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KYANITE AND MG-RICH STAUROLITE AS INCLUSIONS IN GARNET; MORE EVIDENCE OF A HIGH PRESSURE EVENT IN THE SWEDISH EASTERN SEGMENT Eva Danielsson, Department of Earth Sciences, Earth Science Centre, Göteborg University, Box 460, S-405 30 Göteborg, Sweden Abstract The Borås Mafic Intrusion is a large zoned magmatic body which melted an envelope of its country rocks to form dacitic magma during intrusion at 1674 Ma. It was affected by Sveconorwegian metamorphism around 970 Ma, dated on zircon by ion probe and on garnet by Sm-Nd and Lu-Hf. Samples of garnet amphibolite with a basaltic composition are found to contain peraluminous assemblages such as Mg-rich staurolite (XMg 0,35-0,40), kyanite and clinozoisite included in garnet. These minerals have been chemically analyzed by SEM-EDS and confirmed by Electron Backscatter Diffraction (EBSD). The thermodynamic packages winTWQ, Theriak and Domino have been used to investigate the conditions under which these parageneses formed, and the bulk compositions from which they could form. We provisionally conclude that they formed in rocks which experienced plagioclase-out reactions due to high-pressure, low-temperature conditions analogous to the blueschist facies. Furthermore the bulk rock composition does not have a stability field for these parageneses. This suggests a two-stage process in which an aluminous assemblage first became isolated from the whole rock by inclusion in garnet, followed by the development of the parageneses we observed. I speculate about the original paragenesis and discuss implications for the evolution of the Eastern Segment. One possible original paragenesis for these inclusions is represented by Almandine + (Diopside or Jadeite) + Mg-chloritoid + Lawsonite + Quartz + Kyanite + H2O with a stability field at 582°C and 23-23,5 kbar. Another possible early paragenesis consists of Almandine + Diopside + Chlorite + Chloritoid + Lawsonite + Quartz and H2O. The temperature and pressure for this paragenesis is 480°C and 17,5 kbar. These pressures correspond to a depth of 50-70 km, indicating that the original paragenesis should have formed during high-pressure blueschist or eclogite facies metamorphism. A model has been suggested in which slices of eclogite were tectonically emplaced into the Eastern Segment from depth, implying that the Eastern Segment as a whole did not experience a high-pressure event. This cannot explain our findings in the Borås Intrusion, which is clearly an integral part of the Eastern Segment and shows no evidence of such a tectonic process. Keywords: inclusions, mg-rich staurolite, kyanite, high pressure, eastern segment ISSN 1400-3821 B540 2008

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KYANITE AND MG-RICH STAUROLITE AS INCLUSIONS IN GARNET; MORE EVIDENCE OF A HIGH PRESSURE EVENT IN THE SWEDISH EASTERN SEGMENT Eva Danielsson, Institution för Geovetenskaper, Göteborg Universitet, Box 460, S-405 30 Göteborg Sammanfattning Den mafiska intrusionen i Borås är en stor zonerad magmatisk kropp som smälte upp den omgivande berggrunden och bildade en dacitisk magma vid 1674 Ma. Den blev sedan påverkad av Svekonorvegisk metamorfos omkring 970 Ma, daterad med hjälp av zirkoner och Sm-Nd och Lu-Hf i granater. Prover av granat amfibolit med en basaltisk sammansättning innehåller mineraler associerade med peraluminös magma såsom Mg-rik staurolit (XMg 0,35-0,40), kyanit och clinozoisit som är inneslutna i granaterna. Dessa mineral har blivit kemiskt analyserade av SEM-EDS och sedan bekräftade av Electron Backscatter diffraction (EBSD). Termodynamiska dataprogram såsom winTWQ, Theriak and Domino användes för att kontrollera under vilka förhållanden dessa mineraler kunde har bildats och vilken bulk sammansättning de hade vid bildning. En lösning till hur dessa mineraler har bildats är att bergarten utsattes för en utfasning av plagioklas genom hög tryck och låg temperatur förhållanden motsvarande blåskiffer facies metamorfos. Vidare finns det inget stabilitetsfält för kyanit, staurolit och clinozoisit i en bergart med mafisk bulksammansättning. Detta faktum antyder en tvåstegs-process där först en aluminiumrik sammansättning blev isolerad från sin omgivande bergart som inklusioner i granater. Detta följdes sedan av den paragenesutvecklingen som vi idag observerar. Jag spekulerar om en original-paragenes och diskuterar vad detta kan medföra för utvecklingen av det Östra segmentet. En möjlig original paragenes för dessa inklusioner representeras av Almandin + (Diopsid eller Jadeit) + Mg-kloritoid + Lawsonit + Kvarts + Kyanit + H2O och denna kombination är stabil vid 582°C och 23-23,5 kbar. Ytterligare en möjlig tidig paragenes består av Almandin + Diopsid + Klorit + Kloritoid + Lawsonit + Kvarts och H2O. Temperaturen och trycket för denna paragenes är 480°C och 17,5 kbar. Dessa tryck skulle motsvara ett djup av 50-70 km, dvs att en tidig paragenes har bildats under blåskiffer eller eklogit facies metamorfos. En model har föreslagits där skivor av eklogiter blev tektoniskt placerade i det Östra Segmentet från djupet, vilket i sin tur skulle antyda att vissa delar av det Östra Segmentet inte blev påverkade av en högtryckshändelse. Denna model kan inte förklara våra fynd i Borås-intrusionen, vilket definitivt är en del av Östra Segmentet. Fynden där uppvisar inga bevis för en sådan tektonisk process. Nyckelord: inclusions, mg-rich staurolite, kyanite, high pressure, eastern segment ISSN 1400-3821 B540 2008

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Table of contents: 1. Introduction .......................................................................................................................... 4

1.1 Regional geology.............................................................................................................. 4 1.1.1 Eastern Segment........................................................................................................ 5 1.1.2 Western Segment....................................................................................................... 7 1.1.3 Geological setting at Borås ....................................................................................... 7

1.2 Petrography of samples from Borås and Viared .............................................................. 9 1.2.1 Hornblende gabbro samples AA9680, AA9619A and AA9619B ............................ 9 1.2.2 Garnet amphibolite sample DC0201, DC07200 and DC07201 ................................ 9 1.2.3 The Viared locality.................................................................................................. 10

1.3 Fluid and mineral Inclusions .......................................................................................... 10 1.4 Chemenda Model ........................................................................................................... 11

2. Methods ............................................................................................................................... 12 2.1 Electron microanalysis ................................................................................................... 12 2.2 Electron backscatter diffraction ..................................................................................... 12 2.3 WinTWQ........................................................................................................................ 12 2.4 Domino-Theriak ............................................................................................................. 13

3. Analysis and results............................................................................................................ 14 3.1 Electron microanalysis ................................................................................................... 14 3.2 Electron backscatter diffraction ..................................................................................... 14 3.3 Reliability test of databases from Domino-Theriak and winTWQ ................................ 15 3.4 Domino-Theriak ............................................................................................................. 16 3.5 winTWQ calculations..................................................................................................... 19 3.6 XMg for Staurolite ........................................................................................................... 21 3.7 Finding an Early Paragenesis ......................................................................................... 23

4. Discussion............................................................................................................................ 26 5. Conclusion........................................................................................................................... 28 6. Acknowledgement .............................................................................................................. 28 7. References ........................................................................................................................... 29 Appendix ................................................................................................................................. 34

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1. Introduction The aims of this masters thesis are to positively identify and chemically analyse all the mineral inclusions in garnet in several samples from the Borås mafic intrusion using electron microanalysis and electron backscatter diffraction. The analyses will be used to calculate phase diagrams and establish P-T conditions and a possible petrogenetic history of the rocks. The Borås Mafic Intrusion is a large zoned magmatic body which melted an envelope of its country rocks to form dacitic magma during intrusion at 1674 Ma (Åberg, 1997). It was later affected by Sveconorwegian metamorphism around 970 Ma (Scherstén et al, 2004), dated on zircon by ion probe U-Pb and on garnet by Sm-Nd and Lu-Hf (E. Hegardt pers comm. 2008). Samples of garnet amphibolite with a basaltic composition were found to contain peraluminous assemblages included in garnet, such as Mg-rich staurolite (XMg 0,35 to 0,40), kyanite, chlorite, clinozoisite and other phyllosilicates. Mafic boudins found at Viared, close to Borås, contain evidence of eclogite facies peak pressure conditions of 15-17 kbar and 719-811°C (Hegardt et al, 2005). Several other localities in the Eastern Segment are also known to have preserved retrograde eclogite mineral assemblages (Möller, 1998). Therefore it would be interesting to investigate the garnet inclusions at the Borås intrusion for their temperature and pressure of origin and to also establish a possible P-T-t history for the inclusions based on calculated phase diagrams. According to Hellman et al (1979), the occurrence of Mg-staurolite (defined as XMg = Mg / (Mg+Fe) >0.30 by Deer et al. 1982) usually is restricted to P >12 kbar and temperatures ranging from ~700°C to 1000°C. Further investigation of Mg-staurolite by Fockenberg et al. (1998), indicate that Mg-staurolite is stable at pressures between 12 and 66 kbar with a lower temperature limit of 608±8°C and an upper temperature limit of 918±8°C. “Formation of staurolite and kyanite (or sillimanite) with hornblende in pure mafic rocks has been interpreted as a result of either different bulk composition or of specific P–T conditions” (Faryad et al 2006). In the work by Arnold et al. (2000) pseudosections for mafic rocks (mostly amphibolites) of different compositions that contain kyanite and staurolite were calculated. The result was a wide range of P–T conditions permitting the association of aluminosilicates with hornblende, but the occurrence of staurolite is mostly restricted to a specific bulk composition and over a narrow P–T range (8-10 kbar and ~600°C).

1.1 Regional geology The continental crust of the Fennoscandian (Baltic) Shield was formed between 3,5 and 1,5 Ga according to Gaál and Gorbatschev (1987). The shield area grew by southwestern accretion and large-scale crustal formation during a number of orogenic events. The shield is characterised by a regular geochronological zonation, with ages getting younger from the northeast towards the southwest. The shield can be divided into three main domains; the Archean Domain, the Svecofennian Domain and the Southwest Scandinavian Domain. The oldest bedrock in the southern part of the Baltic Shield is divided into three main areas; the Svecokarelian Province (or Svecofennian Orogen, 1,90-1,75 Ga, Fig. 1), the Transscandinavian Igneous Belt (1,85-1,67 Ga) and the Sveconorwegian Province (1,2-0,9 Ga). The Southwest Scandinavian Domain, which constitutes the southwestern part of the Baltic Shield (Gaál and Gorbatschev, 1987), is thought to have formed 1,69 and 1,55 Ga ago

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through eastward subduction and westward accretion, followed by crustal thickening (Åhäll and Gower, 1997). Throughout the Sveconorwegian orogeny 1,2-0,9 Ga (Wahlgren et al., 1994) crustal reworking and metamorphism affected the Southwest Scandinavian Domain. In the east the Transscandinavian Igneous Belt (Persson and Wikström, 1993) separates the Sveconorwegian Province from the Svecofennian Orogen. The Sveconorwegian Province in Sweden is composed of different crustal segments, the Eastern and Western Segments (Fig. 1), separated by the Mylonite Zone. The Protogine Zone marks the eastern limit of the Eastern Segment and separates the Trans-Scandinavian Igneous Belt (or Småland-Värmland Granitoid Belt) from the Eastern and Western Segments (Larson et al., 1986). The Protogine Zone is considered as equivalent to the Grenville Front in North America, due to similarities in lithology, structural style and geological history (Gower and Owen, 1984). The steeply west-dipping Sveconorwegian Frontal Deformation Zone (SFDZ) marks the eastern limit of the Sveconorwegian Orogeny and the sub-vertical Protogine Zone marks the limit between Sveconorwegian penetrative and non-penetrative deformation (Wahlgren et al., 1994). The Mylonite zone is a 400 km long west-dipping ductile deformation zone, which separates the Eastern Segment from the structurally overlying units in the west, and features Sveconorwegian transpressional (oblique convergence) deformation in its northern and central parts (Stephens et al., 1996; Park et al., 1991; Möller, 1998). East of the Protogine Zone and Sveconorwegian Frontal Deformation Zone the 1,85-1,67 Ga old igneous rocks of the Transscandinavian Igneous Belt and younger intrusive rocks are essentially undeformed and show no sign of metamorphism (Johansson, 1993).

1.1.1 Eastern Segment The Eastern Segment (Fig. 1), which is located between the Mylonite Zone and Protogine Zone, consists of a strongly reworked cratonic margin of the Fennoscandian (Baltic) Shield. The majority of the exposed rocks in this segment are complex polymetamorphic granitoid gneisses with polydeformed character. They have a calc-alkaline affinity, with a composition of intermediate to acid and are regarded as orthogneisses (Ahlin, 1983; Larson et al., 1986).

Fig. 1. Map of southern Sweden showing the major geologic units (figure from Scherstén et al 2004) Abbreviations which are not given in the text; B – Bamble region, U – Ullared, K – Kedum.

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East of the Mylonite Zone, primarily banded and veined granodioritic gneisses are found while more granitic gneisses and supracrustal rocks are found in the area west of the Protogine Zone. This regional change in rock types is considered to reflect the exposure of different crustal depths (Larson et al., 1986; Larson and Berglund, 1992). The metamorphism caused by reworking the crust of the Baltic Shield resulted in widespread high-pressure granulite-facies assemblages in the southernmost part of the Eastern Segment. P-T estimates based on geothermobarometry of high-pressure granulite and upper amphibolite facies minerals give temperatures of 680-800 °C and pressures of 8-12 kbar (Johansson et al., 1991; Johansson and Kullerud, 1993; Wang and Lindh, 1996). Distinctly higher pressure (>15 kbar) are recorded by the preservation of eclogites in the Ullared Deformation Zone (Möller, 1998), 30 km east of the Mylonite Zone. In the central parts of the Eastern Segment, Sveconorwegian metamorphism reached upper amphibolite facies conditions, and in the Ulricehamn area P-T estimates are as high as 750 °C and 9 kbar (Cornell et al., 1996). North of Lake Vänern in the northern parts of the Eastern Segment, Sveconorwegian metamorphism grades from greenschist facies at the Sveconorwegian Frontal Deformation Zone in the east to amphibolite facies at the Mylonite Zone in the west (Wahlgren et al., 1994). The oldest rocks (gneisses) of the Eastern Segment were formed 1,68 Ga ago. These gneisses as well as 1,55 Ga old mafic dykes can be found eastward across the Sveconorwegian Frontal Deformation Zone into the Transscandinavian Igneous Belt. This fact indicates that the northern and possibly the southern part of the Eastern Segment consist of tectonically reworked Transscandinavian Igneous Belt rocks (Söderlund et al., 1999). The granites of the Eastern Segment were intruded by younger granites and quartz-monzonites at 1,55 Ga (Lindh, 1996; Johansson et al., 2001), 1,4-1,37 Ga and 1,225 Ga (Berglund and Connelly, 1994; Welin, 1994; Lindh, 1996; Andersson et al., 1999). The large quantity of granitic and mafic intrusions in the central and southern parts of the Eastern Segment suggests thermal activity at 1,5-1,36 Ga according to Connelly et al., (1996). There are several generations of mafic dykes within and immediately east of the Protogine Zone. Their ages are approximately 1,56 Ga (Ask, 1996), 1,4 Ga, 1,18 Ga and 960 Ma (Johansson et al., 2001). Syenitic intrusions and mafic dykes cut through the Transscandinavian Igneous Belt granites along the Protogine Zone. The oldest mafic dykes have been dated to 1,57-1,55 Ga (Johansson and Johansson, 1990). Within and to the east of the Protogine Zone large-scale Sveconorwegian extensional deformation is evidenced by the younger, 960-925 Ma mafic dykes. Metamorphosed mafic rocks, of unknown ages, are common in the Eastern Segment and may be equivalents to the mafic dykes east of Protogine Zone described above (Johansson et al., 2001). Zircons from well-preserved mafic complexes in the eastern part of the Eastern Segment give ages around 1,56 Ga and 1,4 Ga (Wang, 1996). Geochronological data concerning the Sveconorwegian deformation and metamorphism from the Eastern Segment show some regional variation with a weak tendency of younger ages towards the south. 40Ar-39Ar hornblende ages in the northern part fall within the interval 1010-960 Ma and in the southern part 1030-920 Ma (Page et al., 1996a; Page et al., 1996b; Wang et al., 1996; Johansson et al., 2001).

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1.1.2 Western Segment The Western Segment is bounded to the east by the Mylonite Zone and to the west by the Oslo Graben. The Western Segment comprises the Åmål-Horred Belt to the east and the Stora-Le-Marstrand Formation to the west, both of which are dominated by calc-alkaline felsic to intermediate granitoids and associated supracrustal rocks, reworked at amphibolite facies and locally lower greenschist facies conditions (Lundqvist, 1994). These rocks are considered younger than the Transscandinavian Igneous Belt rocks and associated supracrustals (i.e. 1,64-1,59 Ga according to Connelly and Åhäll, 1996). Important intrusions in the Western Segment are the 920 Ma Bohus Granite (Eliasson and Schöberg, 1991) and the Vinga Porphyry (Åhäll, 1995). Both the Western and Eastern Segments carry imprints of the Mid-Proterozoic Sveconorwegian orogeny and thus belong to the Sveconorwegian Province. The oldest Sveconorwegian magmatism is a number of WNW–ESE trending undeformed rare mineral pegmatites (Scherstén et al 2004). The 1,03 Ga Högsbo pegmatite is one of them, which obliquely cross cuts foliation and veins of a deformed granite that belongs to the 1.34–1.31 Ga Askim Suite (Lundqvist, 2000, Hegardt et al 2007). The main phase of Sveconorwegian magmatism is actually post-tectonic represented by the 0.95 Ga Vinga quartz monzodiorite to monzogranite intrusion 0.92 Ga Blomskog and Bohus granites. These undeformed intrusions are contemporaneous with extension and normal faulting along the Mylonite Zone (Johansson and Johansson, 1993 and Berglund, 1997).

1.1.3 Geological setting at Borås The ultramafic-mafic intrusion in Borås is situated in the Eastern Segment. Three major orogenies are believed to have created the gneissic foliation and shear zones in the region. At 1,75 – 1,55 Ga the Gothian orogeny may have occurred and it is usually characterized by accretion of crustal segments on to the Svecofennian shield. During a crust-forming episode of subduction-related magmatism between 1,6 and 1,7 Ga, the granitoid gneisses were formed (Andersson et al., 1992). Metamorphism in the Eastern Segment was of high grade and represents different crustal depths, according to Johansson et al. (1991). The area has also been affected by tectonometamorphic reworking during the Hallandian orogeny at 1.45–1.42 Ga resulted in migmatization and formation of a coarse gneissic layering, eg. the migmatitic fabric at Viared, dated by Hegardt et al (2005). Hubbard (1975) first coined the term “Hallandian” for an isolated granitic-monzonitic magmatism at 1,40-1,38 Ga and later overprinting of high-grade metamorphism, which was dated as Sveconorwegian (Johansson et al., 1991). Möller et al (2007) suggested that the term “Hallandian” should be used for the ~1,43 G regional metamorphism and also for the younger 1,40-1,38 G intrusions. The term Hallandian has been used for high-grade metamorphism and granitic to monzonitic intrusions in the Eastern Segment for over 30 years. Another reason to call it Hallandian is that structural relationships, petrology and geochronology for these events are characteristic of a geographical region, where the term was coined (Möller et al., 2007). During the 1,2-0,9 Ga Sveconorwegian orogeny often correlated with the Grenvillian orogeny in the North America, a collision event was followed by reworking of the different crustal segments, along N-S trending shear zones (Park et al. 1991). The Borås ultramafic-mafic intrusion and surrounding rocks have been studied in detail by Åberg (1997), whose map is reproduced in Fig.2, showing sample localities. According to the

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geological map from SGU (7c BORÅS SO, Ahlin 1983), two possibly related ultramafic-mafic bodies lie close to each other, stretched out in the foliation direction of the Eastern Segment gneisses. The bodies are separated by a tonalite with gneissic appearance and gneissic granodiorite. They could be interpreted as either two parts of the same intrusion, which stretched apart during regional deformation, or two channels of the same intrusion

Fig. 2. Geological map of Borås mafic intrusion (from Åberg 1997) Locality DC07200 and DC07201 are added on this map.

DC0201

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(Åberg, 1997). The tonalite was interpreted by Åberg (1997) as due to melting of the country granites by the mafic intrusion and some mixing between them gave the intermediate composition. There is good field evidence for this mixing, such as hornblende microxenoliths in the tonalite. Close to Borås in the Viared area, some eclogite facies mafic rocks occur as boudins in strongly folded granodioritic orthogneisses. The margins of the boudins are retrograded sheared and well-foliated dark amphibolites. The boudins are dark-grey in the centre and paler towards the edges. The amphibolites contain garnet, clinopyroxene, plagioclase, amphiboles, quartz and additional minor phases. Locally the boudins exhibit very garnetiferous layers as well as more felsic layers (i.e. quartz and plagioclase). One kyanite inclusion was found in a garnet in Viared, confirming that a plagioclase-out reaction must have occurred (Claesson, 2002, Hegardt et al 2005).

1.2 Petrography of samples from Borås and Viared Petrography has been done for the Borås samples AA9680 and AA9619 by Åberg (1997) and for the Viared sample by Hegardt et al (2005). A summary is given below. Samples DC0201, DC07200 and DC07201 (Borås; garnet amphibolites) have been studied in thin section and investigated in hand samples collected by the writer from the field.

1.2.1 Hornblende gabbro samples AA9680, AA9619A and AA9619B These rocks show a weak foliation defined by hornblende- and biotite bands with preferred orientation. The main minerals are hornblende and plagioclase. The rock is mainly medium grained with anhedral to subhedral inequigranular texture. There seems to be a recrystallization of smaller grains of hornblende on the edge of the larger grains. Plagioclase is bimodal in both shape and size. According to Åberg (1997) the composition is An40. Light-brown to brown (pleochroic) biotite can be seen growing over the hornblende and in same places replaced by chlorite. Accessories are garnet, apatite, epidote and opaque minerals. Samples AA9619B and AA9619A differ slightly. 9619A is more fine-grained, contains no biotite and has more abundant garnet than seen in 9619B (Åberg 1997).

1.2.2 Garnet amphibolite sample DC0201, DC07200 and DC07201 The main minerals in DC0201, DC07200 and DC07201 are hornblende, diopside, garnet, plagioclase and quartz. The grain size is fine- to medium grained. Hornblende, diopside and quartz have relatively euhedral grains. There is a preferred orientation of the minerals. Hornblende shows some twinning within the grains. The pleochroism varies between pale green to yellow green and blue green. The garnets are relatively cracked and usually have rims of plagioclase which could be interpreted as retrograde coronas. They contain opaque minerals and small inclusions, with the following paragenesis: clinozoisite, kyanite, staurolite and chlorite, later investigated using SEM-EDS. Regarding inclusions of chlorite in garnet sample DC0201f, a question is whether this chlorite is considered to be primary or secondary. In the specific inclusion containing the mineral assemblage garnet, kyanite and chlorite there were no visible fractures. In that case the chlorite could be considered to be primary and therefore evidence of an earlier assemblage in the rocks. The composition of this chlorite (site 24) can be seen in Table 8, Appendix 6. The

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garnet inclusions from sample DC07200 and DC07201 contain no staurolite or kyanite. Most of the inclusions in these two samples were either plagioclase or K-feldspar, with some quartz.

1.2.3 The Viared locality Retrograde eclogite samples from this locality have been investigated in detail by Hegardt et al., (2005). Most of the samples (DC0155-161) are from the boudins. The boudins are dominated by garnet, clinopyroxene showing symplectitic exsolution of plagioclase, hornblende and plagioclase grains, with minor occurrences of quartz, titanite and rutile. Accessory ilmenite, zircon, zoisite and apatite are present.

1.3 Fluid and mineral Inclusions “Fluids in the lower crust are thought to play an important role on the stability and transformation of mineral assemblages in high-grade metamorphic rocks. It is therefore important to characterize the chemical and physical properties of fluids at various stages of metamorphism. Several attempts have been made to infer the compositions of synmetamorphic fluids, including thermodynamic calculations of mineral assemblages and geochemical studies” (cited from Ohyama et al. 2007). “Fluid inclusions trapped in individual metamorphic minerals sometimes yield potential information on the nature and activity of synmetamorphic fluids. Detailed petrographic and microthermometric observations therefore provide important clues about the composition and density of the fluids involved in deep crustal metamorphism. Such results have been widely used to infer the P–T–X conditions and exhumation paths for high-grade rocks” (cited from Ohyama et al. 2007). Generally when staurolite is a product of the prograde high-pressure stage of metamorphism (e.g., Shimpo et al., 2006), the re-healed cracks commonly found within mineral grains probably formed at the high-pressure stage or subsequent UHT (Ultra High Temperature) stage. Minerals occurring as inclusions in refractory minerals such as garnet but not in the matrix of the rock do not belong to the main matrix assemblage. The inclusion of chlorite, kyanite, clinozoisite and staurolite in garnet can be evidence for an earlier assemblage in the rock. In the Borås case, the following minerals occur together in the garnet inclusions:

1) staurolite + clinozoisite + kyanite 2) staurolite + kyanite 3) staurolite + kyanite + chlorite

There are also some inclusions comprising of kyanite, muscovite and plagioclase. In the course of a metamorphic process some earlier-formed minerals may become metastable and react to form a new, more stable assemblage. However, metastable relics of the early assemblage may partly survive (Bucher & Frey, 1994).

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1.4 Chemenda Model Hegardt (2000) suggested that the Mylonite Zone could have formed as a Sveconorwegian crustal suture, instead of an intra- continental shear zone, which agrees with work by Söderlund (1999). Application of the Chemenda (1995, 1996 and 1997) model suggests that the crust of Svecofennian and Transscandinavian Igneous Belt collided with a continent to the west, now represented by the Western Segment. The subducted crustal slab acquired a high-pressure eclogite facies imprint, then broke off and came back up along the subduction zone, partly regressed to amphibolite facies assemblages and developed into the present Eastern Segment. The Chemenda (1995, 1996 and 1997) tectonic model explains the burial and uplift of eclogites and the Sveconorwegian evolution of the south western Sweden, better than previous models by Berglund (1997) and Åhäll (1995). According them the Mylonite Zone formed by crustal thickening. In this work I aim to establish whether the crust at Borås had experienced sub-crustal metamorphism, which if true would suggest crustal subduction.

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2. Methods The following methods were used to identify all the mineral inclusions in garnet in several samples from the metabasites in the Borås mafic intrusion. The aim was to fully characterise the mineral assemblages containing kyanite, staurolite and other minerals. These would be used for P-T calculations and to determine a petrogenetic history that could explain the formation of these mineral assemblages.

2.1 Electron microanalysis The composition of different minerals was determined on polished thin sections using a Hitachi S-400N scanning electron microscope. Each thin section was cleaned with alcohol and then coated with carbon before putting it into the SEM. The analytical conditions were: 20 kV, working distance 10 mm, specimen current ~3,5 nA, yielding an EDS detector dead time just less than 50% on cobalt. The cobalt reference standard was used and checked every hour, in order to monitor the analytical drift. The easiest way to find Al-rich minerals is to make X-ray maps of (dimensions e.g. 1 mm square) areas of the garnet and to identify minerals by their major element combinations. Backscattered electron images are also useful in distinguishing one mineral from another, since the brightness, the backscattered electron image is proportional to the mean atomic number of each mineral.

2.2 Electron backscatter diffraction Electron backscatter diffraction (EBSD) is a microstructural-crystallographic technique used to reveal the crystallography and orientation of any crystalline materials. EBSD can be used to identify and index diffraction lines in all seven crystal systems, and can be applied to crystal orientation mapping, defect studies, grain boundary and the identification of different polymorphs of minerals which have the same chemical composition. Traditionally this type of study has been carried out using X-ray diffraction (XRD), neutron diffraction or electron diffraction in a transmission electron microscope (Pennock et al 2006). Experimentally EBSD is conducted using a scanning electron microscope (SEM) equipped with a backscatter diffraction camera. A polished thin section is placed in the normal position in the specimen chamber, but is tilted 70° from horizontal towards the diffraction camera.

2.3 WinTWQ The winTWQ software by Berman (1991, 2006) is used for P-T calculation based on the compositions of minerals in a paragenesis. For each mineral-reaction proposed winTWQ calculates P-T stability lines based on a thermodynamic dataset, minimising the Gibbs free energy by varying temperature at a number of fixed pressures. If equilibrium was attained between the analysed minerals the intercept of two or more reactions lines gives the P-T conditions of equilibrium (Bucher and Frey, 1994). The prefix given in the input oxi-file is g for garnet and z for kyanite, staurolite, chlorite and clinozoisite. The prefix z is given for any other Fe-Mg mineral, for which only XFe and XMg will be calculated. Since the mineral assemblages found using the SEM contain garnet with

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inclusions of kyanite, staurolite, chlorite, plagioclase and clinozoisite, the (2006) database version 2.32 (which does not have data for hornblende) could be used for the inclusions in garnet. Version 1.02, by Mäder (1992, 1994) had to be used for rock samples containing hornblende. The garnets are generally surrounded by hornblende and usually have a corona (rim) of plagioclase due to retrograde metamorphism, but there was no hornblende in the inclusions.

2.4 Domino-Theriak The pressure and temperature conditions of stability fields for specific parageneses in the metamorphic rocks were determined by calculating equilibrium phase diagrams using the Domino-Theriak software (de Capitani & Brown, 1987; de Capitani, 1994). A modified internally consistent mineral database based on JUN92 of Berman (1988) was supplemented with thermodynamic data for ferro- and magnesio-carpholite, and magnesio- and ferrochloritoid from Le Bayon (2002). Data for glaucophane and ferro-glaucophane (El-Shazly & Liou, 1991), daphnite and phengite (Massonne & Szpurka, 1997) were also added by Capitani in 2006. Theriak calculates the stable mineral assemblage and phase compositions for a given bulk composition at specified P-T conditions. Domino calculates equilibrium assemblage diagrams with selectable axes (P, T, activity of components and logarithms of activities), pseudo-binary or pseudo-ternary phase diagrams and phase compositional isopleths as well as density, volume or modal amount distributions. We learned how to use these programs during a short course given by De Capitani at Gothenburg University in 2007, sponsored by the Nordic Mineralogical Network and NORFA.

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3. Analysis and results The minerals were chemically analyzed by SEM-EDS and the identifications were confirmed by Electron Backscatter Diffration (EBSD). These results were then used for P-T calculations in Domino, Theriak and winTWQ software.

3.1 Electron microanalysis Five thin sections DC0201a-e and an epoxy mount DC0201f from the Borås mafic intrusion was investigated using the SEM, in order to find mineral inclusions in garnets. Assemblages containing kyanite and staurolite with zoisite, clinozoisite and chlorite were found in the garnet as illustrated in Fig. 3. This inclusion is from garnet number 1 in sample DC0201f (see Fig. 12, Appendix 1). The paragenesis found was kyanite, clinozoisite and staurolite. There were also some inclusions that contain only kyanite, sometimes together with plagioclase, quartz or chlorite. Mineral analyses for each assemblage are given in Table 8, Appendix 6.

3.2 Electron backscatter diffraction The inclusions were also investigated using electron backscattered electron imaging. The crystal structures of kyanite, staurolite and clinozoisite were confirmed using electron backscatter diffraction (EBSD). In the EBSD image, two different grains of both kyanite and staurolite within the same inclusion were seen (Fig. 4).

Kyanite Staurolite

Clinozoisite

Fig. 3 One of the inclusions containing kyanite, clinozoisite and staurolite.

Fig. 4 EBSD pattern from one of the inclusions.

Ky St

cZo

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3.3 Reliability test of databases from Domino-Theriak and winTWQ Can Domino-Theriak and winTWQ reproduce results from other authors who produced Mg-staurolite experimentally? This is a test of the reliability of the database used (winTWQ version 1.02 by Berman 1991 and Domino-Theriak database jun92.bs). According to Christian Capitano (pers. comm. 2008), developer of Domino-Theriak, these databases are similar in endmember properties, but not in solution models. This fact could complicate the match between whole rock analysis and mineral composition from the different authors. Enami et al. (1988) and Faryad et al. (2006) produced Mg-staurolite experimentally, see their geochemical data in Table 4-5 in Appendix 2-3 and Table 7 in Appendix 5. A summary of the results received from Domino and winTWQ are given in Table 1 below. These results are compared with the data given in the published paper. WinTWQ diagrams for Enami and Faryad are given in Fig. 13-14, Appendix 7. Table. 1 Domino winTWQ Results from authors

Author Temp. (°C)

Pressure (kbar)

Temp. (°C)

Pressure (kbar)

Temp. (°C)

Pressure (kbar)

Enami et al 1988 695 13-14 700-800 13-15 730-770 11-14 Faryad et al 2006 580 11,3 550 9 530-580 10-11,5 Conclusion – there was reasonably good correspondence between Domino-Theriak, winTWQ and the experimental results given by Enami et al (1988) and Faryad et al (2006). Therefore it is applicable to use these software packages in this study of garnet inclusions at Borås mafic intrusion.

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3.4 Domino-Theriak The stability field for parageneses including garnet, clinozoisite, staurolite and kyanite was sought in whole rock compositions from Borås mafic intrusion. AA9680 and AA9619 – hornblende gabbro, seen in Table 7, Appendix 5, are thought to represent the composition of the garnet-bearing amphibolite, for use with Domino-Theriak. However no stability field was found for these minerals in these samples from the Borås mafic intrusion. Assuming a peraluminous starting composition (PER1, Table 7 in Appendix 5) compiled from the analysed garnet, chlorite, kyanite and clinozoisite, the stability field of some appropriate parageneses were sought. These are: 585°C and 11,1 kbar Alm+FeSt+Chl+cZo+Ky+H2O 592°C and 13,9 kbar Alm+FeSt+Chl+cZo+Ky+H2O Mineral abbreviations can be found in Table 2 below. These fields are quite small (Fig. 5) and the fields with the lowest temperature and pressure are missing garnet. Regarding whether the staurolites are FeSt or MgSt, this is determined by Domino-Theriak when the endmember is more than 50%. This differs from XMg at 30% in the literature. If all phases were calculated, the inclusions should have been in equilibrium at upper amphibolite facies conditions. Other parageneses in figure 5 are: Alm+Chl+FeCtd+cZo+aQz+H2O (1) Alm+FeSt+Chl+aQz+Mar+H2O (2) Alm+FeSt+Chl+cZo+Ky+Tep+H2O (3) * marks the temperature and pressure that Åberg (1997) got from his calculation on the mafic intrusion in Borås (700°C and 8,5 ± 0.6 kbar). The composition (peraluminous start composition, PER1) used in Domino-Theriak is an average of all the minerals involved, given in Table 7, Appendix 5. Some elements were removed due to small amounts and usually restricted to one mineral, for example CO2 and Ti2O. The MnO-content is generally low and can expand the stability field for garnet.

Fig. 5 Stability field (indicated by arrow) for an assumed peraluminous start composition PER1 composed of garnet, chlorite, clinozoisite and kyanite.

1

2

3

*

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Table 2. Abbreviations used for minerals in the text and their chemical formulas. Abbrev. Mineral Chemical formula Ab Albite NaAlSi3O8 Alm Almandine Fe3Al2(SiO4)3 An Anorthite CaAl2Si2O8 Cd Corderite Mg2Al4Si5O18 Chl Chlorite (Mg,Fe)5Al(Si3Al)O10(OH)8 Clc Clinochlore (chlorite) (Mg,Fe)5Al(Si3Al)O10(OH)8 Coe Coesite SiO2 Cor Corundum Al2O3 Ctd Chloritoid (Fe,Mg,Mn)Al2SiO5(OH)2 cZo Clinozoisite Ca2Al3(Si2O7)(SiO4)(O,OH)2 Di Diopside CaMgSi2O6 Dia Diaspore AlO(OH) Epi Epidote Ca2FeAl2(Si2O7)(SiO4)(O,OH)2 En Enstatite (Mg,Fe)SiO3 Fa Fayalite Fe2SiO4 FeCtd Fe-chloritoid (Fe,Mg,Mn)Al2SiO5(OH)2 Femg Mg-Fe pyroxene (Mg,Fe)2Si2O6 FePar Fe-pargasite (hornblende) (Na,K)0-1Ca2(Mg,Fe2,Al)5Si6-7,5Al2-0,5O22(OH)2 FeSt Ferrostaurolite Fe2Al9O6(SiO4)4(OH)2 Gla Glaucophane Na2Mg3Al2Si8O22(OH)2 Grs Grossular Ca3Al2(SiO4)3 Gt Garnet X3Y2(SiO4)3 X(Mg,Fe,Mn or Ca), Y(Al,Fe or Cr) Hd Hedenbergite CaFeSi2O6 Hem Hematite Fe2O3 Her Hercynite FeAl2O4 Ilm Ilmenite FeTiO3 Jd Jadeite NaAlSi2O6 Ky Kyanite Al2SiO5 Lw Lawsonite CaAl2(Si2O7)(OH)2 x H2O Mag Magnetite Fe3O4 Mar Margarite (mica) CaAl2(Si2Al2)O10(OH)2 MgCtd Mg-chloritoid (Fe,Mg,Mn)Al2SiO5(OH)2 MgSt Mg-staurolite (Mg,Fe2+,Zn)2Al9(Si,Al)4O22(OH)2 Ms Muscovite KAl2(Si3Al)O10(OH,F)2 Nep Nepheline (Na,K)AlSiO4 Pag Paragonite (mica) NaAl2(Si3Al)O10(OH)2 Par Pargasite (hornblende) (Na,K)0-1Ca2(Mg,Fe2,Al)5Si6-7,5Al2-0,5O22(OH)2 Phl Phlogopite K(Mg,Fe)3(Si3Al)O10(F,OH)2 Prh Pyrophyllite Al2Si4O10(OH)2 Prp Pyrope Mg3Al2(SiO4)3 Ru Rutile TiO2 Sil Sillimanite Al2SiO5 Sph Sphene CaTiO(SiO4) St Staurolite (Fe2+,Mg,Zn)2Al9(Si,Al)4O22(OH)2 Ta Talc Mg3Si4O10(OH)2 Ts Tschermakite (hornblende) (Na,K)0-1Ca2(Mg,Fe2,Al)5Si6-7,5Al2-0,5O22(OH)2 Tep Tephroite Mn2SiO4 Tr Tremolite Ca2(Mg,Fe)5Si8O22(OH)2 Zo Zoisite Ca2Al3(Si2O7)(SiO4)(O,OH)2 αQz Quartz SiO2

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An assumed whole rock composition, PER2 (Table 7, Appendix 5), compiled from the analyzed kyanite, plagioclase, chlorite and garnet gave one small stability field for garnet, kyanite, clinozoisite and staurolite. The small field is located at 556°C and 11,6 kbar (Fig. 6 above) and consist of two parageneses: 556,2°C and 11,62 kbar FeSt+FeCtd+cZo+aQz+Ky+H2O 556,2°C and 11,64 kbar Alm+FeCtd+cZo+aQz+Ky+H2O Other parageneses in Fig.6 are: 1. FeCtd+cZo+aQz+Mar+Pag+H2O 2. Alm+cZo+aQz+Ky+Pag+Par+H2O 3. FeCtd+cZo+aQz+Ky+Pag+H2O This outcome is similar to the result calculated from the assumed whole rock compositon PER1 (see Fig. 5).

Fig. 6 Stability field (indicated by arrow) for an assumed peraluminous start composition PER2 composed of garnet, chlorite, plagioclase and kyanite.

1

2 3

19

3.5 winTWQ calculations Investigation of the individual mineral compositions analysed by SEM using winTWQ (version 1.02) for a stable system containing kyanite, staurolite, chlorite, clinozoisite and garnet, gave no intersection as can be seen in Fig. 7 below. This is probably due to disequilibria between the minerals in the inclusion. One factor could be very small fractures to and from the inclusion and this will give contamination of the inclusion, causing disequilibria. Another factor could be incomplete data and solution models for several of the minerals in the winTWQ system.

Mineral composition for PER10, scenario one could be seen in the table above. These mineral compositions are used in Fig. 7.

Activity for garnet, chlorite and staurolite are given below: GARN [-Gr-][-Py-][-Alm][-Sp-] GARN .1137 .2612 .5880 .0372 MgFe [xMg-][xFe-] chlorite MgFe .6784 .3112 MgFe [xMg-][xFe-] staurolite MgFe .3955 .6045 Since the analyzed clinozoisite also has XFe equal to 0.38 this is given as the activity for epidote.

Element Ky Gt cZo Chl St

SiO2 38,25 38,84 38,57 26,77 35,61

Al2O3 61,6 21,55 28,1 21,11 33,09

FeO 1,052 28,23 7,3 17,28 13,46

MnO 0 1,643 0 0,57 0,553

MgO 0 6,825 0 21,13 6,989

CaO 0 4,513 23,35 0 6,966

Na2O 0 0 0 0 0

K2O 0 0 0 0 0

TiO2 0 0 0 0 0

P2O5 0,828 0 0 0 0,207

ZnO 0 0 0 0 0

Total 101,7 101,6 97,32 86,86 96,87

Fig. 7 Stable reactions containing the minerals in the assemblage PER10 above and also H2O.

inclusion1 ver102.plt

Temperature (°C)130012501200115011001050100095090085080075070065060055050045040035030025020015010050

Pre

ssur

e (k

bar)

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1. 5Prp+12H2O=3Clc+2Ky+4aQtz2. 4Grs+5Ky+aQtz+3H2O=6cZo3. 30St=85aQtz+72Grs+78H2O+40Alm+20cZo4. 24St+125Prp=4H2O+32Alm+75Clc+22Ky5. 46Ky+8Alm+12H2O=25aQtz+6St6. 16Grs+29aQtz+6St=24cZo+26Ky+8Alm

20

Scenario two with mineral composition comprised of kyanite, plagioclase, staurolite and garnets gave an intersection temperature of 525°C and pressure of 4-5 kbar, see Fig 8. This combination of minerals occurs in one of the inclusions from sample DC0201e.

Mineral composition for PER10, scenario two could be seen in the table above.

‘

Activity for garnet, plagioclase and staurolite are given below: GARN [-Gr-][-Py-][-Alm][-Sp-] Fe3+:calc-3%-used .07-.05-.00 GARN .1137 .2612 .5880 .0372 MgFe [xMg-][xFe-] staurolite MgFe .3955 .6045 PLAG [-An-][-Ab-][-Or-] PLAG .8743 .1257 .0000

Element Ky Gt Chl Plag St

SiO2 38,25 38,84 26,77 42,9 36,25

Al2O3 61,6 21,55 21,11 34,05 33,53

FeO 1,052 28,23 17,28 0,95 17,17

MnO 0 1,643 0,57 0 1,036

MgO 0 6,825 21,13 0 1,706

CaO 0 4,513 0 18,76 6,966

Na2O 0 0 0 1,49 0,008

K2O 0 0 0 0 0

TiO2 0 0 0 0 0

P2O5 0,828 0 0 0 0,207

ZnO 0 0 0 0 0

Total 101,7 101,6 86,86 98,15 96,87

Fig. 8 Stable reactions containing the minerals in the assemblage PER10 above and also H2O.

inclusion3-1.plt

Temperature (°C)130120011001000900800700600500400300200100

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1. Grs+2Ky+aQtz=3An2. 46Ky+8Alm+12H2O=25aQtz+6St3. 96Ky+25Grs+8Alm+12H2O=75An+6St4. 23Grs+48aQtz+6St=69An+8Alm+12H2O

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3.6 XMg for Staurolite The structural formula for staurolite is [(IV)Fe2+,Mg,Zn]2

(VI)Al9(Si,Al)4O22(OH)2. Mg enrichment of staurolite is according to Enami (1988) controlled by Mg substitution for VIAl and by the Mg – Fe substitution in the IVFe sites. Staurolite is normally a typical mineral of pelitic and other siliceous and aluminous rocks metamorphosed under intermediate pressure conditions during the amphibolite-facies. But these are not magnesian staurolites, that is with atomic Mg/(Fe+Mg) =XMg >0.3, according to Deer et al. (1982) and metamorphic conditions indicated for their formation lie within the stability field for Fe-staurolite + quartz determined in the laboratory, that is pressures above 1,5 kbar and temperatures between 500° and 700°C (Richardson 1968). The XMg for the staurolites from the Borås mafic intrusion lies between 0,35 and 0,40. According to the experimental results of Schreyer (1988), pure Mg-staurolite (Mg,Li)1,5-

2Al9Si4O22(OH)2) is stable in the MASH system at P>14 kbar and T>710-760°C. Fockenberg (1998) re-investigated Mg-staurolite (XMg >0,55) stability and obtained P-T conditions of 12-66 kbar and 608-918°C. The formation of magnesium staurolite implies a high pressure of metamorphism. Schreyer and Seifert (1969) synthesized Mg-staurolite in an iron-free system at high pressures and temperatures, but could not find stability field below 12 kbar and 800°C. In contrast Fe-staurolite is stable to pressures as low as 1 kbar (Richardson, 1968), implying that the Mg- content of staurolite in Mg-Fe systems will be strongly pressure dependent (Ward, 1984). Some of the occurrences of the Mg-rich staurolite in the world are as inclusions in other minerals, indicating that they may be relics of earlier metamorphic stages and occur in local silica-deficient environments (Schreyer et al 1984). Examples of Mg-staurolite (with high XMg) occurrences are given in Table 4 by Peacock et al. (1995).

In the Borås mafic intrusion, staurolite inclusions in garnet have a relatively high XMg (between 0,35 and 0,40) compared with staurolite from pelites (typically XMg ~0,20), see Table 3 below. Staurolites with XMg above 0,35 are quite rare on Earth. The garnet itself in the Borås mafic intrusion typically has XMg ~ 0,30.

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Table 3. Analyses and XMg value for staurolite, garnet and chlorite in the Borås mafic intrusion (thin section DC0201).

Staurolite S27A-B and garnet S27A-B occur together as do staurolite S11 and garnet S11. Garnet S24 and chlorite S24 occur together with kyanite. All chemical analysis for the minerals can be seen in Table 8, Appendix 6. Ibarguchi et al (1991) suggested the approximate stability fields for clinozoisite, kyanite and Mg-staurolite shown in Fig. 9 Their mineral assemblage in an ultrabasic rock from Cabo Ortegal, northwestern Spain is very similar to the one at Borås mafic intrusion (see Table 6 in Appendix 4 and Table 7 in Appendix 5). They gave slightly higher Al and

Staurolite Garnet Chlorite S5 S27A S27B S11 S27A S27B S11 S24 S24 SiO2 27,45 26,41 26,55 26,59 39,01 38,95 38,71 38,68 26,77

Al2O3 54,84 54,47 53,93 53,37 21,42 21,34 21,74 21,69 21,11

FeO 12,67 12,78 12,8 13,07 28,17 27,82 28,1 28,82 17,28

MnO 0 0 0 0 1,76 1,66 1,73 1,42 0,57

MgO 4,65 4,15 4,09 3,89 7,02 6,54 6,53 7,21 21,13

CaO 0 0 0 0 4,25 5,05 4,93 3,82 0

Na2O 0 0 0 0 0 0 0 0 0

K2O 0 0 0 0 0 0 0 0 0

TiO2 0,67 0,52 0,58 0,53 0 0 0 0 0

P2O5 0 0,75 0,7 0,65 0 0 0 0 0

ZnO 0,86 0,77 0,56 0,92 0 0 0 0 0

Total 101,14 99,85 99,21 99,02 101,63 101,36 101,74 101,64 86,86

Atomic proportions on the basis of 23 oxygens for staurolite, 28 for chlorite and 12 for garnet

Si 3,69 3,6 3,63 3,66 3 3 2,98 2,97 5,43

Al 8,69 8,74 8,7 8,66 1,94 1,94 1,97 1,96 5,18

Fe 1,42 1,46 1,47 1,5 1,81 1,79 1,81 1,85 3,09

Mn 0 0 0 0 0,11 0,11 0,11 0,09 0,09

Mg 0,93 0,84 0,84 0,8 0,81 0,75 0,75 0,83 6,18

Ca 0 0 0 0 0,35 0,42 0,41 0,31 0

Na 0 0 0 0 0 0 0 0 0

K 0 0 0 0 0 0 0 0 0

Ti 0,07 0,05 0,06 0,05 0 0 0 0 0

P 0 0,09 0,08 0,08 0 0 0 0 0

Zn 0,09 0,08 0,06 0,09 0 0 0 0 0

O 23 23 23 23 12 12 12 12 28

XMg 0,40 0,37 0,36 0,35 0,31 0,30 0,29 0,31 0,66667

Fig.9 Stability fields for clinozoisite, kyanite and Mg-rich staurolite according to Ibarguchi et al (1991).

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Mg contents for one of the samples, but otherwise it is quite similar to the hornblende gabbro (sample AA9680) for which the stability fields for chloritoid and kyanite was found in this study. Further investigations of Mg-rich staurolite by Fockenberg (1998) indicate that Mg-staurolite is formed from the assemblage chlorite + kyanite + corundum at pressures lower than 24 kbar, whereas at pressures up to 27 kbar staurolite becomes stable by the breakdown of the assemblage Mg-chloritoid + kyanite + corundum.

3.7 Finding an Early Paragenesis The next step is to find a possible early paragenesis in the observed whole rock compositions which could have become included by garnet to form the present peraluminous paragenesis. We used whole rock analyses from the Borås mafic intrusion by Åberg (1997). The criteria for the early paragenesis should be:

• Peraluminous minerals should occur, probably reflecting plagioclase-out reactions. • A mineral containing Mg, Fe (to produce staurolite) and one with Ca (to produce

clinozoisite) should occur. • At least one of the minerals should contain OH (to produce the present hydrous

minerals). A small stability field or points where these criteria are met for the hornblende gabbro (sample no AA9680) was found at 582°C and 23-23,5 kbar (approximately at 70 km depth), see Fig. 10 below. The paragenesis is: Alm+ (Di or Jd) +MgCtd+Lw+aQz+Ky+H2O Concerning the above assemblage; when the pressure increases Mg-Chloritoid (MgCtd) breaks down and Fe-Mg goes into garnet. Quartz would change into coesite at slightly higher pressure: 25-30 kbar. Kyanite is not present at lower temperatures. The inclusions should have comprised MgCtd+Lw+Ky, excluding clinopyroxene grains, to achieve their present composition (Fig. 11). Another possible early paragenesis could be: Alm+Jd+Chl+FeCtd+Lw+aQz+H2O and it’s stability point is at 482°C and ~17,5 kbar. In this case the inclusion should have comprised of FeCtd+Lw, excluding clinopyroxene grains. If the chloritoid is considered to be Fe or Mg, the amount of each element is determined by Domino-Theriak. If there is more than 50% FeCtd, then FeCtd will be given in the paragenesis above.

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All the parageneses suggested above are calculated for the hornblende gabbro (sample AA9680 and AA9619). In the Borås mafic intrusion, some other rock types are found, but these do not contain any chloritoid- or kyanite-bearing parageneses in the petrogenetic grids received from Domino-Theriak.

Fig. 10 Stability point for the parageneses for whole rock composition AA9680, based on the criteria above. The different colours indicate the stability fields for each mineral in this whole rock composition, chlorite and lawsonite left of the lines etc. The boundary between Mg-ctd and Fe-ctd is marked with a black line. Mg-ctd is above the line and Fe-ctd below it.

Alm+Jd+FeCtd+Lw+aQz+H2O 482°C and 17,5 kbar.

Alm+Di+MgCtd+Lw+aQz+Ky+H2O 582°C and 23 kbar.

Coesite Quartz

Sample AA9680 Hornblende Gabbro (Åberg, 1997)

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Fig.11 ACF-projection showing zoisite, kyanite, lawsonite, chlorite, chloritoid, diopside and staurolite, and the composition of the whole-rock and peraluminous inclusions.

Kyanite Pyrophyllite

Wollastonite

Opx

Plagioclase Lawsonite

Zoisite

Chloritoid

Staurolite

Almandine

Grossular Chlorite

Diopside

Whole rock composition

Composition of inclusions, pyroxene-free

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4. Discussion Mafic rocks that have been metamorphosed in orogenic events usually include high-variance assemblages that are stable over large ranges of pressure, temperature and composition. In the amphibolite facies, mafic rocks typically contain the following assemblages: plagioclase, epidote, hornblende ± garnet or diopside. On the other hand, aluminous minerals such as kyanite, cordierite, staurolite and orthoamphiboles can also occur together with hornblende, quartz and plagioclase in some mafic rocks according to Arnold (2000). Staurolite-bearing amphibolites can occur in bulk compositions comparable to the common assemblage (see Table 1 from Laird 1980 in Appendix 8) over a narrow range of P-T (8-10 kbar, ~600°C), this range of P-T may expand when more aluminous bulk compositions occur (Arnold et al 2000). The inclusion of chlorite in garnet is usually evidence for an earlier assemblage in the rock. Chlorite, garnet and quartz, as well as aluminous minerals are more commonly associated with metapelitic rocks. The Al content (between 15 to 17 wt%) of amphibolites is critical in determining whether assemblages such as kyanite-hornblende and staurolite-hornblende can develop in place of the common assemblage of Laird (1980). In the Borås mafic intrusion the present mineral assemblages in garnet inclusions contain Mg-rich staurolite, kyanite, clinozoisite and chlorite. There are also some inclusions containing kyanite, chlorite and Ca-rich plagioclase. However peraluminous minerals such as kyanite and Mg-staurolite should not occur in rocks with this bulk composition according to our Theriak-Domino calculations. This suggests that, in the course of the metamorphic cycle some earlier-formed minerals in garnet inclusions probably became unstable and reacted to form the observed assemblages. However, metastable relics of the early assemblage could survive according to Bucher & Frey, (1994). Ibarguchi et al (1991) suggested the stability fields for clinozoisite, kyanite and Mg-staurolite shown in Fig.9 above. Their mineral assemblage from northwestern Spain is quite similar to the one at Borås mafic intrusion and can therefore be used for comparison of the results in this study. Comparisons with other experimentally produced Mg-staurolite gave relative good correspondence between the calculations in Domino-Theriak and the experimental results from Enami et al., (1988) and Faryad et al., (2006). According to Faryad et al (2006) their rocks were affected by high pressure amphibolite facies metamorphism that is related to subduction and eclogite formation during the Cretaceous. Enami et al (1988) also pointed out that their rocks are eclogites probably formed during high pressure metamorphism. Their whole rock composition can be seen in Table 7, Appendix 5. The stability field (Fig. 5) for garnet, chlorite, kyanite and clinozoisite calculated from a peraluminous starting composition (PER1) in Borås mafic intrusion is a small one with temperature of 588 ± 4°C and pressure 12,3 ± 1,4 kbar. The temperature is somewhat lower and the pressure higher than those Åberg (1997) calculated for the predominantly amphibolitic rocks (700°C and 8,5 ± 0.6 kbar). Another suggested peraluminous starting composition (PER2) comprised of kyanite, plagioclase, chlorite and garnet gives similar results, 556°C and 11,6 kbar respectively (see Fig. 6). However if we use the true metaluminous whole rock composition for this rock, there is no stability field for this paragenesis. This suggests that the inclusions became isolated by enclosure within garnet at an earlier stage of the metamorphic cycle.

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There are five different rock types in the Borås mafic intrusion, but hornblende gabbro (sample AA9680 and AA9619 from Åberg (1997) is the only rock type containing enough Al to create chloritoid and kyanite in the calculations by Domino-Theriak. Shand’s aluminous index (1943) for the hornblendite and hornblende melagabbro is typically around 0,5 while the hornblende gabbro characteristically have values around 0,8 (see table 7, Appendix 5). None of the rock types in the Borås mafic intrusion are considered to be peraluminous, since the Shand’s aluminous index (1943) is below one. Based on the criteria specified earlier one possible original paragenesis is: Almandine + (Diopside or Jadeite) + Mg-chloritoid + Lawsonite + Quartz + Kyanite + H2O The stability field for this paragenesis is at 582°C and 23-23,5 kbar. Pressures of 23,5 kbar corresponding to a depth around 70 km. The inclusions should have comprised Mg-chloritoid + Lawsonite +Kyanite, excluding clinopyroxene, to achieve their present composition (Fig. 11). The temperature calculated for this possible early paragenesis using Domino-Theriak is lower than both Fockenberg et al (1998) and Ibarguchi et al (1991), suggesting a system containing Mg-rich staurolite, but the pressure is within their range. Concerning the assemblage Alm+ (Di or Jd) +MgCtd+Lw+aQz+Ky+H2O; there is a change from quartz to coesite around 25-30 kbar, however we did not observe coesite. Other changes seen in the calculated petrogenetic grid are:

• Chloritoid ((Fe,Mg,Mn)Al2SiO5(OH)2) is present at temperature between 482-595°C and pressures 17-26 kbar. It becomes richer in Mg at higher pressures. When the pressure increases the chloritoid breaks down and Fe-Mg goes into garnet. Fe-chloritoid is present at lower temperature and pressure (480°C and ~17 kbar) together with chlorite, garnet, lawsonite, diopside and quartz. According to Grambling (1983), chloritoid can contain Zn which later ends up in staurolite. Staurolite from the Borås mafic intrusion typically have 0,80 wt% Zn. Information about the amount of Zn in the chloritoid is not given in Domino-Theriak.

• Kyanite (Al2SiO5) is present at temperatures ~580°C with pressure 23-30 kbar and at 600-715°C with pressures >18 kbar.

• Other polymorphs of Al2SiO5 (sillimanite and andalusite) are not found at any temperatures or pressures in the calculations from Domino-Theriak.

• Lawsonite (CaAl2(Si2O7)(OH)2 x H2O) occurs at various temperatures and pressures (200-650°C and 4-35 kbar).

• Chlorite ((Mg,Fe,Al)3(Si,Al)4O10(OH)2) is present at various temperatures and pressures (200-550°C and 1-20 kbar). Chlorite is not present together with garnet at low temperature and pressure (this relationship starts at 525°C and 8 kbar).

• Pyrophyllite (Al2Si4O10(OH)2) is not present in the calculations from Domino-Theriak and therefore not an option for the early paragenesis-interpretation.

• Garnet is present at 450-1000°C and 4-35 kbar. Almandine dominates throughout the stability fields.

Another possible original paragenesis is: Almandine + Diopside + Chlorite + Fe-Chloritoid + Lawsonite + Quartz + H2O. This paragenesis is missing kyanite and the lowest stability point is located at 480°C and ~17,5 kbar. The inclusions should have comprised Fe-chloritoid +Almandine + Lawsonite to achieve their present composition (Fig. 11). This would mean a depth of 51 km, still in

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eclogite facies. At this temperature and pressure the calculated chloritoid is richer in Fe than Mg (74% Fe versus 26% Mg). The stability fields for each mineral in the early possible paragenesis can be seen in Fig. 10. Based on the earlier specified criteria, there are only limited fields where the original paragenesis could have occurred. You need peraluminous minerals, probably reflecting plagioclase-out reactions, together with a Fe-Mg mineral to produce staurolite and one with Ca to produce clinozoisite. One of the minerals should contain OH to produce the present hydrous minerals.

5. Conclusion The inclusions in garnet in the Borås mafic intrusion most likely formed at 50-70 km depth in blueschist to eclogite facies metamorphic conditions, when grains of Mg-chloritoid, chlorite, lawsonite and kyanite became included in garnet, excluding clinopyroxene, to form isolated, hydrated, peraluminous assemblages. Later in the metamorphic cycle they reacted to form the assemblage kyanite, clinozoisite and Mg-rich staurolite now found as inclusions in garnet.

6. Acknowledgement I would like to thank my supervisor Prof. David Cornell for the support throughout the project, from field comments and assistance during SEM sessions etc., to constructive comments after having read the poster and manuscript. I would also like to thank Ali Firoozan for helping me with the thin sections. A special thanks to Lennart Björklund and Mats Östman for their valuable criticism on the manuscript.

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7. References Åberg, A., 1997: A petrogenetic study of the Borås ultamafic-mafic intrusion, sw Sweden. M.Sc. thesis, Earth Sciences Centre, Göteborg University, Sweden, B105, 51 pp. Ahlin, S., 1983: Beskrivning till berggrundskartan Borås SV. Sveriges Geologiska Undersökning. Serie Af nr 130, 114 pp Ahlin, S., 1983: Beskrivning till berggrundskartan Borås SO. Sveriges Geologiska Undersökning. Serie Af nr 143, 92 pp. Åhäll, K-I., 1993: The southernmost part of the Mylonite Zone, southern Sweden. Sveriges Geologiska Undersökning, rapporter och meddelanden, 76, 23 pp Åhäll, K-I., 1995: Crustal units and role of the Mylonite Zone system in the Varberg-Horred region, SW Sweden. Geologiska Föreningens I Stockholm Förhandlingar, vol. 117, pages 185-198. ISSN 1103-5897. Åhäll, K-I. & Gower, C.F., 1997: The Gothian and Labradorian orogens: variations in accretionary tectonism along a late Paleoproterozoic Laurentia-Baltica margin. Geologiska Föreningens I Stockholm Förhandlingar, vol. 119, pages 181-191. Åhäll, K.I., Cornell, D.H. & Armstrong, R., 1998: Ion probe zircon dating of metasedimentary units across the Skagerrak: new constraints for early Mesoproterozoic growth of the Baltic Shield. Precambrian Research, vol. 87, pages 117-134. Andersson, U.B., Larsson, L. & Wikström, A., 1992: Charnockites, pyroxene granulites and garnet-cordierite at a boundary between early Svecofennian rocks and Småland-Värmland granitoids, Karlskoga, southern Sweden. Geologiska Föreningens i Stockholm Förhandlingar, vol. 114, part 1, pages 1-15. Andersson, J., Söderlund, U., Cornell, D., Johansson, L., Möller, C., 1999: Sveconorwegian (-Grenvillian) deformation, metamorphism and leucosome formation in the SW Sweden, SW Baltic Shield: constraints from a Mesoproterozoic granite intrusion. Precambrian Research, vol. 98 (1), pages 151-171. Andersson, J., Möller, C. & Johansson, J., 2002: Zircon geochronology of migmatite gneisses along the Mylonite Zone (S Sweden): a major Sveconorwegian terrane boundary in the Baltic Shield. Precambrian Research, vol. 114, pages 121-147. Arnold, J., Powell, R. & Sandiford, M., 2000: Amphibolites with staurolite and other aluminous minerals; calculated mineral equilibria in NCFMASH. Journal of Metamorphic Geology, vol. 18, pages 23-40. Ask, R., 1996: Single zircon evaporation Pb-Pb ages from the Vaggeryd syenite and dolerites in the southeastern part of the Sveconorwegian orogon, Småland, southern Sweden. Geologiska Föreningens I Stockholm Förhandlingar, vol. 118, page A8. Austin Hegardt, E., 2000: A Sveconorwegian crustal subduction and exhumation model for the Eastern Segment, south-western Sweden. MSc thesis, Earth Sciences Centre, Göteborg University, Sweden, B220, 1-38 Austin Hegardt, E., Cornell, D., Claesson, L., Simakov, S., Stein, H. & Hannah, J., 2005: Eclogites in the central part of the Sveconorwegian Eastern Segment of the Baltic Shield: Support for an extensive eclogite terrane. Geologiska Föreningens I Stockholm Förhandlingar, vol. 127, pages 221-232. Austin Hegardt, E., Cornell, D.H., Hellström, F.A. & Lundqvist, I., 2007: Emplacement ages of the mid-Proterozoic Kungsbacka Bimodal Suite, SW Sweden. Geologiska Föreningens I Stockholm Förhandlingar 129, pages 227-234. Berglund, J., Connelly, J.N., 1994: Sveconorwegian structural evolution in the Eastern Segment of the southwest Swedish Gneiss Region. Abstract. Precambrian Crustal Evolution in the North Atlantic Regions, Nottingham UK 1994. Terra Abstracts, vol. 2, page 2.

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Appendix Appendix 1 Fig. 12 Scanned image of the epoxy mount DC0201f with garnet. The garnet grains marked with numbers 1-5 contain the inclusion parageneses listed below. 1 – staurolite, kyanite, clinozoisite and garnet (corresponds to site 5 in Table 8, Appendix 6) 2 – kyanite, staurolite and garnet (corresponds to site 27 in Table 8, Appendix 6) 3 – kyanite and garnet (located on thinsection DC0201) 4 – staurolite, kyanite and garnet (corresponds to site 11 in Table 8, Appendix 6) 5 – kyanite, chlorite and garnet (corresponds to site 24 in Table 8, Appendix 6)

1

2

3

45

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Appendix 2 Table 4. Chemical compositions for minerals synthesized by Enami et al 1988 Kyanite Chlorite Garnet Zoisite Staurolite Amph

SiO2 37 28,9 42,5 39,5 29,8 42,3

Al2O3 61,9 22,8 23,6 31,3 55,9 22,4

FeO 0,5 2,38 5,07 1,53 4,69 3,31

MnO 0,06 0 0,14 0,06 0,07 0,05

MgO 0,24 31,8 15,8 0,13 7,38 15,1

CaO 0 0 13,4 23,9 0 13,1

Na2O 0 0,03 0 0 0 2,44

K2O 0 0 0 0 0 0

TiO2 0 0 0 0,06 0 0

P2O5 0 0 0 0 0 0

ZnO 0 0 0 0 0 0

Cr2O3 1,18 0,32 0,34 1,59 0,53 0,31

NiO 0 0,75 0 0 0,16 0,06

Total 100,88 86,98 100,85 98,07 98,53 99,07

Si 0,996 5,45 3,011 3,012 7,917 5,849

Al 1,967 5,067 1,97 2,813 17,502 3,65

Fe 0,01 0,375 0,3 0,088 1,042 0,383

Mn 0,001 0 0,008 0,004 0,016 0,006

Mg 0,01 8,938 1,668 0,015 2,922 3,112

Ni 0 0,114 0 0,004 0,034 0,007

Ca 0 0 1,017 1,952 0 1,941

Na 0 0 0 0 0 0,654

K 0 0 0 0 0 0

Ti 0 0 0 0,003 0 0

P 0 0 0 0 0 0

Zn 0 0 0 0 0 0

Cr 0,025 0,048 0,019 0,096 0,111 0,034

O 5 25 12 22 46 23

XMg n/a 0,96 0,85 n/a 0,737134 0,89

Here is the activity data for these minerals from Enami et al 1988 in winTWQ; MgFe [xMg-][xFe-] chlorite MgFe .9597 .0403 MgFe [xMg-][xFe-] staurolite MgFe .7343 .2618 GARN [-Gr-][-Py-][-Alm][-Sp-] GARN .3397 .5572 .1003 .0028 AMPH [AlM2] AMPH .7442 tschermakite

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Appendix 3 Table 5. Chemical compositions for minerals synthesized by Faryad et al 2006 Chlorite Amphibole Garnet Zoisite Staurolite

SiO2 26,95 42,54 37,81 38,12 27,12

Al2O3 21,71 17,3 21,77 31,34 56,18

FeO 12,48 10,89 24,74 1,28 11,74

MnO 0,03 0,16 0,53 0,04 0,49

MgO 22,72 11,6 7,63 0,17 1,96

CaO 0,05 10,76 6,46 23,68 0,03

Na2O 0,07 1,83 0,07 0,01 0,01

K2O 0,07 0,33 0 0 0

TiO2 0,09 0,5 0,06 0,1 0,35

P2O5 0 0 0 0 0

ZnO 0 0 0 0 0,13

Total 84,17 95,91 99,07 94,74 98,01

Si 5,544 6,241 2,982 2,993 7,611

Al4 2,456 1,759 1,964 2,9 18,582

Al6 2,808 1,231 n/a n/a n/a

Fe3+ 0 0,335 0,063 0,066 0,023

Fe2+ 2,147 0,968 1,646 1,524 2,732

Mn 0,005 0,02 0,202 0,035 0,116

Mg 6,968 2,536 0,477 0,874 0,82

Ca 0,011 1,691 0,657 0,532 0,009

NaM4 0,028 0,164 0,003 0,01 0,005

Na(A) n/a 0,357 n/a n/a n/a

K 0,018 0,062 0 0 0

Ti 0,014 0,055 0,005 0,003 0,074

P 0 0 0 0 0

Zn 0 0 0 0 0,027

O 25 22 12 22 46

XMg 0,765 0,72 0,22 n/a 0,230855856

Here is the activity data for these minerals from Faryad et al 2006 in winTWQ; MgFe [xMg-][xFe-] chlorite MgFe .7637 .2353 MgFe [xMg-][xFe-] staurolite MgFe .2221 .7464 GARN [-Gr-][-Py-][-Alm][-Sp-] GARN .2157 .1568 .5613 .0663 AMPH [AlM2] AMPH .5833 tschermakite Zoisite and kyanite are assigned activity 1, being pure phases.

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Appendix 4 Table 6. Chemical compositions for minerals synthesized by Ibarguchi et al 1991 Kyanite Amphibole Garnet Zoisite

SiO2 36,52 49,39 39,41 39,5

Al2O3 58,39 11,32 22,95 32,34

FeO 0,21 3,02 15,03 1,18

MnO 0,04 0 0,61 0,16

MgO 0,02 18,35 13,19 0,09

CaO 0 12,51 7,85 24,53

Na2O 0,03 1,2 0,03 0

K2O 0,02 0,17 0,03 0,01

TiO2 0,01 0,11 0,03 0,06

P2O5 0 0 0 0

ZnO 0 0 0 0

NiO 0,01

Cr2O3 3,85 0 0 0

Total 99,1 96,07 99,13 97,87

Si 1,007 6,924 2,92 6,003

Al 1,899 1,871 2,005 5,794

Fe3+ 0,08 0,137 0,063 0,135

Fe2+ n/a 0,217 0,869 n/a

Mn 0,001 below det. 0,038 0,02

Mg <0,001 3,834 1,457 0,021

Ni <0,001 n/a 0,005 0,011

Ca below det. 1,879 0,623 3,993

Na 0,001 0,326 0,004 0,001

K 0,001 0,03 0,003 0,002

Ti <0,001 0,012 0,002 0,006

P 0 0 0 0

Zn 0 n/a n/a n/a

Cr 0,084 0,006 0,01 0,027

O 5 22 12 22

XMg n/a n/a n/a n/a

Appendix 5 Table 7.Whole rock analysis from different authors including Åberg (1997). These are used for comparison and calculations in Domino-Theriak and winTWQ.

Ibarguchi **

1991 Hellman

1979 Moeen 1991

Faryad 2006

Gibson 1978

Åberg 1997

Enami ** 1988

Danielsson 2007

Element CO80 CO97 Tholeite Olivinite RS91 RS112 LM185 41001 967D 9619A 9619B 9680 9678 TS03 TM02 PER1 PER2

SiO2 44,21 48,2 49,8 48,1 49,09 59,12 40,68 27,28 44,79 48,48 47,56 47,35 50,36 34,26 47 41,12 42,02

Al2O3 21,53 15,08 16,5 16 12,9 17,62 21,99 54,45 10,33 17,92 19,29 18,17 10,11 34,87 14,1 37,6 39,08

FeO 5,08 12,16 8,4 8,6 20 12,8 10,76 10,66 15,77 10,77 9,78 10,82 12,11 4,72 7,76 9,56 7,98

MnO 0,07 0,17 0,2 0,1 0,3 0,08 0,25 0,2 0,22 0,18 0,14 0,16 0,24 0,18 0,12 0,41 0,41

MgO 13,83 8,3 9,8 10,6 14,11 4,6 8,94 2,78 10,69 5,85 5,66 6,29 11,33 13,4 14,3 1,99 1,99

CaO 12,44 12,17 11,1 11,1 0,45 0,4 9,2 0,02 10,63 9,86 10,04 9,55 9,34 10,9 13,5 7,11 5,97

Na2O 0,96 2,17 2,6 2,5 1,1 1,5 1,19 0,08 1,22 2,99 3,12 2,81 1,68 0,15 0,81 1,04 1,41

K2O 0,4 0 0,2 1,6 0,5 3,14 0,99 0,02 0,59 0,56 0,46 1,41 0,87 0,05 0,02 0,18 0,18

TiO2 0,07 1,31 1,6 1,7 1,4 1,2 0,76 0,58 1,09 0,83 0,67 0,8 0,73 0,02 0,58 0 0

P2O5 0,11 0,19 0 0 0,13 0,07 0,11 1 0,21 0,69 0,49 0,61 0,08 0,33 0,01 0,207 0,207

ZnO 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0

LOI 1,76 0,08 0 0 0 0 4,18 2,16 1,42 0,8 0,85 1,53 1,49 0,44 0 0 0

Total 100,46 99,83 100,2 100,3 99,98 100,53 99,05 100,23 96,96 98,93 98,06 99,5 98,34 99,32 98,2 99,217 99,247

Shand 1943 0,87 0,59 0,67 0,61 4,07 2,67 1,11 287,15 0,47 0,76 0,81 0,77 0,49 1,73 0,54 2,53 2,92 * These whole rock analysis (PER1 and PER2) are calculated from the average value of each mineral and element and therefore the Shand’s aluminous index is higher. Shand’s aluminous index: Al2O3 / (CaO + Na2O + K2O) in molecular proportions. ** The mineral composition in Table 6 from Ibarguchi et al (1991) belong to whole rock sample CO80 and the mineral composition in Table 4 from Enami et al (1988) belong to whole rock sample TS03.

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Appendix 6 Table 8. Chemical composition of each mineral in the garnet inclusions from the Borås mafic intrusion. These data are mainly used for calculations in winTWQ. An average value for each element was used in Domino-Theriak (PER1 and PER2) to calculate the stability fields for an assumed peraluminous whole rock composition. Site 5 Site 27 Site 11 Site 24 Site 1 Ky51 Ky52 St5 cZo5 Ky27 St271 St272 Gt271 Gt272 Ky11 St11 Gt11 Ky24 Gt24 Chl24 Plag1 Mica1 Ky1 Gt1 Chl1

SiO2 37,01 37,02 27,45 38,57 36,79 26,41 26,55 39,01 38,95 36,19 26,59 38,71 44,23 38,68 26,77 43,9 42,3 36,66 38,54 47,83

Al2O3 63,88 63,8 54,84 28,1 63,04 54,47 53,93 21,42 21,34 62,7 53,37 21,74 54,57 21,69 21,11 34,72 35,1 59,69 21,44 38,14

MgO 0 0 4,65 0 0 4,15 4,09 7,02 6,54 0 3,89 6,53 0 7,21 21,13 0 0,31 0 6,59 1,16

FeO 0,88 1,26 12,67 7,3 1 12,78 12,8 28,17 27,82 1,18 13,07 28,1 0,94 28,82 17,28 0,67 1,39 1,17 28 1,67

MnO 0 0 0 0 0 0 0 1,76 1,66 0 0 1,73 0 1,42 0,57 0 0 0 1,78 0

CaO 0 0 0 23,35 0 0 0 4,25 5,05 0 0 4,93 0 3,82 0 18,38 0 0 4,73 0,09

Na2O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0,61 0 0 0 1,15

K2O 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 12,56 0 0 0,14

TiO2 0 0 0,67 0 0 0,52 0,58 0 0 0 0,53 0 0 0 0 0 0 0 0 0

ZnO 0 0 0,86 0 0 0,77 0,56 0 0 0 0,92 0 0 0 0 0 0 0 0 0

P2O5 0,89 0,75 0 0 1,15 0,75 0,7 0 0 0,84 0,65 0 0 0 0 0 0 1,12 0 0

Total 102,7 102,83 101,1 97,32 102 99,85 99,21 101,63 101,36 100,91 99,02 101,74 99,74 101,64 86,86 98,28 91,66 98,64 101,08 90,18

Appendix 7 TWQ diagrams Fig. 13 TWQ diagrams for Enami et al 1988.

Main intersections are located at temperature between 700-800°C and pressures 13-15 kbar.

enami1-3.plt

Temperature (°C)1300120011001000900800700600500400300200100

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1. 15Clc+2Grs+33aQtz+22Zo=25Ts+46H2O2. 10Zo+13aQtz+6Clc=Ky+10Ts+19H2O3. 9Clc+38Grs+46Ky+29aQtz=42Zo+15Ts4. 3Clc+44Zo=5Ts+33Ky+26Grs+29H2O5. 4Grs+5Ky+aQtz+3H2O=6Zo6. 9Clc+10Grs+11Ky+22aQtz=15Ts+21H2O7. 4Grs+11Prp+18H2O=6Ts+3Clc8. 5Prp+12H2O=4aQtz+2Ky+3Clc9. 46Ky+8Alm+12H2O=25aQtz+6St10. 12aQtz+7Prp+6Ky+8Grs+3Clc=12Ts11. 2aQtz+3Prp+Ky+2Grs+3H2O=3Ts12. 8Alm+9Clc+22Grs+72Ky=18Zo+15Ts+6St13. 8Alm+100Grs=85Ky+87H2O+106Zo+6St=80Alm+31Clc+6Grs+7Ky+119Ts+124St+5H2O15. 125Prp+24St=4H2O+22Ky+75Clc+32Alm16. 32Alm+33Clc+56Grs=22Ky+29Prp+84Ts+24St17. 75Ts+12St=16Alm+50Grs+117Ky+75Prp+99H2O

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Fig. 14 Faryad et al 2006 (sample lm185) – winTWQ database version 1,02.

Main intersection is located at 550°C and 9 kbar.

faryad-4.plt

Temperature (°C)130120011001000900800700600500400300200100

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1. 4Grs+11Prp+18H2O=6Ts+3Clc2. 15Clc+2Grs+33aQtz+22Zo=25Ts+46H2O3. 5Prp+12H2O=3Clc+2Ky+4aQtz4. 6Clc+13aQtz+10Zo=10Ts+Ky+19H2O5. 69Clc+117aQtz+6St=115Prp+8Alm+32H2O6. 8Alm+20Clc+61aQtz=52Zo+52Ts+6St+94H2O7. 4Grs+5Ky+aQtz+3H2O=6Zo8. 2aQtz+3Prp+Ky+2Grs+3H2O=3Ts8. 2aQtz+3Prp+Ky+2Grs+3H2O=3Ts=72Grs+85aQtz+30St+78H2O+20Zo+40Alm10. 8Alm+46Ky+12H2O=6St+25aQtz11. 9Clc+38Grs+46Ky+29aQtz=42Zo+15Ts12. 3Clc+8Grs+6Ky+7Prp+12aQtz=12Ts13. 3Clc+44Zo=5Ts+33Ky+26Grs+29H2O14. 9Clc+10Grs+11Ky+22aQtz=15Ts+21H2O15. 117Clc+94Grs+20aQ=118St+74Zo+61Ts+72Alm16. 90Zo=85Clc+88Alm+126Grs+66St+29Ts+72H2O16. 90Zo=85Clc+88Alm+126Grs+66St+29Ts+72H2O=98Clc+52Grs+7aQ+66St+78Ts+88Alm+74H2O18. 48Ky+3Clc+8Alm=5Prp+21aQtz+6St19. 125Prp+24St=4H2O+22Ky+75Clc+32Alm20. 75Prp+117Ky+50Grs+16Alm+99H2O=12St+75Ts21. 32Alm+33Clc+56Grs=22Ky+29Prp+84Ts+24St22. 56Alm+36Clc+40Grs+110Ky=60Ts+42St+87aQtz22. 56Alm+36Clc+40Grs+110Ky=60Ts+42St+87aQtz=80Alm+31Clc+6Grs+7Ky+119Ts+124St+5H2O

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Appendix 8 Table 1. from Laird (1980) common assemblage for mafic rock from Vermont and other occurrences of this rock type.