rare in Finland. Model ages older than 3.3 Ga have been obtained for some rocks from Tojot-tamanselkä in Central Lapland (Jahn et al. 1984, Hanski et al. 2001), Iisalmi (Hölttä et al. 2000, Lauri et al. 2011) and Suomussalmi (Fig. 5). The rocks which have yielded the oldest reliable Sm-Nd model ages up to ca. 3.7 Ga are the 3.5 Ga Siurua gneisses in Pudasjärvi, which also are the oldest rocks in Finland and Fennoscandia (Mu-tanen & Huhma 2003, Lauri et al. 2011). Indica-tions of similar old ages were also obtained from the few lower crustal xenoliths (Peltonen et al. 2006).

Kuhmo-Tipasjärvi & Suomussalmi greenstone belt

Depleted Mantle

CHUR

A1821 gabbro

A1429

A1428

A1000

A976 gabbro

A1213

A1593

-8

-6

-4

-2

0

2

4

2700 2800 2900 3000

Age (Ma)

Nd

-e

ps

ilo

n

"old crust, >>3 Ga"

Fig. 18. Epsilon-Nd vs. age diagram showing evolution lines for mostly felsic samples from the Tipasjärvi-Kuhmo-Suomussal-mi greenstone complex. Initial values are shown for samples, for which the age is based on U-Pb zircon dating. Suomussalmi: blue squares and dotted evolution lines. Kuhmo-Tipasjärvi: red circles and solid evolution lines. Komatiites and komatiitic basalts from the Pahakangas-Siivikkovaara area in Kuhmo: red x at 2810 Ma, basalts from other sites in Kuhmo belt: red +. DM is the depleted mantle evolution according to DePaolo (1981).

200


Archaean rocks in Finland

A260

A1192

A1179C

A930A889

TM-04-3.2

A1813

TM-04-3.1A1602b

A1602KML-00-77.1

TM-04-9.3.2

TM-04-9.2

A79

A76

2500

2700

2900

3100

3300

3500

3700

0.06 0.08 0.10 0.12 0.14 0.16147Sm/144Nd

T-DM

(Ma)

SuomussalmiTojottamanselkäSiurua, PudasjärviIisalmi

Fig. 20. Sm-Nd model ages TDM for Archaean whole rock samples from Finland. Red triangles denote the average 147Sm/144Nd ratios for bulk (0.1179) and upper (0.1053) crust by Rudnick and Gao (2004).

Archaean rocks in Finland, T-DM model ages (n=343)

2500 2700 2900 3100 3300 3500 3700

T-DM (Ma)

Rela

tive

pro

bab

ilit

y

Fig. 19. Probability density plot of Sm-Nd model ages TDM on 343 Archaean rocks from Finland. TDM has been calculated according to DePaolo (1981) and only for rocks which have 147Sm/144Nd <0.16.

201


CONCLUSIONS

Abundant combined Sm-Nd and U-Pb isotopic results available on the Archaean rocks in Fin-land provide a powerful means to evaluate the importance of crustal growth versus crustal re-cycling in petrogenesis of the various domains of this large part of the Fennoscandian Shield and Karelia Province. However, further studies are needed to better combine the isotope results with the comprehensive geochemical information.

Despite problems related to secondary REE mobility, the Sm-Nd results show that mantle res-ervoirs with time-integrated depletion in LREE were important sources of magmas already during the Archaean time. On the other hand, the range in initial Nd isotopic compositions of various rocks, particularly in high-REE alkaline rocks, suggests heterogeneity in the Archaean mantle.

Metamorphic effects seriously limit the use of the Sm-Nd method in studying the geochro-nology and genesis of komatiites. However, it is tempting to consider the εNd(2.8 Ga) values of +0.5, obtained for many komatiitic samples from the Kuhmo belt, as primary signatures. This would be consistent with the conclusions by Maier et al. (in prep), who consider that the geochemistry of the Kuhmo komatiites indicate that the lavas were derived from a source more similar to a primitive

upper mantle plume source in an oceanic plateau setting rather than an NMORB-type depleted source.

Most Archaean felsic rocks in Finland, repre-senting >80% of the Archaean crust, have model ages of ca. 2.75-3.15 Ga, which suggests, together with the U-Pb zircon ages, that much of the Ar-chaean consists of relatively juvenile crust. This concerns particularly the Kuhmo area. Felsic rocks in the Kuhmo and Tipasjärvi greenstone belts represent new crustal materials ultimately derived from depleted mantle-type sources with εNd(2.8 Ga) ~ +2. The bulk of the surrounding grani-toids postdates the volcanism, and the isotope re-sults as a whole suggest that the contribution of older crustal material is negligible and does not support the concept of formation of the Kuhmo belt in a rift-basin on an ancient sialic basement. In contrast, in the Suomussalmi belt, isotope re-sults indicate a major involvement of significantly older crustal material (>3 Ga).

Model ages in excess of 3.1 Ga are few, over 3.3 very few, the >3.3 Ga ages being almost restricted to the ca. 3.5 Ga Siurua gneisses in the Pudas-järvi area. No signs of that similar 3.5 Ga crust exposed elsewhere in Finland or Fennoscandian Shield are evident in the Sm-Nd data available.

ACKNOWLEDGEMENTS

We are grateful to Hugh O’Brien for discussions and comments on the manuscript.

REFERENCES

DePaolo, D. J. 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Protero-zoic. Nature 291, 684−687.

Dupre, B., Chauvel, C. & Arndt, T. 1984. Pb and Nd isotopic study of two Archean komatiitic flows from Alexo, Ontar-io. Geochimica et Cosmochimica Acta, 48, 1965−1972.

Gruau, G., Tourpin, S., Fourcade, S. & Blais, S. 1992. Loss of isotopic (Nd, O) and chemical (REE) memory during metamorphism of komatiites: new evidence from eastern Finland. Contributions to Mineralogy and Petrology 112, 66–82.

Halla, J. 2005. Late Archean high-Mg granitoids (sanuki-toids) in the southern Karelian domain, eastern Finland: Pb and Nd isotopic constraints on crust–mantle interac-tions. Lithos 79, 161−178.

Hanski, E., Walker, R. J., Huhma, H. & Suominen I. 2001. The Os and Nd isotopic systematics of c. 2.44 Ga Akan-vaara and Koitelainen mafic layered intrusions in north-ern Finland Precambrian Research, 109, 73–102.

Heilimo, E., Halla, J. Andersen, T. & Huhma, H. 2013. Neoarchean crustal recycling and mantle metasoma-tism: Hf-Nd-Pb-O isotope evidence from sanukitoids of the Fennoscandian shield. Precambrian Research (in press). Available at: http://dx.doi.org/10.1016/j.precam-res. 2012.01.015.

Henry, P., Stevenson, R. K., Larbi, Y. & Gariépy, C. 2000. Nd isotopic evidence for Early to Late Archean (3.4-2.7 Ga) crustal growth in the Western Superior Province (Ontar-io, Canada). Tectonophysics 322, 135−151.

Hölttä, P., Huhma, H., Mänttäri, I. & Paavola J. 2000. P-T-t developement of Archaean granulites in Varpaisjärvi, Central Finland II. Dating of high-grade metamorphism with the U-Pb and Sm-Nd methods. Lithos 50, 121−136.

Huhma, H. 1986. Sm-Nd, U-Pb and Pb-Pb isotopic evidence for the origin of the Early Proterozoic Svecokare-lian crust in Finland. Geological Survey of Finland, Bulletin 337. 48 p.

Huhma, H. 1987. Provenance of Early Proterozoic and Ar-

202


chaean metasediments in Finland: a Sm-Nd isotopic study. Precambrian Res. 35, 127−143.

Huhma, H., O’Brien, H., Lahaye, Y. & Mänttäri, I. 2011. Iso-tope geology and Fennoscandian lithosphere evolution. In: Nenonen, K. & Nurmi, P. A. (eds.) Geoscience for Society 125th Anniversary Volume. Geological Survey of Finland, Special Paper 49, 35−48.

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho,T., Hanski., E., Hokkanen. T., Hölttä, P., Juop-peri, H., Konnunaho, J., Lahaye, Y., Luukkonen., E., Pie-tikäinen, K., Pulkkinen, A., Sorjonen-Ward, P., Vaasjoki, M. & Winehouse, M. 2012. The age of Archean green-stone belts in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Jahn, B-M., Vidal, P. & Kröner, A. 1984. Multi-chronometric ages and origin of Archaean tonalitic gneisses in Finnish Lapland: a case for long crustal residence time. Contribu-tions to Mineralogy and Petrology 86, 398−408.

Käpyaho, A., Mänttäri, I. & Huhma, H. 2006. Growth of Archaean crust in the Kuhmo district, eastern Finland: U-Pb and Sm-Nd isotope constraints on plutonic rocks. Precambrian Research 146, 95−119.

Kontinen, A., Paavola, J. & Lukkarinen, H. 1992. K-Ar ages of hornblende and biotite from late Archaean rocks of eastern Finland–interpretation and discussion of tecton-ic implications. Geological Survey of Finland, Bulletin 365, 1−31.

Kontinen, A., Käpyaho, A., Huhma, H., Karhu, J., Matukov, D., Larionov, A. & Sergeev, S. 2007. Nurmes paragneisses in eastern Finland, Karelian craton: Provenance, tectonic setting and implications for Neoarchaean craton correla-tion. Precambrian Research 152, 119–148.

Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M., Ekdahl, E., Honkamo, M., Idman, H. & Pekkala, Y. (eds.) 1997. Suomen kallioperäkartta – Berggundskarta över Finland – Bedrock map of Finland 1:1000 000. Espoo: Geological Survey of Finland.

Kouvo, O. & Tilton, G. 1966. Mineral ages from the Finnish Precambrian. Journal of Geology 74, 421−442.

Lauri, L. S., Rämo, O. T., Huhma, H., Mänttäri, I. & Rä-sänen, J. 2006. Petrogenesis of silicic magmatism related to the ~ 2.44 Ga rifting of Archean crust in Koillismaa, eastern Finland. Lithos 86, 137−166.

Lauri, L. S., Andersen, T., Hölttä, P., Huhma, H. & Graham, S. 2011. Evolution of the Archaean Karelian province in the Fennoscandian Shield in the light of U–Pb zircon ages and Sm–Nd and Lu–Hf isotope systematics. Lon-don: Journal of the Geological Society, Vol. 168, 201–218.

Lobach-Zhuchenko, S. B., Arestova, N. A. & Chekulaev, V. P. et al. 1999. Evolution of the South Vygozero greenstone belt, Karelia. Moscow: Petrology, 7(2), 160−176.

Lobach-Zhuchenko, S. B., Chekulaev, V. P., Arestova, N. A., Levskii, L. K. & Kovalenko, A. V. 2000. Archaean ter-ranes in Karelia: geological and isotopic–geochemical evidence. Geotectonics, v. 34, 452−466.

Ludwig, K. R. 2003. User’s manual for Isoplot/Ex, Version 3.00. A geochronological toolkit for Microsoft Excel. Berkeley Geochronology Center Special Publication No.4.

Luukkonen, E. J. 2001. Lentiiran kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Lentiira Map-Sheet area. Geological Map of Finland 1:100 000, Ex-planation to the Maps of Pre-Quaternary Rocks, Sheeet 4414+4432. Geological Survey of Finland. 51 p. (in Finn-

ish with English summary).Maier, W., Peltonen, P. & Halkoaho, T. (in prep.). Geochem-

istry of komatiites from the Tipasjärvi, Kuhmo, Suomus-salmi, Ilomantsi and Tulppio greenstone belts, Finland: implications for Ni sulphide prospectivity. In prep.

Martin, H., Chauvel, C., Jahn, B.-M. & Vidal, P. 1983. Rb–Sr and Sm–Nd ages and isotopic geochemistry of Archaean granodioritic gneisses from eastern Finland. Precambri-an Res. 20, 79–91.

Martin, H. & Querré, G. 1984. A 2.5 Ga reworked sialic crust: Rb-Sr ages and isotopic geochemistry of late Archaean volcanic and plutonic rocks from E. Finland. Contribu-tions to Mineralogy and Petrology 85, 292−299.

McCulloch, M. T. & Wasserburg, G. J. 1978. Sm-Nd and Rb-Sr chronology of continental crust formation. Science 200, 1003−1011.

Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011a. Archean crustal evolution of the Suomussalmi district as part of the Kianta Complex, Karelia: Con-straints from geochemistry and isotopes of granitoids. Lithos 125, 287−307.

Mikkola, P., Salminen, P., Torppa, A. & Huhma H. 2011b. The 2.74 Ga Likamännikkö complex in Suomussalmi, East Finland: Lost between sanukitoids and truly alka-line rocks? Lithos 125, 716−728.

Mutanen, T. & Huhma, H. 2003. The 3.5 Ga Siurua trond-hjemite gneiss in the Archaean Pudasjärvi Granulite Belt, nortern Finland. Bulletin of the Geological Society of Finland 75, 51−68.

O‘Brien, H., Huhma, H. & Sorjonen-Ward, P. 1993. Petro-genesis of the late Archean Hattu schist belt, Ilomantsi, eastern Finland: geochemistry and Sr, Nd isotopic com-position. In: Nurmi, P. & Sorjonen-Ward, P. (eds.) Geo-logical development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 147−184.

Patchett, J., Kouvo, O., Hedge, C. & Tatsumoto, M. 1981. Evolution of continental crust and mantle heterogeneity: evidence from Hf isotopes. Contributions to Mineralogy and Petrology 78, 279−297.

Peltonen, P., Mänttäri, I., Huhma, H. & Whitehouse, M. J. 2006. Multi-stage origin of the lower crust of the Kare-lian craton from 3.5 to 1.7 Ga based on isotopic ages of kimberlite-derived mafic granulite xenoliths. Precambri-an Research 147, 107−123.

Puchtel, I. S., Hofmann, A. W., Mezger, K., Jochum, K. P., Shchipansky, A. A. & Samsonov, A. V. 1998. Oceanic pla-teau model for continental crustal growth in the Archae-an: a case study from the Kostomuksha greenstone belt, NW Baltic Shield. Earth and Planetary Science Letters, 155, 57−74.

Puchtel, I. S., Hofmann, A. W., Amelin, Yu, V., Garbe-Schon-berg, C. D., Samsonov, A. V. & Shchipansky, A. A. 1999. Combined mantle plume-island arc model for the forma-tion of the 2.9 Ga Sumozero-Kenozero greenstone belt, SE Baltic Shield: isotope and trace element constraints. Geochimica et Cosmochimica Acta, 63(21), 3579−3595.

Rasilainen, K., Lahtinen, R. & Bornhorst, T. J. 2007. The Rock Geochemical Database of Finland Manual (on-line). Geological Survey of Finland, Report of Investiga-tion 164. 38 p. Available at: http://arkisto.gtk.fi/tr/tr164/tr164.pdf

Richard, P., Shimizu, N. & Allégre, C. J. 1976. 134Nd/146Nd, a natural tracer: an application to oceanic basalts. Earth Planet. Sci. Lett. 31, 269−278.

http://arkisto.gtk.fi/tr/tr164/tr164.pdf

http://arkisto.gtk.fi/tr/tr164/tr164.pdf

203


Rudnick, R. L. & Gao, S. 2004. The Composition of the Con-tinental Crust. In: Rudnick, R. L. (ed.) The Crust, vol 3., 1–64 In: Holland, H. D. & Turekian, K. K. (eds.) Treatise on Geochemistry. Oxford: Elsevier-Pergamon.

Slabunov, A. I., Lobach-Zhuchenko, S. B., Bibikova, E. V., Sorjonen-Ward, P., Balagansky, V. V., Volodichev, O. I., Shchipansky, A. A., Svetov, S. A., Chekulaev, V. P., Aresto-va, N. A. & Stepanov, V. S. 2006. The Archean nucleus of the Baltic/Fennoscandian Shield. In: Gee, D. G. & Ste-phenson, R. A. (eds.) European Lithosphere Dynamics. Geological Society of London, Memoirs, v. 32, 627–644.

Sorjonen-Ward, P. & Claoué-Long, J. 1993. Preliminary note on ion probe results for zircons from the Silvevaara granodiorite, Ilomantsi, Eastern Finland. In: Autio, S. (ed.) Geological Survey of Finland, Current Research 1991−1992. Geological Survey of Finland, Special Paper 18, 25–29.

Sorjonen-Ward, P. & Luukkonen, E. J. 2005. Archean rocks. In: Lehtinen, M., Nurmi, P. A. & Rämö, O. T. (eds.) Pre-cambrian Geology of Finland – Key to the Evolution of the Fennoscandian Shield. Amsterdam: Elsevier B.V., 19−99.

Svetov, S. A., Svetova, A. I. & Huhma, H. 2001. Geochemis-try of the komatiite-tholeiite rock association in the Ved-lozero-Segozero Archean greenstone belt, central Kare-lia. Geochemistry International 39 (Suppl. 1), S24−S38.

Svetov, S. A., Huhma, H., Svetova, A. I. & Nazarova, T. N. 2004. The oldest adakites of the Fennoscandian Shield. Doklady Earth Sciences 397A (6), 878−882.

Tourpin, S., Gruau, G., Blais, S. & Fourcade, S. 1991. Reset-ting of REE, and Nd and Sr isotopes during carbonitiza-tion of a komatiite flow from Finland. Chemical Geol-ogy, 90, 15−29.

Vaasjoki, M., Taipale, K. & Tuokko, I. 1999. Radiometric ages and other isotopic data bearing on the evolution Of Archaean crust and ores in the Kuhmo-Suomussalmi area, eastern Finland. Bulletin of the Geological Society of Finland 71, 155−176.

Vidal, P., Blais, S., Jahn, B.-M., Capdevila, R. & Tilton, G. 1980. U-Pb and Rb-Sr systematics of the Suomussalmi Archaean greenstone belt (eastern Finland). Geochimica et Cosmochimica Acta 44, 2033−2044.

204

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.

Appendix 1. Sm-Nd isotope data on the Archean rocks in Finland.Sample Location Rock type Sm Nd 147Sm/144Nd 143 Nd/144Nd 2sm Age(T) eNd(T) TDM Reference comment (* map YKJ-North YKJ-East

(ppm) (ppm) (± 0.4%) (Ma) (Ma) for Sm-Nd

Pudasjärvi areaSiurua-Kolkkoaho zone (N->S)KML-00-77.1 Kolkkoaho tonalite gneiss 2.30 13.41 0.1037 0.510606 10 2700 -7.5 3404 L00013111 352404 7286564 3477464TM-04-9.1 Kolkkoaho tonalite gneiss 1.73 8.12 0.1285 0.510928 10 2700 -9.8 3864 open system? 352304 7286550 3477470TM-04-9.2 Kolkkoaho tonalite gneiss 2.14 11.22 0.1151 0.510705 10 2700 -9.5 3665 352304 7286550 3477470TM-04-9.3.1 Kolkkoaho tonalite gneiss 2.18 14.24 0.0925 0.510567 10 2700 -4.3 3127 352304 7286540 3477460TM-04-9.3.2 Kolkkoaho tonalite gneiss 2.13 12.50 0.1031 0.510620 20 2700 -7.0 3364 352304 7286540 3477460JON-00-4.1 Sumusuo granite 3.68 25.86 0.0860 0.510391 10 2700 -5.5 3179 L00013101 352301 7285759 3467663JON-00-53.1 Karhunpesäkumpu tonalite gneiss 2.08 15.10 0.0832 0.510390 10 2700 -4.5 3108 L00013112 352504 7285465 3479638KML-00-11.1 Iso Yömaa granite 2.58 16.00 0.0976 0.510585 10 2700 -5.7 3245 L00013103 352304 7284229 3473166JON-00-82.1 Pauvankangas tonalite gneiss 2.29 14.58 0.0949 0.510651 10 2700 -3.5 3080 L00013116 352307 7281982 3483072A1603 Isokumpu felsic granulite 0.81 6.10 0.0799 0.510408 11 2960 1.0 3009 M03 351406 7279400 3476550JON-00-55.3 Isokumpu enderbite 4.77 29.83 0.0967 0.510721 10 2700 -2.8 3037 L00013123 351406 7279253 3476538TM-04-3.2 Siurua tonalite gneiss 12.26 87.43 0.0847 0.509966 10 3500 -1.7 3667 L11 351408 7267172 3480526A1812 Siuruankangas mafic granulite 2.82 9.11 0.1872 0.512436 11 2700 -0.7 L11 eHf(T)=+2.6±2.0 351402 7267127 3480533A1813 Siuruankangas granite leucosome 3.64 19.91 0.1106 0.510688 10 3500 0.8 3523 L11 eHf(T)=+3.5±5.0 351402 7267127 3480533TM-04-3.1 Siurua tonalite gneiss 11.29 80.12 0.0852 0.509990 10 3500 -1.4 3650 L11 351408 7267102 3480537A1602 Siurua trondhjemite gneiss 10.44 78.18 0.0807 0.510025 10 3500 1.4 3481 M03 eHf(T)=-4.8±3.1 351408 7267090 3480520A1602b Siurua granitic leucosome 1.26 5.44 0.1396 0.511284 20 3500 -0.7 3696 L11 351408 7267090 3480520TM-04-3.3 Siurua mafic granulite 2.09 6.44 0.1960 0.512707 10 2700 1.5 L11 351408 7267010 3480515TM-00-13 Soidinmaa alaskite (granite) 1.04 6.41 0.0984 0.510956 10 2700 1.3 2763 M03 351408 7262035 3481408A1686A Soidinmaa trondhjemite pegmatite 0.43 4.15 0.0627 0.510033 20 2700 -4.4 3042 3514/R301/94.55-95.25 351408 7262029 3481475A1686B Soidinmaa granite/ inclusion? 98 820 0.0722 0.510150 20 2700 -5.4 3123 3514/R301/94.55-95.25 351408 7262029 3481475A1687 Soidinmaa dyke, Proterozoic? 6.14 25.28 0.1470 0.511911 20 2700 3.0 2595 3514/R307/15.8-18.0 351408 7261330 3481421TM-04-2.3 Livojoen silta tonalite gneiss 2.86 22.54 0.0767 0.510218 10 2700 -5.6 3153 351410 7256816 3491411TM-04-2.1 Livojoen silta tonalite gneiss 2.26 18.96 0.0719 0.510163 10 2700 -5.0 3103 351410 7256815 3491401TM-04-2.2 Livojoen silta amphibolite 2.99 9.19 0.1969 0.512730 10 2700 1.7 351410 7256813 3491403Oijärvi greenstone beltA1782 Käärmevaara W (Ranua) gabbro 1.47 4.20 0.2112 0.513048 11 2802 2.7 36-PTP-04 352210 7314017 3451513A1783 Puljunlehto Ranua dacite 0.55 2.27 0.1463 0.511725 10 2820 0.4 3020 23-PTP-04 352112 7305915 3455670A1553 Pitkäkumpu tonalite 2.64 15.94 0.1001 0.511012 10 2728 2.1 2728 352111 7298570 3457880A1533 Surmakumpu qu-fspar-porphyry dyke 7.32 53.63 0.0825 0.510460 14 2670 -3.3 3006 352111 7296640 3456110Other Pudasjärvi (N->S)93001872 granodiorite 2.92 18.60 0.0950 0.510892 20 2700 1.2 2768 352209 7336660 3444840R4 Runkaus granite 4.24 34.08 0.0752 0.510404 28 2700 -1.4 2910 H86 2544 7329846 3428973A1611 Korkia-aho diorite (Ranua) 6.67 35.79 0.1126 0.511186 10 2703 0.9 2808 M03 eHf(T)=-2.5±2.0 352405 7322230 3476750A1717 Simontaival albite-egirine-rock 0.43 2.08 0.1257 0.511228 20 2700 -2.9 3170 3524/R172/72.0-74.0 352405 7321465 3479200A1814 Pitkäpalo Ranua mica gneiss 4.69 26.18 0.1082 0.511101 10 2700 0.7 2815 352201 7311210 3439510A1490 Tuore Ristisuonpalo granodiorite 1.95 14.65 0.0805 0.510562 10 2815 1.6 2841 352112 7308300 3454020A1534 Keväpalo tonalitic gneiss 1.48 8.25 0.1088 0.511248 10 2820 4.8 2609 L11 open system? 352112 7305902 3457646A1534#2 Keväpalo tonalitic gneiss 1.47 8.14 0.1089 0.511266 10 2820 5.1 2586 L11 eHf(T)=+1.4±1.9 352112 7305902 3457646A1954 Tervonkangas gneiss (trondhjemite) 0.96 6.68 0.0865 0.510730 11 2700 1.0 2777 352303 7302751 3466397A1739 Veskanmaa granodiorite 1.74 11.21 0.0939 0.510762 20 2780 0.1 2909 352108 7291080 3440100L05029441 47-PSH-04 granodiorite 4.47 33.57 0.0804 0.510403 20 2700 -3.3 3028 7288134 3429931L05028739 35-PSH-04 diorite 8.90 41.43 0.1299 0.511441 20 2700 -0.2 2936 7283902 3417477

205

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland

Appendix 1. cont.Sample Location Rock type Sm Nd 147Sm/144Nd 143 Nd/144Nd 2sm Age(T) eNd(T) TDM Reference comment (* map YKJ-North YKJ-East


Other Pudasjärvi (N->S)A1966 Pudasjärvi granodiorite 2.46 16.62 0.0893 0.510813 10 2700 1.6 2738 93001908 351403 7278860 3462400A1842 Jäkälämaa, Pudasjärvi mica gneiss 5.94 33.67 0.1066 0.511120 10 2700 1.6 2744 351409 7271905 3485074A1809 Ärrönperä Kuivaniemi amphibolite 3.67 14.78 0.1501 0.511881 10 2700 1.4 2813 L11 253408 7268810 3421258A1810 Ärrönperä Kuivaniemi granodioritic leucosome 0.43 3.25 0.0800 0.510601 12 2682 0.5 2788 L11 eHf(T)=-3.3±2.7 253408 7268810 3421258A1811 Ärrönperä Kuivaniemi granite leucosome 3.13 24.09 0.0784 0.510502 10 2700 -0.6 2868 L11 eHf(T)=+1.2±4.6 253408 7268810 3421258A1740 Palomaa 2 monzonite 3.26 22.47 0.0877 0.510583 20 2682 -2.6 2983 351402 7263103 3469274L05028727 10.1-PSH-04 amphibolite 4.06 17.00 0.1442 0.511710 20 2720 0.2 2957 7257618 3429116A1741 Pahkakoski granodiorite 2.19 13.47 0.0983 0.510913 20 2758 1.2 2816 351210 7253200 3455500L05028737 30-PSH-04 granodiorite 2.92 14.97 0.1179 0.511304 20 2700 1.3 2779 7251640 345532493001846 granitegneiss 8.82 40.67 0.1310 0.511548 10 2700 1.5 2772 351303 7248480 3463070A1742 Viitakangas granite 4.23 26.37 0.0969 0.510573 20 2700 -5.7 3240 351106 7247308 343702593001430 quartzdiorite 1.70 9.63 0.1070 0.511133 20 2700 1.8 2734 351306 7246350 3479710A1601 Rankkila mafic granulite 2.27 8.27 0.1660 0.512145 10 2700 1.0 M03 351309 7241173 3485072L05028797 162-PSH-04 tonalitegneiss 6.22 43.46 0.0864 0.510410 20 2700 -5.3 3168 7215005 3491679A1965 Pudasjärvi tonalitegneiss 5.57 36.94 0.0911 0.510866 10 2700 2.1 2710 94003693 344202 7207930 3505480L05028791 155-PSH-04 enderbite 1.94 21.42 0.0547 0.510178 20 2700 1.3 2746 7197685 3508558L05028793 159-PSH-04 tonalite 3.04 17.54 0.1048 0.510971 20 2700 -0.7 2912 7193494 3494215L05028786 147-PSH-04 tonalite 6.16 36.50 0.1020 0.510926 20 2700 -0.6 2899 7189686 350575494002795 granitegneiss 5.30 36.10 0.0887 0.510721 20 2700 0.1 2837 342311 7174620 3492960Koillismaa granitoids (N->S):A1644 Hanhimännikkö gneiss 1.65 10.24 0.0976 0.510920 10 2700 0.9 2791 L06 452409 7341660 362074395001676 granitegneiss 2.90 24.02 0.0730 0.510501 20 2700 1.3 2755 452409 7339208 3621792TTU$-2004-148 Kuusamo granodiorite (sanukitoid) 4.11 24.79 0.1001 0.510956 10 2718 0.9 2805 Hetal 452409 7333650 3624183TTU$-2004-156 Kuusamo granodiorite (sanukitoid) 4.38 24.91 0.1063 0.511078 10 2718 1.1 2795 Hetal 452408 7328398 3623888TTU$-2004-162 Kuusamo granodiorite (sanukitoid) 7.08 38.76 0.1104 0.511146 11 2718 1.0 2806 Hetal 454103 7312019 3639916TTU$-2004-160.1 Kuusamo granodiorite (sanukitoid) 5.28 29.57 0.1080 0.511079 10 2718 0.6 2834 Hetal 452312 7304904 3631405TTU$-2004-167 Kuusamo granodiorite (sanukitoid) 5.65 36.75 0.0930 0.510853 11 2718 1.4 2768 Hetal 454102 7302068 3640066TTU$-2004-154 Kuusamo granodiorite (sanukitoid) 4.02 23.56 0.1032 0.511005 11 2718 0.8 2816 Hetal 452311 7295974 3630652A1643 Meskusvaara qu-fspar-porphyry 2.72 16.11 0.1022 0.510980 10 2733 0.8 2825 452211 7326529 358788595001753 Kuusamo granodiorite 7.18 38.05 0.1141 0.510937 10 2700 -4.6 3251 452207 7319762 3579539Soilu TTG Soilu Kuusamo tonalite gneiss 4.22 30.20 0.0844 0.510523 12 2700 -2.3 2978 L06 452204 7316238 3574281A415 Soilu granite 1.88 12.94 0.0875 0.510627 10 2700 -1.4 2924 L06 452204 7315530 357311495001741 granitegneiss 3.56 24.98 0.0862 0.510499 20 2700 -3.4 3052 452109 7305143 3577816A1652 Kostonjärvi Taivalkoski felsic volcanic rock 2.36 14.43 0.0987 0.510754 10 2700 -2.8 3045 354309 7302787 3565073A1642 Raatekalliot granite 3.29 30.46 0.0652 0.510213 10 2700 -1.7 2906 L06 452302 7301403 3601082A1887 Haapovaara Taivalkoski tonalite 3.72 21.88 0.1028 0.510866 10 2700 -2.0 3005 354308 7298185 3562389A1888 Pyöreälampi Taivalkoski trondhjemite 0.63 5.07 0.0752 0.510387 20 2700 -1.8 2929 354111 7294405 3537974A1889 Elehvä Taivalkoski tonalite 2.27 15.21 0.0903 0.510670 20 2700 -1.5 2939 452105 7291062 3575504A1656 Aholamminvaara granite 6.33 64.15 0.0596 0.510095 10 2711 -1.9 2917 L06 4521 7287103 3579170A1661 Kaplaskumpu tonalite (pyroxene) 5.18 41.73 0.0750 0.510294 10 2808 -1.8 3026 L06 eHf(T)=-5.6±3.0 354304 7282484 3557732A1662 Matovaara tonalite 6.57 32.84 0.1208 0.511148 10 2800 -1.8 3134 L06 353409 7278648 356450095001765 granite 1.82 11.49 0.0958 0.510759 10 2700 -1.7 2963 451403 7278218 3605233A1657 Harjavaara granite 0.85 8.70 0.0590 0.509991 10 2700 -3.9 3010 L06 eHf(T)=-8.1±3.0 4512 7275684 3569976A1890 Kylmävaara Taivalkoski trondhjemite 0.78 5.64 0.0835 0.510432 20 2827 -1.9 3069 353405 7268659 3550610

206

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.



Suomussalmi greenstone belt:A1191 Ala-Luoma metasediment/ tuffite 2.61 12.62 0.1249 0.511188 10 2820 -2.3 3223 451303 7244464 3605840A1191#2 Ala-Luoma metasediment/ tuffite 2.70 13.14 0.1241 0.511182 12 2820 -2.1 3202 451303 7244464 3605840A1179A Ala-Luoma tuffite/ metasediment 3.23 15.64 0.1248 0.511166 15 2820 -2.7 3256 Vaasjoki et al 1999 451303 7244464 3605840A1179C Ala-Luoma tuffite/ metasediment 4.09 21.92 0.1126 0.510814 13 2820 -5.2 3400 Vaasjoki et al 1999 451303 7244464 3605840A1065A (KR-27) Ala-Luoma volcanogenic

schist, sheared2.43 12.20 0.1202 0.510712 11 2820 -9.9 3878 open system? 453103 7244873 3606241

A1192 Saarikylä felsic volcanic rock, sheared

2.01 10.81 0.1125 0.510631 11 2940 -7.4 3689 open system? 451303 7244557 3606757

A1467 Saarikylä felsic volc. (cataclastic) 1.01 3.85 0.1582 0.510726 11 2940 -23.0 7452 open system 451303 7244420 3606603A1467#2 Saarikylä felsic volc. (cataclastic) 1.00 3.84 0.1573 0.510701 12 2940 -23.1 open system 451303 7244420 3606603A1593 Saarikylä qu-porphyry 2.04 12.11 0.1018 0.510656 10 2942 -2.8 3275 KJP-96-105 451303 7244289 3606589A1593#2 Saarikylä qu-porphyry 2.09 12.31 0.1025 0.510607 20 2942 -4.0 3367 KJP-96-105 451303 7244289 3606589A260 Haaponen greywacke 1.38 7.18 0.1163 0.510806 10 2820 -6.7 3548 low REE 451303 7242347 3606372A1180A Saarikylä basalt 2.54 7.62 0.2016 0.512831 10 2820 1.9 Vaasjoki et al 1999 451303 7243107 3607416A1428 Mesa-aho qu-porphyry 5.89 52.16 0.0683 0.510109 10 2817 -2.8 3080 451303 7242081 3605002EJL-92-71 Mesa-aho felsic volcanic rock 6.91 35.92 0.1162 0.510975 10 2820 -3.3 3264 451303 7242111 3605001EJL-92-71#2 Mesa-aho felsic volcanic rock 6.95 36.09 0.1164 0.510984 10 2820 -3.2 3256 451303 7242111 3605001A1594 Mesa-aho tuffite/ metasediment 2.51 11.36 0.1338 0.511456 11 2820 -0.3 3057 EJL-92-70 451303 7242022 3605035A1594#2 Mesa-aho tuffite/ metasediment 2.50 11.27 0.1339 0.511441 10 2820 -0.6 3093 EJL-92-70 451303 7242022 3605035A1514 Kiannanniemi andesite 5.05 30.45 0.1002 0.510706 12 2820 -2.8 3154 451111 7231377 3596370ASM-94-684 Hiirelä 1, Kiannanniemi rhyolite (fragment) 3.87 21.89 0.1069 0.510941 10 2820 -0.6 3015 451110 7229424 3596143ASM-94-685 Hiirelä 2, Kiannanniemi andesite-basalt lava 5.17 29.87 0.1045 0.510857 10 2820 -1.4 3069 451110 7229437 3596202A1429 Kilpasuo Tormua andesite 4.55 25.11 0.1096 0.510939 10 2822 -1.6 3099 451309 7249545 3620447A1821 Tormua gabbro (mafic volc.) 1.92 5.63 0.2061 0.512895 10 2866 1.5 87-PTP-03 451309 7246318 3620818Suomussalmi granitoids (N->S):A1913 Välivaara tonalite 1.91 15.18 0.0762 0.510368 10 2950 1.4 2973 M11a PSH$-2006-70 451211 7267953 359337495001760 granitegneiss 3.63 26.49 0.0828 0.510526 10 2700 -1.7 2938 451408 7267858 3624201A1906 Taka-aho tonalitegneiss (paleos.) 2.38 15.09 0.0955 0.510731 10 2824 -0.5 2992 M11a PIM$-2003-128.1 451407 7255650 3619820A1907 Taka-aho leucogranodiorite (neos) 1.12 7.02 0.0968 0.510756 10 2706 -2.0 2993 M11a PIM$-2003-128.2 451407 7255650 361982095001798 granodiorite 2.06 13.53 0.0921 0.510690 10 2700 -1.7 2960 451306 7250790 3612308A1904 Marjosuo tonalite (hornblende-) 2.69 15.28 0.1067 0.510983 10 2795 0.0 2948 M11a KKK1-2005-39 451306 7246290 3613635A1856 Portinkuru tonalite 1.13 5.80 0.1173 0.510991 15 2950 -2.1 3276 M11a 451303 7243917 3602274A1857 Teerivaara granodiorite dyke 1.78 10.53 0.1019 0.510837 15 2821 -0.8 3022 M11a 451303 7243917 3602274A1915 Tausvaara leucotonalite 0.99 5.08 0.1184 0.511137 13 2744 -1.7 3071 M11a JJE$-2006-132 353309 7242170 3565648A1193 Saarikylä tonalite (cataclastic) 0.73 3.27 0.1339 0.511458 12 2800 -0.5 3063 451305 7241490 3611739A28bA Kaapinsalmi granodiorite (sanukitoid) 3.58 21.72 0.0998 0.510812 11 2717 -1.8 2994 eps-Hf= -1.5 451302 7239741 3600438EPHE-2004-347.2 Kaapinsalmi granodiorite (sanukitoid) 4.70 24.85 0.1142 0.511073 10 2722 -1.7 3035 Hetal 451303 7242785 3603530EPHE-2005-40.1 Kaapinsalmi granodiorite (sanukitoid) 3.86 24.96 0.0935 0.510711 10 2722 -1.5 2965 Hetal 451303 7242569 3602975EPHE-2004-353.2 Kaapinsalmi granodiorite (sanukitoid) 5.39 27.86 0.1170 0.511097 10 2722 -2.2 3080 Hetal 451303 7241716 3603778EPHE-2004-345.1 Kaapinsalmi granodiorite (sanukitoid) 4.59 26.21 0.1057 0.510920 11 2722 -1.7 3010 Hetal 451303 7241621 3602733EPHE-2004-332.1 Kaapinsalmi granodiorite (sanukitoid) 4.08 26.70 0.0923 0.510696 11 2722 -1.4 2954 Hetal 451302 7238380 3603673EPHE-2004-336.1 Kaapinsalmi granodiorite (sanukitoid) 4.77 28.29 0.1021 0.510836 11 2722 -2.1 3023 Hetal 451302 7236960 3603278A1831 Kiviniemi leucotonalite 1.51 10.63 0.0861 0.510539 10 2700 -2.6 3001 M11a 451302 7236862 3596605A79 Päivärinta tonalitic melanosome 2.41 11.59 0.1258 0.511026 10 2835 -5.7 3558 4512 7229489 3591184

207

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland



Suomussalmi granitoids (N->S):A79#2 Päivärinta tonalitic melanosome 2.37 11.41 0.1256 0.511006 10 2835 -6.0 3583 4512 7229489 3591184A80a Päivärinta leucosome 1.97 11.45 0.1040 0.510966 11 2700 -0.5 2900 4512 7229489 3591184A80b Päivärinta leucosome 3.59 22.08 0.0981 0.510852 15 2700 -0.7 2901 4512 7229489 3591184A1962 (95001782) Kuikkavaara granodiorite 2.33 17.18 0.0818 0.510359 10 2960 -0.7 3114 cf. A1909 451107 7227560 3583835A1909 Kuikkavaara tonalite 3.28 25.60 0.0775 0.510285 10 2960 -0.5 3097 M11a PIM$-2003-322 451107 7227559 3583838A1902 Pärsämönselkä granodioriteg-

neiss (paleos.)2.45 18.77 0.0789 0.510436 10 2719 -1.8 2955 M11a EPHE-2004-245.1 451301 7224137 3606561

A1903 Pärsämönselkä leucotonalite (leucos.) 0.96 8.61 0.0679 0.510208 10 2700 -2.7 2969 M11a EPHE-2004-245.2 451301 7224137 360656194003728 quartzdiorite 18.51 103.40 0.1082 0.511045 10 2700 -0.4 2899 344406 7214700 3556940A1840 Riihivaara, Suomussalmi mica gneiss 3.69 21.66 0.1029 0.510964 20 2700 -0.1 2869 344408 7207502 3563317A1858 Riihivaara tonalite dyke 5.51 33.98 0.0981 0.510887 15 2702 0.1 2849 M11a 344408 7207502 3563317A1841 Riihivaara granite (leucosome) 0.95 3.32 0.1723 0.511550 25 2700 -12.9 open system? 344408 7207498 3563267A1901 Seppäsensuo tonalite 3.68 26.41 0.0844 0.510493 10 2818 -1.2 3015 M11a PIM$-2003-616 344402 7204658 3549296A1910 Peuravaara granodiorite (porphyritic) 3.78 27.37 0.0836 0.510555 10 2713 -1.2 2922 M11a PIM$-2003-534 442402 7203114 3604761A1908 Joutenvaara granodiorite 1.52 9.38 0.0980 0.510898 10 2760 1.1 2834 M11a PIM$-2003-213 442404 7200009 3621583A1905 Vaamankallio leucogranite 2.34 15.55 0.0911 0.510883 10 2688 2.2 2689 M11a PIM$-2003-12 442210 7198616 3593550A1905 #2 Vaamankallio leucogranite 2.32 15.34 0.0913 0.510880 10 2688 2.1 2696 M11a 442210 7198616 3593550PIM-2003-12 Vaamankallio leucogranite 0.70 2.94 0.1438 0.510944 11 2700 -14.8 4813 M11a open system 442210 7198616 3593550A1912 Likamännikkö quartz diorite 7.09 39.59 0.1082 0.511032 10 2742 -0.2 2919 M11b PIM$-2006-193 353307 7226964 3564760L07084727 (193.1)Likamännikkö syenite 14.96 95.27 0.0949 0.510894 10 2742 1.9 2762 M11b PIM$-2006-193.1 3533 07 B 7226964 3564760L07084728 (193.2)Likamännikkö mafics 48.19 257.90 0.1129 0.511160 10 2742 0.7 2861 M11b PIM$-2006-193.2 3533 07 B 7226964 3564760L07084729 (193.3)Likamännikkö carbonatite 48.37 278.40 0.1050 0.511084 10 2742 2.0 2754 M11b PIM$-2006-193.3 3533 07 B 7226964 3564760L08065994 Likamännikkö carbonatite 45.53 268.90 0.1023 0.511028 10 2742 1.9 2765 M11b 3534 07 B 7226964 3564760L08065996 Likamännikkö carbonatite 45.76 259.22 0.1067 0.511085 11 2742 1.4 2798 M11b 3535 07 B 7226964 3564760L07115671 Likamännikkö mafics 23.07 135.08 0.1032 0.511026 10 2742 1.5 2791 M11b 3536 07 B 7226964 3564760L07115654 Likamännikkö mafics 42.06 245.63 0.1034 0.511028 10 2742 1.5 2796 M11b 3537 07 B 7226964 3564760L07115670 Likamännikkö syenite 17.43 92.78 0.1135 0.511139 10 2742 0.0 2913 M11b 3538 07 B 7226964 3564760L07115652 Likamännikkö syenite 6.92 41.84 0.0999 0.510957 10 2742 1.3 2802 M11b 3539 07 B 7226964 3564760Kuhmo greenstone belt (N->S):A120a Ruokojärvi felsic volcanic rock 1.12 6.49 0.1039 0.510955 40 2818 0.8 2913 442302 7180686 3607567A120b Ruokojärvi felsic volcanic rock 0.93 4.87 0.1151 0.511082 12 2818 -0.8 3049 442302 7180686 3607567A1000a Ruokojäri felsic volcanic rock 1.28 7.26 0.1065 0.510962 10 2818 -0.1 2974 442302 7180657 360773081062 Moisiovaara mica schist 2.09 10.88 0.1158 0.510992 12 2800 -3.1 3219 M86 7177590 3605211S4 Moisiovaara mica schist 1.78 5.33 0.2022 0.512746 10 2800 0.0 7177590 3605211A976 Moisiovaara mafic sill/ pegmatoid 3.20 8.97 0.2154 0.513123 20 2823 2.6 eps-Hf=+14! 442110 7168454 3601719A1213 Pitkäperä felsic volcanic rock 2.94 16.58 0.1073 0.511008 10 2842 0.9 2931 441402 7144884 3610162A788 Polvilampi felsic volcanic rock 1.69 5.57 0.1837 0.511246 20 2799 -22.7 open system? 441211 7144664 3601262A1773 Hetteilä Kuhmo intermed volcanic rock 3.76 20.25 0.1123 0.511055 10 2836 -0.1 3004 441212 7140594 3604137A1774 Hetteilä Kuhmo mica schist/dyke? 4.31 28.55 0.0913 0.510943 13 2740 4.1 2617 441212 7140592 3604087A1346 Lampela felsic volcanic rock 3.57 17.56 0.1229 0.511341 10 2798 1.2 2878 441210 7136051 3601218A1560 Huuhilonkylä felsic volcanic rock 3.78 17.80 0.1285 0.511446 10 2798 1.3 2876 441210 7133793 3600464A1418 Niittylahti gabbro 1.12 3.86 0.1747 0.512321 50 2788 1.6 441210 7131725 3600772A1418#2 Niittylahti gabbro 1.13 3.91 0.1744 0.512295 14 2788 1.2 441210 7131725 3600772A1771 Kuhmo, Kellojärvi gabbro 1.67 6.58 0.1533 0.511936 10 2798 1.9 2823 441112 7130834 3601214

208

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.



Kuhmo greenstone belt (N->S):A1503 Mäkisensuo felsic volcanic rock 5.69 25.64 0.1343 0.511610 10 2800 2.4 2771 441112 7128835 3600958A1377 Siivikko crustal xenolith

in komatiite2.51 12.92 0.1175 0.511282 11 2795 2.0 2806 4411 7128059 3601375

A1822 Pahakangas mafic volcanic rock (gabbroic)

2.21 6.88 0.1945 0.512645 10 2800 0.9 20-PTP-03 441112 7127527 3601305

A511 Katerma, Kuhmo felsic volcanic rock 6.55 35.54 0.1113 0.511168 10 2799 2.0 2798 eps-Hf=+6 441111 7120960 36030826-EJH-96 (A2027) Siivikko qu-porphyry dyke 2.52 10.52 0.1450 0.511322 10 2795 -7.2 3944 open system? 441112 7128130 36026646-EJH-96#2 Siivikko qu-porphyry dyke 2.58 10.87 0.1433 0.511302 10 2795 -7.0 3875 open system? 441112 7128130 3602664A1746 Petäjäniemi Kuhmo metasediment 0.84 3.38 0.1502 0.511221 20 2700 -11.6 open system? 441302 7118594 3609220A1747 Petäjäniemi Kuhmo metasediment 1.36 6.96 0.1179 0.511303 20 2740 1.7 2776 441302 7118594 360922081064 Koitto Kuhmo mica schist 2.73 13.72 0.1202 0.511301 24 2740 0.8 2851 M86 7113842 3612228Kuhmo greenstone belt komatiites and basalts:48-PTP-03 Moisiovaara N komatiitic basalt 2.06 6.10 0.2047 0.512915 10 2800 2.5 442302 7175646 360421352-PTP-03 Koivulehto komatiitic basalt 2.05 6.58 0.1880 0.512636 10 2800 3.0 441212 7151793 359832453-PTP-03 Arola W komatiite 0.72 1.84 0.2354 0.513345 60 2800 -0.2 large error 441211 7151046 3598464R400/64.80-67.00 Vuosanka high-Cr basalt 1.62 3.93 0.2499 0.513753 10 2800 2.5 441202 7138098 3605017R400/73.50-75.50 Vuosanka high-Cr basalt 1.37 3.45 0.2395 0.513556 10 2800 2.4 441202 7138098 360501722-PTP-03 Mäkisensuo Cr-basaltti 2.19 6.98 0.1901 0.512525 10 2800 0.1 441112 7129486 360078011-PTP-03 Siivikkovaara-Näätäniemi high-Cr basalt 1.22 2.59 0.2854 0.514320 17 2800 0.8 441112 7129344 36007047A-PTP-03 Siivikkovaara S komatiitic basalt 1.62 4.85 0.2015 0.512800 10 2800 1.4 441112 7128010 36022587D-PTP-03 Siivikkovaara S komatiite 1.24 3.75 0.2005 0.512809 10 2800 1.9 441112 7128010 36022587B-PTP-03 Siivikkovaara S komatiite 1.15 3.23 0.2149 0.513009 10 2800 0.6 441112 7128010 36022587F-PTP-03 Siivikkovaara S komatiite 1.07 2.98 0.2165 0.513016 16 2800 0.2 441112 7128010 36022587E-PTP-03 Siivikkovaara S komatiite 1.60 5.37 0.1801 0.512568 10 2800 4.6 441112 7128010 36022582B1-PTP-03 Pahakangas profile komatiitic basalt 1.27 3.27 0.2349 0.513360 10 2800 0.2 441112 7127619 36015882E-PTP-03 Pahakangas profile komatiitic basalt 1.31 3.28 0.2410 0.513318 10 2800 -2.8 441112 7127619 36015882C-PTP-03 Pahakangas profile komatiitic basalt 1.45 4.02 0.2189 0.513068 10 2800 0.3 441112 7127619 36015882D-PTP-03 Pahakangas profile komatiitic basalt 1.32 3.41 0.2335 0.513355 10 2800 0.6 441112 7127619 36015882H-PTP-03 Pahakangas profile komatiite 0.93 2.57 0.2184 0.513066 10 2800 0.5 441112 7127619 360158856-PTP-03 Hietaperä komatiitic basalt 1.68 5.21 0.1951 0.512710 20 2800 1.9 441112 7123890 3603424TOH-206-93 Kellojärvi Kuhmo serpentinite (komatiitic) 0.45 1.34 0.2003 0.512929 17 2800 4.3 4412Tipasjärvi greenstone belt:A1174C Taivaljärvi felsic volcanic rock 1.44 6.48 0.1344 0.511602 29 2798 2.2 2792 shaft, 485 m down 432212 7094249 3600135A1174A Taivaljärvi felsic volcanic rock 0.96 6.66 0.0875 0.510693 10 2798 1.3 2841 shaft, 95 m down 432212 7094249 3600135A1886 Tipasjärvi Sotkamo felsic volcanic rock 5.32 26.84 0.1197 0.511298 10 2794 1.5 2844 432208 7088033 3593943A1922 Tipasjärvi felsic volcanic rock 4.45 24.84 0.1082 0.511083 10 2828 1.8 2842 432208 7085155 3592389A1921 Tipasjärvi felsic volcanic rock 1.55 10.17 0.0918 0.510784 10 2810 1.7 2833 432208 7083631 3594042A1588 Alakolkonjärvi garnet-amphibolite 6.76 18.05 0.2264 0.513252 10 2800 1.2 432208 7081873 3590726A1588 garnet 1.91 0.27 4.3740 0.566500 200A1748 Aarreniemi Tipasjärvi greywacke 3.14 16.42 0.1156 0.511094 20 2746 -1.5 3045 432212 7093916 3606458Kuhmo granitoids (N->S):A337 #1 Säynäjävaara tonalite gneiss 4.36 25.14 0.1049 0.510898 10 2717 -1.9 3023 442112 7189227 3596599A337 #2 Säynäjävaara tonalite gneiss 4.56 26.75 0.1030 0.510902 10 2717 -1.2 2962 442112 7189227 3596599A1146 Kaartojärvet gabbro (sanukitoid) 3.61 20.89 0.1046 0.510989 10 2722 0.0 2884 K06 442312 7188084 3633531

209

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland



Kuhmo granitoids (N->S):A1146 plag plagioclase 0.08 1.27 0.0398 0.510225 20 2700 7.4 442312 7188084 3633531A1146 hbl hornblende 6.10 30.38 0.1215 0.511321 12 2700 0.4 442312 7188084 3633531A27-1 Konivaara granodiorite 1.37 9.35 0.0883 0.510661 10 2705 -0.9 2903 K06 4421 7177694 3574219A27-2 Konivaara granodiorite 1.73 15.77 0.0662 0.510270 10 2705 -0.8 2872 K06 4421 7177694 3574219A27-4 Konivaara granodiorite 5.98 41.63 0.0869 0.510696 10 2705 0.3 2828 K06 4421 7177694 3574219A1960 Kuhmo tonalite 2.29 15.54 0.0892 0.510650 10 2700 -1.5 2940 94002667 442306 7173438 3618354A1927 Honkavaara Ristijärvi granodiorite 3.79 30.73 0.0745 0.510397 11 2700 -1.3 2903 421C-ATK-06 344307 7164475 3565018AAK-02-117 Suolahdenkallio granodiorite (sanukitoid) 6.11 34.62 0.1066 0.511042 10 2734 0.5 2857 K06 7163832 3597772AAK-02-59 Halmejärvi leucogranite 6.90 50.59 0.0820 0.510557 10 2705 -0.7 2891 K06 7159194 3592668A1183 Naavala tonalite gneiss 1.01 5.04 0.1212 0.511074 20 2750 -3.9 3283 441409 7159156 3630364A1183 #2 Naavala tonalite gneiss 1.04 5.13 0.1226 0.511078 10 2750 -4.3 3328 441409 7159156 3630364Naa3#2 Naavala 3 #2 tonalite gneiss 0.99 4.74 0.1263 0.511235 10 2750 -2.5 3190 441409 7159156 3630364Naa5 Naavala 5 tonalite gneiss 0.95 4.54 0.1269 0.511186 16 2750 -3.7 3305 441409 7159156 3630364Naa 2 Naavala 2 granitic dyke 2.67 19.28 0.0838 0.510440 20 2750 -3.0 3069 441409 7159156 3630364Naa2#2 Naavala 2 #2 granitic dyke 2.67 19.39 0.0833 0.510417 10 2750 -3.3 3083 441409 7159156 3630364A1183p Naavala small sample/ A1183 1.28 7.85 0.0984 0.510942 107 2750 1.7 large error 441409 7159156 3630364A1183p#2 Naavala small sample/ A1183 1.20 7.56 0.0958 0.510927 10 2750 2.3 2740 441409 7159156 3630364Naa1 Naavala 1 granodiorite, mobilized 1.30 7.44 0.1052 0.510995 13 2750 0.3 2892 441409 7159156 3630364Naa 4 Naavala 4 granodiorite, dyke? 10.00 94.00 0.0643 0.510358 10 2750 2.3 2741 441409 7159156 3630364Naa4#2 Naavala 4 #2 granodiorite, dyke? 9.43 86.50 0.0659 0.510377 10 2750 2.1 2752 441409 7159156 3630364Naa6 Naavala 6 coarse granite dyke 0.49 2.47 0.1198 0.511253 54 2750 0.1 2927 441409 7159156 3630364Naa7 Naavala 7 amphibolite 1.99 5.61 0.2140 0.512972 10 2750 0.3 441409 7159156 3630364AAK-02-09 Vitikko, Vartius granodiorite 1.29 8.14 0.0959 0.510812 15 2700 -0.7 2894 K06 7157360 3637311A1704 Vartius granodiorite 1.34 6.50 0.1015 0.510954 31 2700 0.2 2846 K06 441412 7156717 3639073A404b#2 Lylyvaara tonalitic melanosome 4.55 23.82 0.1154 0.511050 10 2942 -0.3 3114 441409 7153484 3627739AAK-02-48 Syvänoro granodiorite/granite 7.80 40.59 0.1161 0.511160 30 2686 -1.1 2955 K06 7152855 3588839A1702 Purnu tonalite 1.99 14.30 0.0842 0.510657 10 2747 1.1 2811 K06 441103 7152723 3606741A1707 Pohjanjärvi leucogranite 2.17 11.16 0.1182 0.511210 26 2705 -0.6 2941 K06 441212 7152140 3595059A572 Arola granodiorite 4.14 24.61 0.1017 0.510979 10 2734 1.0 2814 K06 441212 7151667 3596926AAK-02-57B Arola felsic inclusion

in Arola grdr3.81 23.19 0.0993 0.510932 10 2700 0.5 2817 441212 7151652 3596897

AAK-02-179A Riihivaara granodiorite 1.03 5.89 0.1051 0.510486 10 2686 -10.5 3629 K06 open system? 7149989 3582291AAK-02-21 Raatolehto granodiorite (sanukitoid) 4.00 22.73 0.1064 0.510974 10 2734 -0.8 2949 K06 7148475 3631560AAK-02-81 Iso Niskavaara granodiorite (sanukitoid) 5.83 32.62 0.1081 0.511087 10 2734 0.9 2827 K06 7147109 3596734A1706 Pieni Tuomaanjärvi granodiorite 3.04 19.07 0.0965 0.510692 10 2695 -3.3 3068 K06 441205 7146616 3580113A402 Härmäjoki granodiorite dyke 5.05 28.24 0.1080 0.511081 10 2742 0.9 2837 K06 441211 7146491 3598393AAK-02-83 Lauttajärvi granite 5.40 38.30 0.0849 0.510633 10 2700 -0.3 2863 7144925 3590913AAK-02-87 Latvalampi granodiorite (sanukitoid) 6.75 38.45 0.1061 0.511066 10 2734 1.2 2808 K06 7144421 3597300A1147 Lentiira microtonalite 14.95 99.66 0.0907 0.510734 10 2701 -0.4 2871 441410 7142378 363808761-1-ATK-86 Pitämänsuo Sotkamo diorite (Loso sanukitoid) 11.90 69.10 0.1044 0.511022 10 2700 0.5 2830 K06 343407 7138480 3565290AAK-02-77 Majakangas granodiorite (sanukitoid) 5.48 30.85 0.1074 0.511082 10 2734 1.0 2818 K06 7137384 3598014A331 Loso diorite (Loso sanukitoid) 8.41 50.24 0.1011 0.510944 12 2719 0.3 2849 K06 343407 7135100 3563200A1928 Sarvilampi Sotkamo granodiorite (nebulitic) 2.24 18.19 0.0743 0.510160 10 2965 -1.7 3164 343407 7134499 3568058A1926 Ansosuo Sotkamo diorite gneiss (“Loso”) 15.46 81.93 0.1140 0.511183 10 2715 0.4 2857 437-ATK-07 343407 7133922 3564832

210

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.



Kuhmo granitoids (N->S):AAK-02-84 Kauppinen granodiorite gneiss 2.61 18.04 0.0875 0.510782 16 2700 1.7 2732 7132153 3594695AAK-02-157 Lampovaara leucogranite 1.42 10.75 0.0797 0.510475 10 2697 -1.7 2926 K06 7128565 3581076A1705 Viitavaara tonalite 2.69 13.92 0.1166 0.511274 11 2785 2.1 2785 K06 441109 7121621 3591704 A1719 Siikalahti granodiorite (sanukitoid) 5.08 33.18 0.0926 0.510802 10 2695 0.2 2825 K06 AAK-02-177 7119821 3614489AAK-02-167A Romuvaara leucogranite 1.75 10.62 0.0996 0.510860 10 2697 -1.1 2925 K06 7106738 359547394002593#3 granodiorite 6.08 33.39 0.1100 0.511093 10 2700 -0.1 2879 443104 7106131 3658934A1703 Katajavaara leucogranite 2.55 17.76 0.0867 0.510739 12 2697 1.1 2766 K06 441107 7105667 359587894002606 granitegneiss 3.52 16.61 0.1283 0.511465 10 2700 0.8 2832 441304 7103485 3619776AAK-02-100 Risteli tonalite 2.25 10.28 0.1324 0.511489 10 2830 0.9 2830 K06 7103410 3619440A1086 Haasiavaara tonalite 2.44 13.30 0.1108 0.511118 10 2832 1.6 2860 K06 432209 7100126 3594392AAK-02-166 Vetelänvaara tonalite 3.44 19.46 0.1067 0.511073 10 2830 2.2 2814 K06 7090977 3588767A1089 Huuskovaara tonalite 1.51 7.69 0.1188 0.511211 10 2814 0.3 2958 K06 432211 7089923 360606693002713 tonalitegneiss 7.60 37.97 0.1210 0.511254 10 2700 -0.8 2962 334408 7088720 3569860A1085 Halmejärvi tonalite 2.71 10.83 0.1513 0.511837 10 2745 0.3 2982 K06 432207 7075307 358907294003191 quartzdiorite gneiss 9.11 38.02 0.1449 0.511659 10 2700 -1.2 3109 432407 7074206 3631667A790 Pohjanjärvi granite 1.74 8.45 0.1245 0.511273 10 2700 -1.6 3044 441212 7152182 3595099A790uusi Pohjanjärvi granite 8.76 31.38 0.1688 0.512252 10 2700 2.1 2714 441212 7152182 3595099Ilomantsi (Hattu) schist belt:M8603917 Poikapää mafic pillow lava 3.21 9.79 0.1984 0.512305 22 2750 -7.2 O93 open systems 433307M8603917 #2 Poikapää mafic pillow lava 3.49 10.73 0.1964 0.512344 14 2750 -5.8 O93 open systems 433307M8603967 Tiittalanvaara amphibolite 1.63 4.49 0.2187 0.513108 10 2750 1.3 O93A1038 Poikapää andesite 3.67 16.94 0.1311 0.511331 10 2754 -2.3 3201 O93 open systems? 433307 6993805 3713236A1038 #2 Poikapää andesite 3.87 17.72 0.1320 O93 open systems? 433307 6993805 3713236A1038 #3 Poikapää andesite 3.92 17.96 0.1318 0.511328 16 2754 -2.6 3230 open systems? 433307 6993805 3713236A1038b Poikapää andesite 3.75 14.10 0.1606 0.511534 10 2754 -8.9 open systems 433307 6993805 3713236A1039 Poikapää metasediment 3.07 18.30 0.1013 0.510996 11 2750 1.7 2786 O93 433307 6993805 3713236A1039 #2 Poikapää metasediment 3.15 18.80 0.1013 O93 433307 6993805 3713236A1039 #3 Poikapää metasediment 3.18 18.83 0.1019 0.510994 10 2750 1.4 2802 433307 6993805 3713236A1039b Poikapää metasediment 4.57 27.51 0.1003 0.510951 11 2750 1.2 2820 second sample 433307 6993805 3713236A282#3 Vehkavaara felsic dyke 3.32 18.65 0.1076 0.510951 12 2750 -1.5 3021 4244 6968216 3697163A301#3 Vehkavaara felsic dyke 2.40 13.38 0.1084 0.510941 12 2755 -1.9 3061 4244 6968216 3697163A1095 Kivisuo felsic porphyry dyke 3.14 18.62 0.1019 0.510982 10 2756 1.3 2818 O93 424408 6974009 3714000S21 Ilomantsi mica gneiss 3.17 14.20 0.1349 0.511386 32 2750 -2.6 3254 H87 133-SL-69 424402 6965830 3695191S18 Ukkolanvaara Ilom mica schist 2.11 10.02 0.1276 0.511422 14 2750 0.7 2893 O93 53-SL-67 424409 6977221 3717596S19 Ilomantsi/Eno mica schist 3.56 17.64 0.1221 0.511225 10 2750 -1.2 3053 O93 15/68 424210 6961361 3692996S20 Leppärinne Ilom mica schist 2.80 14.37 0.1176 0.511174 11 2750 -0.6 2986 O93 95-SL-68 424408 6971208 3716024A221 Hattuvaara mica schist 3.94 22.39 0.1063 0.511060 10 2750 1.2 2826 O93 433307 6987579 3717193Ultramafic rocks from Hattu schist beltL05071816 Ilomantsi ultramafic rock 0.83 3.43 0.1457 0.511764 20 2750 0.9 2898 HJO-86-30 433307 6995360 3715648L05071817 Ilomantsi ultramafic rock 0.72 2.71 0.1617 0.512041 20 2750 0.7 2989 HJO-86-32 433307 6994985 3715775L05071818 Ilomantsi ultramafic volcanic rock 0.50 1.88 0.1608 0.511998 20 2750 0.2 3070 KJP-87-80.2 433308 6997601 3717957L05071819 Ilomantsi ultramafic volcanic rock 2.21 10.00 0.1334 0.511606 20 2750 2.2 2744 KJP-87-80.1 433308 6997601 3717957L05071820 Ilomantsi ultramafic volcanic rock 2.66 14.67 0.1096 0.511236 20 2750 3.4 2652 KJP-87-14.2 433308 7003532 3712622L05071821 Ilomantsi ultramafic volcanic rock 2.46 12.36 0.1204 0.511345 20 2750 1.7 2785 KJP-87-16 433308 7003931 3712603L05092835 Ilomantsi mafic volcanic rock 2.52 7.44 0.2051 0.512406 20 2750 -7.6 433307 6989794 3717520

211

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland



Kovero schist belt:A1622 Otravaara felsic volcanic rock 1.59 4.62 0.2073 0.512962 10 2750 2.5 424106 6945072 3673746A1623 Turula tonalite gneiss/ volcanics? 6.08 36.75 0.1000 0.510941 10 2750 1.1 2823 424109 6948327 3674878A1624 Hämälänniemi felsic volcanic rock 5.86 39.00 0.0908 0.510908 10 2877 5.5 2648 open systems? 424108 6942496 3674651A1624#2 Hämälänniemi felsic volcanic rock 5.94 39.51 0.0909 0.510899 10 2877 5.2 2662 open systems? 424108 6942496 3674651A1625 Rasisuo 1 porphyry dyke 3.17 14.75 0.1298 0.511154 10 2757 -5.3 3484 open systems? 424108 6942918 3675005A1625#2 Rasisuo 1 porphyry dyke 3.17 14.80 0.1293 0.511126 10 2757 -5.7 open systems? 424108 6942918 3675005A1626 Rasisuo 2 gabbro 6.93 32.27 0.1298 0.511517 10 2756 1.8 2785 424108 6944375 3674468A1627 Rasisuo 3 felsic tuff 2.86 18.99 0.0912 0.510598 10 2878 -0.8 3052 424108 6943876 3675201A1628 Hämälänniemi gabbro 1.42 3.99 0.2151 0.513133 10 2750 3.1 424108 6941671 3675077A1629 Turula 2 felsic volcanic rock 2.17 7.50 0.1744 0.512227 10 2750 -0.2 high Sm/Nd 424109 6948211 3674940A1154 Löytöjärvi dacitic schist 5.61 37.63 0.0901 0.510829 10 2750 2.4 2734 424106 6945952 3668957A1155 Linnasuo porphyry (tonalitic dyke) 5.52 30.31 0.1101 0.511172 10 2758 2.1 2761 424108 6943513 3676802A1520 Kiukoinvaara granodiorite (dyke

in mica schist)3.16 24.19 0.0791 0.510783 10 2754 5.5 2558 424105 6942270 3673334

Ipatti schist beltA1749 Kokkokallio, Koli qu-fspar-porphyry 3.50 17.76 0.1191 0.511242 20 2811 0.8 2914 431309 7010076 3639521Ilomantsi granitoids (N->S):94003175 tonalite 5.23 31.47 0.1004 0.510900 20 2700 -0.5 2894 432308 7059053 3633080A1772 Änäkäinen Lieksa gabbro (essexite) 58.4 300.3 0.1176 0.511224 10 2712 -0.1 2900 434102 7057845 3653013A1763 Ollikkalanvaara tonalite 2.04 11.10 0.1112 0.511170 10 2722 1.3 2794 432304 7043837 361976994003163 granodiorite 4.40 29.72 0.0896 0.510856 20 2700 2.4 2688 432110 7042789 3608691A1764 Persauslammet amphibolite 2.87 9.39 0.1848 0.512492 20 2700 1.2 433206 7040755 3663941A1767 Karppinen 1 granite 15.82 94.61 0.1010 0.510967 10 2690 0.5 2817 431408 7032730 3634136A1768 Karppinen 2 tonalite 3.02 21.06 0.0867 0.510734 10 2822 2.8 2776 431408 7032730 3634136A1765 Jamali 1 mica gneiss (mesosome) 2.18 10.40 0.1265 0.511399 10 2700 0.2 2893 431411 7031233 3644756A1766 Jamali 2 granite (leucosome) 0.52 3.04 0.1042 0.510978 15 2700 -0.3 2884 431411 7031233 364475693002466 gneiss 3.94 17.72 0.1343 0.511488 10 2700 -0.8 3014 431411 7029555 3641442PK-50 Lieksa granodiorite (sanukitoid) 6.54 39.79 0.0993 0.510941 10 2700 0.7 2804 H05 433211 7029368 3682789PK-49 Lieksa granodiorite (sanukitoid) 7.66 44.72 0.1035 0.511024 10 2700 0.8 2798 H05 433208 7028199 3671937PK-47 Lieksa granodiorite (sanukitoid) 6.03 35.86 0.1016 0.510964 10 2700 0.3 2832 H05 433208 7027646 3671252A1762 Emonvaara tonalite 5.23 33.51 0.0944 0.510847 15 2732 1.0 2812 433205 7027479 3661337PK-100 Lieksa granodiorite (sanukitoid) 7.80 49.51 0.0952 0.510904 10 2700 1.4 2754 H05 433205 7026409 3669868PK-42 Lieksa granodiorite (sanukitoid) 6.37 41.97 0.0917 0.510814 10 2700 0.8 2788 H05 433205 7025522 3669319PK-45 Lieksa granodiorite (sanukitoid) 6.91 46.76 0.0893 0.510744 24 2700 0.3 2820 H05 433204 7023545 3670293A1964 Ilomantsi granite 7.05 40.36 0.1056 0.511004 10 2700 -0.3 2887 94002572 433210 7021049 3685422A1339 (PK-27) Iso Kiimalampi tonalite (sanukitoid) 6.35 37.96 0.1010 0.510966 13 2730 0.9 2815 H05 433210 7020121 3683802A1336 Sourisuo tonalite (sanukitoid) 6.03 33.10 0.1100 0.511140 10 2730 1.2 2805 H05 433107 6989109 367272493002484 granodiorite gneiss 8.85 43.55 0.1228 0.511349 10 2700 0.5 2858 433306 7012294 3707655A1094 Tasanvaara tonalite 4.69 25.30 0.1120 0.511148 10 2744 0.8 2851 O93 433307 6989342 3715899A339 Silvevaara granodiorite 3.51 19.51 0.1088 0.510941 10 2750 -2.1 3077 O93 424406 6983787 3706753A339b Silvevaara granodiorite 3.91 22.25 0.1064 0.510983 10 2750 -0.4 2942 O93 second sample 424406 6983787 3706753A285 Kuittila tonalite (sanukitoid) 4.09 24.02 0.1029 0.511019 10 2746 1.5 2795 O93 4244 6974252 3714489A284#2 Lehtovaara granodiorite (Silvevaara) 5.96 32.40 0.1111 0.511054 10 2750 -0.7 2974 O93 4244 6973076 3710317A1963 Ilomantsi granodiorite 4.05 25.04 0.0977 0.510870 10 2700 -0.2 2865 90010130 424404 6959880 3708970A91 Kutsu Tohmajärvi granite 5.73 40.61 0.0853 0.510727 10 2617 0.2 2751 423207 6914462 3684841

212

Geological Su

rvey of Fin

land, Special P

aper 54

Hannu H

uhma, Irm

eli Mänttäri, P

etri Peltonen, A

sko Kontinen, T

apio Halkoaho, E

ero Hanski, T

uula Hokkanen,

Pentti H


onnunaho et al.



Archean “domes”:R27 Sotkuma granodiorite gneiss 1.98 11.19 0.1067 0.511039 60 2700 0.0 2869 H86 large error 4224 6959795 3627757S55 Oravinsalo granitoid (sheared) 9.44 52.52 0.1086 0.511123 10 2700 1.0 2792 421406 6917763 3630813Iisalmi complex (N->S):A1959 Iisalmi gneiss 2.60 17.09 0.0920 0.510819 10 2700 0.8 2791 94003640 343101 7101160 3500970L05029450 190-PSH-04 amphibolite 3.19 10.38 0.1859 0.512165 20 2710 -5.6 open system? 7096414 351764293002622 granitegneiss 4.08 24.20 0.1020 0.510982 20 2700 0.5 2820 334206 7095070 3512530A1513 Naimakangas diorite 6.79 36.00 0.1140 0.511224 10 2706 1.2 2789 334203 7093430 3507620L05028811 179.1-PSH-04 amphibolite 4.95 25.38 0.1178 0.511241 20 2710 0.2 2879 7075136 3498485A1958 Iisalmi tonalite 8.10 52.10 0.0940 0.510870 10 2700 1.1 2772 93003031 334302 7057160 3547420PSH-90-53 Luotosenkoski px-amphibolite 5.85 26.84 0.1320 0.511377 11 3100 1.2 3147 H00 334110 7049600 3535150A1145 Kumisevanmäki mesos. of interm. grl 5.48 29.60 0.1119 0.510917 11 3200 1.3 3213 H00 eHf(T)=+0.6±1.5 334110 7047040 3533200A1332 Kumisevanmäki leucos. of interm. grl 1.91 6.63 0.1753 0.512135 11 2700 -2.5 H00 eHf(T)=-5.7±5.0 334110 7047040 3533380A1332b Kumisevanmäki mesosome 2.29 8.17 0.1697 0.512096 10 2700 -1.3 H00 334110 7047040 353338093002664 tonalite 6.74 37.77 0.1079 0.511108 20 2700 0.9 2797 334110 7042270 3533520A1222 Rokuankangas px-grt-amphibolite 2.57 8.59 0.1809 0.512500 80 2700 2.7 H00 333212 7039640 3535510A1222#2 (2000) Rokuankangas px-grt-amphibolite 2.62 8.73 0.1811 0.512460 10 2700 1.9 333212 7039640 3535510A979 Lampiensalmi enderbite 8.24 39.93 0.1247 0.511410 10 2700 1.0 2815 H00 333209 7039460 3527870A844 Varpaisjärvi enderbite 6.84 34.81 0.1187 0.511263 10 2716 0.4 2873 H00 eHf(T)=-0.3±1.0 333403 7031920 3540840A1331 Jouhimäki leucos. of mafic granulite 3.86 38.61 0.0605 0.510269 10 2700 1.1 2759 H00 eHf(T)=-1.0±2.0 333403 7030260 3547250A1391 Jouhimäki mesos. of mafic granulite 4.62 24.50 0.1140 0.511141 11 2700 -0.6 2926 H00 eHf(T)=+0.5±2.9 333403 7030260 3547250A1326 Jouhimäki grt-sill-gneiss 3.74 17.70 0.1276 0.511470 10 2700 1.2 2804 H00 eHf(T)=-0.3±1.5 333403 7030000 3547000A1142b Jouhimäki grt-crd-sill-rock 15.81 68.58 0.1393 0.511732 10 2700 2.2 2703 H00 333402 7029530 3546920A1142b#2 Jouhimäki grt-crd-sill-rock 15.59 68.79 0.1370 0.511710 10 2700 2.6 2667 H00 333402 7029530 3546920A76 Romonmäki tonalitic mesosome 8.24 37.21 0.1338 0.511260 10 3173 -1.3 3458 L11 eHf(T)=-1.0±1.2 333208 7028220 3528760A76#3 Romonmäki tonalitic mesosome 8.47 38.27 0.1337 333208 7028220 3528760A76#4 Romonmäki tonalitic mesosome 8.47 38.37 0.1337 0.511260 20 3173 -1.2 3458 333208 7028220 3528760A645 Kiikkukallio trondhjemitic leucosome 3.08 19.16 0.0972 0.510640 10 3100 0.7 3161 L11 333208 7024960 3525700A937 Kiikkukallio tonalitic mesosome 3.31 18.45 0.1085 0.510819 10 3181 0.6 3252 L11 eHf(T)=-0.2±1.5 333208 7024800 3525600A937#2 Kiikkukallio tonalitic mesosome 3.83 21.60 0.1072 0.510800 10 3181 0.8 3239 333208 7024800 3525600A937#4 Kiikkukallio tonalitic mesosome 3.71 21.11 0.1062 333208 7024800 3525600A937#5 Kiikkukallio tonalitic mesosome 3.72 21.05 0.1067 0.510803 10 3181 1.0 3218 333208 7024800 3525600PK-113A Nilsiä augen gneiss 11.29 63.01 0.1081 0.511122 11 2700 1.2 2780 H05 333407 7016810 3564360PK-121 Nilsiä augen gneiss 8.95 59.23 0.0913 0.510817 10 2700 1.0 2775 H05 333410 7014930 3570080PK-120A Nilsiä augen gneiss 7.08 45.65 0.0937 0.510879 10 2700 1.4 2750 H05 333410 7010000 3571340A279 Kivimäki quartz diorite 4.78 27.01 0.1070 0.511104 20 2692 1.1 2778 333103 7008320 3509380A300 Siilinjärvi carbonatite, sövite 21.00 143.30 0.0885 0.510781 10 2609 0.0 2757 33312 7000140 3537250A187 Siilinjärvi “inclusion” in carbonatite 2.55 18.01 0.0856 0.510731 10 2609 0.0 2751 33312 7000000 3537100Apatite-concentrate

Siilinjärvi carbonatite/ apatite 107.40 706.20 0.0919 0.510821 10 2609 -0.3 2783 33312 7000000 3537100

Manamasalo A1401 Multasuo qudioritic paleosome 6.80 39.79 0.1033 0.510838 11 2700 -2.8 3058 343206 7156500 3513240A1515 Multasuo syenite (diopside-) 67.30 344.80 0.1180 0.511018 10 2700 -4.4 3254 343206 7156500 3513240A1291 Kaivanto trondjhemite leucosome 0.21 2.05 0.0621 0.510182 76 2700 -1.2 2878 large error 343202 7145130 350858094003658 gneiss 4.43 20.03 0.1337 0.511542 10 2700 0.4 2883 343103 7129400 3501150

213

Geological Su

rvey of Fin

land, Special P

aper 54

The age of the A


inland



Manamasalo 94003664 gneiss 5.03 33.44 0.0910 0.510552 20 2700 -4.1 3108 343112 7122480 3538130L05028800 167.1-PSH-04 tonalite 4.42 36.28 0.0736 0.510724 20 2700 5.4 2521 Proterozoic rock? 7150858 3486830L05028807 175.1-PSH-04 granodiorite 5.05 37.24 0.0819 0.510433 20 2700 -3.2 3029 7160836 3517091A1837 Karankalahti Kajaani tonalitegneiss 7.45 31.63 0.1424 0.511564 10 2700 -2.2 3211 343111 7119308 3537523A1897 Rahajärvi Pyhäntä tonalite 2.58 13.89 0.1121 0.511185 20 2700 1.0 2798 341310 7103794 3490519A1925 Saaresjärvi Vuolijoki tonalitegneiss 5.83 32.30 0.1092 0.511087 13 2700 0.1 2863 57-ATK-06 341310 7109495 3492521Central Puolanka GroupA1292 Haapalanmäki dacitic tuff 6.16 32.28 0.1154 0.511114 20 2700 -1.6 3007 343208 7149860 3525280ATK-14B Haapalanmäki andesite 4.74 19.62 0.1461 0.511740 10 2700 -0.0 2978 343209 7150780 3525560A1235 Kivesvaara felsic tuffite 4.17 20.70 0.1219 0.511292 20 2700 -0.3 2929 343208 7149780 3525380A1251 Petäjäniemi Paltamo porphyry 5.09 29.39 0.1046 0.511056 10 2718 1.3 2785 343208 7147020 3524020Nurmes paragneisses and related amphibolites, Kontinen et al 2007:53-PGN-90 Lemetinkangas Hyryns mica gneiss 4.37 24.17 0.1092 0.511106 10 2700 0.5 2839 K07 344407 7197220 356294044-PGN-90 Polvela Kuhmo mica gneiss 1.63 7.59 0.1296 0.511273 10 2700 -3.4 3251 K07 open system? 441310 7107214 364473344-PGN-90 #2 0.1300 K0757-3A-ATK-8 Romeikonsuo Sotkamo mica gneiss 4.90 26.77 0.1106 0.511122 10 2700 0.3 2854 K07 343408 7140390 3568120A1081 Nenämäki (=389-ATK-83) mica gneiss 3.71 20.9 0.1074 0.511112 10 2700 1.2 2776 K07 344307 7161640 35684001-KUH-88 Saarela Kuhmo mica gneiss 2.91 14.04 0.1252 0.511147 10 2700 -4.4 3308 K07 open system? 441304 7111827 3621285S22 Kuhmo mica gneiss 2.47 12.38 0.1205 0.511194 40 2700 -1.8 3050 H87 441304 7111769 3621337A73b Säyneinen mica gneiss 5.27 33.84 0.0942 0.510847 10 2700 0.6 2810 K07 333410 7013600 357180013A-NUR-90 Maaselän as. mica gneiss 4.46 23.78 0.1134 0.511097 20 2700 -1.2 2974 K07 432203 7087375 35738289-NUR-90 Nurmes mica gneiss 4.03 21.61 0.1126 0.511105 12 2700 -0.8 2940 K07 432110 7051065 360797235-PGN-90 Hirvivaara Rautavaara mica gneiss 4.19 23.19 0.1093 0.511098 23 2700 0.3 2854 K07 431205 7025742 358633237-PGN-90 Petäisjoki mica gneiss (pelitic) 7.11 41.12 0.1044 0.511085 10 2700 1.7 2736 K07 431205 7025895 35900291-VAL-88 Iso Juomasuo Valtimo mica gneiss 4.00 21.34 0.1133 0.511103 10 2700 -1.1 2965 K07 432207 7072359 3590252204-2A-ATK- Paloniemi Ristijärvi amphibolite (within

mica gneiss)4.12 14.25 0.1750 0.512343 10 2700 1.7 K07 3434 7153300 3567440

204-2B-ATK- Paloniemi grt amphibolite 8.21 27.63 0.1797 0.512422 12 2700 1.6 K07 3434 7153300 356744057-1A-ATK-8 Romeikonsuo Sotkamo amphibolite (within

mica gneiss)5.45 19.77 0.1668 0.512178 11 2700 1.4 K07 343408 7140450 3568080

57-1B-ATK-8 Romeikonsuo grt amphibolite 4.40 17.43 0.1528 0.511939 10 2700 1.6 2797 K07 343408 7140450 3568080391-ATK-83 Pieni Löytösuo Risti amphibolite (within

mica gneiss)2.15 6.44 0.2021 0.512840 20 2700 2.0 K07 344307 7161740 3568440

17-8-ATK-87 Pieni Löytösuo amphibolite 2.35 7.31 0.1943 0.512680 20 2700 1.6 K07 344307 7161720 356906057-1C-ATK-8 Kuppalampi Sotkamo amphibolite 1.25 3.79 0.2001 0.512660 40 2700 -0.8 K07 343407 7137780 3564670

Measurements since 1990 at GTK were made on VG Sector 54 mass-spectrometer. 143Nd/144Nd ratio is normalized to 146Nd/144Nd=0.7219, error is 2 standard error of the mean in last significant digits, Measurements on the La Jolla standard have yielded a ratio of 0.511850±10 (standard deviation for 220 measurements during years 1996-2010).# denotes duplicated analysisTDM is calculated according to DePaolo (1981)Age is in bold, if it is based on U-Pb dating on the same sample (reference or associated U-Pb paper), othervise it is 2700 Ma or age obtained for rocks in the same associationItalics - Sm-Nd published elsewhere (reference for Sm-Nd: H86 &87=Huhma 1986 &1987, H00=Hölttä et al 2000; H05=Halla 2005; Hetal=Heilimo et al 2013; K06=Käpyaho et al 2006; K07=Kontinen et al 2007; L06=Lauri et al 2006; L11=Lauri et al 2011;M86=Miller et al 1986; M03=Mutanen & Huhma 2003; M11a&b=Mikkola et al 2011a &b; O93=O’Brien et al 1993)(* eHf(T) average±standard deviation are calculated from the zircon analyses by Lauri et al (2011), other eHf(T) from Patchett et al (1981)

214


OVERVIEW OF NEOARCHAEAN SANUKITOID SERIES IN THE KARELIA PROVINCE,

EASTERN FINLAND

byEsa Heilimo1,2), Jaana Halla3) and Perttu Mikkola2)

Heilimo, E., Halla, J. & Mikkola, P. 2012. Overview of Neoarchaean sanukitoid se-ries in the Karelia Province, eastern Finland. Geological Survey of Finland, Special Paper 54, 214−225, 3 figures and 2 tables.

Late- to post-tectonic, relatively small volume sanukitoids (~ 2.74–2.72 Ga) are found in the Karelia Province on both sides of the border between Finland and Russia. The major and trace element geochemistry of the intrusions shows typical sanukitoid affinities: a mantle signature (high content of MgO, Ni, Cr and high Mg#) combined with enrichment in LILE (especially K2O, Ba and Sr). The sanuki-toid series can be distinguished from the TTG suite by its high Ba–Sr signature, low Na2O/K2O ratio and uniform HREE pattern. A compiled geochronological data set from the Karelia Province confirms the occurrence of two temporally diverging sanukitoid zones. The probable source of the sanukitoid series is an enriched sub-continental lithospheric mantle. The accumulation of K2O, Ba and Sr in the mantle source may have occurred as a consequence of complex metasomatic events: sub-duction-related fluids/melts and possibly asthenospheric upwelling. Slab breakoff at the end stage of subduction is a viable trigger for partial melting of the metaso-matized mantle, the sanukitoid source.

Keywords (GeoRef Thesaurus, AGI): intrusions, sanukitoids, geochemistry, genesis, mantle, Neoarchean, Finland, Republic of Karelia, Russian Federation

1) Department of Geology, P.O. Box 64, FI-00014, University of Helsinki, Finland2) Geological Survey of Finland, P.O. Box 1237, FI-70211 Kuopio, Finland3) Finnish Museum of Natural History, P.O. Box 17, FI-00014, University of Helsinki, Finland


215

Geological Survey of Finland, Special Paper 54Overview of Neoarchaean sanukitoid series in the Karelia Province, eastern Finland

INTRODUCTION

The sanukitoid series (or high-Mg granitoids) is a minor and divergent group of Neoarchaean ig-neous rocks, found in Archaean domains world-wide, whose geochemistry differs significantly from the Archaean tonalite-trondhjemite-grano-diorite (TTG) suite. Sanukitoids were first found by Shirey and Hanson (1984). They used the word sanukitoid for mantle-derived Archaean rocks, the composition of which resembles Miocene high-Mg andesites, i.e. sanukites in Japan (e.g. Tatsumi & Ishizaka 1982). The term sanukitoid series is a broader definition comprising grani-toids enriched in both compatible elements (Mg, Ni and Cr) and incompatible elements (LILE (K, Ba, Sr) and LREE) and having high Mg# at a given SiO2 content. The high contents of com-patible elements indicate a direct mantle origin, whereas the enrichment in incompatible elements suggests a significant crustal contribution in their genesis. The petrogenesis of sanukitoids has been explained by a two-stage process in a convergent tectonic setting. The lithospheric mantle wedge was enriched with incompatible elements by

melts/fluids from a subducted oceanic slab. After-wards, the enriched mantle wedge was partially melted, forming sanukitoid magmas (Stern & Hanson 1991, Smithies & Champion 2000, Ko-valenko et al. 2005, Martin et al. 2009). A possi-ble scenario for the trigger of partial melting is a breakoff of the descending oceanic slab followed by mantle upwelling that resulted in sanukitoid magmas (e.g. Halla et al. 2009). O and Pb–Pb iso-topic studies indicate that sediments subducted along with the oceanic crust might have played an important role in sanukitoid petrogenesis (King et al. 1998, Halla 2002, 2005). Another extraordi-nary feature in sanukitoids is their limited tempo-ral occurrence. All the known sanukitoid intru-sions fall in the age range between 2.95–2.53 Ga, with a distinct peak between 2.76–2.66 Ga (e.g. Heilimo et al. 2011 and references therein). The composition and temporally limited occurrence of sanukitoid magmatism suggest a unique tec-tonic process consisting of series of short-term events, such as frequent slab breakoffs, operating in the late Archaean.

SANUKITOID INTRUSIONS IN FINLAND

Neoarchaean late- to post-tectonic sanukitoid intrusions are found in the Finnish and Russian parts of the Karelia Province and are often relat-ed to major shear zones (e.g. Lobach-Zhuchenko et al. 2005, Heilimo et al. 2010, Figure 1). To date, ~ 20 sanukitoid intrusions have been de-scribed from the Karelia Province, 14 of which are located in eastern Finland (Fig. 1). The size of the intrusions is generally small, exceptions being the Koitere (a.k.a. Lieksa) and Kuusamo sanukitoids. U–Pb zircon ages and available εNd data on the intrusions are listed in Table 1. The rocks are variably even-grained or K-feldspar porphyritic and form a series from diorites to to-nalites and granodiorites. U–Pb age determina-tions give an age of 2.74–2.72 Ga for the sanuki-toid magmatism in Finland, which falls between the last peak of TTG magmatism (Käpyaho et al. 2006, Mikkola et al. 2011, ~2.75 Ga) and the age of the GGMs (granodiorite-granite-monzogran-ite) and quartz diorites in the Karelia Province (Käpyaho et al. 2006, Lauri et al. 2011, Mikkola et al. 2011, ~2.7 Ga). Bibikova et al. (2005) and

Lobach-Zhuchenko et al. (2005) argued that sa-nukitoid intrusions in the Russian side of the Ka-relia Province occur as two temporally, spatially and geochemically different groups termed the eastern and western sanukitoid zones. Compiled single-grain zircon U–Pb age data from the Finn-ish and Russian parts of the Karelia Province confirm the occurrence of two temporally dif-fering sanukitoid zones throughout the Province (Heilimo et al. 2011). The western zone shows a younger average age of ~2718 Ma and the eastern zone an older average age of ~2740 Ma, with an apparent age difference of ~20 Ma between the zones. Most of the sanukitoid intrusions in Fin-land belong to the western sanukitoid zone, but the southernmost intrusions can be regarded as a part of the eastern sanukitoid zone. Most felsic sanukitoids contain inherited zircon cores with ages up to ~ 3.2 Ga, reflecting the importance of inheritance processes in the petrogenesis of sanukitoids (Bibikova et al. 2005, Heilimo et al. 2011).

216

Geological Survey of Finland, Special Paper 54Esa Heilimo, Jaana Halla and Perttu Mikkola

Eastern zoneMean weighted =2740±3 MaMSWD=1.8

2680

2700

2720

2740

2760

WE

ST

SA

NU

KIT

OID

ZO

NE

EA

ST SA

NU

KIT

OID

ZO

NE

FINLAND

RUSSIAPaleoproterozoic rocks

Lentuacomplex

Ilomantsi complex

100 km

RUSSIA

Siuruacomplex

N Archean granitoids

Metasedimentary belts

Greenstone belts(3.02-2.93 Ga)


Sanukitoid intrusion

KARELIA PROVINCE

FINLAND

Iisalmicomplex

Western zoneMean weighted=2718±3 Ma 95% conf. MSWD=2.7

Ku

rge

lam

pi 1

Nju

k 1

Ku

rge

lam

pi 2

Ka

art

ojä

rve

t

Nju

k 2

Ku

rge

lam

pi 2

Lo

so

Ka

ap

insa

lmi

Ko

itere

Aro

la

Nils

iä

Ilo

ma

nts

injä

rvi

Pa

no

zero

1

Pa

nze

ro 2

Pa

no

ze

ro 3

Ku

ittila

Sja

rgo

ze

ro Elm

us

Ha

uta

vaa

ra 1

Ha

uta

va

ara

2

Sys

mä

njä

rvi

Archean granitoids

Metasedimentary belts



Sanukitoid intrusionwestern zone

Sanukitoid intrusioneastern zone

B

KAAPINSALMI

AROLA

SIIKALAHTI

NILSIÄ

KOITERE

KUITTILA

HAUTAVAARA 2743 8 Ma 2742 ± 23 Ma

±

ELMUS2742 ± 8 Ma

PANOZERO 2742 ± 18 Ma 2734 ± 17 Ma 2741 ± 12 Ma

SJARGOZERO 2742 ± 16 Ma

NJUK 2709 ± 10 Ma 2716 ± 11 Ma

KURGELAMPI 2707 9 Ma 2719 ± 6 Ma 2712 ± 9 Ma

±

ILOMANTSIN-JÄRVI

KUUSAMO

KAARTOJÄRVET

SYSMÄJÄRVI2744 ± 5 Ma

2728 ± 7 Ma

2741 ± 6 Ma

2722 ± 6 Ma

2724 ± 28 Ma

~ 2680 Ma

LOSO2719 ± 19 Ma

2723 ± 4 Ma

2722 ± 4 Ma

2718 ± 5 Ma

2715 ± 3 Ma

SURMANSUONo age data

RAATE

2713 ± 3 Ma

KUOPIONo age data

A Ranuacomplex

Kalpiocomplex

Kuopiocomplex

Rauta-vaara

complex

Manamansalocomplex

Fig. 1. A) Geological map of the Karelia Province and known sanukitoid intrusions with ages. Map after Lobach-Zhuchenko et al. (2005) and Heilimo et al. (2010) and references therein. Abbreviations for Karelia subprovinces: 1) Western Karelia sub-province, 2) Central Karelia subprovince, 3) Vodlozero subprovince. Sanukitoid intrusion ages are after Bibikova et al. (2005), Heilimo et al. (2011), Mikkola et al. (2011), and Huhma et al. (2012). B) Mean weighted averages of interpreted single grain U–Pb ages showing the eastern and western sanukitoid zones of the Karelia Province.

217

Geological Su

rvey of Fin

land, Special P

aper 54

Overview

of Neoarchaean sanu

kitoid series in the K

arelia Province, eastern F

inland

Table 1. Summary of sanukitoid intrusions in Finland including the size, name, mineralogy, terrain, U–Pb age and method, εNd and TDM (De Paolo 1981).

Intrusion / age sample Size Rock name Major minerals Complex Age (Ma) U–Pb method εNd TDM (Ga) ReferencesKuittila A285 ~ 2 km * 7 km Tonalite Plg, Qz, Bt Ilomantsi 2741±9 SIMS 0.5–2.3 2.80–2.73 1, 2, 3

Ilomantsinjärvi A50 ~ 7 km * 42 km Granodiorite Plg, Qz, Kfs, Bt±Hbl Ilomantsi 2728±7 SIMS n.d. n.d. 3,4

Sysmänjärvi A1078 ~ 7 km * 23 km Tonalite/quatz diorite Plg, Qz, Hbl, Bt Ilomantsi 2744±5 SIMS n.d. n.d. 3,4

Koitere A1339 ~ 40 km * 50 km Granodiorite Plg, Kfs, Qz, Bt ±Hbl ±Cpx ±Opx

Lentua 2722±6 SIMS 0.6–1.2 2.78–2.86 3, 5

Nilsiä A1918 ~ 8 km * 22 km Granodiorite Plg, Kfs, Qz, Bt Rautavaara 2724±28 SIMS 0.9–1.4 2.78–2.80 3, 5, 6

Kuopio domes no detail information Granodiorite Plg, Kfs, Qz, Bt ±Hbl Kuopio n.a. n.a. n.d. n.d. 7

Siikalahti A1719 ~ 1.5 km * 1.5 km Granodiorite Plg, Kfs, Bt, Qz Lentua 2683±9 SIMS 0.1 2.83 8, 9

Loso A1926 ~ 3 km *4 km Diorite Plg, Qz, Bt, Hbl Lentua 2715±2 TIMS 0.1–0.5 2.83–2.85 9, 10

Surmansuo >5 km * 15 km a Granodiorite Plg, Kfs, Qz, Bt±Hbl Lentua n.a. n.a. n.a. n.a. 11

Arola A572 ~ 2 km * 25 km Granodiorite Plg, Kfs, Bt, Qz Lentua 2723±6 SIMS 0.5–1.2 2.81–2.86 3, 8, 12, 13

Kaartojärvet A1146 ~ 1 km * 3 km Gabbro Hbl, Bt Lentua 2715±3 SIMS 0.1 2.88 3, 8, 14,

Raate A1910 few stocks, ~ 5 km * 5 km a

Granodiorite Plg, Kfs, Qz, Bt ±Hbl Lentua 2713±3 TIMS -1.2 2.92 15, 16

Kaapinsalmi A28 10 km * 25 km Tonalite Plg, Qz, Hbl, Bt Lentua 2722±4 SIMS -1.4– -2.2 2.95–3.08 3, 17, 18, 19

Kuusamo A1919 < 30 km * 45 km a Granodiorite Plg, Kfs, Qz, Bt, Hbl Lentua 2718±5 SIMS 0.6–1.2 2.79–2.84 3, 18, 19

References: 1) O’Brien et al. (1993), 2) Vaasjoki et al. (1993), 3) Heilimo et al. (2011), 4) Lavikainen (1986), 5) Halla (2002), 6) Paavola (1980), 7) Lukkarinen (2008),

8) Käpyaho (2006), 9) Käpyaho et al. (2006), 10) Huhma et al. (2011), 11) Mikkola & Paavola (unpublished) data; 12) Querre (1985); 13) Hyppönen (1983),

14) Luukkonen (1988), 15) Mikkola, (2008), 16) Mikkola et al. (2011), 17) Heilimo et al. (2007), 18) Heilimo et al. (2010), 19) Heilimo et al. (2013)

a) Continue to the Russian side

n.a.= not analysed

218


Intrusions of the eastern zone

The southernmost sanukitoid intrusions in Fin-land are found within the Hattu supracrustal belt in the Ilomantsi complex. The 2741 ± 9 Ma Kuittila sanukitoid tonalite was first described by Nurmi and Sorjonen-Ward (1993) in connection with gold exploration. Later, it was classified as a part of the sanukitoid series (Lobach-Zhuchenko

et al. 2005). The spatial association of the Kuitti-la sanukitoid with potential gold mineralizations of the Hattu schist belt is notable. The nearby Ilomantsinjärvi (2728 ± 7 Ma) and Sysmänjärvi (2744 ± 5 Ma) intrusions also show sanukitoid geochemical affinities (Heilimo et al. 2011).

Intrusions of the western zone

The Nilsiä sanukitoid (2724 ± 28 Ma) within the Rautavaara complex is a K-feldspar porphyritic granodiorite, which was intensively deformed during the Svecofennian orogeny (Halla 2002, 2005, Halla & Heilimo 2009). Based on bedrock mapping (Äikäs 2000, Äikäs, personal commu-nication 2010) and field revision, the same rock continues south from Nilsiä towards Kuopio, al-though there are no available geochemical data. Several of the Kuopio complex domes contain porphyritic granodiorites that, based on chemis-try, belong to the sanukitoid series (analyses in Rasilainen et al. 2007). The exact proportion of the sanukitoids and other rock types in the Kuo-pio complex cannot be estimated, because the sanukitoid-type granodiorites are not separated from the TTG granitoids in the bedrock map of the area (Lukkarinen 2008).

There are several sanukitoid intrusions in the Lentua complex. The southern part of the Len-tua complex includes abundant porphyritic sa-nukitoid granodiorites known as the Koitere sa-nukitoid. This 2722 ± 6 Ma old sanukitoid is an exceptionally large intrusion (~ 40 km * 50 km), showing locally high-grade mineral assemblages in the northernmost part (Halla 2002, 2005, Hei-limo et al. 2010). In addition to previously known ones, observations and geochemical results of an ongoing mapping project indicate that the por-phyritic Surmansuo granodiorite in the eastern part of the Kuhmo area belongs to the sanuki-toid series; no age data are yet available for it. The ~2.68 Ga K-feldspar porphyritic Siikalahti gran-odiorite is in several aspects an atypical member

of the series. Firstly, it is distinctly younger than the main population, although the interpretation of the single-grain age data is not straightforward (Käpyaho et al. 2006). Additionally, the measured δ18O values from Siikalahti are distinctly higher (Mikkola et al. 2011: average 8.5 ± 0.5‰) than those reported for the other intrusions of the western sanukitoid zone (Heilimo et al. 2013). The 2715 ± 2 Ma even-grained Loso diorite, located in the vicinity of the Kainuu schist belt, provides a minimum age estimate for the deposition of the Nurmes-type paragneisses in the area (Huhma et al. 2012). The 2723 ± 6 Ma K-feldspar porphyritic Arola granodiorite intrudes the western flank of the Kuhmo greenstone belt and also cross-cuts it as a dyke (Hyppönen 1983, Querre 1985, Heilimo et al. 2011). Further north is the 2715 ± 3 Ma Kaartojärvet gabbro Luukkonen 1988, Heilimo et al. 2011). In the terms of mafic composition and sanukitoid-like characteristics, the little-re-searched Kaartojärvet gabbro is unique in Fin-land (Käpyaho et al. 2006). Near Suomussalmi, the K-feldspar porphyritic Raate-type granodior-ites displaying sanukitoid geochemistry form at least five small intrusions (Mikkola 2008, Mikkola et al. 2011), one of which is dated at 2713 ± 3 Ma. Further north in Suomussalmi, the Kaapinsalmi sanukitoid (2722 ± 4 Ma) has intruded in the western margin of the Suomussalmi greenstone belt (Heilimo et al. 2007, Heilimo et al. 2011). The northernmost sanukitoid in the Kianta complex is found in Kuusamo and dated at 2718 ± 5 Ma (Heilimo et al. 2010, 2011).

Geochemistry

All described sanukitoids have elevated contents of compatible elements Mg, Ni, Cr and incom-patible elements K, Ba, Sr and LREE compared with the TTG suite. Mg# at a given SiO2 content and HREE ratios are also higher than in the TTG suite (Figs. 2 & 3, and Table 2). These features are

typical for the sanukitoid intrusions in the Kare-lia Province, which do not generally fit into the strict classification of Stern et al. (1989) (SiO2 = 55–60%, MgO > 6%, Mg# > 60, Sr > 600–1800 ppm, Ba > 600–1800 ppm, Cr > 100 ppm, Ni > 100 ppm). Therefore, we use wider constrains

219


Fig. 2. Harker diagrams for whole-rock compositions of sanukitoids (Heilimo et al. 2010 and references therein), and low- and high-HREE TTGs (Halla et al. 2009) in Finland.

220


for sanukitoid series in Finland: SiO2 = 55–70 wt%, K2O = 1.5–5.0 wt%, Na2O/K2O = 0.5–3, MgO = 1.5–9 wt%, Mg# = 45–65, Ba+Sr > 1400 ppm, and (Gd/Er)N = 2–6 (Heilimo et al. 2010). There is some compositional variation between the intrusions (Fig. 2). The SiO2 content varies from 55 wt% to 70 wt%, excluding the Kaarto-järvet gabbro. The Loso and Kaapinsalmi intru-sions show higher average contents of Mg, Ni, Cr and higher Mg# compared with those of the Nilsiä and Koitere granodiorites. The Nilsiä, Koitere and Siikalahti intrusions are more en-

riched in K2O and Ba, while the Loso and Kaa-pinsalmi intrusions display lower contents of the same elements. The Sr concentration of the Kaapinsalmi sanukitoid is low, and close to the average Sr content of the TTGs in Finland. This whole-rock geochemical variation within the sa-nukitoid series might be derived from moderate compositional disparity between the sources of sanukitoid intrusions (Heilimo et al. 2010). In general, the composition of sanukitoid series in eastern Finland is similar to the western sanuki-toid zone in Russia.

Pb isotopes

Pb isotopic studies of the Koitere and Nilsiä K-feldspar and whole-rock samples (Halla 2002, 2005) indicated that the source of sanukitoids may carry a significant crustal Pb isotope com-ponent. This was evidenced by the Pb isotope compositions of K-feldspars from high-grade orthopyroxene-bearing varieties in the northern part of the Koitere massive. These dry rocks did not show any disturbance in their Pb isotopic systematics or petrographic microstructures fol-

lowing the last high-grade event at the time of or soon after formation (at 2.68 Ga at the latest). However, most of the deformed samples showed Paleoproterozoic redistribution of Pb between K-feldspar and the whole-rock. This isotopic ex-change occurred at ~1.9 Ga during deformation at temperatures between 400–500 ºC, as indicated by the microstructures of K-feldspars (Halla & Heilimo 2009).

Fig. 3. Representative chondrite (Taylor & McLennan 1985) normalized REE patterns of the sanukitoids and low- and high-HREE TTGs (Heilimo et al. 2010, Halla et al. 2009) in Finland.

221

Geological Su

rvey of Fin

land, Special P

aper 54

Overview

of Neoarchaean sanu

kitoid series in the K

arelia Province, eastern F

inland

Intrusion Kuittila 1) Ilomantsinjärvi2) Sysmänjävi2) Koitere 3) Nilsiä 3) Kuopio domes 4) Siikalahti 5) Loso 5) Kuusamo 9) Low-HREE TTG10) High-HREE TTG10)

Sample P497/6.8 TTU$-2004-257 TTU$-2004-233 PK-50 PK-121 232-PAH-97 AAK-03-8 280-TMB-88 TTU$-2004-156 average average

Mg# 51.06 48.54 51.70 49.79 48.54 51.42 50.61 59.07 51.36 38.00 39.30

SiO2 (wt.%) 62.60 67.10 58.60 63.47 62.93 63.00 66.50 61.30 63.90 70.80 67.30

TiO2 (wt. %) 0.47 0.44 0.70 0.54 0.63 0.60 0.41 0.58 0.49 0.31 0.59

Al2O3 (wt. %) 17.40 15.90 17.10 16.67 16.25 16.4 15.00 15.60 15.90 15.50 15.00

Fe2O3tot (wt. %) 4.12 3.49 7.35 4.63 4.76 4.68 3.77 5.78 5.03 2.44 4.81

MnO (wt. %) 0.06 0.05 0.13 0.07 0.07 0.08 0.07 0.11 0.09 0.03 0.07MgO (wt.%) 2.17 1.66 3.97 2.32 2.27 2.5 1.95 4.21 2.68 0.82 1.70

CaO (wt. %) 2.17 3.43 4.04 3.83 3.66 4.24 3.30 4.67 4.33 2.88 3.76

Na2O (wt.%) 4.53 5.18 4.98 4.52 5.06 4.62 4.46 4.30 4.40 4.81 4.23

K2O (wt. %) 2.72 2.13 2.45 3.23 3.41 3.11 3.75 2.70 2.55 1.99 1.93

P2O5 (wt. %) 0.15 0.16 0.26 0.27 0.41 0.31 0.22 0.39 0.21 0.10 0.17

Ba (ppm) 1260 1074 913 1730 1570 1310 1550 1180 1027 663 485

Rb (ppm) 120.0 48.5 78.5 75.7 57.6 67 85.8 n.a. 61.1 60.3 68.4

Sr (ppm) 820 826 698 840 650 753 831 600 833 427 314

Pb (ppm) 24.0 b.d.l. b.d.l. 23.2 15.2 31.8 48.0 n.a. b.d.l. 8.6 9.2

Th (ppm) 4.20 3.38 2.37 6.12 11.30 10.8 15.90 n.a. 3.81 7.44 7.60

U (ppm) 2.30 0.65 0.50 0.31 0.60 0.6 2.78 n.a. 0.80 0.64 1.05

Hf (ppm) 3.80 3.07 2.58 4.24 5.31 n.a. 3.98 n.a. 3.84 3.31 4.32

Zr (ppm) 80 120 101 170 242 220 143 170 153 120 171

Nb (ppm) 10.0 4.9 3.5 3.9 7.2 n.a. 5.3 n.a. 5.1 3.4 8.3

Ta (ppm) 0.60 0.33 0.20 0.20 0.21 n .a. 0.51 n.a. b.d.l. 0.19 0.57

Y (ppm) 10.0 10.9 13.5 12.2 14.4 14.2 11.1 n.a. 10.6 4.5 18.6

Sc (ppm) 11.20 6.13 16.10 9.96 7.56 10.8 7.78 n.a. 11.00 3.48 9.37

V (ppm) 82 37 127 70 70 93 53 100 77 27 57

Cr (ppm) 69 20 38 70 50 60 57 160 89 <30 44

Co (ppm) 11.0 9.3 22.6 n.a. n.a. n.a. 9.3 n.a. 13.3 5.0 10.8

Ni (ppm) 26 20 25 20 30 34.6 25 70 28 <20 27

Cu (ppm) 29 b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. b.d.l. n.a. b.d.l. 114 31

Zn (ppm) 71 78 123 90 80 89 79 100 77 49 78

Ga (ppm) n.a. 29.00 25 n.a. n.a. n.a. 24 n.a. n.a. n.a. n.a.

La (ppm) 29.80 26.60 26.80 47.70 66.10 69.00 47.20 n.a. 21.80 25.6 26.4

Ce (ppm) 48.00 61.50 56.30 90.40 135.00 137.00 96.20 n.a. 45.50 48.6 55.5

Table 2. Representative major and trace element analyses of sanukitoid intrusions and low- and high-HREE TTGs in Finland.

godangshaban

Highlight

godangshaban

Highlight

godangshaban

Highlight

godangshaban

Highlight

godangshaban

Highlight

222

Geological Su

rvey of Fin

land, Special P

aper 54

Esa H

eilimo, Jaana H

alla and Perttu M

ikkola

Table 2. cont.

Intrusion Kuittila 1) Ilomantsinjärvi2) Sysmänjävi2) Koitere 3) Nilsiä 3) Kuopio domes 4) Siikalahti 5) Loso 5) Kuusamo 9) Low-HREE TTG10) High-HREE TTG10)

Sample P497/6.8 TTU$-2004-257 TTU$-2004-233 PK-50 PK-121 232-PAH-97 AAK-03-8 280-TMB-88 TTU$-2004-156 average average

Pr (ppm) b.d.l. 7.13 6.77 10.50 15.50 16.10 10.90 n.a. 5.40 4.9 6.3

Nd (ppm) 22.00 27.10 28.0 38.60 54.20 59.70 41.10 n.a. 23.40 17 24.3

Sm (ppm) 3.99 4.75 5.13 6.41 8.46 9.19 6.29 n.a. 3.81 2.4 4.6

Eu (ppm) 0.40 1.03 1.46 1.53 1.64 1.97 1.40 n.a. 0.91 0.6 1.0

Gd (ppm) b.d.l. 3.74 4.53 4.78 6.07 6.93 5.03 n.a. 3.32 2 4.7

Tb (ppm) 0.30 0.47 0.52 0.60 0.74 0.88 0.55 n.a. 0.42 0.2 0.7

Dy (ppm) b.d.l. 2.25 2.68 2.33 2.64 3.40 2.12 n.a. 2.00 1 3.7

Ho (ppm) n.a. 0.39 0.00 0.40 0.47 0.59 0.38 n.a. 0.35 0.2 0.7

Er (ppm) b.d.l. 1.05 0.46 1.08 1.14 1.61 0.88 n.a. 1.06 0.4 2.1

Tm (ppm) n.a. 0.15 1.26 0.13 0.15 0.22 0.12 n.a. 0.13 <0.1 0.3

Yb (ppm) 0.99 0.89 0.18 0.92 1.01 1.32 0.86 n.a. 0.94 0.4 2

Lu (ppm) 0.15 0.17 1.20 0.13 0.14 0.18 0.12 n.a. 0.14 <0.1 0.3

Cl (ppm) n.a. n.a. n.a. 110 140 138 n.a. n.a. 230 n.a. n.a.

Li (ppm) 42.00 n.a. n.a. n.a. n.a. n.a n.a. n.a. n.a. n.a. n.a.

Cs (ppm) 7.30 n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a. n.a.

References: 1) O’Brien et al. 1993. 2) Heilimo et al. 2011. 3) Halla 2002. 2005. 4) Lukkarinen 2008. 5) Käpyaho 2007. 6) this study. 7) Mikkola 2008. 8) Heilimo et al. 2007. 9) Heilimo et al. 2010. 10) Halla et al. 2009b.d.l. = below detection limitn.a. = not analysed

223


SANUKITOIDS AND THE EVOLUTION OF THE KARELIA PROVINCE

There is general agreement that sanukitoid mag-mas were directly derived by partial melting of variably enriched subcontinental lithospheric mantle (SCLM) underlying the Karelia Province (Stern & Hanson et al. 1991, Martin et al. 2009, Heilimo et al. 2010). According to the current view, the SCLM below the Karelia Province was formed by accretion of metasomatically over-printed mantle wedges by successive collisions between 2.9–2.7 Ga (Lobach-Zhuchenko et al. 2005). As evidenced by Pb isotopes, components of continent-derived sediments were recycled into the mantle source, which may also account for the crustal characteristics of sanukitoids. The heterogeneity of the mantle source is thought to be a consequence of diverse metasomatic process-es and agents (slab melts and/or fluids) acting on the mantle wedge during subduction. According to experimental studies (Wyllie & Sekine 1982), interaction of hydrous fluids/melts with a perido-titic mantle can produce a phlogopite pyroxenite, partial melting of which is capable of producing

high-K melts. The partial melting of these sourc-es was a consequence of a late- to post-tectonic thermal event at the stabilization stage of the province, possibly a slab break off (e.g. Halla et al. 2009). The compositional variation of the sa-nukitoid intrusions partly reflects the geochemi-cal and isotopic variations of the heterogeneous source. For example, Nd-isotope data (Heilimo et al. 2013, Table 1) indicate a greater/older crustal component for the Kaapinsalmi sanukitoid than for the rest of the group.

Some of the compositional variation within the group can be attributed to fractional crystalliza-tion processes (Heilimo et al. 2010) and to differ-ences in the depth and temperature of melting, as well as the degree of partial melting. The low K and Ba contents and strong crustal isotopic sig-nature of the Kaapinsalmi sanukitoid could be explained, for example, by a deep (high-T) mantle source with low phlogopite contents, but a high degree of isotopic contamination with crustal material.

SANUKITOIDS AND ARCHAEAN SUPERCONTINENTS

At the time of the sanukitoid formation, the Ka-relia Province was probably a part of a larger con-tinent. Bleeker (2003) and Käpyaho (2007) have discussed the possibility that the Karelia and the Superior Provinces together formed a part of the Neoarchaean supercontinent called Superia. The temporally limited occurrence (2.74 Ga in eastern Karelia, 2.72 Ga in western Karelia, 2.68 Ga in

the Superior province) and the linear orientation of sanukitoid belts might be useful in correlating Archaean domains and rotating them in the cor-rect position. For the reasons above, combining sanukitoid data with palaeomagnetic or other supporting data can also be potentially valuable in the reconstruction of the first supercontinents.

CONCLUSIONS

Neoarchaean late- to post-tectonic granitoids of the sanukitoid type are found in the Karelia Prov-ince on both sides of the border between Finland and Russia. These variable-sized, but generally small intrusions show a high content of incompat-ible elements (MgO, Ni and Cr) and high Mg#, which has been related to the mantle origin, and a strong enrichment in LIL elements (especially K2O, Ba and Sr) pointing to effective mantle en-richment processes. The Karelian sanukitoid se-ries can be defined as follows: SiO2 = 55–70 wt%, Na2O/K2O = 0.5–3, MgO = 1.5–9 wt%, Mg# = 45–65, K2O = 1.5–5.0 wt%, Ba+Sr >1400 ppm and (Gd/Er)N = 2–6. Sanukitoids can be distin-

guished from the TTG suite especially by their high Ba–Sr signature, low Na2O/K2O ratio and uniform HREE patterns.

A compiled geochronological data set from the Karelia Province confirms the occurrence of two temporally different sanukitoid zones: the ~2.74 Ga eastern zone in the Central Karelia subprov-ince and the 2.72 Ga western zone in the Western Karelia subprovince, with an apparent age dif-ference of ca. 20 Ma. Sanukitoids post-date the long-lived TTG and greenstone belt magmatism (~2.95–2.75 Ga) and precede, or partly overlap with, the GGMs and quartz diorites (~2.70–2.68 Ga) in Western Karelia subprovince. The Ilo-

224


mantsi complex can be interpreted as a part of the Central Karelia subprovince on the basis of the sanukitoid ages (the ~2740 Ma eastern sanukitoid zone) and temporally simultaneous occurrence of volcanism and plutonism in the area.

The probable source of the sanukitoid series is an enriched subcontinental lithospheric mantle. The accumulation of K2O, Ba and Sr in the man-tle source may have occurred as a consequence

of complex metasomatic processes and agents, such as subduction-related fluids or melts. Slab breakoff at the end stage of subduction may have caused mantle upwelling, further metasomatism and partial melting in the sanukitoid source man-tle.

The occurrence of sanukitoids could be related to convergent accretion of different crustal frag-ments in the Meso- and Neoarchaean eons.

REFERENCES

Äikäs, O. 2000. Juankoski. Geological Map of Finland 1:100 000, Pre-Quaternary Rocks, Sheet 3333. Geological Sur-vey of Finland.

Bibikova, E. V., Petrova, A. & Claesson, S. 2005. The tem-poral evolution of sanukitoids in the Karelian Province, Baltic Shield: an ion microprobe U−Th−Pb isotopic study of zircons. Lithos 79, 129–145.

DePaolo, D. J. 1981. Neodymium isotopes in the Colorado Front Range and crust-mantle evolution in the Protero-zoic. Nature 291, 684–687.

Halla, J. 2002. Origin and Paleoproterozoic reactivation of Neoarchean high-K granitoid rocks in eastern Finland. Annales Academiae Sciantiarum Fennicae, Helsinki: Ge-ologica-Geographica 163. Academica Scientiarum Fen-nica103. (Ph.D. Thesis)

Halla, J. 2005. Late Archean high-Mg granitoids (sanuki-toids) in the Southern Karelian domain, Eastern Fin-land. Lithos 79, 161–178.

Halla, J. & Heilimo, E. 2009. Deformation-induced Pb iso-tope exchange between K-feldspar and whole rock in Neo-archean granitoids: Implications for assessing Pro-terozoic imprints. Chemical Geology 265, 303–312.

Halla, J., van Hunen, J., Heilimo, E. & Hölttä, P. 2009. Geo-chemical and numerical constraints on Neoarchean plate tectonics. Precambrian Research 174, 155–162.

Heilimo, E., Mikkola, P. & Halla, J. 2007. Age and petrol-ogy of the Kaapinsalmi sanukitoid intrusion in Suomus-salmi, eastern Finland. Bulletin of the Geological Society of Finland 79, 117–125.

Heilimo, E., Halla., J. & Hölttä. P. 2010. Discrimination and origin of the sanukitoid series: Geochemical constraints from the Neoarchean western Karelian Province (Fin-land). Lithos 115, 27–39.

Heilimo, E., Halla, J. & Huhma, H. 2011. Single-grain zircon U-Pb age constraints of the western and eastern sanuki-toid zones in the Finnish part of the Karelian Province. Lithos 121, 87–99.

Heilimo, E., Halla, J., Andersen, T. & Huhma, H. 2013. Neoarchean crustal recycling and mantle metasoma-tism: Hf–Nd–Pb–O isotope evidence from sanukitoids of the Fennoscandian shield. Precambrian Research (in press). Available at: http://dx.doi.org/10.1016/j.precam-res.2012.01.015

Huhma, H., Mänttäri, I., Peltonen, P., Kontinen, A., Halkoaho,T., Hanski., E., Hokkanen. T., Hölttä, P., Juop-peri, H., Konnunaho, J., Lahaye, Y., Luukkonen., E., Pie-tikäinen, K., Pulkkinen, A., Sorjonen-Ward, P. , Vaasjoki, M. & Winehouse, M. 2012. The age of Archean green-stone belts in Finland. In: Hölttä, P. (ed.) The Archaean

of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Hyppönen, V. 1983. Ontojoen, Hiisijärven ja Kuhmon kartta-alueiden kallioperä. Summary: Pre-Quaternary Rocks of the Ontojoki, Hiisijärvi and Kuhmo Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Maps odf Pre-Quaternary Rocks, Sheets 4411, 4412, 4413. Geological Survey of Finland. 60 p. (in Finnish with English summary)

Käpyaho, A. 2006. Whole-rock geochemistry of some to-nalite and high Mg/Fe gabbro, diorite, and granodiorite plutons (sanukitoid suite) in the Kuhmo district, Eastern Finland. Bulletin of The Geological Society of Finland 78, 121–141.

Käpyaho, A. 2007. Archaean crustal evolution in eastern Fin-land: New geochronological and geochemical constraints from the Kuhmo terrain and the Nurmes belt. Espoo: Geological survey of Finland 20. (Ph.D. Thesis)

Käpyaho, A. Mänttäri, I. & Huhma, H. 2006. Growth of Archaean crust in the Kuhmo district, Eastern Finland: U−Pb and Sm−Nd isotope constraints on plutonic rocks. Precambrian Research 146, 95–119.

King, E. M., Valley, J. W., Davis, D. W. & Edwards, G. R. 1998. Oxygen isotope ratios of Archean plutonic zircons from granite–greenstone belts of the Superior Province: indicator of magmatic source. Precambrian Research 92, 1998, 365–387.

Kovalenko, A., Clemens, J. D. & Savatenkov, V. 2005. Petroge-netic constraints for the genesis of Archaean sanukitoid suites: geochemistry and isotopic evidence from Karelia, Baltic Shield. Lithos 79, 147–160.

Lauri, L. S., Andersen, T., Hölttä., P., Huhma, H. & Graham, S.T. 2011. Evolution of the Archaean Karelian Province in the Fennoscandian Shield in the light of U–Pb zircon ages and Sm–Nd and Lu–Hf isotope systematic. Journal of the Geological Society London 168, 201–218.

Lavikainen, S. 1986. Oskajärven kartta-alueen kallioperä. Summary: Pre-Quaternary Rocks of the Oskajärvi Map-Sheet area. Geological Map of Finland 1:100 000, Ex-planation to the Map of Rocks, Sheet 4243. Espoo: Geo-logical Survey of Finland. 42 p. (in Finnish with English summary)

Lobach-Zhuchenko, S. B., Rollinson, H. R., Chekulaev, V. P., Arestova, N. A., Kovalenko, A. V., Ivanikov, V. V., Guseva, N. S., Sergeev, S. A., Matukov, D. I. & Jarvis, K. E. 2005. The Archaean sanukitoid series of the Baltic Shield: geo-logical setting, geochemical characteristics and implica-tion for their origin. Lithos 79, 107–128.

Lukkarinen, H. 2008. Siilinjärven ja Kuopion kartta-aluei-

225


den kallioperä. Summary: Pre-Quaternary Rocks of the Siilinjärvi and Kuopio Map-Sheet areas. Geological Map of Finland 1:100 000, Explanation to the Map of Rocks, Sheets 3331 and 3242. Geological Survey of Finland. 228 p. + 2 app. maps. (Electronic publication, in Finnish with English summary)

Luukkonen, E. J. 1988. Moisiovaaran ja Ala-Vuokin kartta-alueiden kallioperä. Summary: Pre-Quaternary rocks of the Moisiovaara and Ala-Vuokki map-sheet areas. Geo-logical Map of Finland 1:100 000, Explanation to the Map of Rocks, Sheets 4421, 4423+4441. Geological Sur-vey of Finland. 90 p. (in Finnish with English summary)

Martin, H., Smithies, R. H., Rapp, R., Moyen, J.-F. & Cham-pion, D. 2005. An overview of adakite, tonalite-trond-hjemite-granodiorite (TTG), and sanukitoid; relation-ships and some implications for crustal evolution. Lithos 79, 1–24.

Martin, H., Moyen, J-F. & Rapp, R. 2009. The sanukitoid series: magmatism at the Archaean–Proterozoic transi-tion. Earth and Environmental Science Transactions of the Royal Society of Edinburgh 100, 1–19.

Mikkola, P. 2008. Koillis-Kainuun kallioperä. Summary: Pre-Quaternary rocks of Northeast Kainuu. Geological Survey of Finland, Report of Investigation 175. 53 p. + 5 app. (Electronic publication, in Finnish with English summary)

Mikkola, P., Huhma, H., Heilimo, E. & Whitehouse, M. 2011. Archean crustal evolution of the Suomussalmi district as part of the Kianta Complex, Karelia; constraints from geochemistry and isotopes of granitoids. Lithos 125, 287–307.

Nurmi, P. A. & Sorjonen-Ward, P. (ed.) 1993. Geological de-velopment, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17. 386 p.

O’Brien, H. E., Huhma, H. & Sorjonen-Ward, P. 1993. Petro-genesis of the late Arhean Hattu Schist belt, Ilomantsi, eastern Finland: Geochemistry and Sr, Nd isotopic com-position. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) Geological development, gold mineralization and explo-ration methods in the late Archean Hattu schist belt, Ilo-mantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 103–132.

Paavola, J. 1980. Nilsiä. Geological Map of Finland 1:100 000, Pre-Quaternary Rocks, Sheet 3334. Geological Survey of Finland.

Querre, G. 1985. Palingenèse la croûte continentale à’Archéen : les granitoides tardifs (2.5−2.4 Ga) de Fin-lande orientale. Pétrologie et géochemie. Memories et documents du Centre Armorician d’Etude Structurales des Socles; 2. Université de Rennes. 193 p. (in French)

Rasilainen, K., Lahtinen, R. & Bornhorst, T. J. 2007. The Rock Geochemical Database of Finland Manual. Geo-logical Survey of Finland. Geological Survey of Finland, Report of Investigation 164. 38 p. (Electronic publica-tion)

Shirey, S. B. & Hanson, G. N. 1984. Mantle-derived Ar-chaean monzodiorites and trachyandesites. Nature 310, 222−224.

Smithies, R. H. & Champion, D. C. 2000. The Archaean high-Mg diorite suite: links to tonalite−trondhjemite−grano-diorite magmatism and implications for early Archaean crustal growth. Journal of Petrology 41, 1653–1671.

Stern, R. A., Hanson, G. N. & Shirey, S. B. 1989. Petrogenesis of mantle-derived, LILE-enriched Archean monzodior-ites and trachyandesites (sanukitoids) in southwestern Superior Province. Canadian Journal of Earth Sciences 26, 1688–1712.

Stern, R. A. & Hanson, G. N. 1991. Archaean high-Mg gran-odiorite: a derivative of light rare earth element-enriched monzodiorite of mantle origin. Journal of Petrology 32, 201–238.

Tatsumi, Y. & Ishizaka, K.1982. Origin of high-magnesium andesite in the Setouchhi volcanic belt, southwest Japan, 1. Petrographical and chemical characteristics. Earth and Planetary Science Letters 60, 293–304.

Taylor, S. R. & McLennan, S. M. 1985. The continental crust: its composition and evolution. Oxford: Blackwell. 312 p.

Vaasjoki, M., Sorjonen-Ward, P. & Lavikainen., S. 1993. U-Pb age determinations and sulfide Pb-Pb characteris-tics from the late Archean Hattu Schist belt, Ilomantsi, eastern Finland. In: Nurmi, P. A. & Sorjonen-Ward, P. (eds.) Geological development, gold mineralization and exploration methods in the late Archean Hattu schist belt, Ilomantsi, eastern Finland. Geological Survey of Finland, Special Paper 17, 103–132.

Wyllie, P. J. & Sekine, T. 1982. The formation of mantle phlogopite in subduction zone hybridization. Contribu-tions to Mineralogy and Petrology 79, 375−380.

226


GEOCHEMICAL AND PETROPHYSICAL CHARACTERISTICS OF PLUTONIC ROCKS

FROM THE ARCHAEAN KARELIA PROVINCE IN FINLAND

byTapio Ruotoistenmäki

Ruotoistenmäki, T. 2012. Geochemical and petrophysical characteristics of plutonic rocks from the Archaean Karelia Province in Finland. Geological Survey of Finland, Special Paper 54, 226−243, 6 figures and 5 tables.

This study considers the geochemical and petrophysical characteristics of plutonic rocks from four terrains in the Archaean Karelia Province in central Finland: Pudas-järvi, Iisalmi, Kuhmo and Ilomantsi terrains. The samples investigated are mainly dior-itic to granodioritic in composition, although some mafic intrusions have been sampled from each of the areas with the exception of the Ilomantsi terrain. The densities and magnetic susceptibilities of the samples are generally low; this reflects their relatively felsic compositions and general paucity of magnetite.

The majority of the samples show enrichment in LREE and compatible elements relative to HREE when normalized against averages calculated from nearly 3000 plu-tonic rock samples representing the Proterozoic and Archaean bedrock in Finland. These features are especially striking in plagioclase-rich adakitic rocks (TTGs, sanuki-toids), whose chemical spectra are consistent with fractionation in the lower crust or upper mantle, at depths greater than 40–60 km. Using normalized Nd/Zr, La/Ce and Er/Lu ratios, the restitic minerals of adakitic melts can be estimated to mainly consist of clinopyroxenes, amphiboles and garnet, with lesser amounts of orthopyroxene. An im-portant observation is the similarity of the adakitic samples from each of the terrains, suggesting similarities in their respective evolutionary history.

The evolution of adakitic rocks can be explained with respect to subduction-related magmatism and fractionation at great depth. However, when considering the wide dis-tribution and large volume of Archaean adakitic rocks compared to those that are un-equivocally interpreted as resulting from Archaean subduction processes, an alternative explanation is favoured here, involving crustal thickening by tectonic stacking, com-bined with underplating by anomalously hot upper mantle material. The underplating processes generated plagioclase-rich adakitic melts, leaving restites rich in compatible elements and HREE, which are locally evident as high velocity layers in the lower crust (assuming that they have not been removed by delamination).

Adakitic plutonic rocks appear to represent a continuous compositional series, from TTGs with variable Na2O/K2O and low Ba+Sr to sanukitoids with low Na2O/K2O and increasing Ba+Sr. These compositional variations can be explained by varying frac-tionation depths and degrees of subduction-related mantle metasomatism.

Keywords (GeoRef Thesaurus, AGI): crust, plutonic rocks, adakites, sanukitoids, geo-chemistry, petrophysics, tonalite-trondhjemite-granodiorite magmas, Archean, Finland

Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland


mailto:[email protected]

Geological Survey of Finland, Special Paper 54Geochemical and petrophysical characteristics of plutonic rocks from the Archaean Karelia Province in Finland

227

INTRODUCTION

When studying the Tertiary lavas on Adak Island in the Aleutian arc, Kay (1978) concluded that they represented the products of slab melting. Similar magmatic rocks, subsequently known as adakites, have since been identified elsewhere and studied widely. For example Drummond and De-fant (1990) and Defant and Drummond (1990) interpreted adakites as the products of partial melting of a young (< 20–30 Ma), gently dip-ping subducted slab. Defant and Drummond (1990) and Thorkelson and Breitsprecher (2005) summarized adakites as high-silica (SiO2 > 56%), high-alumina (Al2O3 > 15%), plagioclase- and amphibole-bearing lavas with Na2O > 3.5%, high Sr (> 400 ppm), low Y (< 18 ppm), high Sr/Y (> 40), low Yb (< 1.9) and high La/Yb (> 20). These chemical criteria were applied in selecting adakitic plutonites from the database used in the present study.

Martin et al. (2005) considered the characteris-tics of adakites, Archaean TTGs (tonalite–trond-hjemite–granodiorites) and sanukitoids, all of which they linked to slab melting and interaction with peridotitic mantle. Late Archaean TTGs and high-silica adakites represent slab melts that have interacted with peridotite to a varying extent, whereas sanukitoids and low-silica adakites cor-respond to the melting of peridotite previously metasomatised by slab melt.

In his review of adakites, Castillo (2006) noted that numerous examples of adakitic rocks are not directly related to slab-melting processes in sub-duction environments. Moreover, the volume of adakite produced by slab melting is probably less than the amount that can be produced by other processes. In particular, slab melting is unlikely to be the most effective mechanism to produce the large observed volumes of Archaean TTGs.

Moyen (2009) defined adakites in a somewhat broader sense, placing emphasis on the high Sr/Y and La/Yb ratios as defined above. He concluded that such a signature can be generated by various processes, including: 1) melting of a high Sr/Y and La/Yb source, 2) deep melting, with abundant re-sidual garnet, 3) fractional crystallization or AFC, or 4) interactions of felsic melts with the mantle, causing selective enrichment in LREE and Sr over HREE. He concluded that the classical model of “slab melting” provides the best explanation for the genesis of high-silica adakites, while the low-silica adakites are better explained as the products of an adakite-metasomatised mantle in the pres-ence of garnet. Moreover, he noted that so-called “continental”, high-potassium adakites represent

diverse petrogenetic processes and that most of them are different from both low- and high-silica adakites. The Archaean adakites show a bimodal compositional range, with some very high Sr/Y examples reflecting deep melting (>2.0 GPa) of a basaltic source, while lower Sr/Y rocks are formed by shallower (1.0 GPa) melting of similar sources. The Archaean TTGs are relatively heterogeneous, which is inferred to indicate a diversity of both sources and processes in their genesis.

Scaillet and Prouteau (2001 and references therein) emphasized that Archaean TTGs have been less contaminated by mantle interaction than typical Cenozoic adakites. They proposed relatively high T, low P, and possibly higher H2O melts from gently dipping slabs as a source of Archaean TTG-type magmatism having adakitic characteristics. Smithies (2000) considered that the relatively low magnesium content of Archae-an TTGs might be due to gently dipping under-thrusting of oceanic plateaus, thus obviating a significant influence from the underlying perido-titic mantle.

Condie (2005) also agreed that adakites are probably slab melts, while concluding that TTGs may also be produced by partial melting of hy-drous mafic rocks in the lower crust in arc sys-tems or, in the case of Archaean tectonic settings, possibly in the root zones of oceanic plateaus. He correlated depletion in heavy REE and low Nb/Ta ratios in high-Al TTGs with the retention of garnet and low-Mg amphibole in restite in the source region, whereas moderate to high Sr val-ues allow for little, if any, plagioclase in the restite. Thus, the melting is inferred to have occurred in the hornblende-eclogite stability field at depths of about 40–80 km and temperatures between 700 and 800 ºC.

Svetov et al. (2004) studied 3.0 Ga adakitic rocks found in basalt–andesite–dacite–rhyolite (BADR) island-arc association of the Vedlozero–Segozero greenstone belt in the Fennoscandian Shield, concluding that these rocks indicate the existence of convergent (interplate) ocean–conti-nent transition zones and subduction-related tec-tonics already in the Mesoarchaean.

Kröner et al. (2011) investigated the still more ancient 3.65 to 3.53 Ga tonalitic gneisses of the Gneiss Complex in Swaziland and a 3.53 Ga felsic metavolcanic sample from the Theespruit Forma-tion, the oldest unit of the Barberton Greenstone Belt, South Africa. They challenge the popular view that early Archaean TTGs and greenstones are principally of juvenile origin, formed in primi-

228

Geological Survey of Finland, Special Paper 54Tapio Ruotoistenmäki

tive arc or oceanic environments. Instead, they suggest extensive recycling of even earlier grani-toid crust and mixing with juvenile material to produce successive generations of TTGs and as-sociated felsic volcanic rocks.

Halla et al. (2009) considered granitoid mag-matism in relation to Neoarchaean plate tecton-ics in Karelia and Kola cratons. They divided granitoids into three groups: 1–2) high- and low HREE (heavy rare earth elements) TTGs related to low- and high-angle (-pressure) subduction and 3) high Ba-Sr sanukitoids related to melting of an enriched mantle source, probably as a result of a slab breakoff following a continental collision or attempted subduction of a thick oceanic plateau or TTG protocontinent.

From the above considerations it becomes clear that the genetic link between slab melting and adakites and adakitic rocks (as well as TTGs and sanukitoids) is ambiguous. Castillo (2006) noted that adakite studies have generated confu-sion because the definition of adakite combines compositional criteria with genetic interpretation. Moyen (2011) emphasized that the term TTG is also imprecisely defined in much of the litera-ture. Therefore, in this study the terms ‘adakitic’ or ‘adakitoid’ are used to refer to rocks having

adakitic (or TTG or sanukitic) characteristics, as defined above, and apparently lower crust–upper mantle fractionation depths.

In the following, I consider the characteristics of 642 plutonic rock samples from four terrains of the Archaean Karelia Province in central Finland. The data used in this work are selected from the sub-group ‘plutonic’ of the rock geochemistry da-tabase described by Rasilainen et al. (2007). The sampling sites are indicated in Figure 1. The char-acteristics of the terrain samples are considered as a whole and their adakitic samples separately.

Plutonic rocks were selected for this study be-cause it is assumed that they correspond more closely to (present) upper crustal compositions compared to supracrustal rocks that may have been more susceptible to alteration processes. It must be emphasized, however, that the sampling strategy was designed such that the number of samples per given area depends on the lithological variation seen on geological maps (Rasilainen et al. 2007). Thus, sampling density is not uniform, as is evident from Figure 1, so that calculated sam-ple averages are only indicative of general trends and not strictly related to weighted areal averages of Finnish bedrock.

SAMPLES AND STANDARDS USED IN THIS STUDY

The Archaean terrains considered or referred to in this study are (Fig. 1): the Iisalmi terrain (IC = Iisalmi and Rautavaara complexes in Hölttä et al. (2012a), the East Finland - Kuhmo terrain (EFK = northern part of the Lentua complex), the East Finland - Ilomantsi terrain (EFI = Ilo-mantsi complex and the SW part of the Lentua complex), the Pudasjärvi terrain (PDj = Ranua and Siurua complexes) and the Kainuu belt (Kb), which is a Palaeoproterozoic supracrus-tal belt separating EFK, IC and Pdj. The sub-division and boundaries of terrains are in part adapted from Nironen et al. (2002) and modi-fied in detail using airborne geophysical data and maps (e.g. Hautaniemi et al. 2005). A geological overview of these terrains is provided by Hölttä et al. (2012a).

The elements analysed, together with stand-ards, units and analytical techniques are pre-sented in Table 1. The samples have been nor-malized against both the C1 chondrite (Kerrich and Wyman, 1996) and the geometric mean of all Finnish plutonic rocks samples (AFP), includ-ing 3059 samples in all from both Archaean and

Proterozoic terrains. The resolution of slopes and peaks in AFP-normalized ‘spectra’ varying around a value of one is much better compared to spectra normalized against chondrite (or MORB), for which ratios vary over many orders of mag-nitude, from about 0.01 to 1000. Accordingly, in this article, the main emphasis of the geochemical comparisons will be placed on the high-resolution AFP-normalized data.

The use of geometric means of parameters is based on the observation that distributions of almost all elements in Finnish plutonic rocks are positively skewed (i.e. there is a long ‘tail’ on the maximum end of the distribution curve). In such cases, the arithmetic average would be too high – a fact that often appears to have been neglected in the literature when presenting statistics from the analysis of a large number of samples. If the distribution curve approaches the normal Gauss-ian ‘bell shape’ (i.e. ‘normal’ starting from zero) or is negatively skewed (with a tail on the mini-mum side, which is observed for SiO2 in Finnish plutonic rocks), both averages converge upon one another.


229

Fig. 1. Schematic map of bedrock of Finland. Modified from the map by Korsman et al. (1997). The dots indicate the sample locations. The abbreviations and names of the Archaean terrains considered or referred to in this study are:IC: Iisalmi terrain (for simplicity, the term ‘terrain’ is used for the sub-areas)EFK: East Finland - Kuhmo terrainEFI: East Finland - Ilomantsi terrainPdj: Pudasjärvi terrainKb: Kainuu belt; Supracrustal terrain separating EFK, IC and Pdj

230


From Table 1 it is apparent that the abundances of some elements can vary significantly depending on the analytical method used and the position of the element in host mineral, e.g. silicates or oxides (see e.g. Sandström 1996 for more details). How-ever, it has also been observed that the trends of element averages for given rock groups from sepa-rate terrains can share many similar characteris-tics, even where internal variations are substantial

(see e.g. Fig. 4 and Table 3). Such variations can therefore be considered reliable and their use ac-ceptable for the purpose of mutual comparison. The reasons behind such variations are not con-sidered here in detail, the main emphasis being instead on the comparison of general trends and relative variations within and between various lithological terrains.

Element Method UnitAFP

gmeanAFP

nbdatC1

Chondrite Element Method UnitAFP

gmeanAFP

nbdatC1

ChondriteAl ICPAES [ppm] 9622.43 3051 8679.70 Nd ICPMS [ppm] 23.37 3052 0.45Al2O3 XRF [%] 14.75 3059 1.64 Ni ICPAES [ppm] 11.10 2627 11000.00Ba ICPAES [ppm] 89.70 2983 2.34 P ICPAES [ppm] 407.52 3053 1221.98Ba XRF [ppm] 577.90 3044 2.34 P2O5 XRF [%] 0.14 2825 0.28Ca ICPAES [ppm] 3165.02 3058 9219.63 Pb XRF [ppm] 30.08 2982 2.47CaO XRF [%] 2.56 3059 1.29 Pr ICPMS [ppm] 6.86 2965 0.09Ce ICPMS [ppm] 54.30 3054 0.60 Rb XRF [ppm] 90.16 2970 2.30Co ICPAES [ppm] 6.60 2921 502.00 Rb ICPMS [ppm] 79.45 3030 2.30Co ICPMS [ppm] 9.64 2634 502.00 Sc ICPMS [ppm] 10.14 2542 5.82Cr ICPAES [ppm] 19.22 2404 2660.00 Sc ICPAES [ppm] 2.88 2951 5.82Dy ICPMS [ppm] 2.89 2891 0.24 SiO2 XRF [%] 65.28 3059 22.80Er ICPMS [ppm] 1.54 2841 0.16 Sm ICPMS [ppm] 4.44 3003 0.15Eu ICPMS [ppm] 0.88 3021 0.06 Sr XRF [ppm] 283.44 3051 7.80Fe ICPAES [ppm] 20946.00 3056 190443.40 Sr ICPAES [ppm] 12.32 3033 7.80FeO XRF [%] 3.10 3059 24.50 Ta ICPMS [ppm] 0.51 2931 0.01Ga XRF [ppm] 25.16 3037 10.00 Tb ICPMS [ppm] 0.55 2986 0.04Gd ICPMS [ppm] 3.94 3003 0.20 Th ICPMS [ppm] 6.39 3013 0.03Hf ICPMS [ppm] 3.86 3047 0.10 Th ICPAES [ppm] 15.51 2272 0.03Ho ICPMS [ppm] 0.54 2912 0.06 Ti ICPAES [ppm] 3058 437.64K ICPAES [ppm] 4686.19 3055 556.21 Ti ICPMS [ppm] 3055 437.64K2O XRF [%] 2.55 3053 0.07 TiO2 XRF [%] 0.38 3054 0.07La ICPMS [ppm] 28.01 3043 0.24 Tm ICPMS [ppm] 0.20 2958 0.02La ICPAES [ppm] 24.66 2957 0.24 U ICPMS [ppm] 1.52 2981 0.01Li ICPAES [ppm] 19.41 2872 1.50 V XRF [ppm] 54.63 2940 56.50Lu ICPMS [ppm] 0.19 2968 0.02 V ICPMS [ppm] 36.60 2915 56.50Mg ICPAES [ppm] 4745.62 3058 98910.04 V ICPAES [ppm] 25.02 2972 56.50MgO XRF [%] 1.13 2946 16.40 Y XRF [ppm] 16.57 2909 1.56Mn ICPAES [ppm] 258.64 3031 1990.36 Y ICPMS [ppm] 14.72 3056 1.56MnO XRF [%] 0.06 2990 0.26 Y ICPAES [ppm] 6.73 3047 1.56Na ICPAES [ppm] 772.78 3049 5000.07 Yb ICPMS [ppm] 1.36 2910 0.16Na2O XRF [%] 3.56 3036 0.67 Zr ICPMS [ppm] 141.36 3051 3.94

Nb ICPMS [ppm] 7.29 3045 0.25 Zr XRF [ppm] 157.87 3041 3.94

Analytical methods:

• XRF: X-ray fluorescence spectrometry using pressed powder pellets.

• ICPAES: Inductively coupled plasma atomic emission spectrometry after aqua regia digestion.

• ICPMS: Inductively coupled plasma mass spectrometry after hydrofluoric acid-perchloric acid

dissolution and lithium metaborate/sodium perborate fusion.

For detailed descriptions of the analytical methods, see Sandström (1996) and Rasilainen et al. (2007).

Table 1. Elements, standards, measurement units and analytical methods used in this study. Values of C1 chondrite are from Kerrich and Wyman (1996). AFP gmean = geometric mean of all Finnish plutonic rock samples. AFP nbdat = number of data used for calculation of AFP gmean. The samples have been analysed at the chemical laboratory of the Geological Survey of Finland (see Rasilainen et al. 2007).


231

CLASSIFICATION AND GROUPING OF THE SAMPLES

In this study, the lithological (‘lithogeochemi-cal’) classifications of the samples are based on the Na2O+K2O vs SiO2 diagram of Cox et al. (1979) and the R1-R2 diagram by De La Roche et al. (1980), as illustrated in Figure 2. Moreo-ver, samples are classified by the incompatible – compatible diagrams proposed by Pearce and Peate (1995), as shown in the diagrams in Figure 4, where the geochemical ‘spectra’ of samples are presented as values normalized against both

C1 chondrite (Kerrich & Wyman 1996) and the geometric averages of all Finnish plutonic rocks (AFP), whose values are given in Table 1. The diagrams in Figure 4 were prepared separately for all plutonic rocks in each terrain, and also separately for adakitic plutonic rocks, which will be considered in more detail below. The relative variations of sample densities and susceptibilities are demonstrated by the diagrams in Figure 3.

GEOCHEMICAL CHARACTERISTICS OF THE TERRAINS

The classifications of adakitic rocks, and also of all plutonic rock samples using the Na2O+K2O vs SiO2 diagram of Cox et al. (1979) and the R1-R2 diagram of De La Roche et al. (1980) are pre-sented in Figure 2. From the diagrams, it can be seen that the samples from the East Finland – Ilo-mantsi terrain (EFI) are exceptionally felsic and mainly granitic - monzogranitic. Granitic and granodioritic rocks also dominate in the Pudas-järvi area (Pdj), while in the Kuhmo (EFK) and Iisalmi (IC) terrains the relative proportion of more mafic rocks is higher. In the Cox diagrams,

the adakitic samples mainly plot in the sub-alka-line field with the exception of the Ilomantsi area, where the samples are more alkaline. In the tec-tonomagmatic De La Roche diagram, the adaki-toids of the Ilomantsi terrain mainly plot in the post-collision – late-orogenic fields, while in other sub-areas the sample distribution is less distinct, ranging from pre- to post-collisional samples. From the De La Roche diagrams it also appears that adakitic rocks tend to cluster in the dioritic – granodioritic fields and that ‘granitic’ adakitic rocks are less common.

PETROPHYSICAL CHARACTERISTICS OF THE SAMPLES

Figure 3 illustrates the cumulative distributions of densities and susceptibilities of all plutonic rock samples from each of the sub-areas. From this figure, it is evident that the densities of the more felsic rocks in the Pudasjärvi (Pdj) area are lowest while those of the Iisalmi terrain (IC) are highest, due to the large number of more mafic samples. In addition, samples from the Ilomantsi (EFI) and Kuhmo (EFK) areas are less dense

than the Finnish average (AFP). The susceptibili-ties of samples are mainly below the Finnish av-erage reflecting the low abundance of magnetic minerals (mainly magnetite) in Finnish Archaean rocks. The low paramagnetic susceptibilities (be-low 1000 [SI*106]) of the Kuhmo (EFK), Ilo-mantsi (EFI) and Pudasjärvi (Pdj) terrains is a consequence of the relatively low iron contents of mafic minerals (e.g. Puranen 1989).

CHARACTERISTICS AND CORRELATIONS OF PEARCE-PEATE DIAGRAMS FOR EACH OF THE TERRAINS

Incompatible → compatible diagrams proposed by Pearce and Peate (1995) are presented in Fig-ure 4 for each of the terrains. The diagrams es-sentially describe the preferential tendency or compatibility of elements to reside in restitic, more mafic minerals (e.g. garnet, pyroxenes and amphiboles) at higher pressures and can thus be

used in analysing the genesis and evolution of rocks and minerals.

From the diagrams in Figure 4 it can be seen that the LREE-HREE slopes of the adakitic se-ries ‘spectra’ (red curves) are much steeper than those for all samples (including adakitic rocks; black curves). The high Ba, Eu, Sr and Sr/Y

232

Geological Su

rvey of Fin

land, Sp

ecial Pap

er 54T

apio Ruotoistenm

äki

Fig. 2. Lithological classification of samples for each terrain according to the Na2O+K2O vs SiO2 diagram of Cox et al. (1979) and the R1-R2 -diagram of De La Roche et al. (1980). The tectonomagmatic fields have been adopted from Batchelor and Bowden (1985) and rock type boundaries have been digitized from Rollinson (1993). The alkaline / sub-alkaline boundary zone in the Cox diagram (which is not precisely located – hence two curves) has been adopted from Rickwood (1989). The red boxes in the diagrams refer to adakitic samples.

Geological Su

rvey of Fin

land, Special P

aper 54

Geo

chemical and p

etrophysical characteristics of plutonic ro

cks from the A

rchaean Karelia P

rovince in Fin

land

233 Fig. 2 cont.

234


Fig. 3. Cumulative distributions of densities and susceptibilities of the sub-areas compared with all Finnish plutonite (AFP) distributions.


235

Table 2. Number of all samples and adakitic samples in the sub-areas.

EFK EFI Pdj ICAll 317 104 98 123

Adakitoids 66 41 18 11

and steep increase in abundance of compatibles relative to HREE all signify lower crust – upper mantle fractionation depths, where plagioclase is unstable. A possible mantle component is dis-cernible in the marked increase in V, Mn, Fe and Mg (but high Cr and Ni are only observed in the Ilomantsi (EFI) samples). It must be noted that the amplitude scale in the diagrams is highly vari-able, particularly because of the constant sum ef-fect due to varying values of SiO2 (see e.g. Wilson 1989 and Rollinson 1993). Thus, in the following discussion, the main emphasis is not on absolute values, but on relative amplitudes and trends of chemical variations.

Table 2 provides the number of samples in each of the terrains. The total number of plu-tonic rock samples from the Iisalmi terrain is 123, of which 11 samples (about 9%) are classified as adakitic, based on the definitions given above by Defant and Drummond (1990) and Thorkelson and Breitsprecher (2005). The number of samples from the Eastern Finland terrain (EFK) is 317, of which 66 samples (about 21%) are classified as adakitic. Of the 104 samples from the Ilomantsi (EFI) terrain, as many as 41 samples (39%) clas-sify as adakitic. The total number of plutonic rock samples from the Archaean Pudasjärvi ter-rain (Pdj) is 98, of which 18 samples (19%) are adakitic. Thus, with the exception of Iisalmi ter-rain, the Archaean terrains are characterized by abundant adakitic rocks.

The cross-correlations of the Pearce-Peate spectra shown in Figure 4 for all samples and for adakitic samples separated according to terrain are provided in Table 3. From the table it can be seen that the correlation between Kuhmo and Ilo-mantsi terrains (EFK and EFI) is very high when considering the entire dataset and slightly less with the Pudasjärvi terrain (Pdj). The Iisalmi ter-rain correlates significantly with the Kuhmo data, while correlations between Ilomantsi and Pudas-järvi data are weak. These correlations indicate that EFK, EFI and Pdj terrains form a relatively homogeneous group of Archaean terrains, while IC is more ‘exotic’, possibly due to the complex structure of the terrain (e.g. Hölttä et al. 2000) and the effect of Proterozoic overprinting, as de-scribed by e.g. Sorjonen-Ward and Luukkonen (2005). It must also be noted that Figure 3 indi-cates that the densities of the Iisalmi terrain rocks are highest and that susceptibilities are also high. These features, as well as the fact that the Iisalmi terrain samples have lowest observed concentra-tions of incompatible elements in the whole data spectrum in Figure 4, can be attributed to the rela-tively high mafic component in these rocks.

Table 3. Correlations of the AFP-normalized element values for each terrain.

ALL DATA EFK EFI Pdj

IC 0.65 0.43 0.34

EFK 0.84 0.79

EFI 0.69ADAKITOIDS EFK Adak EFI Adak Pdj AdakIC Adak 0.88 0.78 0.87

EFK Adak 0.89 0.94EFI Adak 0.86

In Table 3, the correlation between the adakitic samples from each of the terrains, including the Iisalmi Complex, is significant, which strongly suggests a similar evolution of adakitoids, inde-pendent of their location in the respective ter-rains. From the table it can be concluded that the Archaean terrains in central Finland form a rela-tively coherent group, with the slight exception of the more complex Iisalmi terrain (IC), even though the Eastern Finland Terrain is separated from the Iisalmi and Pudasjärvi terrains by the supracrustal Kainuu belt.

Table 4 contains geometric averages of SiO2 values, densities and susceptibilities of all sam-ples and the subset of adakitic samples from each terrain. In addition, the table gives the LREE/HREE and compatibles/HREE ratios (* see box below) of the group averages of their Pearce-Peate spectra (see Figure 4). These ratios can be assumed to correlate with the degree of increas-ing fractionation (depth) and the role of the upper mantle, respectively. It is evident from the table that the average SiO2 contents of the samples from each terrain are relatively high, corresponding to granitic – granodioritic – tonalitic compositions. In the rock geochemistry database described by Rasilainen et al. (2007), plutonic rock samples having densities between 2685–2755 kg/m3 are mainly granodioritic (371/759 samples = 42%), tonalitic (144/759 = 19%) and granitic (89/759 = 12%). These samples have low susceptibilities and are paramagnetic, due to the low abundance of magnetite, with iron mainly being concentrated in mafic silicates.

In Table 4 the LREE/HREE and compatibles/HREE ratios of the adakitic group averages are

236


Fig. 4. Classification of the samples of sub-areas using the incompatible-compatible diagram of Pearce and Peate (1995); compatibility increasing from left to right (excluding the SiO2value at furthest right). The black curve represents the geometric average of the elements normalized by the geometric averages of all Finnish plutonic rocks (AFP; left vertical axis; see Table 1). The red curve shows corresponding variations for adakitic-only plutonic samples from each terrain. The grey bars give the element values of all samples normalized by C1 chondrite (Kerrich & Wyman 1996; right vertical axis). The darker grey bars and triangles indicate the location of rare earth elements (REE). The location of Light REE (LREE), heavy REE (HREE) and compatible elements considered in the text have been emphasized in the diagrams for the EFK. The last number in the element names in parentheses () gives the % of rejected samples (mainly due to values below detection limits).


237

Fig. 4. cont.

238


Table 4. Geometric averages of petrophysical parameters and some characteristic ratios of Pearce-Peate diagrams for each of the terrains. For LREE, HREE and compatible elements, see the EFK diagram in Figure 4. ‘D’ denotes density and ‘K’ magnetic susceptibility.

ALL Data: IC EFK EFI PdjSiO2 [%] 62.24 66.35 67.00 68.59

D [kg/m3] 2755 2713 2692 2685

K [*106SI] 526 396 500 192

LREE/HREE 1.04 1.55 1.57 1.54

Compatibles/HREE 1.36 1.74 1.51 1.53

Adakitoids: IC Adak EFK Adak EFI Adak Pdj AdakSiO2 [%] 64.63 67.03 66.73 68.22

D [kg/m3] 2715 2714 2697 2690

K [*106SI] 1071 412 599 679

LREE/HREE 2.29 2.33 2.04 2.26

Compatibles/HREE 2.16 2.42 2.09 2.14

much higher than those obtained by combin-ing all samples from each of the terrains, which clearly indicates the effectiveness of fractionation processes and the possible involvement of mafic, upper mantle material in the sources of adakitic melts. The highest and lowest LREE/HREE and compatibles/HREE ratios of EFK and EFI adak-itoids may refer to deepest and lowest fractiona-tion depths of these blocks, respectively.

The Pearce-Peate diagram characteristics can be summarized as follows:• TheadakiticgroupshavehigherLREE,lower

HREE and higher compatible element abun-dances than corresponding values for the group combining all samples. The adakitic population can be distinguished from the com-bined sample data in the Pearce-Peate spectra for most groups.

• In the Iisalmi terrain (IC), the difference be-tween adakitoids and the combined data for all samples is strongest. For example, the ra-tio (LREE/HREEAdak) / (LREE/HREEAll) is highest in this terrain, presumably reflecting the complex structure of the terrain. In con-

trast, the data for the Ilomantsi terrain (EFI) are much closer, which is attributed to the pre-dominantly adakitic composition of the ter-rain as a whole.

• Adakitic rocks typicallyhaveelevatedBa,Sr,(Sr/Y) and Eu, all of which can be related to the presence of plagioclase (and fluid) in the melt phase and thus fractionation at depths greater than the plagioclase stability field (about 40 – 80 - … km). Lower crustal or up-per mantle processes are also implicated by low values of Rb, Th, Nb, U and Y. It is also interesting to note the high K (ICPAES) val-ues relative to K2O (XRF) in adakitic rocks. This can be explained by biotite being more abundant relative to potassium feldspar (see e.g. Tarvainen et al. 1996). Moreover, low Sc and Cr in adakitic rocks can be attributed to the presence of clinopyroxene, and low Ni to olivine in the restite (e.g. Stosch 1981).

• Thus,itisapparentthatadakiticmagmashavefractionated at greater depths where garnet ± amphiboles ± pyroxenes, which have affinities for HREE, are stable and where an excess of mafic material is available during melting.

(*) Elements used for ratios:

LREEave/HREEave =

Average [La(ICPMS), La(ICPAES), Ce(ICPMS)] / Average [Ho(ICPMS), Er(ICPMS), Tm(ICPMS), Yb(ICPMS), Lu(ICPMS)]

(Compatiblesave/HREEave) =

Average [Ca(ICPAES), CaO(XRF), Al(ICPAES), Al2O3 (XRF), Ga(XRF), V(XRF), V(ICPMS), V(ICPAES), Sc(ICPMS), Sc(ICPAES), Mn(ICPAES), MnO(XRF), Fe(ICPAES), FeO(XRF), Co(ICPAES), Co(ICPMS), Mg(ICPAES), MgO(XRF), Cr(ICPAES), Ni(ICPAES),] / Average [Ho(ICPMS), Er(ICPMS), Tm(ICPMS), Yb(ICPMS), Lu(ICPMS)]


239

DETERMINATION OF RESTITE MINERALOGY FOR ADAKITIC ROCKS

Table 5. Ratios of mineral/melt partition coefficients for ba-saltic and basaltic andesite liquids using coefficients summa-rized by Rollinson (1993 and references therein).

Restite: opx cpx hornblende garnet

Nd/Zr <1 >1 <1 <1

La/Ce >1 (*) <1 <1 <1

Er/Lu <1 >1 >1 <1(*) = evaluated for andesitic liquids

The characteristics of restite remaining in the lower crust / upper mantle after removal of the adakitic melt fraction is evaluated using ratios of partition coefficients for basaltic and basaltic andesite liquids, whose values have been summa-rized by Rollinson (1993). Table 5 lists the rela-tive ratios for the coefficient pairs used here. For simplicity, it can be said that if the value of the ratio is less than one, the denominator dominates in the restitic mineral, and vice versa. For exam-ple, if orthopyroxene dominates in the restite, Zr is more likely to be retained in the mineral phase and Nd in the adakitic melt phase. Hence, the AFP-normalized Nd/Zr ratio of adakitic samples should be relatively enriched in Nd.

It must be emphasized that the estimated values of partition coefficients can vary widely, and their relative effect on the concentrations of elements in melt and the remaining restite fraction can thus only roughly be evaluated. Therefore, the results

Fig. 5. Modelled restite mineralogy of the adakitic plutonic rocks in the study area.

given in the maps in Figure 5 must be taken as indicative only.

Assuming that clinopyroxene, orthopyroxene, garnet and amphibole represent the most prob-able restite phases for preferential retention of the compatible elements, the possible enrichment of elements in adakitic melts can be defined as fol-lows from the AFP-normalized ratios of adakitic rocks:

240


Orthopyroxene: Nd/Zr > 1, La/Ce < 1, Er/Lu > 1 Clinopyroxene: Nd/Zr < 1, La/Ce > 1, Er/Lu < 1Hornblende: Nd/Zr > 1, La/Ce > 1, Er/Lu < 1Garnet: Nd/Zr > 1, La/Ce > 1, Er/Lu > 1

These results can be expressed in a more simpli-fied form, demonstrating the uniqueness of the combinations:Orthopyroxene: (1,0,1)Clinopyroxene: (0,1,0)Hornblende: (1,1,0)Garnet: (1,1,1)

These combinations now allow us to evaluate the distributions of all these restite minerals in the study area. These ratios were calculated for AFP-normalized samples, and the locations of adakit-ic rocks containing any of these four restite-phase minerals were plotted on the maps in Figure 5. It is evident from the maps that the most evenly

distributed restite minerals appear to be clinopy-roxene, amphiboles and garnet. Orthopyroxenes are also present but in lesser amounts, and mainly south of 65°N.

It must be noted, that the method gives only one apparently dominating mineral in the restite. Their relative combinations could be possibly evaluated by considering e.g. paired groups of the ratios above. Moreover, analyses for some sam-ples were incomplete. Thus, it was not possible to determine the restite-phase elements for all sam-ples using this method.

The method was also tested using normaliza-tion by geometric means of all Finnish adakitic samples, which gave results very similar to the AFP normalization used here. It must be empha-sized that these minerals are assumed to dominate in restitic rocks deep in the lower crust – upper mantle, not in outcrops at the present erosion level

During this study I also tested the distribution of sanukitoid plutonic rocks in the database using

RELATIONSHIPS BETWEEN ADAKITOIDS, TTGS AND SANUKITOIDS

the criteria applied by Halla (2005 and references therein): SiO2 = 55–60%, Mg numbers > 0.6, Ni

Fig. 6. Na2O/K2O vs. Ba + Sr plot for discriminating the high Ba–Sr sanukitoid group from the TTG groups. The hypothetic source end members are enriched mantle (high Ba + Sr, low Na2O/K2O) and primitive basalt (low Ba + Sr, high Na2O/K2O). Adopted from Halla et al. (2009).


241

>100 ppm, Cr > 200 ppm, K2O > 1%, Sr and Ba > 500 ppm and Rb/Sr ratios < 0.1. However, very few ‘sanukite-like’ plutonic rocks were found us-ing their criteria. Later, it was observed that using broader definitions given by Heilimo et al. (2010), many of the Archaean adakitic rocks in Finland are also sanukitic.

Figure 6 presents all Archaean adakitic rock samples considered here on a Na2O/K2O vs. Ba + Sr diagram adopted from Halla et al. (2009). It is apparent from the diagram that the adakitic samples considered in this study represent a con-

tinuum from TTGs to sanukitoids. It is therefore difficult to discriminate between potential primi-tive basaltic and enriched mantle sources on the basis of this diagram. Although this makes at-tempts at classification somewhat arbitrary, all samples from the Ilomantsi terrain (EFI) classify as sanukitic. The Kuhmo terrain (EFK) contains both TTG and sanukitic plutonic rocks, while the samples from the Iisalmi and Pudasjärvi terrains show more random scatter within and around the TTG and sanukitic fields.

DISCUSSION

This study considered four separate terrains in the Archaean crust in central Finland: the Iis-almi terrain (IC), East Finland - Kuhmo ‘terrain’ (EFK), East Finland - Ilomantsi ‘terrain’ (EFI) and Pudasjärvi terrain (Pdj). Each of these areas is characterized by predominantly felsic, dioritic to granodioritic plutonic rocks. Some mafic plu-tons were also sampled, except from the Ilomant-si area, where almost all samples are from felsic rocks. Petrophysically, the plutonic rock samples are relatively low in density and magnetite poor.

A characteristic feature of the samples is that they are relatively enriched in LREE and compat-ible elements relative to HREE (compared to the reference group of ‘all Finnish plutonic rock sam-ples’, AFP). These features are especially striking in plagioclase-rich adakitic rocks, whose chemi-cal spectra probably record fractionation at low-er crustal or upper mantle depths, i.e. at depths greater than ca. 40–60 km. Using normalized Nd/Zr, La/Ce and Er/Lu ratios, the restitic minerals of adakitic melts can be estimated to predomi-nantly consist of clinopyroxenes, garnet and am-phiboles, with lesser amounts of orthopyroxene. The high potassium contents in adakitic rocks may be a result of high-pressure melting of phlo-gopite in the source material. Moreover, low Sc and Cr contents can be attributed the presence of clinopyroxene and low Ni to olivine in the restite. The chemical spectrum of adakitoids is broad, forming a continuum from TTGs to sanukitoids, thus indicating complex melting processes and di-verse primary sources, ranging from a primitive basaltic source to enriched mantle.

An important observation is the compositional similarity between the adakitic samples from the various terrains, resulting in a high degree of sta-tistical correlation. For example, even though the correlation of the combined data for all plutonic

rocks is relatively poor between the Iisalmi terrain and the other terrains, the Iisalmi adakitic rocks nevertheless correlate strongly with adakitic rocks from the other terrains.

The evolution of Archaean adakitic rocks has been interpreted in terms of subduction processes by Svetov et al. (2004). Subduction results in par-tial melting of the overriding plate, thus produc-ing enriched magmas contaminated by mantle material. O’Brien et al. (1993) and Hölttä et al. (2012, this volume) noted that calc-alkaline vol-canic rocks, crustal signatures in the geochemistry of ultramafic rocks and high abundances of vol-caniclastic greywackes in the sanukitic Ilomantsi belt (here ‘terrain’) are consistent with arc-type tectonic settings, and hence may indeed be related to subduction processes.

However, there is still an apparent contradiction between the considerable volume of Archaean adakitic plutonitic rocks and the relatively small proportion of rocks that can be unequivocally in-terpreted as being related to subduction. There-fore, an alternative explanation, preferred here for most Archaean adakitic / TTG terrains lacking direct indications of ‘modern type’ subduction is crustal thickening due to collision-related stack-ing and melting by underplating and mixing with hot upper mantle material. Underplating process-es could be expected to generate high-velocity lay-ers in the lower crust, which may still be evident in deep seismic sections. However, much of the lower crust has apparently been eroded or delaminated during later processes, as modelled by Kukkonen et al. (2008) for the Svecofennian crust in western Finland.

This type of process can be linked with a model proposed by Kröner et al. (2011), who suggested extensive recycling of early-formed granitoid crust and mixing with juvenile material to produce suc-

242


cessive generations of TTGs and associated fel-sic volcanic rocks. Thus, in the model introduced here, the repeated stacking corresponds to the re-cycling concept of Kröner et al. (2011) and under-plating represents the mixing of juvenile material in their model. It must, however, be emphasized that Archaean subduction-related collision and stacking processes are not excluded by this model. Moyen (2011) also commented that crustal recy-cling was already a rather prominent process in

the Archaean, because sizeable portions of grey gneiss complexes have old model ages, pointing to a long term continental history.

Thus, a comprehensive answer to these ques-tions needs to be addressed by isotopic analysis of carefully selected samples: A wide range of ages in sampled zircons may refer to multi-stage stack-ing / recycling processes instead of relative rapid ‘single-stage’ subduction-related crustal growth.

ACKNOWLEDGEMENTS

I want to thank Pentti Hölttä and Perttu Mikkola for their valuable comments during this work.

REFERENCES

Batchelor, R. A. & Bowden P. 1985. Petrogenetic interpreta-tion of granitoid rock series using multicationic param-eters. Chemical Geology 48, 43−55.

Castillo, P. R. 2006. An overview of adakite petrogenesis. Chinese Science Bulletin 51(3), 257−268.

Condie, K. C. 2005. TTGs and adakites: are they both slab melts? Lithos 80, 33–44.

Cox, K. G., Bell, J. D. & Pankhurst, R. J. 1979. The Inter-pretation of Igneous Rocks. London: Allen and Unwin. 450 p.

De La Roche, H., Leterrier, J., Grandclaude, P. & Marchal, M. 1980. A classification of volcanic and plutonic rocks using R1R2-diagram and major element analyses - Its relationships with current nomenclature: Chemical Geol-ogy, v. 29, 183−210.

Defant, M. J. & Drummond, M. S. 1990. Derivation of some modern arc magmas by melting of young subducted lith-osphere. Nature 347, 662– 665.

Drummond, M. S. & Defant, M. J. 1990. A model for trond-hjemite–tonalite–dacite genesis and crustal growth via slab melting; Archean to modern comparisons. Journal of Geophysical Research 95, 21503–21521.

Halla, J. 2005. Late Archean high-Mg granitoids (sanuki-toids) in the southern Karelian domain, eastern Finland; Pb and Nd isotopic constraints on crust-mantle interac-tions. Lithos 79, 161–178.

Halla, J., van Hunen, J., Heilimo, E. & Hölttä, P. 2009. Geo-chemical and numerical constraints on Neoarchean plate tectonics. Precambrian Research 174, 155−162.

Hautaniemi, H., Kurimo, M., Multala, J., Leväniemi, H. & Vironmäki, J. 2005. The “Three In One” aerogeophysical concept of GTK in 2004. In: Airo, M.-L. (ed.) Aerogeo-physics in Finland 1972−2004: methods, system charac-teristics and applications. Geological Survey of Finland. Special Paper 39, 21−74.


Huhma, H. 1986. Sm-Nd, U-Pb and Pb-Pb isotopic evidence for the origin of the Early Proterozoic Svecokarelian

crust in Finland. Geological Survey of Finland, Bulletin 337. 48 p. + 2 app.

Hölttä, P. 2000. High-grade metamorphic rocks at the bot-tom and on the surface: Granulites and evolution of the Earth’s crust in the Archaean of eastern Finland. Geo-logical Survey of Finland. 104 p.

Hölttä, P., Huhma, H., Mänttäri, I. & Paavola, J. 2000. P-T-t development of Archaean granulites in Varpaisjärvi, Central Finland: II. Dating of high-grade metamor-phism with the U-Pb and Sm-Nd methods. Lithos 50, 121−136.

Hölttä, P., Heilimo, E., Huhma, H., Juopperi, H., Konti-nen, A., Konnunaho, J., Lauri, L,, Mikkola, P., Paavo-la, J. & Sorjonen-Ward, P. 2012. Archaean complexes of the Karelia Province in Finland. In: Hölttä, P. (ed.) The Archaean of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Kay, R. W. 1978.Kerrich, R. & Wyman, D. A. 1996.Kors-man, K. (ed.), Koistinen, T. (ed.), Kohonen, J. (ed.), Wen-nerström, M. (ed.), Ekdahl, E. (ed.), Honkamo, M. (ed.), Idman, H. (ed.) & Pekkala, Y. (ed.) 1997. Suomen kalli-operäkartta = Berggrundskarta över Finland = Bedrock map of Finland 1:1 000 000. Geological Survey of Fin-land. Special maps 37.

Korsman, K., Korja, T., Pajunen, M. & Virransalo, P. 1999. The GGT/SVEKA transect: Structure and evolution of the continental crust in the Paleoproterozoic Svecofenn-ian orogen in Finland. International Geology Review 41, 287−333.

Kröner, A., Wan, Y., Xie, H., Wu, F., Münker, C., Hegner, E. & Schoene, B. 2011. Origin of Early Archaean tonalitic gneisses and greenstone felsic volcanic rocks on the basis of zircon ages and Hf-Nd isotopic systematics. Abstract in: Abstracts volume. 23rd Colloquium of African Geol-ogy (CAG23), University of Johannesburg, Republic of South Africa 8th–14th January 2011.

Martin, H., Smithies, R. H., Rapp, R., Moyen, J.-F. & Cham-pion, D. 2005. An overview of adakite, TTG and sanuki-toid: Relationships and some implications for crustal evolution. Lithos 79, 1−24.

Moyen, J.-F. 2009. High Sr/Y and La/Yb ratios: The mean-


243

ing of the “adakitic signature”. Lithos, v 112, Issues 3−4, 556−574.

Moyen, J.-F. 2011. The composite Archaean grey gneisses: Petrological significance, and evidence for a non-unique tectonic setting for Archaean crustal growth. Lithos 123, 21–36.

Mutanen, T. & Huhma, H. 2003. The 3.5 Ga Siurua trond-hjemite gneiss in the Archean Pudasjärvi Granulite Belt, northern Finland. Bulletin of the Geological Society of Finland, Vol. 75 (1–2), 51–68.

Nironen, M., Lahtinen, R. & Koistinen, T. 2002.O’Brien, H., Huhma, H. & Sorjonen-Ward, P. 1993. Pearce, J. A. & Peate, D. W. 1995.Puranen, R. 1989.Rasilainen, K., Lahtinen, R. & Bornhorst, T. J. 2007.Rickwood, P. C. 1989.Rollinson H. R. 1993.Sandström, H. 1996. Scaillet, B. & Prouteau, G. 2001.Smithies, R. 2000.Sorjonen-Ward, P. & Luukkonen, E. J. 2005. Archean rocks. In: Lehtinen, M., Nurmi, P. A. & Rämö, O. T. (eds.) Precambrian geol-ogy of Finland: Key to the evolution of the Fennoscan-

dian Shield. Developments in Precambrian geology 14. Amsterdam: Elsevier, 19−99.

Stosch, H.-G. 1981. Sc, Cr, Co and Ni partitioning between minerals from spinel peridotite xenoliths. Contrib Min-eral Petrol 78, 166−174.

Svetov, S. A., Huhma, H., Svetova, A. I. & Nazarova, T. N. 2004. The oldest adakites of the Fennoscandian Shield. Doklady Earth Sciences 397A (6), 878−882.

Tarvainen, T., Aatos, S. & Räisänen, M.-L. 1996. A method for determining the normative mineralogy of tills. In: En-vironmental geochemistry: selected papers from the 3rd International Symposium, Kraków, Poland, 12−16 Sep-tember 1994. Applied Geochemistry 11 (1−2), 117−120.

Thorkelson, D. J. & Breitsprecher, K. 2005. Partial melting of slab window margins: Genesis of adakitic and non-adakitic magmas. Lithos 79, 25–41.

Wilson M. 1989. Igneous petrogenesis. London: Chapman & Hall. 466 p.

244


FLUID-CONTROLLED MELTING OF GRANULITES AND TTG-AMPHIBOLITE ASSOCIATIONS IN THE

IISALMI COMPLEX, CENTRAL FINLAND

byFranziska Nehring

Nehring, F. 2012. Fluid-controlled melting of granulites and TTG-amphibolite as-sociations in the Iisalmi Complex, Central Finland. Geological Survey of Finland, Special Paper 54, 244−254, 5 figures and 1 table.

Granulites and upper-amphibolite facies migmatites from the Iisalmi Complex in Central Finland were produced by partial melting of Archean crust during a major tectonothermal event at 2.6-2.7 Ga. Melt forming reactions in different lithologies strongly depend on the activity of H2O in the peak-metamorphic fluid. While granulites represent the anhydrous residues of dehydration melting reactions involving amphibole, the lower P-T-conditions determined for the migmatitic TTG gneisses and amphibolites require the presence of a hydrous fluid to allow melting at the wet solidus. Melting of the TTG gneisses yielded leucosomes that are rich in Na2O and have a trondhjemitic affinity while leucosomes within granulites are CaO-rich and classify as tonalites. This indicates that remelting of a Na2O-rich precursor under conditions that allow plagioclase to participate in melt-forming reactions is a viable mechanism for producing trondhjemitic melts.

Keywords (GeoRef Thesaurus, AGI): granulites, gneisses, migmatites, partial melt-ing, leucosomes, Archean, Iisalmi, Finland

FIELAX Company for Scientic Data Management, Schleusenstr.14, D-27568 Bremerhaven, Germany


mailto:[email protected]

245

Geological Survey of Finland, Special Paper 54Fluid-controlled melting of granulites and TTG-amphibolite associations in the Iisalmi Complex, Central Finland

Granulites and upper-amphibolite facies mig-matites (tonalitic-trondhjemitic-granodioritic gneisses, amphibolites) from the Iisalmi area in Central Finland record reworking and partial melting of older Archean crust during a ma-jor tectonothermal event at 2.6-2.7 Ga. Vast amounts of new crust formed throughout the

INTRODUCTION

Fennoscandian Shield at the same time suggest-ing a close connection between crustal recycling and crustal growth. The aim of this study was to ascertain melting processes in varying lithologies and to constraint the amount of melt formation and melt composition.

The dominant rock types of the Iisalmi area are

Fig. 1. Generalized geological map of the study area, modified after Hölttä and Paavola (2000). Shear zones, dolerite dykes, gabbros and granitoid intrusion are of Paleoproterozoic age.

246

Geological Survey of Finland, Special Paper 54Franziska Nehring

migmatitic TTG gneisses that contain abundant schollen and lenses of amphibolites, including py-roxene- and garnet-bearing intermediate and maf-ic granulites. The study area was subdivided into three major units based on general appearance of rocks in outcrop and mineral assemblages in the granulites. From NW to SE the three rock units defined are the Iisalmi-Sukeva area, the Varpanen-Pallikäs area and the Jonsa area (Fig. 1).

Ion microprobe dating on zircon as well as Sm-Nd model ages of granulites from the Varpanen area indicate protolith ages of 3.2-3.1 Ga (Hölttä et al. 2000, Mänttäri & Hölttä 2002). This is in accordance with 3.2 Ga ages of palaeosomes of

TTG gneisses from the western part of the study area (Mänttäri et al. 1998). In contrast, zircon ages of granulites from the Jonsa area are 2.73-2.70 Ga and the Sm-Nd model age is 2.93 Ga (Hölttä et al. 2000). The major age difference between rocks from the NW and SE parts of the working area suggests terrane accretion during the late Ar-chean and coeval metamorphism in both terranes between 2.70-2.63 Ga (Mänttäri & Hölttä 2002, Hölttä et al. 2000). In the classification by Hölttä et al. (2012) the Jonsa area belongs to the Rauta-vaara complex and the other units to the Iisalmi complex.

PARTIAL MELTING IN UPPER-AMPHIBOLITE FACIES TTG GNEISSES AND AMPHIBOLITES

The textures of the TTG gneisses varies between metatexites that represent small scale segregation of melt, and schlieren migmatites showing a higher degree of protolith disaggregation. Palaeosomes

of the migmatites are predominantly tonalitic and consist of pl + qtz ± kfs ± amph ± bt ± ep (Table 1). Clinopyroxene was present in amphi-bole-bearing gneisses at peak metamorphism but

Table 1. Observed mineral assemblages of the various rock types. Leucosomes represent samples that are adjacent to palaeo-somes on the exposures.

Rock type palaeosome leucosome

mafic granulite Grt-Cpx-Plg-Mgt-Ilm Plg-Qtz

Grt-Cpx-Plg Plg-Qtz-Grt-Amph

Grt-Cpx-Amph-Plg-Mgt-Ilm Plg-Qtz±Cpx

intermediate granulite Grt-Cpx-Amph-Plg-Mgt-Ilm-Ap Plg-Qtz-Bt±Opx

Opx-Cpx-Amph-Plg-Mgt-Ilm-Ap Plg-Qtz±Cpx±Opx

Grt-Cpx-Amph-Plg-Qtz Plg-Qtz-Cpx-Amph

Opx-Cpx-Amph-Plg Plg-Qtz

Grt-Cpx-Opx-Amph-Plg-Mgt-Ilm-Ap

diatexite Opx-Cpx-Amph-Plg-Mgt-Ilm Plg-Qtz-Amph-Bt

amphibolite Amph-Cpx-Plg-Qtz Plg-Qtz ± Bt ± Amph

Amph-Cpx-Plg-Qtz Plg-Qtz-Kfs-Bt

Amph-Bt-Plg Plg-Qtz-Bt

Amph-Cpx-Plg Plg-Qtz-Cpx-Amph

Amph-Cpx-Plg Plg-Qtz-Amph-Bt

Amph-Bt-Pl-Qtz Plg-Qtz-Bt-Amph

TTG gneiss Plg-Qtz-Amph Plg-Qtz-Amph

Plg-Qtz-Bt Plg-Qtz-Bt

Plg-Qtz-Bt-Amph Plg-Qtz ± Bt ± Amph

Amph-Bt-Plg

247


it has been extensively altered to secondary am-phibole. The REE-patterns of TTG gneisses are strongly fractionated, as is typical for Archean TTG complexes (Martin 1994). Two groups of TTG gneisses can be distinguished with (La/Yb)

N = 37-56 in Group I gneisses and (La/Yb)N < 20 in Group II gneisses (Fig. 2d).

Amphibolitic layers intercalated within TTG gneisses are interpreted as disrupted mafic intru-sions that pre-date metamorphism. They consist essentially of amphibole with minor biotite (Ta-ble 1); clinopyroxene also occurs sporadically al-though it is usually to secondary, green amphibole. Plagioclase is the dominant feldspar but potassic

feldspar is occasionally present in those amphibo-lite lenses that contain biotite. The amphibolites have SiO2 contents of 46-51 wt%, which is com-parable to that of the mafic granulites. Like the mafic granulites, they exhibit high Cr, Ni, Sc and V contents, although CaO abundances are slightly lower and their REE pattern are essentially flat (Fig. 2e).

Amphibole-plagioclase thermometry follow-ing Holland and Blundy (1994), applied in com-bination with the Al-in-hornblende barometer calibrated by Anderson and Smith (1995), yields P-T estimates of 700-750°C at 5-6 kbar for the gneisses and amphibolites. Carbonic fluid inclu-

Fig. 2. Extended trace element diagrams for the mafic lithologies from the study area. Intermediate granulites from the Jonsa area as well as LREE-enriched granulites from other granulites block strongly resemble modern island-arc basalts, showing dis-tinct negative Nb-Ta, Zr- and Ti-anomalies. Mafic granulites as well as amphibolite lenses and layers from the Iisalmi-Sukeva area correspond to tholeiitic basalts.

248


sions are absent in the upper-amphibolite facies rocks whereas aqueous fluid inclusions are abun-dant. The high abundance of aqueous inclusions in TTG gneisses and amphibolites indicates that partial melting and migmatisation within these rock types took place in the presence of a hydrous fluid, which promoted melting in rocks that could not otherwise have melted at the metamorphic conditions under consideration. According to Jo-hannes (1984), the onset of melting in the water-saturated granite system qz-kfs-ab-an-H2O var-ies systematically from 690°C at 2 kbar to 630°C at 17 kbar. This early stage of melt formation is enabled by the low stability of plagioclase in a hy-drous environment.

The transition from stromatic migmatites to

strongly disaggregated schlieren migmatites ob-served in some outcrops of TTG gneisses resem-bles metatexite to diatexite transitions described by White et al. (2005). The amount of melt re-quired to produce diatexites is estimated in the order of 20-40 vol% (Greenfield et al. 1996, Sawyer 1998). Since most migmatitic gneisses in the Iisalmi study area preserve pre-migmatitic textures and can be classified as metatexites the proportion of melt in the system was most like-ly less than 25 vol%. Major and trace element abundances of individual leucosomes reflect the compositions of the respective host lithologies, indicating that melt injection and melt mixing did not play an important role in the petrogen-esis of the TTG gneisses.

PARTIAL MELTING IN GRANULITES

Mafic granulites

The petrographical and geochemical characteris-tics of granulites from the study area have been described in detail by Paavola (1984), Hölttä (1997), Hölttä and Paavola (2000) and Nehring et al. (2009). Granoblastic grt-cpx-pl±hbl assem-blages are typical for the mafic granulites from the Iisalmi-Sukeva area. They display steep fraction-ation trends on element variation diagrams and have high CaO contents (8-16 wt%). Chondrite normalized trace element characteristics show flat REE patterns and increased abundances of compatible elements, resembling trends generally observed in tholeiitic basalts (Fig. 2a).

Maximum peak metamorphic P-T conditions were previously constrained by analyses from grt-cpx-pl-qtz assemblages at 800-950°C and 9-11 kbar respectively (Hölttä & Paavola 2000). The highest pressures were obtained from mafic granulites in the Iisalmi-Sukeva area, suggesting a deeper crustal origin for the rocks from the NW. Granulites characteristically contain a high abun-dance of carbonic fluid inclusion (Nehring et al. 2009). Few of these carbonic inclusions record peak metamorphic conditions, which is attributed to the extensive Paleoproterozoic thermal over-printing throughout the Iisalmi area. In general, however, the abundance of carbonic fluid inclu-sionsin granulites, as well as the characteristic preservation of anhydrous mineral assemblages, is interpreted to indicate that granulites formed in an anhydrous environment.

The anhydrous character of the rocks can be accounted for by two scenarios.

i) The igneous precursor of the mafic granu-lites intruded into the middle to lower crust and never experience hydration so that the rock was dry at the onset of metamorphism. In this case the mineralogical assemblage of the mafic granulites represents re-crystallized igneous minerals and their trace element abundances have been inher-ited from a source rock with a composition com-parable to N-MORB. However, porphyroblastic growth and the irregular distribution of garnet suggests mineral growth during metamorphism.

ii) If the rocks were moderately hydrous at the onset of metamorphism (amphibolites) the ob-served mineral modes would have been generated by dehydration melting reactions of amphibole. In this case, the trace element characteristics of mafic granulites should be modelled as residual compositions formed melting of amphibolites.

We favour amphibole dehydration melting for the petrogenesis of mafic granulites from the Iisalmi-Sukeva area, particularly given that most rocks are extensively migmatised. In some cases the mafic granulites are weakly migmatized, which has been attributed to the loss of melt dur-ing deformation (Hölttä & Paavola 2000, Nehring et al. 2009). Temperatures in excess of 800°C and pressures of 9-11 kbar determined for the granu-lites lie well above the dry solidus for mafic rocks (Beard & Lofgren 1991, Sisson et al. 2005, Rush-

249


mer 1991) and enable partial melting in accord-ance with following general dehydration melting reaction (Wolf & Wyllie 1994, Hartel & Pattison 1996):

hbl + pl + qtz = cpx + grt + melt (1)

The abundant amphibolite lenses and layers in the TTG gneisses resemble mafic granulites in terms of major elements and compatible trace elements. A batch melting model was therefore applied using observed modal compositions of mafic granulites as likely residues from melting of an average amphibolitic composition from the study area. About 10 % partial melting of such amphibolites, leaving a residue comprising 10 % garnet, 35 % plagioclase, 45 % clinopyroxene and 10 % amphibole, is sufficient to explain the trace element pattern of most of the mafic granulites (Fig. 3a). Some more strongly fractionated maf-ic granulites require up to 30 % partial melting, higher amounts of residual garnet (30 %) and low amounts of residual plagioclase (20 %). These strongly fractionated granulites also record pres-sures in excess of 11 kbar, which may correspond to increased incorporation of plagioclase into the melt phase, as observed for example by Sen and Dunn (1994).

Mafic granulites contain abundant clinopyrox-ene and subsolidus clinopyroxene formation is required to satisfy mineral modes. Alternatively, extensive prograde clinopyroxene-formation in a CaO-rich environment may have taken place ac-cording to reaction (2) before the rocks entered the stability field of garnet (Rushmer 1991).

hbl + pl 1 + qtz = cpx + pl 2 + melt ± ilm (2)

Thus, during prograde metamorphism, condi-tions for melt-production may have progressed from a garnet-absent reactions to reactions oc-curring in the presence of garnet.

The low Ba contents observed in the mafic granulites are only found in modelled residues if Ba in the source rock is less than 150 ppm. Ba contents <20 ppm as observed in mafic granulites with strongly fractionated REE-pattern are not reproduced by our model. Likewise low Sr con-tents in strongly fractionated mafic granulites are only reproduced by modelling at low source rock Sr abundances (~100 ppm) and with low modal plagioclase in the residue (10 %). The melting model requires the presence of a phase that pref-erentially retains Nb and Ta (Fig. 3b), such as ilmenite, which is a common accessory phase in granulites; in-situ LA-ICP-MS analyses of ilmen-

Fig. 3. Numerical models for petrogenesis of mafic granu-lites. Mafic granulites are modeled as residues from partial melting of amphibolites from the study area. Residual miner-alogies are constrained for slightly and strongly fractionated mafic granulites and modal abundances are based on point counting. The strongly fractionated REE patterns of model melts resemble the typical patterns of Archean TTG crust.

ite grains from the study area are also typically characterized by high abundances of Nb and Ta.

Although the results of trace element modeling are consistent with observed rock compositions, mass balance considerations showed that the ac-tual source rocks of mafic granulites must have been richer in CaO, Al2O3, SiO2 and lower in MgO

250


than the amphibolitic layers preserved in in the Iisalmi area. If extraction of 10-20 % tonalitic melt is assumed, then the original source rocks of the mafic granulites would resemble low Mg-tholeiites.

The retention of restitic garnet in mafic granu-lites results in strong REE fractionation in cor-responding melts (Fig. 3c). Therefore, dehydra-tion melting of amphibolite under lower crustal conditions leaves residual garnet-bearing mafic

granulites produces tonalitic melts similar to typi-cal Archean TTGs (Fig. 4a). However, Sr and Eu abundances in the melt are strongly influenced by the amount and composition of residual pla-gioclase. High Sr contents (>250 ppm), which are typical for Archean TTG (Martin 1994, Martin et al. 2005) can only arise in the melt phase if pla-gioclase abundance in the residue progressively decreases at pressures above 11 kbar.

Intermediate granulites

Prograde, granoblastic orthopyroxene is charac-teristic of the intermediate granulites m the Jonsa area, which show LREE-enrichment and have lower CaO contents than the mafic granulites (Fig. 2b). On multi-element plots intermediate granulites resemble modern island-arc andesites due to their negative Nb-Ta, Ti- and Zr-anoma-

lies. Granulites from the Varpanen-Pällikäs area show compositional overlap with both groups. Mineralogical compositions vary such that some samples are more similar to grt-cpx-pl granulites from the Iisalmi-Sukeva area, having high CaO contents and characteristically steep fractionation trends, while others are intermediate in composi-

Fig. 4. Geochemical characteristics of leucosomes. A) Normative feldspar classification of leucosomes according to Barker (1979). Granulite leucosomes are displaced towards the Anorthite-apex and classify as tonalites while most migmatite leuco-somes plot along the boundary of the tonalite and trondhjemite fields due to lower Ca / Na ratios. B) The linear trend of Na2O vs. Al2O3 reflects the important control exerted by plagioclase on leucosome major element composition. Chondrite-normal-ized REE-pattern for granulite and migmatite leucosomes (D). Most leucosomes display strong positive Eu-anomalies (Eu*) and have very low HREE contents. Note the small negative Eu-anomaliin the leucosomes having highest REE abundances. High HREE in some granulite leucosomes are related to the presence of peritectic garnet.

251


Metamorphism and melting of a layered suite of rocks such as the protoliths of the Jonsa and Varpanen area granulites will produce inhomoge-neous restites with residualmineralogy being de-pendent upon source rock composition and the extent of amphibole-breakdown. Consequently, intermediate granulites exhibit significant varia-tions in modal mineralogy. By assuming that all clinopyroxene in the intermediate granulites was produced by the breakdown of amphibole in the presence of quartz it is possible to calculate the amount of melt that formed via Reaction (2). The melt proportion was relatively small, varying between 5-10 % for most of the samples. Since amphibole is still present in most intermediate

granulites they may be considered as fertile with respect to melt formation, with the availability of quartz being the controlling factor of the reac-tion progress.

Negative Eu- and Sr-anomalies may be charac-teristic of melts derived from intermediate gran-ulites because of the relatively high proportion of of restitic plagioclase retained in the source. The absence of a residual phase such as garnet, which retains HREE, implies that partial melts formed at pressures below 10 kbar, leaving res-titic intermediate granulites that differ composi-tionally from typical Archean TTG, even though they are tonalitic with respect to major element composition.

NEOSOME FORMATION

Granulites as well as the lower-grade TTG gneiss-es and amphibolites contain neosomes (or leu-cosomes) which represent leucocratic material produced by partial melting. Mineral composi-tions of these neosomes are listed in Table 1. Leu-cosomes within mafic granulites consist of thin veins and small melt patches while intermediate granulites are stromatic with leucosomes typically forming layers several centimeters thick. Addi-tionally, diatexites with a high leucosome / palaeo-some ratio are present in the Jonsa and Varpanen areas. The proportion of leucosome in the TTG gneisses varies considerably; in some outcrops ex-tensive melting and mobilization has nearly oblit-erated original host rock features. Leucosomes in all lithologies consist of large subhedral or euhe-dral grains of plagioclase with interstitial quartz. Most mafic phases in leucosomes are considered to be crystals that have been disaggregated from the host rock although large, euhedral crystals in some melt patches within granulite most likely represent peritectic phases of the melting reaction.

Leucosomes from granulites are tonalitic in composition with Ca / Na >1, while leucosomes

within TTG gneisses contain more Na2O and show trondhjemitic affinity (Fig. 4a). Few leu-cosomes in either rock type have K2O contents > 1 wt%. Trends of increasing Na2O and CaO vs. Al2O3 reflect the abundance and composition of plagioclase in the respective leucosome (Fig. 4b). High Sr contents in leucosomes occur in source rocks with sodic plagioclase, which is character-istic of most intermediate granulites and TTG gneisses, whereas lower Sr contents are observed in leucosomes within amphibolites and from the mafic and more calcic granulites.. The abun-dance of Zr in leucosomes varies markedly but is generally below 150 ppm. A strong positive Eu-anomaly is typical for the REE pattern of most of the leucosomes and demonstrates the influence of plagioclase in determining the overall REE-budget of leucosomes. Leucosomes enriched in REE lack Eu-anomalies although the most REE-enriched leucosomes do show slight negative Eu-anomalies (Fig. 4c-d).

The origin of leucosomes has long been de-bated. It is obvious that they are related to the anatexis of their host rocks but they may alter-

tion and resemble two pyroxene granulites from the Jonsa area. Both types may occur in a single outcrop, while flat REE patterns are restricted to more mafic, garnet-bearing layers (Fig. 2c). Overall appearance in outcrop and compositional differences within granulites from the Jonsa and Varpanen-Pällikäs areas suggest a that the layer-ing in andesitic and basaltic rocks is of relict pre-

metamorphic origin.The intermediate granulites provide abundant

mineralogical evidence for dehydration melt-ing reactions involving amphibole, such as over-growth of pyroxenes on amphibole. Pyroxenes were produced by a reaction similar to reaction (2) defined by Patiño Douce and Beard (1995).

0.82 hbl + 0.18 qtz = 0.08 pl + 0.45 cpx + 0.22 opx + 0.22 melt + 0.02 il (2a)

252


natively represent minimum melts, equilibrium melts, disequilibrium melts, fractionated melts or cumulates. Strong positive Eu- and Sr-anomalies reflect the strong influence of plagioclase on leu-cosome composition and indicate that plagioclase fractionation was important in the petrogenesis of leucosomes. Leucosomes are therefore con-sidered as melt migration pathways consisting of plagioclase and quartz that crystallized early from a percolating and finally extracted melt phase (Marchildon & Brown 2001, Solar & Brown 2001, Sawyer 2001). This could also explain why plagioclase compositions in many migmatites are typically equivalent in both leucosomes and palaeosomes in (Whitney & Irving 1994, Gupta & Johannes 1982), since plagioclase in both units would have equilibrated with the same melt phase (Marchildon & Brown 2001).

The interpretation of leucosomes as plagio-clase-quartz-assemblages crystallized from a melt phase is supported by the coarse grain-size and the euhedral shape of plagioclase grains (Brown 2001). Furthermore, leucosomes are richer in CaO at high SiO2-contents compared to the vast majority of Archean TTG, indicating that frac-tionated, Ca-rich plagioclase exerts a significant influence on leucosome composition. The anhy-drous nature and the presence of peritectic phases (grt, cpx, opx) in some granulite leucosomes ad-ditionally implies that leucosomes cannot be re-garded as segregated melts since crystallization of the hydrous melts will lead to considerable ret-rogression of the peritectic phases in leucosomes and adjacent palaeosomes (White & Powell 2002).

Several parameters can influence leucosome composition if the fractional crystallization mod-el applies.1) Composition of the parent melt2) Composition of the fractionating plagioclase

and changing partition coefficients with changing XAn

3) Degree of fractional crystallization5) Amount of fractionating plagioclase and

other potential minerals such as quartz or K- feldspar

6) Entrapment of evolved liquids and entrain-ment of host rock minerals

7) Fractionation from already fractionated liquids

In order to apply a fractional crystallization mod-el we determined the modal abundance of plagio-clase in leucosomes by least squares regressions using appropriate plagioclase compositions. Pla-gioclase abundances were found to range between 40 – 60 % and a mean value of 50 % was used in modeling. XAn in the leucosomes ranges between 20 and 40. We used partition coefficients in the calculations appropriate for XAn 30 after Béd-ard (2006). The least constrained variable in the fractional crystallization model for leucosomes is the composition of the parent melt. Two out of 32 analyzed leucosomes from TTG gneisses have smooth REE patterns and major and trace element compositions closely resembling palae-osomes from TTG gneisses. Therefore these two compositions were used as potential parent melts for leucosomes in TTG gneisses. One granulite leu-

Fig. 5. Models for formation of leucosomes by fractional crystallization of respective equilibrium melts. The bold numbers in the diagrams refer to the degree of fractionation. Migmatite leucosomes with low REE contents are consistent with about 10 % fractionation of the parent melt, forming cumulates comprising 50 % pl and 50 % qtz. Higher REE contents in migmatite leucosomes require the entrapment of some fractionated liquid or crystallization from already fractionated liquids. Granulite leucosome compositions may record up to 10-75 % fractional crystallization, but it is important to note that instead of the high degree of fractionation, entrapment of fractionated liquids or crystallization from evolved melts are both equally viable mechanisms.

253


cosome was used as the parent melt for modeling of the granulite leucosomes because of its good agreement with the 10 % model melt composition calculated from the partial melting model.

Leucosomes with the lowest REE contents probably represent the most pristine cumulates. The degree of fractional crystallization to pro-duce such leucosomes from an average melt com-position similar to TTG gneisses was ~ 10 %. Slightly elevated HREE contents in leucosomes can be explained by crystallization of zircon as an accessory phase or by inheritance of zircon from the host rock (Fig. 5). Higher REE contents and less pronounced positive Eu-anomalies in the ma-

jority of leucosomes suggest that they formed by fractionation from an already fractionated liquid or that they contain trapped fractionated melts as suggested by Sawyer (1987). Both processes are equally plausible.

The formation of leucosomes by crystalliza-tion of plagioclase and quartz from a melt phase involves the generation of complementary frac-tionated liquids that will have negative Eu- and Sr anomalies. Very few leucosomes with these fea-tures have been found in the study area. The lack of residual liquids could be due to incomplete sampling but may also indicate efficient melt loss from the system.

SUMMARY

In this work I present an example of internal differentiation of Archean continental crust by coeval partial melting of middle to lower crustal lithologies. Melt forming reactions in different lithologies strongly depend on the activity of H2O in the peak-metamorphic fluid. While granulites represent the anhydrous residues of dehydration melting reactions involving amphibole, the low P-T-conditions determined for the migmatitic TTG gneisses and amphibolites require the pres-

ence of a hydrous fluid to allow melting at the wet solidus.

Melting of the TTG gneisses yielded leu-cosomes that are rich in Na2O and have a trond-hjemitic affinity while leucosomes within granu-lites are CaO-rich and classify as tonalites. This indicates that remelting of a Na2O-rich precursor under conditions that allow plagioclase to partici-pate in melt-forming reactions is a viable mecha-nism for producing trondhjemitic melts.

ACKNOWLEDGEMENTS

Pekka Tuisku is thanked for valuable comments that improved the manuscript.

REFERENCES

Anderson, J. L. & Smith, D. 1995. The effects of temperature and fO2 on the Al-in-hornblende barometer. American Mineralogist 80, 549−559.

Barker, F. 1979. Trondhjemite: Definition, environment and hypotheses of origin. In: Barker, F. (ed.) Trondhjemites, Dacites and related rocks. Amsterdam: Elsevier, 1−12.

Beard, J. S. & Lofgren, G. E. 1991. Dehydration melting and water-saturated melting of basaltic and andesitic green-stones and amphibolites at 1, 3 and 6−9 kb. Journal of Petrology 32, 365−401.

Bédard, J. H. 2006. Trace element partitioning in plagio-clase feldspar. Geochimica et Cosmochimica Acta 70, 3717−3742.

Brown, M. 2001. Orogeny, migmatites and leucogranites: A review. Proceedings of the Indian Academy of Sciences-Earth and Planetary Sciences 110(4), 313−336.

Greenfield, J. E., Clarke, G. L., Bland, M. & Clark, D. J. 1996. In-situ migmatite and hybrid diatexite at Mt. Stafford, Central Australia. Journal of Metamorphic

Geology 14(4), 413−426.Gupta, L. N. & Johannes, W. 1982. Petrogenesis of a stro-

matic migmatite (Nelaug, southern Norway). Journal of Petrology 23(4), 548−567.

Hartel, T. H. D. & Pattison, D. R. M. 1996. Genesis of the Kapuskasing (Ontario) migmatitic mafic granulites by dehydration melting of amphibolite: The importance of quartz to reaction progress. Journal of Metamorphic Ge-ology 14, 591−611.

Holland, T. J. H. & Blundy, J. 1994. Non-ideal interactions in calcic amphiboles and their bearing on amphibole-pla-gioclase thermometry. Contribution to Mineralogy and Petrology 116, 433−447.

Hölttä, P. 1997. Geochemical characteristics of granulite fa-cies rocks in the Archean Varpaisjärvi area, Central Fen-noscandian Shield. Lithos 40(1), 31−53.

Hölttä, P. & Paavola, J. 2000. P-T-t development of Archae-an granulites in Varpaisjärvi, Central Finland. I. Effects of multiple metamorphism on the reaction history of

254


mafic rocks. Lithos 50, 97−120.Hölttä, P., Huhma, H., Mänttäri, I. & Paavola, J. 2000. P-

T-t development of Archaean granulites in Varpaisjärvi, Central Finland. II. Dating of high-grade metamorphism with the U-Pb and Sm-Nd methods. Lithos 50, 121−136.

Hölttä, P., Heilimo, E., Huhma, H., Juopperi, H., Kontinen, A., Konnunaho, J., Lauri, L., Mikkola, P., Paavola, J. & Sorjonen-Ward, P. 2012. Archaean complexes of the Ka-relia Province in Finland. In: Hölttä, P. (ed.) The Archae-an of the Karelia Province in Finland. Geological Survey of Finland, Special Paper 54.

Johannes, W. 1984. Beginning of melting in the granite sys-tem Qz-Or-Ab-An-H2O. Contribution to Mineralogy and Petrology 86, 264−273.

Mänttäri, I., Sergeev, S. A., Paavola, J., Pakkanen, L. & Ves-tin J. 1998. From conventional to ionprobe U-Pb dat-ing of inhomogeneous zircon population: 3.2 Ga base-ment gneiss, Lapinlahti, Central Finland. 23th Nordiske Vintermode, p. 197.

Mänttäri, I. & Hölttä, P. 2002. U-Pb dating of zircons and monazites from Archean granulites in Varpaisjärvi, Cen-tral Finland: Evidence for multiple metamorphism and Neoarchean terrane accretion. Precambrian Research 118, 101−131.

Marchildon, N. & Brown, M. 2001. Melt segregation in late syn-tectonic anatectic migmatites: an example from the Onawa contact aureole, Maine, USA. Physics and Chem-istry of the Earth Part a-Solid Earth and Geodesy 26, 225−229.

Martin, H. 1994. The Archean Grey Gneisses and the gen-esis of continental crust. In: Condie, K. C. (ed.) Archean Crustal Evolution. Developments in Precambrian Geol-ogy, 205−247.

Martin, H., Smithies, R. H., Rapp, R., Moyen, J.-F. & Cham-pion D. 2005. An overview of adakite, tonalite–trond-hjemite–granodiorite TTG), and sanukitoid: relation-ships and some implications for crustal evolution. Lithos 79, 1−24.

Nehring, F., Foley, S. F., Hölttä, P. & van den Kerkhof, A. M. 2009. Internal Differentiation of the Archean Continen-tal Crust: Fluid-Controlled Partial Melting of Granulites and TTG Amphibolite Associations in Central Finland. Journal of Petrology 50, 3−35.

Paavola J. 1984. On the Archean high-grade metamorphic rocks in the Varpaisjärvi area, Central Finland. Geologi-

cal Survey of Finland, Bulletin 327. 33 p.Patiño Douce, A. E. & Beard, J. S. 1995. Dehydration-melt-

ing of biotie gneiss and quartz amphibolite from 3 to 15 kbar. Journal of Petrology 36(3), 707−738.

Rushmer, T. 1991. Partial melting of two amphibolites: con-trasting experimental results under fluid-absent condi-tions. Contribution to Mineralogy and Petrology 107, 41−59.

Sawyer, E. W. 1987. The role of partial melting and frac-tional crystallization in determining discordant migma-tite leucosome compositions. Journal of Petrology 28, 445−473.

Sawyer, E. W. 1998. Formation and evolution of granite magmas during crustal reworking: The significance of diatexites. Journal of Petrology 39(6), 1147−1167.

Sawyer, E. W. 2001. Melt segregation in the continental crust: distribution and movement of melt in anatectic rocks. Journal of Metamorphic Geology 19(3), 291−309.

Sen S. K. & Dunn T. 1994. Dehydration melting of a basaltic composition amphibolite at 1.5 and 2 GPa: implications for the origin of adakites. Contrib Mineral Petrol 117, 394−409.

Sisson, T. W., Ratajeski, K., Hankins, W. B. & Glazner, A. F. 2005. Voluminous granitic magmas from common ba-saltic sources. Contribution to Mineralogy and Petrology 148, 635−661.

Solar, G. S. & Brown, M. 2001. Petrogenesis of migmatites in Maine, USA: Possible source of peraluminous leucogran-ite in plutons? Journal of Petrology 42(4), 789−823.

White, R. W. & Powell, R. 2002. Melt loss and the preserva-tion of granulite facies mineral assemblages. Journal of Metamorphic Geology 20(7), 621−632.

White, R. W., Pomroy, N. E. & Powell, R. 2005. An in-situ metatexite-diatexite transition in upper amphibolite fa-cies rocks from Broken Hill, Australia. Journal of Meta-morphic Geology 23, 579−602.

Whitney, D. L. & Irving, A. J. 1994. Origin of K-poor leu-cosomes in a metasedimentary migmatite complex by ultrametamorphism, syn-metamorphic magmatism and subsolidus processes. Lithos 32, 173−192.

Wolf, M. B. & Wyllie, P. J. 1994. Dehydration-melting of amphibolite at 10 kbar − the Effects of Temperature and Time. Contribution to Mineralogy and Petrology 115(4), 369−383.

ISBN 978-952-217-213-6 (pdf)ISBN 978-952-217-214-3 (paperback)ISSN 0782-8535

www.gtk.fi [email protected]

Archaean rocks cover roughly one-third of the Precambrian region in the Fennoscandian Shield. This volume provides a review of previous studies and presents new data on the geo-chemistry, age determinations, metamorphism, palaeomag-netism and petrophysics of the Archaean rocks of the Finnish part of the Karelia Province, and discusses the magmatic and tectonic processes that could explain its present constitution and structure. Extensive new data are presented on U-Pb age determinations on zircon from volcanic rocks and metasedi-ments in the greenstone belts and adjacent areas, and on Sm-Nd analyses all over the Karelia Province in Finland.

geological survey of finland - 2012 (sp_054)

Documents