report 122: the crustal evolution of the rudall province ...€¦ · tessalina s 2013, the crustal...
TRANSCRIPT
Government of Western Australia
THE CRUSTAL EVOLUTION OF THE
RUDALL PROVINCE FROM AN
ISOTOPIC PERSPECTIVE
Department of
Mines and Petroleum
by CL Kirkland, SP Johnson, RH Smithies, JA Hollis,
MTD Wingate,IM Tyler, AH Hickman, JB Cliff,
EA Belousova, RC Murphy, and S Tessalina
Geological Survey of Western Australia
REPORT122
REPORT 122
THE CRUSTAL EVOLUTION OF THE
RUDALL PROVINCE FROM AN
ISOTOPIC PERSPECTIVE
byCL Kirkland, SP Johnson, RH Smithies, JA Hollis, MTD Wingate,
IM Tyler, AH Hickman, JB Cliff, EA Belousova1, RC Murphy1, and S Tessalina2
Perth 2013
Geological Survey of Western Australia
1 GEMOC, Department of Earth & Planetary Sciences, Macquarie University, Sydney NSW 2109
2 John De Laeter Centre for Isotope Research, GPO Box U1987, Perth WA 6845
MINISTER FOR MINES AND PETROLEUM
Hon. Bill Marmion MLA
DIRECTOR GENERAL, DEPARTMENT OF MINES AND PETROLEUM
Richard Sellers
EXECUTIVE DIRECTOR, GEOLOGICAL SURVEY OF WESTERN AUSTRALIA
Rick Rogerson
REFERENCE
The recommended reference for this publication is:
Kirkland CL, Johnson SP, Smithies RH, Hollis JA, Wingate MTD, Tyler IM, Hickman AH, Cliff JB, Belousova EA, Murphy RC and
Tessalina S 2013, The crustal evolution of the Rudall Province from an isotopic perspective: Geological Survey of Western Australia,
Report 122, 30p.
National Library of Australia Cataloguing-in-Publication entry
Author: Kirkland, C. L., author.
Title: The crustal evolution of the Rudall province from an isotopic perspective / C. L. Kirkland [and ten others]
ISBN: 9781741684995 (ebook)
Subjects: Soil crusting--Western Australia--Rudall Province.
Earth (Planet)--Crust.
Isotopes.
Other Authors/Contributors: Geological Survey of Western Australia, issuing body
Dewey Number: 551.1409941
ISSN 0508–4741
U–Pb measurements were conducted using the SHRIMP II ion microprobes at the John de Laeter Centre of Isotope Research
at Curtin University in Perth, Australia. Isotope analyses were funded in part by the Western Australian Government
Exploration Incentive Scheme (EIS). Lu–Hf measurements were conducted using LA-ICPMS at the ARC National Key Centre
for Geochemical Evolution and Metallogeny of Continents (GEMOC), via the ARC Centre of Excellence in Core to Crust Fluid
Systems (CCFS), based in the Department of Earth and Planetary Sciences at Macquarie University, Australia.
Copy editor: K Coyle
Cartography: M Prause
Desktop publishing: RL Hitchings
Printed by Images on Paper, Perth, Western Australia
Published 2013 by Geological Survey of Western Australia
This Report is published in digital format (PDF), as part of a digital dataset, and is available online at
<www.dmp.wa.gov.au/GSWApublications>.
Further details of geological publications and maps produced by the Geological Survey of Western Australia
are available from:
Information Centre
Department of Mines and Petroleum
100 Plain Street
EAST PERTH WESTERN AUSTRALIA 6004
Telephone: +61 8 9222 3459 Facsimile: +61 8 9222 3444
www.dmp.wa.gov.au/GSWApublications
Cover photograph: Bouguer gravity anomaly map of central Western Australia. The image highlights the Anketell Regional Gravity
Ridge which approximately outlines the location of the Paterson Orogen. The Rudall Province lies within this gravity feature.
iii
Contents
Abstract ..................................................................................................................................................................1
Introduction ............................................................................................................................................................1
Geological setting of the Rudall Province .............................................................................................................2
The Talbot Terrane ..........................................................................................................................................2
The Connaughton Terrane ...............................................................................................................................4
The Tabletop Terrane .......................................................................................................................................4
Structural evolution .........................................................................................................................................4
Lu–Hf and oxygen isotopes, and reinterpreted SHRIMP U–Pb geochronology ...................................................5
Analytical methodology ..................................................................................................................................5
Lu–Hf isotopes .........................................................................................................................................5
Oxygen isotopes .....................................................................................................................................14
Talbot Terrane ...............................................................................................................................................14
Kalkan Supersuite ..................................................................................................................................14
GSWA 112379: biotite monzogranite (augen) gneiss, Split Rock ..................................................14
GSWA 104981: biotite–muscovite monzogranite gneiss, southern part of Graphite Valley ..........14
GSWA 111854: biotite–muscovite granodiorite gneiss, Poonemerlarra Creek west......................14
GSWA 112341: micromonzogranite (meta-aplite) dyke, Rudall airstrip .......................................16
GSWA 110056: biotite–hornblende granodiorite gneiss, Rooney Creek .......................................17
GSWA 112101: biotite-epidote monzogranite gneiss, Larry Creek ...............................................17
GSWA 111843: biotite–muscovite monzogranite gneiss, Poynton Creek ......................................17
GSWA 104980: monzogranite gneiss, Graphite Valley ..................................................................17
GSWA 112310: granodiorite gneiss, Dunn Creek west ..................................................................18
GSWA 112397: coarse-grained porphyritic biotite monzogranite (augen) gneiss,
Watrara Inlier ..................................................................................................................................18
Eastern Association ................................................................................................................................18
GSWA 104989: muscovite quartzite, Fingoon Quartzite................................................................18
Mesoproterozoic granites .......................................................................................................................18
GSWA 112102: seriate biotite metamonzogranite, southern part of the Watrara Inlier .................18
Connaughton Terrane ....................................................................................................................................18
Kalkan Supersuite ..................................................................................................................................18
GSWA 113035: orthogneiss, east of South Rudall Dome ..............................................................18
GSWA 113002: granodiorite gneiss, Cotton Creek ........................................................................18
Unassigned gneissic rocks .....................................................................................................................19
GSWA 112160: garnet microgneiss, Harbutt Range ......................................................................19
Tabletop Terrane .....................................................................................................................................19
GSWA 118914: foliated granite, north of Harbutt Range ...............................................................19
Discussion ............................................................................................................................................................19
Hf isotope signatures of Paleoproterozoic Australia .....................................................................................19
Capricorn Orogen ...................................................................................................................................19
Pilbara Craton ........................................................................................................................................21
Arunta Orogen........................................................................................................................................21
Musgrave Province .................................................................................................................................21
Inherited and detrital zircons of the Rudall Province ....................................................................................22
Hf isotopic signature of the Rudall Province ...............................................................................................23
Crust formation and underplating at 1900 Ma .......................................................................................23
Constraints on the tectonic evolution of the Rudall Province ......................................................................25
Implications for terrane boundaries .............................................................................................................26
Conclusions ...................................................................................................................................................26
References ............................................................................................................................................................27
iv
Figures
1. Simplified geological map indicating the location of the Rudall Province relative to other
Proterozoic orogens and Archean cratons in Western Australia ...................................................................3
2. Simplified geological map of the Rudall Province, indicating the main geological features
and the distribution of terranes .....................................................................................................................3
3. a) and b): Stacked concordia diagrams showing U–Pb zircon analytical data for zircons from
Rudall Province samples analysed by SHRIMP ion microprobe ...............................................................15
4. Hf evolution diagrams for Rudall Province samples compared to potential source regions ....................17
5. Initial 176Hf/177Hf evolution diagram for samples from the Rudall Province compared to
potential source regions ..............................................................................................................................20
6. Hf evolution diagram for inherited zircons from Rudall Province intrusive rocks compared to
potential West Australian Craton source regions ........................................................................................22
7. Magmatic crystallization ages and two-stage Hf model ages for zircons from Rudall Province
magmatic rocks ............................................................................................................................................. 24
8. Oxygen isotope analyses of zircons from Mesoproterozoic metamonzogranite sample
GSWA 112102 ............................................................................................................................................24
9. Comparison of 176Yb/177Hf ratios for zircons from two Mesoproterozoic magmatic rocks with
those from other Rudall Province magmatic rocks of Paleoproterozoic age ............................................24
10. Time-space diagrams showing magmatic and metamorphic U–Pb ages for the Gascoyne
Province, Rudall Province, and Arunta Orogen .........................................................................................25
Tables
1. Lu–Hf isotopic measurement of zircons from the Rudall Province .............................................................6
2. Oxygen isotope analyses from zircons of sample GSWA 112102 .............................................................12
3. Summary of U-Pb SIMS dates for Rudall Province ..................................................................................13
1
The crustal evolution of the Rudall Province
from an isotopic perspective
by
CL Kirkland, SP Johnson, RH Smithies, JA Hollis, MTD Wingate, IM Tyler, AH Hickman, JB Cliff, EA Belousova1, RC Murphy1, and S Tessalina2
AbstractThe Rudall Province, in the Paterson Orogen, is part of the West Australian Craton (WAC) and now lies to the east of the Archean
East Pilbara Terrane. Components within the Rudall Province have previously been linked to the Arunta Orogen of the North
Australian Craton based on similarities in timing of magmatism, deformation, and metamorphism and hence have been regarded
as exotic terranes on the margin of the WAC. The Rudall Province is divided into three lithotectonic elements known as the Talbot,
Connaughton, and Tabletop Terranes. The southern two terranes (Talbot and Connaughton) were affected by magmatism related
to collision between the West and North Australian Cratons during the 1800–1765 Ma Yapungku Orogeny. Zircons within the
Talbot Terrane and Connaughton Terrane indicate crustal residence ages of 3.4 – 2.4 Ga, with strong isotopic and, in the case of
inheritance, temporal affinity to detritus that originated from Capricorn Orogen basement sources (e.g. 2005–1970 Ma Dalgaringa
Supersuite of the Glenburgh Terrane). Furthermore, the range of Hf isotopic compositions in c. 1800 Ma magmatic zircons in the
Rudall Province has similarity to that in the c. 1800 Ma Bridget Suite, which has an undisputed association to the Pilbara Craton.
Hence, sources for all isotopic compositions preserved within the Rudall Province are present within the proximal West Australian
Craton. There is no necessity to invoke transfer of exotic North Australian Craton lithotectonic units to the West Australian Craton
margin and to suggest an accretionary style of orogenesis for the Rudall Province.
The Tabletop Terrane has been regarded as a different far-travelled block with crust unique to the other components of the Rudall
Province. This inference was based on the resemblance of magmatism in this terrane to that in the northern Gawler and Musgrave
regions. However, the similarity of source compositions throughout all three terranes of the Rudall Province implies that the
Tabletop Terrane was derived from crust of similar composition to the Connaughton and Talbot terranes. A phase of crust formation
at 1.9 Ga is indicated by zircons within a Talbot Terrane c. 1450 Ma monzogranite, which have mantle-like oxygen isotope ratios.
This timing of crust formation is distinctive and implies an affinity to a major deep lithospheric source of similar age documented
in the Musgrave Province and could indicate a regional underplate of this age. These data indicate that the major suture between
the North and West Australian Cratons lies to the east of the Rudall Province (present-day coordinates).
KEYWORDS: continental accretion, crustal evolution, earth crust, hafnium isotopes, lutetium isotopes, oxygen isotopes,
radiometric dating, structural evolution, zircon, zircon dating
1 GEMOC, Department of Earth & Planetary Sciences, Macquarie
University, Sydney NSW 2109
2 John De Laeter Centre for Isotope Research, GPO Box U1987, Perth
WA 6845
IntroductionPrecambrian Australia comprises three main cratonic entities — the North, South, and West Australian Cratons — each of which was assembled and stabilized during the Paleoproterozoic. The West Australian Craton, which includes the Pilbara and Yilgarn Cratons and a wedge of exotic Archean to Paleoproterozoic continental crust known as the Glenburgh Terrane (Johnson et al., 2011a, 2012), was assembled along the Capricorn Orogen during two separate and distinct tectonic events. First, the Pilbara Craton and Glenburgh Terrane were sutured during the
2.2 – 2.1 Ga Ophthalmian Orogeny, and second, this combined cratonic block collided with the Yilgarn Craton during the c. 1.9 Ga Glenburgh Orogeny (Johnson et al., 2012). Subsequent tectono-magmatic events include the 1820–1770 Ma Capricorn Orogeny and the 1800–1765 Ma Yapungku Orogeny; the latter recorded within the Rudall Province of the Paterson Orogen along the eastern margin of the West Australian Craton (all directions refer to present-day coordinates). In the Rudall Province, deformation, metamorphism, and magmatism during the Yapungku Orogeny have been interpreted as a response to either accretional events that sutured exotic terranes to the craton margin (Bagas, 2004), or to the collision and amalgamation of the North and West Australian Cratons (Bagas and Smithies, 1997; Tyler, 2000; Li et al., 2008). Deformation and magmatism associated with the Capricorn Orogeny is interpreted as an intraplate response to these far-field plate-margin events (Sheppard et al.,
Kirkland et al.
2
2010a; Johnson et al., 2012). Understanding the tectonic setting of the Rudall Province is important because this province may record the collision between the North and West Australian Cratons and preserve a major crustal suture related to the Proterozoic assembly of Australia. Furthermore, within the region, a range of Neoproterozoic mineral systems exist, including Zn–Pb (Warrabarty; Smith, 1996), Cu (Nifty; Huston et al., 2007), U (Kintyre; Cross et al., 2011) and Au–Cu (Telfer; Maidment et al., 2008; 2010). The isotopic signature of units characterized in this report may be of significance for constraining the influence and role of crystalline basement on these younger mineralizing systems.
This report uses time-constrained Lu–Hf isotope analyses to evaluate the tectonic and crustal evolution of the Rudall Province, including:
1. whether the 1800–1765 Ma Yapungku Orogeny records the collision between the North and West Australian Cratons, or the assembly of exotic lithotectonic units to the West Australian Craton margin during accretionary orogenesis
2. whether terranes within the Rudall Province are (para)autochthonous and related to the thickening of a Proterozoic margin of the Pilbara Craton
or, alternatively,
3. whether terranes within the Rudall Province are exotic entities that:
a. formed part of the opposing North Australian Craton margin, being juxtaposed with the West Australian Craton during collisional orogenesis
or
b. have an entirely exotic source (e.g. part of the northern Gawler and Musgrave regions; (Cassidy et al., 2006), having been accreted to the West Australian Craton margin during accretionary or collisional orogenesis.
Geological setting of the
Rudall Province The ~2000 km long Paterson/Petermann Orogens of Western Australia extend along the eastern margin of the Archean Pilbara Craton, beneath younger sedimentary rocks, and into Central Australia (Fig. 1). The orogen includes Paleoproterozoic to Mesoproterozoic metasedimentary and igneous rocks of the Rudall and Musgrave Provinces, and Neoproterozoic to Paleozoic sedimentary rocks of the Centralian Superbasin (Myers and Hocking, 1988; Williams and Myers, 1990; Clarke, 1991; Bagas and Lubieniecki, 2000; Bagas et al., 2001; Haines et al., 2001; Bagas, 2004; Cawood and Korsch, 2008; Smithies et al., 2011; Reading et al., 2012). The Rudall and Musgrave Provinces are separated by younger sedimentary rocks of the Yeneena, northwest Officer, and Canning Basins, but appear to be connected via a
pronounced gravity high, known as the Anketell Regional Gravity Ridge (GSWA, 2012). Metasedimentary and igneous rocks within the two provinces were deformed and metamorphosed at medium to high metamorphic grades during the Proterozoic. However, the timing of tectono-magmatic events in the two regions is distinctly different, with events in the Rudall Province dominated by the 1800–1765 Ma Yapungku Orogeny (Bagas, 2004), and those in the Musgrave Province by the 1345–1293 Ma Mount West Orogeny, the 1220–1150 Ma Musgrave Orogeny, and the 1085–1040 Ma Giles Event (Smithies et al., 2011). However, both provinces (including parts of the Centralian Superbasin), were reworked at low to medium metamorphic grades during the c. 550 Ma Paterson/Petermann Orogeny, implying that juxtaposition of the Musgrave and the Rudall regions may have occurred during latest Neoproterozoic to Cambrian time (Williams and Myers, 1990).
The Rudall Province is divided into three major lithotectonic elements: the Talbot, Connaughton, and Tabletop Terranes (Hickman et al., 1994; Hickman and Bagas, 1995, 1999a; Bagas and Smithies, 1997; Fig. 2). The Talbot and Connaughton Terranes contain Paleoproterozoic intrusive rocks that formed during the Yapungku Orogeny, whereas the Tabletop Terrane consists of younger Mesoproterozoic granites. The three terranes are bounded by major faults that have been considered a response to terrane juxtaposition during the Yapungku Orogeny, or the c. 650 Ma Miles Orogeny, or both (Bagas and Smithies, 1997; Bagas, 2004).
The Talbot Terrane
The Talbot Terrane occupies the western parts of the Rudall Province (Fig. 2), and consists of multiply deformed and metamorphosed supracrustal and felsic intrusive rocks (Bagas and Smithies, 1997; Hickman and Bagas, 1999b, 1999a). The depositional setting of the siliciclastic rocks has been interpreted as a deltaic to moderately deep-water marine basin on the southeastern margin of the Pilbara Craton (Hickman et al., 1994).
Basement to the supracrustal rocks is not exposed, although a syenogranite gneiss from the Sundowner drillhole was interpreted to have crystallized at c. 2015 Ma (GSWA 104932; Nelson, 1995a). However, it is possible that the granitic protolith to the gneiss is much younger, and contains only inherited zircons. Major zircon age components, at 2715–2577, 2010, and 1960 Ma, are also present in this gneiss (Nelson, 1995a).
The metasedimentary rocks of the Talbot Terrane are divided into a western association of quartzite, amphibolite, serpentinite, and banded iron-formation, and an extensive eastern association containing nearly 5 km of siliciclastic sedimentary rocks. The eastern association consists of quartz-feldspar-mica paragneisses of the Larry Formation, conformably overlain by a succession of quartzite and minor mica schist known as the Fingoon Quartzite (Hickman et al., 1994; Bagas and Smithies, 1998). Quartz-muscovite schist, iron-rich graphitic pelitic schist, banded iron-formation, and chert of the
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
3
CLK88 27.03.13
OfficerBasin
0
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Phanerozoic
Neoproterozoic
Mesoproterozoic
Palaeoproterozoic
Archean
sedim
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YILGARN CRATON
Edmund Basin
Collier
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Basin
Fortescue, Hamersley, and
TureeCreek Basins
Canning
Basin
Carnarvon
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Narryer Terrane
Murchison Domain
Domain
East PilbaraTerrane
200 km
PATERSON O
ROGEN
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Eastern GoldfieldsSuperterane
PILBARA CRATON
AruntaMusgraves
Gascoyne
Province
LRF
CG
GT
Tarcunyah Group
Throssell Group &Lamil Group undivided
Tabletop Terrane
Tabletop Terrane
Talbot Terrane
Talbot Terrane
Connaughton Terrane
Pate
rson O
rogen
Rudall P
rovin
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CLK80 27.03.13
23°
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Camel–Tabletop
McKay
Fault
123°122°
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Thrust
Normal fault
CANNINGBASIN
20 km
Southwest Thrust
Permian
Connaughton
Terrane
Figure 1. Simplified geological map indicating the location of the Rudall Province relative to other Proterozoic
orogens and Archean cratons in Western Australia (modified after Sheppard et al., 2010a). Red dashed
line indicates the approximate coverage of an extensive basin system during the 1820–1770 Ma Capricorn
Orogeny. Inset map (top right) shows the location of the main map as a red rectangle and the WAC (West
Australian Craton) in the context of other tectonic entities. Abbreviations used in figure: CG — Capricorn
Group, GC — Gawler Craton, GT — Glenburgh Terrane, KC — Kimberley Craton, LRF — Lyons River Fault,
NAC — North Australian Craton, PC — Pilbara Craton, SAC — South Australian Craton, YC — Yilgarn Craton,
WAC — West Australian Craton.
Figure 2. Simplified geological map of the Rudall Province,
indicating the main geological features and the
distribution of terranes (modified after Bagas and
Smithies, 1997; Smithies and Bagas, 1997).
Yandagooge Formation rest conformably on the Fingoon Quartzite. The Yandagooge Formation is overlain by banded paragneiss and minor amphibole-chlorite schist of the Butler Creek Formation, and quartzite and quartz-feldspar-mica gneiss of the Poynton Formation. Detrital zircon age data for the Fingoon Quartzite indicate a unimodal zircon age component at 1791 ± 10 Ma (Nelson, 1995e), which also provides a maximum depositional age for the sedimentary protolith to the quartzite and for the lowermost part of the eastern association.
Based on the presence of western association xenoliths within strongly deformed orthogneisses with c. 2015 and c. 1972 Ma zircon age components, the western association has generally been regarded as considerably older than the eastern association (Bagas, 2004). However, it is possible that the protoliths to the orthogneisses are much younger, containing only inherited zircons, and thus the two sequences may be of comparable age (Neumann and Fraser, 2007).
Metasedimentary rocks in both the eastern and western associations of the Talbot Terrane have been intruded by voluminous granites of the 1800–1765 Ma Kalkan Supersuite (Budd et al., 2002). These granitic rocks are characterized by high-K, metaluminous, calc-alkaline chemistry, with large K-feldspar phenocrysts and
Kirkland et al.
4
Sr depleted, Y-undepleted trace-element patterns typical of many Australian Proterozoic granite suites (Wyborn, 2001). These granites have crystallization ages between c. 1800 and c. 1760 Ma (Nelson, 1995i, 1995k), which provide a younger limit for deposition of the protoliths to both metasedimentary associations in the Rudall Province. Compressional shear zones within the Talbot Terrane contain enclaves of deformed ultramafic and mafic rocks, interpreted to represent slivers of dismembered ophiolite (Carr, 1989).
The Talbot Terrane also records minor magmatic episodes during the Mesoproterozoic, including a 1453 ± 10 Ma monzogranite that crosscuts fabrics associated with the Yapungku Orogeny (Nelson, 1996b) and a 1291 ± 10 Ma pegmatite close to the Camel–Tabletop Fault (Nelson, 1995b).
The Connaughton Terrane
The Connaughton Terrane (Fig. 2), within the southeastern part of the province, comprises a series of poorly dated metavolcanic and metasedimentary rocks. This terrane contains a significantly higher proportion of amphibolite than the Talbot Terrane (Bagas and Smithies, 1998). The amphibolite is interlayered with banded iron-formation, quartzite, pelitic metasedimentary rocks, chert, and ultramafic rocks (Hickman et al., 1994). In a situation similar to the Talbot Terrane, basement rocks are not exposed. Importantly, all rocks within the Connaughton Terrane were metamorphosed at upper amphibolite to granulite facies conditions (peak 800°C, 12 kbar) during the Yapungku Orogeny (Smithies and Bagas, 1997).
Preliminary U–Pb geochronology of detrital zircons in quartzite provides a maximum depositional age of c. 2300 Ma, and a provenance signature (age spectrum) significantly different from that of the Fingoon Quartzite of the Talbot Terrane (Maidment et al., in prep. reported in Neumann and Fraser, 2007). Insufficient geochronological data from metasedimentary rocks from both the Talbot and Connaughton Terranes makes it difficult to determine if they had different sedimentary source regions or depositional ages, or both.
Granitic rocks of the 1800–1765 Ma Kalkan Supersuite (Nelson, 1995m; 1996d) form a major component of the Connaughton Terrane. This terrane may also have been subject to minor Mesoproterozoic magmatic activity. A garnet-bearing gneiss, south of Harbutt Range in the Connaughton Terrane, yielded zircon age components at c. 1800, 1672, and 1222 Ma (Nelson, 1996c), with the youngest group interpreted to date crystallization of the felsic intrusive protolith. However, the c. 1222 Ma date was obtained from zircon rims that have elevated thorium and common Pb contents and may have grown during metamorphism.
The Tabletop Terrane
The Tabletop Terrane (Fig. 2) is dominated by weakly deformed and metamorphosed felsic and mafic igneous
rocks of the Krackatinny Suite, with minor quartzite, mafic and ultramafic schists, amphibolite, and banded iron-formation (Bagas et al., 1999). Unpublished geochronology reported in Neumann and Fraser (2007) indicates that most of the felsic and mafic intrusive rocks of the Krackatinny Suite away from the Camel–Tabletop Fault were emplaced between c. 1590 and c. 1550 Ma. Other felsic intrusive rocks in this terrane have been dated at 1476 ± 10 Ma (unpublished result referred to in Bagas, 2004) and 1310 ± 4 Ma (Nelson, 1996e).
Available geochronology suggests that the magmatic history of the Tabletop Terrane is distinctly different from that in the Talbot and Connaughton Terranes, which share a common structural, magmatic, and deformational history (Bagas, 2004). The Tabletop Terrane does not appear to contain evidence for 1800–1760 Ma magmatism, whereas the Talbot and Connaughton Terranes lack 1590–1550 Ma magmatism, possibly implying that the Camel–Tabletop Fault (Fig. 2), which separates these terranes, is a major crustal boundary (Hickman et al., 1994; Bagas and Lubieniecki, 2000).
Structural evolution
The Talbot and Connaughton Terranes share a similar structural history, including two high-grade tectono-magmatic events during the Paleoproterozoic Yapungku Orogeny (Clarke, 1991; Hickman et al., 1994; Bagas and Smithies, 1997; Hickman and Bagas, 1999b; Bagas, 2004). The timing and duration of the Yapungku Orogeny is defined by the age of the oldest and youngest granitic components at c. 1800 and c. 1760 Ma, respectively (Smithies and Bagas, 1997; Bagas, 2004). In the Talbot Terrane, both tectonothermal events occurred prior to c. 1778 Ma, as constrained by the age of undeformed aplite dykes (Nelson, 1995j) that crosscut the major tectonic fabrics. The main phase of deformation and metamorphism in the Connaughton Terrane is not well established, but has been interpreted to be coeval with lower-pressure metamorphism (M2) in the Talbot Terrane (Bagas and Smithies, 1997; Bagas, 2004).
The first deformation event (D1) is preserved as bedding-parallel fabrics in the Talbot Terrane (Clarke, 1991; Bagas and Smithies, 1998). Associated metamorphic features indicate low-pressure metamorphism at amphibolite facies. The timing of D1 in the Talbot Terrane is constrained to be older than 1802 ± 14 Ma, the age of a K-feldspar porphyritic granite that crosscuts D1 fabrics (Nelson, 1995i). Evidence for D1 and M1 in the Connaughton Terrane is preserved only as inclusion trails of epidote, titanite, and amphibole within garnet porphyroblasts (Smithies and Bagas, 1997).
The D2 event produced north–south isoclinal folding, faulting, and crustal thickening in the Talbot and Connaughton Terranes, and was coeval with thrusting and the emplacement of granitic, mafic, and ultramafic (peridotite–dunite) rocks in the Talbot Terrane (Hickman and Bagas, 1995, 1999b). Geochronology of syn-D2 granitic rocks in the Talbot Terrane indicates that the D2 event occurred between c. 1801 and c. 1765 Ma
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
5
(Nelson, 1995i, 1995k, 1995c; Bagas, 2004). In the Connaughton Terrane, peak regional M2 metamorphism was synchronous with, but outlasted, D2 deformation in the Talbot Terrane (Hickman et al., 1994). Pelitic schists within the Talbot Terrane contain peak M2 mineral assemblages of kyanite + garnet + staurolite, which are indicative of metamorphism in the mid-amphibolite facies (Smithies and Bagas, 1997; Bagas, 2004). In the Connaughton Terrane, peak M2 metamorphism is characterized by the presence of amphibolites and mafic granulites that were metamorphosed at high pressures (≤ 1200 MPa) close to the amphibolite–granulite facies transition, indicating that crust from depths of up to 40 km is now exposed at the surface (Smithies and Bagas, 1997). These conditions also imply that the deformation and metamorphism assigned to D2/M2 were in response to crustal thickening in which the Connaughton Terrane was thrust westwards over the Talbot Terrane (Bagas, 2004).
The Rudall Province has also been subject to several Neoproterozoic deformation events (Bagas, 2004). Northwesterly trending folds and north-northeasterly trending faults ascribed to D3/4 were developed during the c. 650 Ma Miles Orogeny (Bagas and Smithies, 1998; Hickman and Bagas, 1999b). Lower-greenschist facies metamorphism prevailed during northeasterly to southwesterly oriented shortening associated with the D4 event. An enigmatic D5 event is believed to be a response to northwest-directed shortening against the Pilbara Craton. The late Neoproterozoic (550 Ma) Paterson Orogeny, ascribed to D6, was responsible for easterly trending transpressional folds (Bagas, 2004).
Lu–Hf and oxygen isotopes,
and reinterpreted SHRIMP
U–Pb geochronologyThis section presents new Lu–Hf (Table 1) and oxygen isotope data (Table 2) for previously dated samples from the Rudall Province. The geochemical characteristics of many of these samples have previously been discussed in Wyborn (2001). We calculate concordia ages from the previously published SHRIMP U–Pb geochronology data for these rocks. Where the location of the mean U–Pb composition can be assumed to fall on the concordia curve (i.e. the zircons have not undergone modern or ancient radiogenic-Pb loss), the ‘concordia age’ makes the optimum use of both 207Pb*/206Pb* and 238U/206Pb* ratios (Ludwig, 1998)1. This approach generally yields a more precise mean age than can be obtained using either ratio alone, and also yields an objective and quantitative measure of concordance. In cases where the U–Pb data do not fall on concordia, it is likely that the zircons have undergone modern or ancient radiogenic-Pb loss. Where the distribution of U–Pb data are consistent with mainly geologically-recent loss of radiogenic Pb, we calculate the weighted mean 207Pb*/206Pb* date. Weighted mean and concordia ages are reported below with 95% confidence intervals. A summary of the U–Pb geochronology is presented in Table 3.
Analytical methodology
Lu–Hf isotopes
Hafnium isotope analyses were conducted on previously dated zircons using a New Wave/Merchantek LUV213 laser-ablation microprobe attached to a Nu Plasma multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICPMS). The analyses employed a beam diameter of c. 40 μm and a 5 Hz repetition rate, and energies of 0.6 – 1.3 mJ per pulse, which resulted in ablation pits typically 40–60 μm deep during a 30–120 second analysis. Total Hf signals were between 1 x 10-11 and 6 x 10-11 amperes. The ablated sample material was transported from the laser cell to the ICPMS torch by a helium carrier gas. Interference of 176Lu on 176Hf was corrected by measurement of interference-free 175Lu, and using the invariant 176Lu/175Lu correction factor of 0.02669 (Debievre and Taylor, 1993). The measurement of accurate 176Hf/177Hf ratios in zircon requires correction of the isobaric interferences of 176Lu and 176Yb on 176Hf. The interference of 176Yb on 176Hf was corrected by measuring the interference-free 172Yb isotope and using the 176Yb/172Yb ratio to calculate the intensity of 176Yb. The appropriate value of 176Yb/172Yb (0.5865) was determined by successively doping a JMC475 Hf standard (100 ppb solution) with various amounts of Yb, and determining the value of 176Yb/172Yb required to yield the value of 176Hf/177Hf in the undoped solution.
Twenty-three zircons from the Mud Tank carbonatite locality were analysed, together with the samples, as a measure of the accuracy of the results. Most of the data and the mean 176Hf/177Hf value (0.282530 ± 0.000022; n = 23) are within two standard deviations (SD) of the recommended value (0.282522 ± 0.000042 (2 ; Griffin, 2007). Temora-2 zircon was run as an independent check on the accuracy of the Yb correction. Temora zircon has an average 176Yb/177Hf ratio of 0.037, which is similar to the average 176Yb/177Hf ratio of Rudall zircon of 0.039. The average 176Hf/177Hf ratio for Temora-2 is 0.282683 ± 0.000022 (1 ), which is consistent with the published value for the Temora-2 standard (0.282686 ± 8, solution ICPMS, Woodhead and Hergt, 2005; 0.282687 ± 24, LA-ICPMS, Hawkesworth and Kemp, 2006).
Calculation of initial 176Hf/177Hf (e.g. 176Hf/177Hfi) is based on the 176Lu decay constant of Scherer et al. (2001; 1.867 x 10-11 yr-1). Since 176Hf/177Hf departures from the CHUR evolution line are very small, the epsilon notation is used whereby one epsilon unit represents a one part per 10 000 deviation from the CHUR composition. Hf values employ the present-day chondritic measurement of Blichert-Toft and Albarède (1997; 0.282772). Calculation of model ages (TDM) is based on a depleted-mantle source with 176Hf/177Hfi = 0.279718 at 4.56 Ga and 176Lu/177Hf = 0.0384 (Griffin et al., 2004).
Measured isotope compositions are referred to model bulk-Earth Hf reservoirs, including Depleted Mantle (DM; Griffin et al., 2000, 2004) and Chondritic Uniform Reservoir (CHUR; Blichert-Toft and Albarède 1997).
1 Pb* refers to radiogenic Pb produced by the in-situ decay of uranium.
Kirkland et al.
6
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
112160-1
.11872
0.2
81396
0.0
00
00
90
.00
04
92
0.0
14
04
20
.28
13
79
-7.6
0.3
22.5
63.0
2C
onnaughto
n
112160-2
.11831
0.2
81358
0.0
00
015
0.0
00
69
90
.02
05
83
0.2
813
34
-10.1
0.5
32.6
33.1
5C
onnaughto
n
112160-3
.11873
0.2
81438
0.0
00
018
0.0
012
86
0.0
36
35
00
.28
13
92
-7.1
0.6
32.5
62.9
9C
onnaughto
n
112160-4
.11764
0.2
81370
0.0
00
017
0.0
00
95
50
.02
874
90
.28
13
38
-11.
50.6
02.6
33.1
9C
onnaughto
n
112160-5
.11684
0.2
81406
0.0
00
04
90
.0016
72
0.0
50
07
70
.28
13
53
-12.8
1.72
2.6
33.2
0C
onnaughto
n
112160-6
.11771
0.2
81369
0.0
00
014
0.0
02
75
90
.09
88
71
0.2
812
76
-13.5
0.4
92.7
63.3
2C
onnaughto
n
112160-7
.11772
0.2
81338
0.0
00
011
0.0
012
55
0.0
36
49
40
.28
12
96
-12.8
0.3
92.6
93.2
7C
onnaughto
n
112160-8
.11629
0.2
81436
0.0
00
015
0.0
00
80
20
.02
35
92
0.2
814
11-1
1.9
0.5
32.5
33.1
1C
onnaughto
n
112160-9
.11274
0.2
81369
0.0
00
013
0.0
014
63
0.0
55
740
0.2
813
34
-22.7
0.4
62.6
63.5
0C
onnaughto
n
112160-9
.211
44
0.2
81410
0.0
00
011
0.0
00
747
0.0
29
04
10
.28
13
94
-23.5
0.3
92.5
63.4
5C
onnaughto
n
112160-1
0.1
1820
0.2
81504
0.0
00
02
00
.00
36
59
0.1
48
09
20
.28
13
78
-8.8
0.7
02.6
33.0
6C
onnaughto
n
112160-1
1.1
1677
0.2
81287
0.0
00
017
0.0
012
20
0.0
36
13
90
.28
12
48
-16.6
0.6
02.7
63.4
4C
onnaughto
n
113002-0
1.1
1769
0.2
81531
0.0
00
00
90
.00
09
01
0.0
26
66
10
.28
15
01
-5.6
0.3
12.4
02.8
2C
onnaughto
n
113002-0
2.1
1787
0.2
81531
0.0
00
010
0.0
00
85
90
.02
49
97
0.2
815
02
-5.1
0.3
52.4
02.8
0C
onnaughto
n
113002-0
3.1
1770
0.2
81519
0.0
00
00
80
.00
06
60
0.0
19
63
60
.28
14
97
-5.7
0.2
92.4
02.8
3C
onnaughto
n
113002-0
5.1
1762
0.2
81539
0.0
00
00
90
.00
08
27
0.0
25
36
10
.28
15
11-5
.40.3
02.3
92.8
0C
onnaughto
n
113002-0
6.1
1780
0.2
81536
0.0
00
00
70
.00
04
36
0.0
12
56
80
.28
15
21
-4.6
0.2
52.3
72.7
6C
onnaughto
n
113002-0
8.1
174
20.2
81553
0.0
00
00
90
.00
07
08
0.0
22
819
0.2
815
30
-5.2
0.3
22.3
62.7
7C
onnaughto
n
113002-0
9.1
1773
0.2
81546
0.0
00
00
90
.00
05
59
0.0
17
819
0.2
815
27
-4.6
0.3
02.3
62.7
6C
onnaughto
n
113002-1
0.1
1772
0.2
81572
0.0
00
00
80
.00
08
72
0.0
26
52
00
.28
15
43
-4.0
0.2
72.3
52.7
2C
onnaughto
n
113002-1
2.1
1777
0.2
81583
0.0
00
00
70
.00
06
67
0.0
20
67
00
.28
15
61
-3.3
0.2
62.3
22.6
8C
onnaughto
n
113002-1
4.1
1760
0.2
81541
0.0
00
00
90
.00
076
30
.02
44
64
0.2
815
16
-5.3
0.3
32.3
82.7
9C
onnaughto
n
113035-0
6.1
1765
0.2
81580
0.0
00
011
0.0
00
47
80
.015
54
70
.28
15
64
-3.4
0.3
92.3
12.6
8C
onnaughto
n
113035-0
7.1
1763
0.2
81696
0.0
00
013
0.0
00
78
00
.02
28
21
0.2
816
70
0.3
0.4
62.1
72.4
4C
onnaughto
n
113035-0
8.1
1765
0.2
81642
0.0
00
014
0.0
00
79
20
.02
43
60
0.2
816
16
-1.6
0.4
92.2
42.5
6C
onnaughto
n
113035-0
9.1
1788
0.2
81618
0.0
00
015
0.0
00
58
80
.019
98
20
.28
15
98
-1.7
0.5
32.2
72.5
9C
onnaughto
n
113035-1
0.1
1785
0.2
81631
0.0
00
017
0.0
00
78
70
.02
83
04
0.2
816
04
-1.6
0.6
02.2
62.5
7C
onnaughto
n
113035-1
1.1
1756
0.2
81623
0.0
00
00
90
.00
06
50
0.0
19
90
50
.28
16
01
-2.3
0.3
22.2
62.6
0C
onnaughto
n
113035-1
2.1
1791
0.2
81608
0.0
00
00
90
.00
08
02
0.0
24
70
60
.28
15
81
-2.3
0.3
22.2
92.6
2C
onnaughto
n
113035-1
3.1
1771
0.2
81648
0.0
00
011
0.0
00
99
30
.03
49
88
0.2
816
15
-1.5
0.3
92.2
52.5
6C
onnaughto
n
118914-0
1.1
1265
0.2
81903
0.0
00
014
0.0
03
001
0.0
976
56
0.2
818
31
-5.3
0.4
92.0
02.4
1Table
top
118914-0
2.1
1495
0.2
81729
0.0
00
013
0.0
03
62
30
.14
10
91
0.2
816
27
-7.3
0.4
62.3
02.7
2Table
top
Tabl
e 1.
L
u–H
f iso
topi
c m
easu
rem
ent o
f zir
cons
from
the
Rud
all P
rovi
nce
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
7
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
118914-0
3.1
1320
0.2
81803
0.0
00
011
0.0
02
519
0.0
85
45
80
.28
174
0-7
.20.3
92.1
22.5
7Table
top
118914-0
4.1
1315
0.2
81802
0.0
00
011
0.0
02
42
70
.08
82
81
0.2
8174
2-7
.30.3
92.1
22.5
7Table
top
118914-0
5.1
1312
0.2
81791
0.0
00
02
10
.00
218
40
.07
37
25
0.2
817
37
-7.5
0.7
42.1
22.5
9Table
top
118914-0
6.1
1324
0.2
81771
0.0
00
017
0.0
02
29
50
.076
76
40
.28
17
14
-8.1
0.6
02.1
52.6
3Table
top
118914-0
7.1
1312
0.2
81826
0.0
00
014
0.0
03
05
70
.1016
81
0.2
817
50
-7.1
0.4
92.1
22.5
6Table
top
118914-0
8.1
1194
0.2
81766
0.0
00
013
0.0
03
03
40
.1018
63
0.2
816
98
-11.
60.4
62.2
02.7
5Table
top
118914-0
9.1
1241
0.2
81798
0.0
00
016
0.0
03
22
90
.09
30
79
0.2
817
22
-9.7
0.5
62.1
72.6
6Table
top
118914-1
0.1
1298
0.2
81780
0.0
00
011
0.0
02
83
50
.10
08
51
0.2
817
11-8
.80.3
92.1
72.6
5Table
top
118914-1
1.1
1297
0.2
8174
20
.00
0018
0.0
04
09
70
.15
78
83
0.2
816
42
-11.
30.6
32.3
12.8
1Table
top
118914-1
2.1
1287
0.2
81776
0.0
00
03
20
.00
22
47
0.0
815
15
0.2
817
21
-8.7
1.12
2.1
42.6
4Table
top
118914-1
5.1
1308
0.2
81765
0.0
00
00
80
.00
27
26
0.1
00
72
00
.28
16
98
-9.0
0.2
82.1
92.6
8Table
top
118914-1
6.1
1311
0.2
81798
0.0
00
02
00
.00
29
38
0.1
13
40
90
.28
17
25
-8.0
0.7
02.1
52.6
1Table
top
118914-1
7.1
1311
0.2
81764
0.0
00
010
0.0
02
95
80
.1019
49
0.2
816
91
-9.2
0.3
42.2
02.6
9Table
top
118914-1
9.1
1311
0.2
81764
0.0
00
00
50
.00
24
45
0.0
82
73
30
.28
17
03
-8.8
0.1
92.1
72.6
6Table
top
112102-4
.11475
0.2
82035
0.0
00
014
0.0
02
52
00
.09
04
35
0.2
819
65
4.2
0.4
91.
79
1.97
Talb
ot
112102-5
.11453
0.2
82033
0.0
00
013
0.0
02
00
90
.06
58
85
0.2
819
78
4.2
0.4
61.
76
1.95
Talb
ot
112102-6
.11452
0.2
82040
0.0
00
013
0.0
02
47
50
.09
33
36
0.2
819
72
4.0
0.4
61.
78
1.96
Talb
ot
112102-7
.11435
0.2
82031
0.0
00
02
80
.00
22
43
0.0
79
45
00
.28
19
70
3.5
0.9
81.
78
1.98
Talb
ot
112102-8
.11414
0.2
82013
0.0
00
011
0.0
02
15
70
.07
18
07
0.2
819
55
2.5
0.3
91.
80
2.0
3Talb
ot
112102-9
.11426
0.2
82054
0.0
00
014
0.0
02
92
20
.09
50
44
0.2
819
75
3.5
0.4
91.
78
1.97
Talb
ot
112102-1
0.1
1460
0.2
82068
0.0
00
02
50
.00
22
70
0.0
84
06
20
.28
20
05
5.3
0.8
81.
73
1.88
Talb
ot
112102-1
1.1
1453
0.2
82094
0.0
00
012
0.0
02
73
00
.10
05
53
0.2
82
019
5.6
0.4
21.
71
1.86
Talb
ot
112101-
01.
21755
0.2
81442
0.0
00
00
80
.00
09
68
0.0
37
09
40
.28
14
10
-9.1
0.2
72.5
33.0
3Talb
ot
112101-
03.1
1810
0.2
81463
0.0
00
00
50
.00
06
98
0.0
25
32
20
.28
14
39
-6.9
0.1
92.4
82.9
3Talb
ot
112101-
04.1
1814
0.2
81472
0.0
00
00
80
.00
08
18
0.0
312
65
0.2
814
44
-6.6
0.2
72.4
82.9
2Talb
ot
112101-
05.1
1796
0.2
81575
0.0
00
013
0.0
013
41
0.0
513
04
0.2
815
29
-4.0
0.4
62.3
72.7
4Talb
ot
112101-
06.1
1784
0.2
81513
0.0
00
012
0.0
017
88
0.0
75
70
60
.28
14
53
-7.0
0.4
22.4
92.9
2Talb
ot
112101-
07.
11790
0.2
81572
0.0
00
013
0.0
00
76
60
.02
65
06
0.2
815
46
-3.5
0.4
62.3
42.7
0Talb
ot
112101-
08.1
1799
0.2
81598
0.0
00
015
0.0
010
44
0.0
42
03
70
.28
15
62
-2.7
0.5
32.3
22.6
6Talb
ot
112101-
16.1
1781
0.2
81591
0.0
00
012
0.0
010
56
0.0
43
86
40
.28
15
55
-3.4
0.4
22.3
32.6
9Talb
ot
112101-
17.
11777
0.2
81597
0.0
00
010
0.0
00
89
10
.03
33
06
0.2
815
67
-3.1
0.3
42.3
12.6
6Talb
ot
Tabl
e 1.
co
ntin
ued
Kirkland et al.
8
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
104980-0
2.1
1717
0.2
81569
0.0
00
02
30
.0018
25
0.0
919
36
0.2
815
10
-6.5
0.8
12.4
12.8
3Talb
ot
104980-0
3.1
1804
0.2
81466
0.0
00
015
0.0
014
07
0.0
65
62
20
.28
14
18
-7.7
0.5
32.5
32.9
8Talb
ot
104980-0
5.1
1800
0.2
81467
0.0
00
02
10
.0010
61
0.0
49
39
90
.28
14
31
-7.4
0.7
42.5
02.9
5Talb
ot
104980-0
6.1
1801
0.2
81451
0.0
00
00
80
.0011
96
0.0
516
47
0.2
814
10
-8.1
0.2
62.5
33.0
0Talb
ot
104980-0
7.1
1795
0.2
81448
0.0
00
00
60
.0013
12
0.0
58
22
40
.28
14
03
-8.5
0.2
12.5
43.0
2Talb
ot
104980-0
8.1
1809
0.2
81453
0.0
00
018
0.0
012
01
0.0
56
86
00
.28
14
12
-7.8
0.6
32.5
32.9
9Talb
ot
104980-0
9.1
1799
0.2
81457
0.0
00
010
0.0
013
02
0.0
618
24
0.2
814
13
-8.0
0.3
42.5
33.0
0Talb
ot
104980-1
2.1
1794
0.2
81442
0.0
00
00
90
.0012
71
0.0
64
20
70
.28
13
99
-8.7
0.3
32.5
53.0
3Talb
ot
104980-1
3.1
1786
0.2
81444
0.0
00
00
80
.0010
45
0.0
49
18
00
.28
14
09
-8.5
0.2
62.5
33.0
1Talb
ot
112341-
02.1
1772
0.2
81564
0.0
00
02
70
.00
67
93
0.2
576
77
0.2
813
36
-11.
40.9
52.7
93.1
9Talb
ot
112341-
03.1
1806
0.2
81572
0.0
00
00
60
.0011
41
0.0
45
45
50
.28
15
33
-3.6
0.2
22.3
62.7
2Talb
ot
112341-
04.1
1797
0.2
81536
0.0
00
012
0.0
011
43
0.0
56
48
30
.28
14
97
-5.1
0.4
22.4
12.8
1Talb
ot
112341-
05.1
1788
0.2
81518
0.0
00
011
0.0
015
34
0.0
75
16
80
.28
14
66
-6.4
0.3
92.4
62.8
8Talb
ot
112341-
06.1
1760
0.2
81502
0.0
00
00
90
.00
07
88
0.0
376
69
0.2
814
76
-6.7
0.3
32.4
42.8
8Talb
ot
112341-
07.
11727
0.2
81515
0.0
00
011
0.0
013
99
0.0
70
912
0.2
814
69
-7.7
0.3
92.4
62.9
2Talb
ot
112341-
09.1
1612
0.2
81572
0.0
00
00
90
.00
08
77
0.0
36
72
40
.28
15
45
-7.6
0.3
02.3
52.8
2Talb
ot
112341-
10.1
1765
0.2
81490
0.0
00
00
90
.0010
27
0.0
43
101
0.2
814
56
-7.3
0.3
02.4
72.9
2Talb
ot
112341-
11.1
1703
0.2
81509
0.0
00
010
0.0
011
97
0.0
65
56
30
.28
14
70
-8.2
0.3
42.4
52.9
3Talb
ot
112341-
12.1
1786
0.2
81535
0.0
00
011
0.0
012
13
0.0
619
97
0.2
814
94
-5.5
0.3
92.4
22.8
2Talb
ot
112341-
13.1
1754
0.2
81524
0.0
00
011
0.0
011
52
0.0
43
213
0.2
814
86
-6.5
0.3
92.4
32.8
6Talb
ot
112341-
14.1
1739
0.2
81518
0.0
00
011
0.0
013
65
0.0
69
14
80
.28
14
73
-7.3
0.3
92.4
52.9
0Talb
ot
112341-
15.1
1717
0.2
81526
0.0
00
014
0.0
012
90
0.0
63
274
0.2
814
84
-7.4
0.4
92.4
32.8
9Talb
ot
111843-0
1.1
1778
0.2
81554
0.0
00
014
0.0
00
90
00
.02
62
60
0.2
815
24
-4.6
0.4
92.3
72.7
6Talb
ot
111843-0
1.2
1877
0.2
81488
0.0
00
010
0.0
00
89
10
.02
57
88
0.2
814
56
-4.7
0.3
52.4
62.8
5Talb
ot
111843-0
2.1
1790
0.2
81483
0.0
00
012
0.0
00
82
20
.02
42
79
0.2
814
55
-6.7
0.4
22.4
62.9
1Talb
ot
111843-0
3.1
2102
0.2
81309
0.0
00
016
0.0
00
58
70
.018
82
00
.28
12
86
-5.7
0.5
62.6
83.0
8Talb
ot
111843-0
4.1
1715
0.2
81477
0.0
00
00
90
.00
07
88
0.0
25
412
0.2
814
51
-8.6
0.3
12.4
72.9
6Talb
ot
111843-0
7.1
1756
0.2
81450
0.0
00
018
0.0
00
93
50
.02
84
99
0.2
814
19
-8.8
0.6
32.5
23.0
1Talb
ot
111843-0
7.2
1807
0.2
81498
0.0
00
015
0.0
010
65
0.0
35
54
60
.28
14
62
-6.1
0.5
32.4
62.8
8Talb
ot
111843-0
8.1
1723
0.2
81430
0.0
00
00
80
.0012
84
0.0
38
48
00
.28
13
88
-10.6
0.2
62.5
73.1
0Talb
ot
111843-0
9.1
1790
0.2
81354
0.0
00
010
0.0
013
73
0.0
46
59
80
.28
13
07
-12.0
0.3
52.6
83.2
4Talb
ot
111843-1
0.1
1809
0.2
81459
0.0
00
016
0.0
011
51
0.0
35
119
0.2
814
20
-7.6
0.5
62.5
22.9
7Talb
ot
Tabl
e 1.
co
ntin
ued
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
9
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
111843-1
0.2
1810
0.2
81475
0.0
00
00
90
.00
09
16
0.0
28
39
10
.28
14
44
-6.7
0.3
22.4
82.9
2Talb
ot
111843-1
1.1
1928
0.2
81253
0.0
00
00
80
.00
09
01
0.0
28
78
20
.28
12
20
-12.0
0.2
92.7
83.3
4Talb
ot
104989-0
1.1
1777
0.2
81589
0.0
00
013
0.0
016
18
0.0
52
24
50
.28
15
34
-4.2
0.4
62.3
72.7
4Talb
ot
104989-0
2.1
1791
0.2
81478
0.0
00
012
0.0
011
25
0.0
39
60
90
.28
14
40
-7.3
0.4
22.4
92.9
4Talb
ot
104989-0
3.1
1796
0.2
81495
0.0
00
011
0.0
00
95
70
.03
413
00
.28
14
62
-6.3
0.3
92.4
62.8
9Talb
ot
104989-0
4.1
1816
0.2
81284
0.0
00
013
0.0
00
30
60
.012
54
60
.28
12
73
-12.6
0.4
62.7
03.3
0Talb
ot
104989-0
5.1
1817
0.2
81488
0.0
00
00
90
.00
09
66
0.0
30
22
70
.28
14
55
-6.1
0.3
22.4
72.8
9Talb
ot
104989-0
6.1
1815
0.2
81587
0.0
00
013
0.0
015
50
0.0
49
10
20
.28
15
34
-3.4
0.4
62.3
72.7
1Talb
ot
104989-0
7.1
1791
0.2
81467
0.0
00
010
0.0
02
49
90
.09
89
45
0.2
813
82
-9.3
0.3
52.6
03.0
7Talb
ot
104989-0
8.1
1810
0.2
81504
0.0
00
015
0.0
010
58
0.0
33
601
0.2
814
68
-5.8
0.5
32.4
52.8
6Talb
ot
104989-0
9.1
1804
0.2
81499
0.0
00
013
0.0
016
76
0.0
60
60
60
.28
14
42
-6.9
0.4
62.5
02.9
3Talb
ot
104989-1
0.1
1777
0.2
81589
0.0
00
00
90
.00
08
84
0.0
28
60
60
.28
15
59
-3.3
0.3
12.3
22.6
8Talb
ot
104989-1
1.1
1791
0.2
81490
0.0
00
011
0.0
011
77
0.0
45
774
0.2
814
50
-6.9
0.3
92.4
82.9
2Talb
ot
104989-1
2.1
1786
0.2
81497
0.0
00
013
0.0
00
701
0.0
24
10
70
.28
14
73
-6.2
0.4
62.4
42.8
7Talb
ot
104989-1
3.1
1777
0.2
81489
0.0
00
00
70
.00
06
98
0.0
22
93
80
.28
14
65
-6.7
0.2
52.4
52.8
9Talb
ot
104989-1
4.1
1775
0.2
81469
0.0
00
011
0.0
02
715
0.1
07
96
40
.28
13
78
-9.8
0.3
92.6
13.0
9Talb
ot
104989-1
6.1
1955
0.2
81316
0.0
00
00
90
.00
076
40
.02
55
57
0.2
812
88
-8.9
0.3
02.6
93.1
7Talb
ot
104989-1
7.1
1805
0.2
81573
0.0
00
013
0.0
00
83
20
.02
60
43
0.2
815
45
-3.2
0.4
62.3
42.7
0Talb
ot
104989-1
8.1
1801
0.2
81517
0.0
00
011
0.0
00
72
40
.02
43
56
0.2
814
92
-5.2
0.3
92.4
12.8
2Talb
ot
104989-1
9.1
1761
0.2
81556
0.0
00
011
0.0
00
57
70
.018
48
30
.28
15
37
-4.5
0.3
92.3
52.7
4Talb
ot
111854-0
1.1
1794
0.2
81495
0.0
00
00
70
.0014
83
0.0
59
610
0.2
814
45
-7.0
0.2
62.4
92.9
3Talb
ot
111854-0
2.1
1785
0.2
81533
0.0
00
011
0.0
012
25
0.0
54
23
80
.28
14
92
-5.6
0.3
92.4
22.8
3Talb
ot
111854-0
4.1
1755
0.2
81504
0.0
00
02
70
.00
212
80
.09
12
38
0.2
814
33
-8.3
0.9
52.5
22.9
8Talb
ot
111854-0
5.1
2327
0.2
81402
0.0
00
010
0.0
010
28
0.0
45
93
80
.28
13
56
2.0
0.3
52.5
92.7
6Talb
ot
111854-0
6.1
1784
0.2
81538
0.0
00
00
90
.0014
33
0.0
617
32
0.2
814
90
-5.7
0.3
12.4
32.8
3Talb
ot
111854-0
8.1
174
60.2
81478
0.0
00
00
80
.0012
10
0.0
55
63
00
.28
14
38
-8.3
0.2
82.5
02.9
7Talb
ot
111854-0
9.1
174
90.2
81498
0.0
00
00
80
.001013
0.0
44
43
90
.28
14
64
-7.3
0.2
92.4
62.9
1Talb
ot
111854-1
1.1
1778
0.2
81452
0.0
00
012
0.0
00
65
10
.02
97
02
0.2
814
30
-7.9
0.4
22.4
92.9
7Talb
ot
111854-1
2.1
1792
0.2
81421
0.0
00
00
90
.0013
33
0.0
48
24
00
.28
13
76
-9.5
0.3
32.5
83.0
8Talb
ot
112310-0
1.1
1977
0.2
81544
0.0
00
00
50
.0015
36
0.0
44
43
20
.28
14
86
-1.4
0.1
92.4
32.7
1Talb
ot
112310-0
2.1
1811
0.2
81512
0.0
00
00
80
.00
07
54
0.0
215
41
0.2
814
86
-5.2
0.2
72.4
22.8
2Talb
ot
Tabl
e 1.
co
ntin
ued
Kirkland et al.
10
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
112310-0
3.1
1963
0.2
81555
0.0
00
015
0.0
011
740
.03
22
89
0.2
815
11-0
.80.5
32.3
92.6
6Talb
ot
112310-0
4.1
1797
0.2
81481
0.0
00
014
0.0
014
73
0.0
43
45
50
.28
14
31
-7.4
0.4
92.5
12.9
6Talb
ot
112310-0
5.1
1816
0.2
81475
0.0
00
02
10
.00
09
77
0.0
27
34
20
.28
14
41
-6.6
0.7
42.4
82.9
2Talb
ot
112310-0
6.1
1972
0.2
81537
0.0
00
013
0.0
016
42
0.0
47
88
20
.28
14
75
-1.9
0.4
62.4
42.7
4Talb
ot
112310-0
7.1
1780
0.2
81419
0.0
00
02
00
.0010
23
0.0
28
09
90
.28
13
84
-9.5
0.7
02.5
63.0
7Talb
ot
112310-0
8.1
1974
0.2
81584
0.0
00
018
0.0
015
98
0.0
47
09
20
.28
15
24
-0.1
0.6
32.3
72.6
3Talb
ot
112310-0
9.1
1975
0.2
81504
0.0
00
018
0.0
018
00
0.0
48
29
10
.28
14
36
-3.2
0.6
32.5
02.8
2Talb
ot
112310-1
0.1
1975
0.2
81601
0.0
00
00
80
.0014
79
0.0
46
07
80
.28
15
45
0.7
0.2
72.3
42.5
8Talb
ot
112310-1
4.1
1932
0.2
81564
0.0
00
00
90
.0014
09
0.0
40
72
50
.28
15
12
-1.5
0.3
32.3
92.6
8Talb
ot
112310-1
6.1
1980
0.2
81569
0.0
00
00
90
.00
07
03
0.0
18
59
70
.28
15
43
0.7
0.3
02.3
42.5
8Talb
ot
112310-1
7.1
1958
0.2
81554
0.0
00
011
0.0
011
44
0.0
32
714
0.2
815
11-0
.90.3
92.3
92.6
7Talb
ot
112310-1
8.1
1937
0.2
81548
0.0
00
011
0.0
00
95
80
.02
36
14
0.2
815
13
-1.3
0.3
92.3
82.6
8Talb
ot
112379-0
1.1
1810
0.2
81499
0.0
00
02
00
.00
07
30
0.0
20
89
60
.28
14
74-5
.60.7
02.4
42.8
5Talb
ot
112379-0
3.1
1760
0.2
81485
0.0
00
016
0.0
00
82
10
.02
54
99
0.2
814
58
-7.3
0.5
62.4
62.9
2Talb
ot
112379-0
4.1
1763
0.2
81527
0.0
00
02
20
.00
05
79
0.0
19
05
20
.28
15
08
-5.5
0.7
72.3
92.8
1Talb
ot
112379-0
5.1
1775
0.2
81455
0.0
00
011
0.0
00
66
80
.02
10
22
0.2
814
33
-7.9
0.3
92.4
92.9
7Talb
ot
112379-0
6.1
1752
0.2
81474
0.0
00
010
0.0
013
69
0.0
45
03
10
.28
14
29
-8.5
0.3
52.5
12.9
9Talb
ot
112379-0
7.1
1788
0.2
81455
0.0
00
00
70
.00
06
42
0.0
215
21
0.2
814
33
-7.6
0.2
62.4
92.9
6Talb
ot
112379-0
8.1
174
10.2
81421
0.0
00
00
90
.00
06
12
0.0
19
913
0.2
814
01
-9.8
0.3
22.5
33.0
6Talb
ot
112379-1
4.1
1802
0.2
81477
0.0
00
011
0.0
00
92
00
.03
03
84
0.2
814
46
-6.8
0.3
92.4
82.9
2Talb
ot
112379-1
5.1
1794
0.2
81445
0.0
00
011
0.0
00
748
0.0
25
45
20
.28
14
20
-7.9
0.3
92.5
12.9
8Talb
ot
112379-1
7.1
174
10.2
81477
0.0
00
013
0.0
00
94
80
.03
18
23
0.2
814
46
-8.2
0.4
62.4
82.9
6Talb
ot
112379-1
8.1
174
60.2
81442
0.0
00
00
90
.00
07
01
0.0
22
22
50
.28
14
19
-9.0
0.3
02.5
13.0
2Talb
ot
112379-1
9.1
1682
0.2
81478
0.0
00
00
90
.00
05
62
0.0
17
87
00
.28
14
60
-9.0
0.3
02.4
52.9
7Talb
ot
112397-
01.
11785
0.2
81469
0.0
00
00
90
.00
05
110
.015
59
90
.28
14
52
-7.0
0.3
02.4
62.9
2Talb
ot
112397-
02.1
1784
0.2
81454
0.0
00
010
0.0
00
50
30
.016
20
70
.28
14
37
-7.5
0.3
42.4
82.9
5Talb
ot
112397-
03.1
1768
0.2
81480
0.0
00
00
90
.00
06
01
0.0
18
63
00
.28
14
60
-7.1
0.3
12.4
52.9
1Talb
ot
112397-
04.1
1771
0.2
81489
0.0
00
010
0.0
00
73
60
.02
34
83
0.2
814
64
-6.8
0.3
52.4
52.9
0Talb
ot
112397-
05.1
1793
0.2
81499
0.0
00
016
0.0
00
54
30
.017
93
20
.28
14
81
-5.8
0.5
62.4
22.8
5Talb
ot
112397-
06.1
1780
0.2
81468
0.0
00
010
0.0
00
614
0.0
19
93
30
.28
14
47
-7.2
0.3
52.4
72.9
3Talb
ot
112397-
07.
11796
0.2
81484
0.0
00
011
0.0
00
69
40
.02
17
57
0.2
814
60
-6.4
0.3
92.4
52.8
9Talb
ot
112397-
08.1
1817
0.2
81448
0.0
00
00
90
.00
07
02
0.0
2174
70
.28
14
24
-7.2
0.3
32.5
02.9
6Talb
ot
Tabl
e 1.
co
ntin
ued
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
11
Analy
sis
No
.207P
b*/
206P
b*
(Ma)
176H
f/177H
f1 S
E176Lu/1
77H
f176Y
b/1
77H
f176H
f/177H
f iH
f1 S
E T
DM
T
DM
2Te
rrane
112397-
09.1
1781
0.2
81416
0.0
00
00
90
.00
05
97
0.0
18
80
00
.28
13
96
-9.0
0.3
12.5
43.0
5Talb
ot
112397-
11.1
1792
0.2
81544
0.0
00
010
0.0
00
35
70
.010
88
40
.28
15
32
-4.0
0.3
52.3
52.7
3Talb
ot
112397-
13.1
1786
0.2
81486
0.0
00
011
0.0
00
58
40
.018
97
70
.28
14
66
-6.4
0.3
92.4
42.8
8Talb
ot
112397-
15.1
1785
0.2
81478
0.0
00
010
0.0
00
76
70
.02
66
62
0.2
814
52
-7.0
0.3
52.4
72.9
2Talb
ot
104981-
3.1
1784
0.2
81547
0.0
00
017
0.0
00
86
00
.02
39
49
0.2
815
18
-4.6
0.6
02.3
82.7
7Talb
ot
104981-
5.1
1766
0.2
81538
0.0
00
013
0.0
00
96
60
.02
60
83
0.2
815
06
-5.5
0.4
62.4
02.8
1Talb
ot
104981-
6.1
1799
0.2
81519
0.0
00
02
40
.0011
49
0.0
311
03
0.2
814
80
-5.7
0.8
42.4
42.8
5Talb
ot
104981-
7.1
1761
0.2
81553
0.0
00
018
0.0
00
83
20
.02
03
66
0.2
815
25
-4.9
0.6
32.3
72.7
7Talb
ot
104981-
8.1
174
80.2
81482
0.0
00
02
00
.00
09
34
0.0
23
56
70
.28
14
51
-7.8
0.7
02.4
72.9
4Talb
ot
104981-
9.1
1795
0.2
81460
0.0
00
02
30
.0010
64
0.0
25
92
10
.28
14
24
-7.7
0.8
12.5
12.9
7Talb
ot
104981-
11.1
1764
0.2
81538
0.0
00
019
0.0
01010
0.0
27
16
80
.28
15
04
-5.6
0.6
72.4
02.8
1Talb
ot
104981-
12.1
1770
0.2
81518
0.0
00
02
10
.0016
45
0.0
45
56
20
.28
14
63
-6.9
0.7
42.4
72.9
0Talb
ot
104981-
13.1
1785
0.2
81545
0.0
00
02
10
.0011
39
0.0
316
77
0.2
815
06
-5.0
0.7
42.4
02.7
9Talb
ot
104981-
14.1
1883
0.2
81516
0.0
00
02
30
.00
07
55
0.0
20
55
70
.28
14
89
-3.4
0.8
12.4
12.7
7Talb
ot
104981-
17.
11805
0.2
81485
0.0
00
017
0.0
00
48
00
.012
87
90
.28
14
69
-5.9
0.6
02.4
42.8
7Talb
ot
104981-
18.1
1761
0.2
81514
0.0
00
019
0.0
00
89
30
.02
13
38
0.2
814
84
-6.4
0.6
72.4
32.8
6Talb
ot
104981-
19.1
174
50.2
81473
0.0
00
018
0.0
010
73
0.0
316
55
0.2
814
37
-8.4
0.6
32.4
92.9
8Talb
ot
110056-1
.11915
0.2
81535
0.0
00
018
0.0
02
26
70
.07
89
92
0.2
814
53
-4.0
0.6
32.4
92.8
3Talb
ot
110056-2
.12422
0.2
81424
0.0
00
02
30
.0016
07
0.0
53
79
00
.28
13
50
4.0
0.8
12.6
02.7
1Talb
ot
110056-4
.11806
0.2
81461
0.0
00
012
0.0
00
63
90
.02
09
33
0.2
814
39
-6.9
0.4
22.4
82.9
3Talb
ot
110056-7
.11994
0.2
81479
0.0
00
013
0.0
00
54
80
.017
72
40
.28
14
58
-2.0
0.4
62.4
52.7
6Talb
ot
110056-1
0.1
1767
0.2
81586
0.0
00
02
20
.0019
62
0.0
67
55
10
.28
15
20
-4.9
0.7
72.3
92.7
8Talb
ot
110056-1
2.1
2078
0.2
81495
0.0
00
02
50
.0011
42
0.0
34
86
20
.28
14
50
-0.4
0.8
82.4
72.7
2Talb
ot
110056-1
4.1
1856
0.2
81449
0.0
00
02
10
.0012
62
0.0
43
53
90
.28
14
05
-7.0
0.7
42.5
42.9
8Talb
ot
110056-1
5.1
2192
0.2
81402
0.0
00
018
0.0
010
62
0.0
33
70
70
.28
13
58
-1.0
0.6
32.5
92.8
5Talb
ot
110056-1
6.1
1759
0.2
81468
0.0
00
012
0.0
00
26
20
.00
84
67
0.2
814
59
-7.3
0.4
22.4
52.9
2Talb
ot
110056-1
7.1
2433
0.2
81237
0.0
00
02
30
.00
05
05
0.0
15
52
00
.28
12
14
-0.6
0.8
12.7
83.0
1Talb
ot
110056-1
8.1
1774
0.2
81548
0.0
00
018
0.0
00
44
40
.013
95
90
.28
15
33
-4.3
0.6
32.3
52.7
4Talb
ot
110056-1
9.1
2005
0.2
81447
0.0
00
019
0.0
00
52
30
.016
70
60
.28
14
27
-2.8
0.6
72.4
92.8
3Talb
ot
NO
TE
:
The A
naly
sis
No. is
the s
am
ple
num
ber
'-' gra
in n
um
be
r '.'
spot
num
ber. 1
76H
f/177H
f i,
Hf
and T
DM o
f zircons a
re c
alc
ula
ted u
sin
g t
he 2
07P
b*/
206P
b*
age o
f gra
in. T
DM
2 is c
alc
ula
ted u
sin
g a
tw
o-s
tage e
volu
tion a
ssum
ing a
mean 1
76Lu/1
77H
f ra
tio o
f cru
st
= 0
.015.
TD
M a
nd T
DM
2 a
re in G
a.
Tabl
e 1.
co
ntin
ued
Kirkland et al.
12
Sample id Background corrected 18O/16O(a) 18O(b) 1 Excluded
Penglai@1 0.0020144 0.006 5.24 0.12 std
Penglai@2 0.0020145 0.020 5.27 0.40 std
Penglai@3 0.0020148 0.007 5.40 0.13 std
Penglai@4 0.0020145 0.007 5.28 0.14 std
Penglai@5 0.0020145 0.006 5.25 0.11 std
Penglai@6 0.0020144 0.006 5.24 0.12 std
112102@1 0.0020146 0.006 5.31 0.11
112102@02 0.0020146 0.008 5.32 0.16
112102@03 0.0020188 0.007 7.42 0.14 yes
112102@04 0.0020147 0.008 5.39 0.15
112102@05 0.0020246 0.014 10.30 0.28 yes
112102@06 0.0020186 0.017 7.28 0.34 yes
112102@07 0.0020138 0.005 4.94 0.10
112102@08 0.0020182 0.009 7.09 0.18 yes
112102@09 0.0020148 0.008 5.40 0.15
112102@10 0.0020149 0.007 5.48 0.14
112102@11 0.0020144 0.007 5.25 0.13
112102@12 0.0020208 0.009 8.40 0.18 yes
112102@13 0.0020138 0.010 4.94 0.19
112102@14 0.0020147 0.011 5.35 0.21
112102@15 0.0020217 0.006 8.86 0.12 yes
112102@16 0.0020151 0.007 5.57 0.14
112102@17 0.0020142 0.006 5.11 0.12
112102@18 0.0020144 0.008 5.21 0.15
112102@19 0.0020172 0.007 6.62 0.14 yes
112102@20 0.0020138 0.008 4.94 0.16
112102@21 0.0020146 0.013 5.33 0.26
Penglai@7 0.0020144 0.008 5.20 0.16 std
Penglai@8 0.0020145 0.006 5.29 0.12 std
Penglai@9 0.0020147 0.006 5.37 0.12 std
Penglai@10 0.0020144 0.012 5.24 0.23 std
Penglai@11 0.0020148 0.010 5.44 0.19 std
NOTES: Each 18O uncertainty (1 ) represents the sum of counting statistics errors for each individual spot and the
external error based on all standards analysed during the session, which were added in quadrature. Table is
in sequential order of analyses.
(a) Raw ratios corrected for measured Faraday offsets and yields.
(b) Normalized to a Penglai value of 5.3 per mil.
Excluded analyses were located on fractures or overlapped inclusions. Accepted analyses are from grains
interpreted to preserve magmatic values. Std denotes standard analysis
Table 2. Oxygen isotope analyses from zircons of sample GSWA 112102
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
13
Mag
mat
icIn
herit
ance
Ag
e(s)
Det
rital
Ag
e(s)
Sam
ple
idU
nit
Lith
olog
yLa
titud
eLo
ngitu
de
Ag
e2σ
Talb
ot T
erra
ne
1123
79K
alka
n S
uper
suite
Bio
tite
mon
zogr
anite
(au
gen)
gne
iss
-22.
5375
212
2.18
105
1762
13
1049
81K
alka
n S
uper
suite
Bio
tite–
mus
covi
te m
onzo
gran
ite g
neis
s-2
2.77
444
122.
2591
717
6413
1118
54K
alka
n S
uper
suite
Bio
tite–
mus
covi
te g
rano
dior
ite g
neis
s-2
2.59
918
122.
2863
317
8212
>23
27
1123
41K
alka
n S
uper
suite
Mic
rom
onzo
gran
ite (
met
a-ap
lite)
dyk
e-2
2.55
919
122.
1741
117
7315
1100
56K
alka
n S
uper
suite
Bio
tite–
horn
blen
de g
rano
dior
ite g
neis
s-2
2.56
808
122.
3580
017
9512
2433
–191
5
1121
01K
alka
n S
uper
suite
Bio
tite-
epid
ote
mon
zogr
anite
gne
iss
-22.
6170
212
2.29
166
1793
831
23
1118
43K
alka
n S
uper
suite
Bio
tite–
mus
covi
te m
onzo
gran
ite g
neis
s-2
2.57
140
122.
3171
717
8916
1049
80K
alka
n S
uper
suite
Mon
zogr
anite
gne
iss
-22.
7323
312
2.30
067
1800
3
1123
10K
alka
n S
uper
suite
Gra
nodi
orite
gne
iss
-22.
5611
312
2.28
161
1801
12
1123
97K
alka
n S
uper
suite
Bio
tite
mon
zogr
anite
(au
gen)
gne
iss
-22.
4694
612
2.06
106
1783
6
1049
89E
aste
rn A
ssoc
iatio
nM
usco
vite
qua
rtzi
te-2
2.67
750
122.
3138
917
91, 1
955
1121
02M
esop
rote
rozo
ic g
rani
tes
Ser
iate
bio
tite
met
amon
zogr
anite
-22.
6209
112
2.12
083
1453
10
Co
nn
aug
hto
n T
erra
ne
1130
35K
alka
n S
uper
suite
Ort
hogn
eiss
-22.
8950
812
2.61
305
1777
6
1130
02K
alka
n S
uper
suite
Gra
nodi
orite
gne
iss
-22.
8014
712
2.57
583
1768
7
1121
60U
nass
igne
d gr
aniti
c ro
cks
Gar
net g
rant
ic g
neis
s-2
2.84
800
122.
8567
2c.
120
0c.
170
0,
1873
–176
4
Tab
leto
p T
erra
ne
1189
14M
esop
rote
rozo
ic g
rani
tes
Fol
iate
d gr
anite
-22.
7845
212
2.85
445
1310
5
NO
TE
: S
umm
ary
of U
–Pb
SIM
S g
eoch
rono
logy
for
R
udal
l Pro
vinc
e sa
mpl
es in
vest
igat
ed in
thi
s w
ork.
U–P
b ge
ochr
onol
ogy
for
thes
e sa
mpl
e is
pub
lishe
d in
Nel
son
(199
5 to
199
6) a
nd is
ava
ilabl
e on
line
at <
ww
w.d
mp.
wa.
gov.
au/g
eoch
ron>
. A
ll ag
es a
re in
Ma.
Tabl
e 3.
Su
mm
ary
of U
-Pb
SIM
S da
tes
for
Rud
all P
rovi
nce
Kirkland et al.
14
Model ages2, (TDM), which are calculated using the measured 176Lu/177Hf of the zircon, provide only a minimum age for the source material of the magma from which the zircon crystallized, because the 176Lu/177Hf ratio of zircon is much lower than the 176Lu/177Hf ratio of all reasonable reservoirs for Hf. Therefore, we have calculated two-stage model ages (TDM
2), which assumes that the parental magma was produced from an average continental crust (176Lu/177Hf = 0.015) that originally was derived from the depleted mantle (Griffin et al., 2004).
In the following text, the term ‘array’ is used to indicate variable 176Hf/177Hfi values at a single point in time, as could be due to mixing of isotopically distinct sources. The term ‘evolution’ refers to the variation of 176Hf/177Hfi values through time, consistent with the increase in daughter isotopes by decay of 176Lu within crust having a specific 176Lu/177Hf ratio.
Oxygen isotopes
Oxygen isotope ratios (18O/16O) were determined using a Cameca IMS 1280 multi-collector ion microprobe located at the Centre for Microscopy, Characterisation and Analysis (CMCA) at the University of Western Australia. Analytical conditions were similar to those outlined in detail by Kita et al. (2009). A static ~3 nA Cs+ beam with an impact energy of 20 keV was focused to a 15 μm spot on the sample surface. Instrument parameters included a magnification of 130x between the sample and field aperture, 400 μm contrast aperture, 4000 μm field aperture, 120 μm entrance slit, 500 μm exit slits, and a 40 eV band pass for the energy slit with a 5 eV gap. Secondary O- ions were accelerated to 10 keV and analysed with a mass resolving power of approximately 2400 using dual Faraday Cup detectors. A normal-incidence electron gun was used to provide charge compensation.
Each analysis spot was pre-sputtered for 10 seconds prior to automated peak-centering using secondary deflectors DTFA-X, DTFA-Y, and DTCA-X. Each analysis consisted of 20 four-second cycles through the mass stations, which gave an average internal precision of 0.17 ‰ (1 SDmean). Bracketing of standards permits instrumental mass fractionation (IMF) and drift to be assessed and corrected. IMF was corrected using the Penglai zircon standard (5.31 ± 0.10‰ 2 , (Li et al., 2010). A single block of 21 sample analyses of GSWA 112102 was bracketed by 11 standard analyses and IMF was calculated using a correction scheme similar to that described by Kita et al. (2009) with propagation of uncertainty as outlined in Appendix A1 of Kirkland et al. (2012). The spot-to-spot reproducibility (external precision) for standard spots on Penglai zircons was 0.08‰ (1 SDext, n=11). Corrected 18O/16O ratios are reported in 18O notation, in per mil variations relative to Vienna Standard Mean Ocean Water (VSMOW).
2 A model age, in its simplest form, is the time at which a sample
was separated from its source in the mantle, assuming the source is
not a mixture. More specifically, it is the time at which the isotopic
signature of the sample was the same as that of a model reservoir
Talbot Terrane
Kalkan Supersuite
GSWA 112379: biotite monzogranite (augen) gneiss, Split Rock
This sample was dated by Nelson (1995k). Zircons isolated from this sample are colourless to yellow, euhedral, and have aspect ratios up to 5:1. Both transmitted and reflected-light images imply that there are no inherited cores within this zircon sample. Excluding one U–Pb analysis that is 14% discordant and has lost radiogenic Pb, the remaining 20 analyses yield a concordia age of 1762 ± 13 Ma (MSWD = 1.8; Fig. 3a), interpreted as the igneous crystallization age of the granite protolith. This result is slightly younger than the 1765 ± 15 Ma date proposed by Nelson (1995k). Hf isotope measurements of 12 zircons yield Hf(t) values that range from –5.5 to –9.8 and are more unradiogenic than CHUR (Fig. 4). The Hf isotope data are well grouped and indicate a TDM
2 of c. 2.8 Ga.
GSWA 104981: biotite–muscovite monzogranite gneiss, southern part of Graphite Valley
The geochronology of this sample was reported by Nelson (1995d). Zircons from this sample are colourless to dark brown, euhedral to subhedral, typically fractured, and have aspect ratios up to 5:1. Transmitted-light images indicate potentially older cores within several zircons, although most crystals are apparently homogeneous. The U–Pb analyses are concordant to strongly discordant. Five analyses >10% discordant are not considered further. Thirteen analyses yield a concordia age of 1764 ± 13 Ma (MSWD = 2.0; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith to the gneiss. This date is younger than the 1775 ± 10 Ma date reported by Nelson (1995d). One analysis yields a 207Pb*/206Pb* date (1 ) of 1883 ± 47 Ma, interpreted as the age of an inherited component (Nelson, 1995d). Hf isotope measurements of 13 zircons yield Hf(t) values of –3.4 to –8.4, and are more unradiogenic than CHUR (Fig. 4). The Hf isotope data define an array indicating a maximum TDM
2 of c. 3.0 Ga.
GSWA 111854: biotite–muscovite granodiorite gneiss, Poonemerlarra Creek west
This sample was dated by Nelson (1995h). Zircons from this sample are colourless to yellow, euhedral, and equant to elongate, with aspect ratios up to 6:1. Transmitted-light images suggest that most crystals are homogeneous with no inherited cores. Four analyses greater than 5% discordant have probably lost radiogenic Pb and are not considered further. One of these discordant analyses is of an inherited core that indicated a minimum age of 2327 Ma. The remaining eight analyses yield a concordia age of 1782 ± 12 Ma (MSWD = 1.6; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith to the gneiss. This date is slightly older than the 1778 ± 17 Ma date reported by Nelson (1995h). Hf isotope
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
15
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GSWA 112379: biotite monzogranite (augen) gneiss, Split Rock
GSWA 104981: biotite-muscovite monzogranite gneiss,
southern part of Graphite Valley
GSWA 111854: biotite-muscovite granodiorite gneiss,
Poonemerlarra Creek west
GSWA 112341: micromonzogranite
(meta-aplite) dyke, Rudall airstrip
GSWA 110056: biotite-hornblende
granodiorite gneiss, Rooney Creek
GSWA 112101: biotite-epidote
monzogranite gneiss, Larry Creek
GSWA 112397:
coarse-grained
porphyritic biotite
monzogranite
(augen) gneiss,
Watrara Inlier
GSWA 112310:
granodiorite
gneiss, Dunn
Creek west
GSWA 104980:
monzogranite
gneiss, Graphite Valley
GSWA 111843: biotite-
muscovite monzogranite gneiss,
Poynton Creek
CLK83_1 27.03.13
Talb
otTerr
ane
Figure 3a. Stacked concordia diagrams showing U–Pb zircon analytical data for zircons from Rudall Province samples analysed
by SHRIMP ion microprobe. Error crosses are shown at the 2-sigma level. All data (see Nelson et al. in the reference
list) are available online (www.dmp.wa.gov.au/geochron). Yellow squares indicate magmatic zircon; red squares
indicate inherited / detrital zircon; blue squares indicate youngest detrital zircon; green squares indicate metamorphic
zircon; grey squares indicate discordant analyses; black squares indicate concordant analyses interpreted to have
undergone radiogenic-Pb loss.
Kirkland et al.
16
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2000
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GSWA 118914:
foliated granite,
north of Harbutt Range
GSWA 104989: muscovite
quartzite, Fingoon Quartzite
GSWA 112102: seriate biotite metamonzogranite,
southern part of the Watrara Inlier
GSWA 113035: orthogneiss,
east of South Rudall Dome
GSWA 113002: granodiorite gneiss,
Cotton Creek
GSWA 112160:
garnet microgneiss,
Harbutt Range
Figure 3b. Stacked concordia diagrams showing U–Pb zircon analytical data for zircons from Rudall Province
samples analysed by SHRIMP ion microprobe. Error crosses are shown at the 2-sigma level. All data (see
Nelson et al. in the reference list) are available online <www.dmp.wa.gov.au/geochron>. Yellow squares
indicate magmatic zircon; red squares indicate inherited / detrital zircon; blue squares indicate youngest
detrital zircon; green squares indicate metamorphic zircon; grey squares indicate discordant analyses;
black squares indicate concordant analyses interpreted to have undergone radiogenic-Pb loss.
measurements of 11 zircons yield Hf(t) values ranging from –5.6 to –9.5, and form an array that is slightly to strongly more unradiogenic than CHUR (Fig. 4), and define a maximum TDM
2 of c. 3.4 Ga. The single discordant core yields an Hf(t) value of +2.
GSWA 112341: micromonzogranite (meta-aplite) dyke, Rudall airstrip
This sample, dated by Nelson (1995j), yielded zircons that are yellow to brown, subhedral to anhedral, and have aspect ratios up to 4:1. Transmitted-light images do not indicate any obvious cores. Excluding one
younger analysis, 15 analyses yield a concordia age of 1773 ± 15 Ma (MSWD = 1.0; Fig. 3a), interpreted as the age of magmatic crystallization of the dyke. This date is slightly younger than the 1778 ± 16 Ma date reported by Nelson (1995j). The single excluded analysis yields a 207Pb*/206Pb* date of 1612 ± 44 Ma (1 ), interpreted by Nelson (1995j) to reflect disturbance by younger metamorphic events. Hf isotope measurements of 13 zircons yield Hf(t) values ranging from –3.6 to –11.4, plot as an array that is slightly to strongly more unradiogenic than CHUR (Fig. 4), and indicate a maximum TDM
2 of c. 3.1 Ga.
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
17
GSWA 110056: biotite–hornblende granodiorite gneiss, Rooney Creek
This sample was dated by Nelson (1995f), and yielded zircons that are brown to black, euhedral to subhedral, and have aspect ratios up to 5:1. Transmitted-light images reveal that many crystals contain apparently older cores. Excluding seven analyses of inherited zircon cores, five analyses >5% discordant, and one analysis with high common Pb (>10% common 206Pb), six analyses yield a concordia age of 1795 ± 12 Ma (MSWD = 1.04; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith to the gneiss. This date is slightly older than the 1790 ± 17 Ma date reported by Nelson (1995f). Inherited cores yield 207Pb*/206Pb* dates of 2433–1915 Ma. Hf isotope measurements of five zircons from the magmatic component in this sample yield Hf(t) values of –0.6 to –7.3, and seven analyses of inherited zircon cores yield Hf(t) values ranging from –0.4 to –4.0 (Fig. 4). The Hf isotope data define an evolution trend from a source with a maximum TDM
2 of 3.0 Ga.
GSWA 112101: biotite-epidote monzogranite gneiss, Larry Creek
The geochronology of this sample was reported by Nelson (1996a). Zircons from this sample are yellow to dark brown, euhedral, and have aspect ratios up to 5:1. Transmitted-light images reveal concentric zoning made visible by variable degrees of radiation damage. Several crystals contain apparently older cores. Seventeen analyses yield a weighted mean 207Pb*/206Pb* date of 1793 ± 8 Ma (MSWD = 1.02; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith. This date is similar to the 1792 ± 9 Ma result reported by Nelson (1996a). A single analysis located on a xenocrystic core yields a 207Pb*/206Pb* date of 3123 ± 16 Ma (1 ) (Fig. 3a). Hf isotope measurements on 10 magmatic zircons yield Hf(t) values of –2.7 to –9.1 (Fig. 4) and define an array
with a maximum TDM2 of 3.0 Ga.
GSWA 111843: biotite–muscovite monzogranite gneiss, Poynton Creek
This sample was dated by Nelson (1995g), and yielded zircons that are colourless to black, euhedral, and have aspect ratios up to 5:1. Many crystals contain apparently older cores. Excluding two analyses >10% discordant, 10 analyses yield a concordia age of 1789 ± 16 Ma (MSWD = 0.81; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith. This date is slightly younger that the 1795 ± 17 Ma date reported by Nelson (1995g). Four other analyses yield dates of 2102– 1877 Ma, interpreted as xenocrystic components (Fig. 3a). Hf isotope measurements of 12 zircons yield Hf(t) values of –4.6 to –12.0 (Fig. 4), and define an array with a maximum TDM
2 of 3.3 Ga. The older inherited zircons yield Hf isotope signatures consistent with evolution from the same source as the c. 1789 Ma magmatism (Fig. 4).
-30
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Hf
Tabletop Terrane
Connaughton Terrane
Talbot Terrane
CLK82a 1 . .14 01 3
D
GT EPT
D
GT EPT
D
GT EPT
M
Figure 4. Hf evolution diagrams for Rudall Province samples
(circles, this study) compared to potential source
regions. Shaded fields illustrate normal crustal
evolution of Hf along a 176Lu/177Hf slope of 0.015.
Abbreviations used in figure: EPT — East Pilbara
Terrane, GT — Glenburgh Terrane (Capricorn
Orogen basement), D — Dalgaringa Supersuite
intrusive rocks. Red line is the depleted mantle
model of Griffin et al. (2000) and the blue line is
CHUR.
GSWA 104980: monzogranite gneiss, Graphite Valley
This sample was dated by Nelson (1995c). Zircons from this sample are colourless to brown, euhedral, elongate to equant, and have aspect ratios up to 5:1. No cores are apparent in transmitted-light images. Fourteen analyses yield a concordia age of 1800 ± 3 Ma (MSWD = 0.84; Fig. 3a), interpreted as the age of magmatic crystallization of the protolith, and identical to the result reported by Nelson (1995c). Hf isotope measurements of 10 zircons yield Hf(t) values ranging from –6.5 to –8.7 (Fig. 4), and indicate a maximum TDM
2 of 3.0 Ga.
Kirkland et al.
18
GSWA 112310: granodiorite gneiss, Dunn Creek west
This sample was dated by Nelson (1995i). Zircons from this sample are colourless to dark brown, euhedral, elongate and have aspect ratios up to 6:1. Idiomorphic zoning is ubiquitous and apparently older cores are visible in transmitted light. Excluding one analysis >10% discordant, four analyses yield a concordia age of 1801 ± 12 Ma (MSWD = 1.8; Fig. 3a), interpreted as the age of magmatic crystallization of the granite protolith. This date is identical to that reported by Nelson (1995i). A further 13 analyses from this sample yield 207Pb*/206Pb* dates of 1980–1932 Ma, interpreted as the ages of inherited components. A significant age component at 1967 ± 10 Ma (MSWD = 2.2; Fig. 3a), was interpreted by Nelson (1995i) as the age of an older granitic component within the orthogneiss. Hf isotope measurements of 14 zircons yield Hf(t) values ranging from +0.7 to –9.5 (Fig. 4). The Hf data from the c. 1800 Ma component define an array with a maximum TDM
2 of 3.0 Ga, whereas the older c. 1970 Ma component defines a more radiogenic array with a maximum TDM
2 of 2.8 Ga (Fig. 4).
GSWA 112397: coarse-grained porphyritic biotite monzogranite (augen) gneiss, Watrara Inlier
This sample was dated by Nelson (1995l). Zircons from this sample are colourless, euhedral, and elongate, with aspect ratios up to 6:1. No older cores are apparent in transmitted light. Fifteen analyses yield a concordia age of 1783 ± 6 Ma (MSWD = 1.3; Fig. 3a), interpreted as the age of magmatic crystallization of the granite protolith. This date is slightly younger than the 1787 ± 5 Ma date reported by Nelson (1995l). Hf isotope measurements of 14 zircons yield Hf(t) values of –3.4 to –9.0 (Fig. 4), and define an array with a maximum TDM
2 of 3.0 Ga.
Eastern Association
GSWA 104989: muscovite quartzite, Fingoon Quartzite
This sample, dated by Nelson (1995e), yielded zircons that are colourless, anhedral to subhedral, and have aspect ratios up to 5:1. Most crystals have strongly rounded terminations, consistent with sedimentary transport. Transmitted-light images reveal mainly homogeneous zircons, including a few that contain apparently older cores. The detrital zircon age spectrum is dominated by 18 analyses that yield a weighted mean 207Pb*/206Pb* date of 1791 ± 10 Ma (MSWD = 0.68; Fig. 3b), representing the age of a significant detrital component within the precursor sediment and a conservative maximum depositional age. One older detrital grain yields a 207Pb*/206Pb* date of 1955 ± 15 Ma (1 ). Hf isotope measurements of 17 zircons from the main detrital age component yield Hf(t) values ranging from –3.2 to –12.6 (Fig. 4). A single analysis of the older detrital zircon yields a Hf(t) value of –8.9. The Hf isotope data define an array with a maximum TDM
2 of 3.2 Ga. The older detrital grain has a similar Hf source to that of the c. 1790 Ma component.
Mesoproterozoic granites
GSWA 112102: seriate biotite metamonzogranite, southern part of the Watrara Inlier
Geochronology of this sample was reported by Nelson (1996b). The zircons are colourless to yellow or brown, euhedral, and predominantly equant with aspect ratios up to 4:1. Transmitted and reflected light images do not indicate the presence of older cores. Eleven analyses indicate variable recent radiogenic-Pb loss and yield a weighted mean 207Pb*/206Pb* date of 1453 ± 10 Ma (MSWD = 0.68; Fig. 3b), interpreted as the igneous crystallization age of the granite (Nelson, 1996b). Hf isotope measurements of eight zircons yield Hf(t) values of +2.5 to +5.6, and plot between CHUR and DM (Fig. 4). The Hf isotope data are well grouped and indicate a TDM
2 of c. 1.9 Ga. Oxygen isotopes were measured in 21 zircons, and include six analyses that ablated through cracks and one analysis that incorporated limonite adhered to the grain margin. These seven analyses yield heavy
18O values of >6.6 ‰ and are considered to represent modified 18O values. The remaining 14 analyses yield
18O values from 4.9 to 5.6 ‰, with a weighted mean of 5.23 ± 0.12 ‰ (MSWD = 2.1; Table 2).
Connaughton Terrane
Kalkan Supersuite
GSWA 113035: orthogneiss, east of South Rudall Dome
This sample was dated by Nelson (1996d). Zircons from this sample are yellow to brown, euhedral, and have aspect ratios up to 5:1. No older cores are apparent in transmitted light. The analyses are slightly reversely discordant. The zircons have relatively low uranium (<300 ppm 238U) and thorium contents; hence, the reverse discordance is unlikely to reflect matrix effects associated with radiation damage (metamictization), commonly observed in analyses of high-U zircons. Thirteen analyses yield a weighted mean 207Pb*/206Pb* date of 1777 ± 6 Ma (MSWD = 1.0; Fig. 3b), interpreted as the age of magmatic crystallization of the granite protolith (Nelson, 1996d). Hf isotope measurements of eight zircons yield Hf(t) values ranging from +0.3 to –3.4 (Fig. 4). The
Hf isotopic data define an array that clusters towards the evolved end (further from CHUR) and indicates a maximum TDM
2 of 2.6 Ga.
GSWA 113002: granodiorite gneiss, Cotton Creek
This sample was dated by Nelson (1995m). Zircons from this sample are yellow to black, euhedral, inclusion-rich, and have aspect ratios up to 5:1. One xenocrystic core is visible in transmitted light, but was not analysed. Excluding one strongly discordant analysis, 13 analyses yield a concordia age of 1768 ± 7 Ma (MSWD = 0.50; Fig. 3b), interpreted as the age of magmatic crystallization of the granite protolith. Nelson (1995m) reports an age of
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
19
1769 ± 7 Ma for this sample. Hf isotope measurements of 10 zircons yield well-grouped Hf(t) values between –3.3 and –5.7 (Fig. 4), and indicate an average TDM
2 of 2.7 Ga.
Unassigned gneissic rocks
GSWA 112160: garnet microgneiss, Harbutt Range
Geochronology of this sample was reported by Nelson (1996c). Zircons from this sample are yellow to brown, subhedral, elongate with rounded terminations, and have aspect ratios up to 5:1. Xenocrystic cores are visible in transmitted light images. It is currently unclear whether the protolith of this rock was igneous or sedimentary in origin. Twelve analyses were conducted of 11 zircons. Seven analyses of zircon cores yield 207Pb*/206Pb* dates of 1873–1764 Ma. Three imprecise and slightly dispersed analyses yield a weighted mean 207Pb*/206Pb* date of 1672 ± 65 Ma (MSWD = 1.2; Fig. 3b). Two analyses of a low-U zircon rim yield very imprecise dates around 1200 Ma (Fig. 3b). The seven analyses of zircon cores are dispersed beyond analytical uncertainty and the dates are interpreted as the ages of inherited components within the gneiss. The date of 1672 ± 65 Ma for three analyses could approximate the age of migmatization of the rock or, if the protolith was of sedimentary origin, could represent a maximum age of deposition, as suggested by Nelson (1996c). The dates of c. 1200 Ma for two analyses of a zircon rim have high Th/U ratios that Nelson (1996c) interpreted as an indication of igneous rather than metamorphic growth. Ten Hf isotope measurements of 10 Paleoproterozoic zircons yield Hf(t) values ranging from –7.1 to –16.6 (Fig. 4), and define a dispersed array with a maximum TDM
2 of 3.4 Ga, consistent with a heterogeneous source. Two analyses sited on the Mesoproterozoic zircon rim yield similar 176Hf/177Hf and 176Lu/177Hf ratios to the rest of the population, which suggests this rim did not grow in the presence of a HREE sequestering phase (e.g. garnet).
Tabletop Terrane
GSWA 118914: foliated granite, north of Harbutt Range
This sample was dated by Nelson (1996e). Zircons from this sample are colourless to yellow, euhedral, and mainly equant, with aspect ratios up to 4:1. Most crystals appear homogeneous in transmitted-light images. Excluding two analyses with high common Pb (>1% common 206Pb), and four analyses interpreted to have undergone minor ancient radiogenic-Pb loss, the remaining 13 analyses yield a weighted mean 207Pb*/206Pb* date of 1310 ± 5 Ma (MSWD = 1.4; Fig. 3b), essentially identical to that reported by Nelson (1996e), and interpreted as the age of magmatic crystallization. Hf isotope measurements of 16 zircons yield Hf(t) values ranging from –5.3 to –11.6 (Fig. 4). The Hf isotope data are well grouped and yield an average TDM
2 of 2.6 Ga, although one analysis indicates a value of 2.8 Ga.
Discussion
Hf isotope signatures of
Paleoproterozoic Australia
During the Proterozoic, Archean crustal fragments were progressively amalgamated into larger cratons that now form the North, West, and South Australian Cratons (Tyler, 2005). Some Proterozoic orogenic belts were produced by continental collision or arc collision, and thus contain oceanic or exotic microcontinental components. The West Australian Craton comprises the Archean Pilbara and Yilgarn Cratons, the Archean to Paleoproterozoic Glenburgh Terrane (Johnson et al., 2012), and other potentially exotic elements such as the Rudall Province. Major additions of crust to the margins of the West Australian Craton in the form of the Albany–Fraser and Pinjarra Orogens occurred during several pulses in the Proterozoic (Kirkland et al., 2012; Spaggiari et al., 2012). Hf isotopes can be used to characterize the influence of new additions from the mantle, and the reworking of pre-existing crust, through time. Thus, the isotopic signatures of well-dated magmatic rocks can be used to examine possible genetic connections between crustal fragments and to diagnose the presence or absence of exotic terranes. The various rifted pieces of a once-united crustal block should share a comparable isotopic signature to their ancestral home, because they would likely share a common time of crust formation. The similar ages of deformation and metamorphism in the Rudall Province, Capricorn Orogen, and Arunta Orogen suggest that the relationships between these lithological blocks and other Proterozoic orogenic belts should be evaluated (Bagas, 2004; Johnson et al., 2012; Fig. 5).
Capricorn Orogen
The Capricorn Orogen is situated to the west of the Rudall Province and is a region of Proterozoic tectono-metamorphism and magmatism that separates the Archean Pilbara and Yilgarn Cratons (Johnson et al., 2011a, 2012). The Capricorn Orogen records the Paleoproterozoic collision of these cratons to form the West Australian Craton, as well as several intracratonic reworking events between Paleoproterozoic and latest Neoproterozoic time (Tyler and Thorne, 1990; Cawood and Tyler, 2004; Johnson et al., 2012). The Gascoyne Province, at the western end of the orogen, contains several Proterozoic granite suites, including the voluminous 1820–1775 Ma Moorarie Supersuite, which is similar in age to magmatic rocks in the Rudall Province.
The Glenburgh Terrane, which forms the basement to the Gascoyne Province, comprises 2555–2430 Ma granitic gneisses of the Halfway Gneiss, mid-Paleoproterozoic metasedimentary rocks, and an arc-related granitic batholith of the 2005–1970 Ma Dalgaringa Supersuite (Johnson et al., 2012). The Hf isotope compositions of zircons within the Glenburgh Terrane indicate a major period of crustal growth between c. 2730 and c. 2600 Ma, although much of this material was reworked during
Kirkland et al.
20
tectono-magmatic events between c. 2555 and c. 2430 Ma (Johnson et al., 2011a). Both the crystallization history and crustal source of the Halfway Gneiss is somewhat dissimilar to the Pilbara and Yilgarn Cratons, which led Johnson et al. (2012) to infer that the Glenburgh Terrane was an element exotic to both these cratons. The Glenburgh Terrane is envisaged to have collided with the Pilbara Craton during the 2215–2145 Ma Ophthalmian Orogeny, and the combined Pilbara Craton–Glenburgh Terrane (‘Pilboyne Craton’) collided with the Yilgarn Craton during the 2005–1950 Ma Glenburgh Orogeny (Johnson et al., 2012).
The 1820–1770 Ma Capricorn Orogeny took place during a similar time interval to the 1800–1765 Ma Yapungku Orogeny in the Rudall Province, the effects of which are recognized throughout most of the Capricorn Orogen (Sheppard et al., 2010b). The orogeny is associated with low- to medium-grade metamorphism and intense structural reworking, the intrusion of voluminous granitic magmas of the 1820–1775 Ma Moorarie Supersuite, and deposition of sedimentary rocks of the upper Wyloo Group (Ashburton Basin), including the c. 1800 Ma Ashburton Formation (Evans et al., 2003; Sircombe, 2003), the c. 1800 Ma Capricorn Group (Blair Basin; Hall et al., 2001), and the 1840–1810 Ma Leake Spring
CLK75a 15.08.12
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West Arunta
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Capricorn Orogen
basins
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17
7
Hf/
Hf
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Figure 5. Initial 176Hf/177Hf evolution diagram for samples from the Rudall Province (circles, this study) compared to potential
source regions. Shaded fields illustrate normal crustal evolution of Hf along a 176Lu/177Hf slope of 0.015. Hf data
are from <www.dmp.wa.gov.au/geochron>. Whole-rock Nd data for the Arunta Orogen are converted to Hf values
assuming a terrestrial array relationship. Abbreviation in figure: MP — Musgrave Province basement. Other notes
as in Figure 4.
Metamorphics (Sheppard et al., 2010b) in the Gascoyne Province (Fig. 1). These sedimentary rocks were deposited in response to the onset of the 1820–1770 Ma Capricorn Orogeny, possibly in a foreland basin setting (Thorne and Seymour, 1991; Sircombe, 2002; Evans et al., 2003). The upper Wyloo Group, including the Ashburton Formation, is mostly a turbiditic deep-marine succession (Thorne and Seymour, 1991). These sedimentary rocks were deformed once, and unconformably overlain by terrestrial, lacustrine to shallow-marine sedimentary rocks of the Capricorn Group (Thorne and Seymour, 1991). Paleocurrent directions in both the Ashburton Formation (Thorne and Seymour, 1991) and Capricorn Group (Thorne and Seymour, 1991; Hall et al., 2001) imply that the sediments were supplied from the southeast and southwest, respectively. The U–Pb age spectrum and Lu–Hf isotopic composition of detrital zircons within both sedimentary successions (Sircombe, 2002; GSWA, unpublished data), combined with the paleocurrent data, indicate that the southern part of the Gascoyne Province was a major source for the sedimentary detritus (Nelson, 2004a,b). In particular, the 2555–2430 Ma Halfway Gneiss and 2005–1970 Ma Dalgaringa Supersuite of the Glenburgh Terrane, and the early c. 1820 to c. 1800 Ma Moorarie Supersuite granites, appear to dominate the detrital signatures.
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
21
The 1840–1810 Ma Leake Spring Metamorphics are a package of low- to medium-metamorphic grade siliciclastic metasedimentary rocks that were deposited across much of the Gascoyne Province, including the Glenburgh Terrane (Sheppard et al., 2010). These sedimentary rocks are thought to pass, with decreasing metamorphic grade, into the Ashburton Formation to the north (Williams, 1986). These metasedimentary rocks were also sourced from the southern part of the Gascoyne Province (Sheppard et al., 2010b).
Pilbara Craton
The boundary between the Pilbara Craton (including the East Pilbara Terrane and the overlying Fortescue, Hamersley, and Turee Creek Basins) and the Rudall Province to the east is covered by unconformably overlying Meso- to Neoproterozoic sedimentary rocks (Fig. 1). During the Archean and prior to 2800 Ma, the Pilbara Craton was dominated by the construction of granite–greenstone terranes (Smithies et al., 1999; Hickman, 2004; Van Kranendonk et al., 2004). These rocks are unconformably overlain by the late Archean to Paleoproterozoic volcanic and sedimentary rocks of the Fortescue, Hamersley, and Turee Creek Groups (Thorne and Trendall, 2001) which in turn are unconformably overlain by siliciclastic rocks of the c. 2200 Ma lower Wyloo Group and the c. 1800 Ma upper Wyloo Group (Thorne and Seymour, 1991). A minor suite of east-northeast-trending kimberlite dykes intruded the eastern Pilbara Craton at c. 1870 Ma (Wyatt et al., 2002).
Calc-alkaline, lamprophyric syenite to monzodiorite granitic rocks of the c. 1800 Ma Bridget Suite (Hickman, 1978; Collins et al., 1988; Budd et al., 2002) form a north-northwest-trending belt within the East Pilbara Terrane and younger parts of the Pilbara Craton, adjacent and subparallel to the northwest−southeast trend of the Paterson Orogen. The rocks have Sr-undepleted, Y-depleted, fractionated compositions. Emplacement of the suite has been interpreted to be a far-field response to continent-continent collision during the Yapungku Orogeny. The crystallization age of a monzodiorite from this suite was dated at 1803 ± 19 Ma (GSWA 169030; Nelson, 2002), and a trondhjemitic pegmatite at 1793 ± 17 Ma (GSWA 178232; Bodorkos et al., 2006). Magmatic zircons from the monzodiorite (GSWA 169030) yield a range of Hf values, from –13.65 to –21.22, while those from the pegmatite yielded a range of Hf, from –4.67 to –7.50 (Fig. 5). Xenocrystic zircon cores dated between c. 3520 to c. 2841 Ma in both samples yielded Hf values from +4.10 to –7.47 (Fig. 5). The ages and
Hf isotopic signatures of the inherited zircons in these magmatic rocks are consistent with incorporation of East Pilbara Terrane crust into Bridget Suite magmas.
Arunta Orogen
The Proterozoic Arunta Orogen lies along the southern margin of the North Australian Craton (Fig. 1; Collins and Shaw, 1995; Dunlap and Teyssier, 1995; Sun et al., 1995; Zhao and Bennett, 1995; Zhao and McCulloch, 1995; Claoue-Long and Hoatson, 2005; Scrimgeour et al., 2005)
and has been divided into a southern Warumpi Province, generally inferred to be exotic, and an autochthonous Aileron Province (Scrimgeour et al., 2005). The Aileron Province had on its southern margin a north-dipping subduction zone during the 1810–1790 Ma Stafford Event (Claoue-Long and Hoatson, 2005). After the Stafford Event, an active margin/back-arc setting developed with several tectono-magmatic events including the c. 1780 Ma Yambah, 1760–1740 Ma Inkamulia, and 1690–1670 Ma Strangways Events (Collins and Williams, 1995; Claoue-Long and Hoatson, 2005).
The 1810–1790 Ma Stafford Event (Claoue-Long and Hoatson, 2005) is coeval with intrusion of the 1800–1765 Ma Kalkan Supersuite in the Rudall Province. Only limited deformation was associated with the Stafford Event, and metamorphism during this event was driven by magmatic heat advection (Claoue-Long and Hoatson, 2005). The c. 1780 Ma Yambah Event in the Arunta Orogen (Collins and Shaw, 1995; Scrimgeour, 2003; Claoue-Long et al., 2008) was also near-synchronous with the youngest components of the Kalkan Supersuite in the Rudall Province. The Yambah Event does not appear to correspond to major crustal thickening (Scrimgeour, 2003) but has been associated with northeast–southwest shortening (Hand and Buick, 2001).
The Warumpi Province records two Paleoproterozoic magmatic events: high-K calc-alkaline magmatism during the 1690–1670 Ma Argilke Event, and magmatism associated with a 1640–1635 Ma accretion event known as the Liebig Orogeny (Scrimgeour et al., 2005). The Argilke event is thought not to have affected the North Australian Craton and has been attributed to an outboard magmatic arc that was subsequently accreted onto the Aileron Province during the 1640–1635 Ma Liebig Orogeny (Scrimgeour et al., 2005). In the westernmost extent of the Arunta Orogen, however, Hf isotope data for a 1690 Ma granite suggests both juvenile input and an Archean source component identical to the Aileron Province (Kirkland et al., 2009). This could imply a situation in which the Warumpi Province developed within proximity to the western Aileron Province during the Argilke Event, either as an autochthonous block that was never substantially displaced or as a rifted fragment that was significantly displaced but subsequently re-accreted onto the southern margin of the Aileron Province during north-directed subduction.
The Hf isotope signature of 1810–1670 Ma zircons from the west Arunta region indicates crustal source regions dominated by components that formed between 2.7 and 2.0 Ga (Fig. 5; Kirkland et al., 2013). Whole-rock Nd isotope data from granites in the central and eastern Arunta imply similar crustal sources, dominated by components formed through mantle extraction at 2.5 – 2.2 Ga (Zhao and McCulloch, 1995).
Musgrave Province
The Musgrave Province lies at the junction of the North, South, and West Australian Cratons. Crystalline basement rocks, dated at 1600–1500 Ma and c. 1400 Ma (Edgoose et al., 2004; Wade et al., 2006; Wade et al., 2008; Kirkland
Kirkland et al.
22
et al., 2013), are subordinate to 1345–1293 Ma magmatic rocks of the Mount West Orogeny (Howard et al., 2011a; Howard et al., 2011b). The 1220–1150 Ma Musgrave Orogeny, and the 1085–1040 Ma Giles Event are younger, possibly intracontinental, tectono-magmatic events (Evins et al., 2010; Smithies et al., 2010; Smithies et al., 2011). Although the nature of Musgrave Province basement is cryptic, the Nd and Hf isotope evolution of nearly all rocks in the Musgrave Province requires the presence of sources derived from Archean, c. 1900 Ma, and c. 1600 Ma crust with subsequent juvenile additions after c. 1220 Ma. Although there are no physical remnants of c. 1900 Ma juvenile material, radiogenic addition into the crust at this time is required to account for the correspondence between mantle extraction ages and reworking of Archean material, and is indicated by mantle-like oxygen isotope ratios in zircons with c. 1900 Ma Hf model ages (Fig. 5; Kirkland et al., 2013).
Inherited and detrital zircons of
the Rudall Province
In order to appropriately interpret the zircon Hf isotope data with respect to the regional evolution of the Rudall Province and the potential exotic (e.g. North Australian Craton) or endemic (West Australian Craton) nature of basement terranes, an important step is to consider the origin of the inherited zircons in the 1800–1765 Ma Kalkan Supersuite granitic rocks. The zircons may be of local provenance, having been entrained within the granites from basement terranes. In this case, the Hf isotopic evolution of the magmatic and inherited zircons will provide critical information on the nature and origin of the Rudall Province basement. If, however, the zircons are distally-derived (as part of a regionally-sourced sedimentary sequence, having been entrained within the granites during the emplacement of the magmas into the sedimentary succession), little information can be gained on the nature of the local basement, as these data reflect the geological development of all the distal sources of detritus in the region (e.g. the eastern Pilbara margin and Gascoyne Province).
In the eastern association, siliciclastic paragneiss contains c. 1790 Ma detrital zircons (Nelson, 1995e), and is intruded by the 1800–1765 Ma Kalkan Supersuite granites (Bagas, 2004). This indicates deposition of the eastern sedimentary association close to c. 1790 Ma, which is in a similar timeframe for the deposition of sedimentary rocks in the Capricorn Orogen to the west, specifically the c. 1800 Ma Ashburton Formation (Evans et al., 2003; Sircombe, 2003), the c. 1800 Ma Capricorn Group (Hall et al., 2001), and the 1840–1810 Ma Leake Spring Metamorphics (Sheppard et al., 2010b) (Fig. 1). The U–Pb age modes and Lu–Hf isotope composition of inherited zircons within the Kalkan Supersuite granitic rocks from both the Talbot and Connaughton Terranes are similar (Fig. 6). The granitic rocks are dominated by isotopically evolved ( Hf between 0 and –20) zircon with discrete age modes at c. 1800 Ma and c. 2000 Ma, similar to the zircon detritus within the Capricorn Orogen basins (Fig. 6). The presence of a c. 2015 Ma granitic rock in
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Figure 6. Hf evolution diagram for inherited zircons from
Rudall Province intrusive rocks (green circles)
compared to potential West Australian Craton
source regions (yellow and blue triangles). The
histogram shows 207Pb*/206Pb* ages of inherited
zircons from Rudall Province intrusive rocks.
The isotopic signature of the inherited material is
consistent with generation from crust similar to
that in the Capricorn Orogen. Lines define fields
for evolution of a source with similar composition
to zircons in basins of the Capricorn Orogen (dash)
and Dalgaringa Supersuite (dash-dot). The red line
is model depleted mantle and the blue line is CHUR.
the province, here reinterpreted as a Kalkan Supersuite granite with abundant c. 2015 Ma-aged inherited zircons, led Clark (1991) and Bagas (2004) to suggest that the Glenburgh Terrane of the Gascoyne Province may form basement to the Talbot Terrane, since rocks of this age have not been documented in the Arunta Province. A recent deep crustal seismic reflection survey through the western part of the Capricorn Orogen (Johnson et al., 2011b), however, indicates that the Glenburgh Terrane is sutured to the southern margin of the Pilbara Craton along a southeast-trending, south-dipping suture zone (Fig. 1; the Lyons River – Minga Bar – Minnie Creek Fault System). The orientation of this suture means that the Glenburgh Terrane is progressively truncated toward the east against the northern margin of the Yilgarn Craton, making it highly unlikely that this terrane forms basement to any part of the Rudall Province.
The similarity in isotopic composition and age of inherited zircons within granitic rocks of the Kalkan Supersuite with detrital zircons in sedimentary rocks in the Capricorn Orogen (Fig. 6) suggests that the Kalkan Supersuite granites may have assimilated similar sedimentary material during their emplacement into the upper crust. The sedimentary rocks of the eastern association of the Talbot Terrane were deposited in a similar timeframe to those in the Capricorn Orogen. The similar timing of basin formation during the early stages (c. 1820 to c. 1800 Ma)
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
23
of the Capricorn Orogeny imply the development of a single large basin — or a series of smaller linked basins — around the southern and eastern margins of the Pilbara Craton (Fig. 1). Synchronous regional-scale uplift along the southern margin of the Gascoyne Province provided abundant sedimentary detritus that was transported northward into the developing basin(s).
Considering the data presented above, we suggest that:
were derived by the assimilation of sedimentary material during emplacement of the granites into the upper crust
of a wider, regional-scale Capricorn Orogeny-aged basin(s), the detritus for which was derived from upland areas in the southern part of the Gascoyne Province
to the eastern Pilbara Craton margin (e.g. Hickman et al., 1994), consistent with the view presented by Reading et al. (2012) that thinned and extended Pilbara Craton crust occurs as basement beneath the Talbot Terrane
zircons within the Kalkan Supersuite granites are largely influenced by a variety of autochthonous source regions, including the sedimentary successions into which they were intruded.
Hf isotopic signature of the Rudall
Province
The Talbot and Connaughton Terranes are dominated by granitic rocks of the 1800–1765 Ma Kalkan Supersuite. In the Talbot Terrane, magmatic zircon crystals from these rocks show a range of isotopically evolved compositions with model ages (TDM
2) between 3.4 and 2.6 Ga (Fig. 7), whereas in the Connaughton Terrane model ages (TDM
2) range between 3.4 and 2.4 Ga (Fig. 7). The granites contain abundant inherited zircon cores (that were most likely derived from the sedimentary succession into which the magmas were intruded) that have contributed significantly to the isotopic composition of the granitic magmas. The inherited zircons are interpreted to have been derived from the Glenburgh Terrane (specifically the Halfway Gneiss and Dalgaringa Supersuite) of the Gascoyne Province, and the isotopic compositional range of the granites is also comparable to that for the Glenburgh Terrane (Figs. 5 and 6). The most evolved magmatic grains (those with Hf c. –17), however, are also comparable with the isotopic composition of the East Pilbara Terrane, including the granitic rocks of the Bridget Suite (Fig. 5). The lack of East Pilbara Terrane-aged (3500–3200 Ma) inherited zircons within the Kalkan Supersuite indicates that the most evolved isotopic component of the granites may not have been derived as an inherited sedimentary component, but reflect a contribution directly from the underlying Talbot Terrane basement, with an evolved isotopic signature identical to that of the East Pilbara Terrane.
The magmatic zircons from c. 1300 Ma granitic rocks of the Tabletop Terrane are dominated by mildly evolved compositions with model ages of 2.6 Ga. The average 176Yb/177Hf value of zircons from Tabletop Terrane granite sample GSWA 118914 are high to extreme (176Yb/177Hf = 0.100 ± 0.022). However, the average stable 178Hf/177Hf ratio is 1.467241 ± 0.000047 (1SD; n=16), which is within the range of values reported by Thirlwall and Anczkiewicz (2004). The elevated 176Yb/177Hf ratio in this sample, as compared to other typical crustal melts, suggests crystallization either from a strongly fractionated magma or by direct melting of a garnet-bearing source. The Hf isotopic range of the magmatic zircon from the Tabletop Terrane granites is similar to that for the Kalkan Supersuite in the Connaughton Terrane, implying derivation from a similar crustal source.
Crust formation and underplating at
1900 Ma
A post-D2 metamonzogranite in the southern part of the Watrara Inlier in the Talbot Terrane is dated at c. 1450 Ma (GSWA 112102; Nelson, 1996b), and contains zircon crystals with the least evolved Hf isotopic signature in the Rudall Province. The Hf isotopic data indicate that either the granitic material was extracted from the mantle at 1.96 Ga or that it represents a homogenized mix of sources with a component younger than 1.96 Ga. However, oxygen isotopes can be used to determine whether the parental magma from which these zircons grew contained a contribution from near-surface rocks (e.g. those with 18OVSMOW >6.3 ‰). This provides a means to screen the corresponding Hf model age for supracrustal contamination into the magma and to identify a model age that represents a mixing of source materials rather than a discrete crust-forming episode. Whereas zircon in equilibrium with mantle-derived melts has a 18OVSMOW value of 5.3 ± 0.6 ‰ (2 SD; Valley, 2003), incorporation of high- 18O material (i.e. rocks or minerals altered by low-temperature near-surface processes) will increase the
18O value of a melt, so that zircons crystallized from such melts will also have elevated 18O values. Oxygen isotope values for all zircons from this sample (Table 2) are within the mantle zircon field (Fig. 8); hence, the 1.96 Ga model age likely reflects a crust-forming fractionation event in the lithosphere.
Further constraint on the location of this fractionation event can be placed by examining the isotopic signature of this sample. The average 176Yb/177Hf values of zircon crystals from GSWA 112102 are high (176Yb/177Hf = 0.085 ± 0.012; Fig. 9). However, during the course of the analysis of this sample, the average 178Hf/177Hf ratio was 1.467168 ± 0.000051 (1SD; n=8), which is in the range of values reported by Thirlwall and Anczkiewicz (2004), indicating that Yb interference has been satisfactorily dealt with. Hence, the elevated 176Yb/177Hf ratio in these zircon crystals could imply anatexis of residual garnet (Fig. 9).
There is only limited additional evidence for crust formation at c. 1.9 Ga in the West Australian Craton and its marginal terranes. Magmatic and metasedimentary rocks of the Musgrave Province are dominated by two major juvenile Proterozoic crust formation events —
Kirkland et al.
24
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Figure 7. Magmatic crystallization ages (left) and two-stage Hf model ages (right) for zircons from
Rudall Province magmatic rocks. Crystallization age data are colour-coded according to
Hf value. Although the timing of magmatism in the Tabletop Terrane is different from that
in the Connaughton and Talbot terranes, the Hf isotopic signatures of all three are broadly
similar, implying that each originated from the same, or a similar, crustal source.
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CLK99 28.03.13
Figure 8. Oxygen isotope analyses of zircons from
Mesoproterozoic metamonzogranite sample GSWA
112102 (Nelson, 1996b). Error bars are 2 . Analyses
located on fractures or inclusions are excluded. The
line indicates the weighted mean 18O value for
the analysed zircons; the grey field represents the
range of values expected from zircon crystallized
in equilibrium with the mantle (5.3 ± 0.6 ‰ (2 SD),
e.g. Valley, 2003).
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CLK76 28.03.13
Figure 9. Comparison of 176Yb/177Hf ratios for zircons from
two Mesoproterozoic magmatic rocks (circles) with
those from other Rudall Province magmatic rocks
of Paleoproterozoic age (squares). The zircons in
Mesoproterozoic rocks have elevated Yb contents
compared to most of those in Paleoproterozoic
rocks.
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
25
one at 1600–1550 Ma and a more significant event at 1950– 1900 Ma (Kirkland et al., 2013). Although no juvenile rocks or minerals are known from c. 1900 Ma in the Musgrave Province, addition of radiogenic material into the crust at this time is required to account for consistent Nd and Hf evolution patterns that show no indication of mixing processes, and mantle-like oxygen isotope signatures in zircons with 1.9 Ga model ages (Kirkland et al., 2013).
The Edmund Basin is an intracratonic sedimentary basin of early Mesoproterozoic age located between the Pilbara and Yilgarn Cratons (Fig. 1). Metasedimentary strata of the Edmund Group are intruded by voluminous mafic sills of the c. 1465 Ma Narimbunna Dolerite (Martin and Thorne, 2004). Hf isotopes in baddeleyite and zircon crystals from this magmatic suite consistently suggest a juvenile source component formed at 1950–1900 Ma (GSWA, unpublished data). Whole-rock Nd isotopes from these rocks also yield model ages (TCHUR) with a mode of 1.9 Ga (Morris and Pirajno, 2005).
Isotope data for c. 1450 Ma magmatic zircons in Talbot Terrane monzogranite sample GSWA 112102 fall directly on a normal-crustal evolution line from a c. 1900 Ma crust-formation event. This is also the case for isotope evolution in rocks of the Musgrave Province and the Edmund Basin. At c. 1.9 Ga, the timing of this crust formation event is unusual within Proterozoic Australia and supports the idea of an extensive 1.9 Ga underplate beneath these regions.
Constraints on the tectonic
evolution of the Rudall Province
Metasedimentary rocks of the eastern association in the Talbot and Connaughton Terranes have a similar structural and metamorphic history to the northern and central Arunta Orogen (Collins and Shaw, 1995; Bagas, 2004; Claoue-Long and Hoatson, 2005), and this has been considered as evidence that the Rudall Province and Arunta Orogen formed part of the North Australian Craton prior to the Yapungku Orogeny (Bagas, 2004; Fig. 10). However, it appears that the Rudall Province has more in common with a Capricorn Orogen source than it does with the Arunta Orogen.
The Arunta Orogen contains 1690–1670 Ma magmatic rocks, whereas those in the Rudall Province are dominated by the 1800–1765 Ma Kalkan Supersuite. With regard to the age of crustal residence within these terranes, only the Connaughton Terrane has somewhat similar model ages to the Aileron Province of the Arunta Orogen (Kirkland et al., 2013), implying that this terrane could have a North Australian Craton heritage. However, the U–Pb age and Hf isotopic signature of inherited
YapungkuOrogeny
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Figure 10. Time-space diagrams showing magmatic and
metamorphic U–Pb ages for the Gascoyne Province,
Rudall Province, and Arunta Orogen. Data include
all GSWA U–Pb zircon and baddeleyite ages <www.
dmp.wa.gov.au/geochron> and Arunta Orogen data
compiled in Neumann and Fraser, (2007).
Kirkland et al.
26
zircons within all the Kalkan Supersuite granites, from both terranes, are most similar to sources in the West Australian Craton, in particular the Glenburgh Terrane in the southern part of the Gascoyne Province (Fig. 1). The presence of 2.0 and 1.8 Ga inherited zircons are consistent with the magmatic rocks of the Kalkan Supersuite having incorporated material from metasedimentary rocks of the eastern association, which was deposited in a similar timeframe to the Capricorn Orogeny-aged basins. The presence of 2715–2577 Ma-aged inherited zircons in a syenogranitic gneiss of the Talbot Terrane (GSWA 104932, Nelson, 1995a) are consistent with their derivation from the Fortescue and Hamersley Groups of the Pilbara Craton. The Hf isotopic evolution of granitic rocks within the Talbot and Connaughton Terranes also implies the involvement of unradiogenic crust, probably as basement to the sediments of the eastern succession (Fig. 5). This crust likely had a composition similar to that of the East Pilbara Terrane, consistent with the recent results of passive seismic study across the province, which suggests that thinned East Pilbara Terrane crust extends as basement beneath the western part of the Rudall Province (Reading et al., 2012), thus implying an autochthonous setting for the Talbot Terrane.
The Tabletop Terrane has been regarded as geologically distinct from the Connaughton and Talbot Terranes (Bagas, 2004). However, crust within the Tabletop Terrane appears to have been generated at the same time as that in the Connaughton Terrane and also from a similar source to inheritance in the Talbot Terrane (Fig. 7). It has, however, a distinct magmatic and overprinting history.
In addition, the Paleoproterozoic isotope evolution of the Rudall Province is different from that of the Musgrave Province (Fig. 5). The isotopic composition of the Rudall Province lies mainly in the gap between the 3.0 and 1.9 – 1.6 Ga crustal evolution lines that are characteristic of the Musgrave Province, implying that the crust of the two provinces is broadly dissimilar (Fig. 5). The Archean source within the Musgrave Province is unidentified, although it could be the Gawler Craton (Kirkland et al., 2013). This Archean component overlaps the array from the most unradiogenic components of the Talbot and Connaughton Terranes, although such a signature is common to many Archean crustal blocks.
These data imply an autochthonous setting for the Rudall Province on the margin of the East Pilbara Terrane, and do not necessitate any connection to the Arunta Orogen, the North Australian Craton or the Musgrave Province. Therefore, a model of suturing at 1800–1765 Ma of an allochthonous block (Arunta Orogen) of the North Australian Craton to the Pilbara Craton margin is inconsistent with the distinctly different post-1765 Ma tectonic histories of these two regions (Neumann and Fraser, 2007). Such a model predicts a shared history of post-suturing events. Although the Arunta Orogen records late Paleoproterozoic tectonic events such as the 1680– 1650 Ma Argilke tectonic event and the 1620– 1580 Ma Chewings Orogeny (Claoue-Long and Hoatson, 2005), no contemporaneous events are known in the Rudall Province.
Implications for terrane
boundaries
The 1800–1765 Ma Yapungku Orogeny is considered to represent collision of the North Australian Craton with the West Australian Craton. Isotope data demonstrate that the Rudall Province is a (para)autochthonous assemblage that developed on the eastern margin of the Pilbara Craton. Such a finding is consistent with the initial interpretation, based on regional 1:250 000 scale geological mapping, that the >5-km-thick clastic succession of the Talbot Terrane was deposited on the eastern margin of the Pilbara Craton, and immediately thereafter was intruded by the Kalkan Supersuite during southwest-directed thrusting (Hickman et al., 1994; Hickman and Bagas, 1995; Bagas and Smithies, 1997; Hickman and Bagas, 1999a). Therefore, the suture zone between the North and West Australian Cratons should be located to the east (in present-day coordinates) of the province. The Connaughton Terrane was thrust westwards over the Talbot Terrane during the latter stages of the Yapungku Orogeny (Bagas, 2004).
The Camel–Tabletop Fault (Bagas and Lubieniecki, 2000) is a post-Yapungku structure, along which pieces of the same crustal block were reorganized. The timing of reworking in the Tabletop Terrane is similar to that of Mesoproterozoic events in the Musgrave Province. Magmatism at c. 1450 Ma in the Talbot Terrane appears to have tapped a more radiogenic source, in contrast to all other magmas of the Rudall Province. This radiogenic source shares similarities to the isotopic signature of the Musgrave Province, with a dominant isotopic crust formation age of c. 1900 Ma. Narimbunna Dolerites in the Mesoproterozoic Edmund Basin of the Capricorn Orogen (Fig. 1), also indicate a juvenile source formed at 1950–1900 Ma. The potential of a c. 1900 Ma source in the basement of the Rudall Province, Edmund Basin and Musgrave Province could support a regional underplate of this age in the deep geology of the West Australian Craton. Such a structure could indicate a c. 1950–1900 Ma subduction zone dipping and underplating oceanic crust towards the present-day southwest. Nonetheless, the crustal source of the Kalkan Supersuite is vastly different from the crust of the Musgrave Province, which implies at least some dissimilar basement components within these two regions.
Conclusions
The U–Pb age and Hf isotopic composition of inherited zircons within Kalkan Supersuite granitic rocks throughout the Rudall Province are consistent with these magmas incorporating material from sedimentary rocks that were sourced from the Glenburgh Terrane of the Gascoyne Province. The >5-km-thick eastern association of sedimentary rocks in the Talbot Terrane were deposited at c. 1790 Ma, in a similar timeframe to other sedimentary rocks in the Capricorn Orogen, which were also sourced from the Glenburgh Terrane. This suggests that during the 1800–1765 Ma Yapungku Orogeny and 1820–1770 Ma
GSWA Report 122 The crustal evolution of the Rudall Province from an isotopic perspective
27
Capricorn Orogeny, the southern margin of the Gascoyne Province was uplifted to supply detritus into an extended sedimentary basin, or series of linked basins, that wrapped around the southern and eastern margins of the Pilbara Craton.
The Hf isotopic composition of magmatic zircons in the Kalkan Supersuite has similarity to components within the c. 1800 Ma Bridget Supersuite of the East Pilbara Terrane. This implies that the East Pilbara Terrane extends eastward to form basement to the Talbot and Connaughton Terranes, a view supported by a recent passive seismic study of the area (Reading et al., 2012).
The broad similarity of crustal residence ages for all terranes in the Rudall Province indicates that they share a common heritage, although Mesoproterozoic reworking (infra-crustal magmatism) apparently occurred only in the Tabletop Terrane. These data indicate that the Rudall Province formed in an autochthonous setting and thus all components are endemic to the West Australian Craton. There is no necessity to invoke transfer of North Australian Craton terranes to the West Australian Craton margin or an accretionary style of orogenesis for the Rudall Province. The major suture between the North and West Australian Cratons must lie to the present-day east of the Rudall Province.
A younger phase of crust formation at 1.96 Ga is indicated by Hf isotopes of a c. 1450 Ma monzogranite in the Talbot Terrane. This isotope signature appears to be similar to a dominant basement component in the Musgrave Province.
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Kirkla
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This Report outlines the crustal evolution of the Rudall Province,
with particular emphasis on the development of the Talbot and
Connaughton Terranes. Components within the Rudall Province have
been linked to the Arunta Orogen of the North Australian Craton
and hence regarded as exotic terranes on the margin of
the West Australian Craton. This work presents
time constrained Hf isotopes to elucidate
the affinity of the Rudall Province and
refine models for its genesis. The
Rudall Province is divided into three
lithotectonic elements known as the
Talbot, Connaughton, and Tabletop
Terranes. The Talbot and Connaughton
Terranes were affected by magmatism
produced during the collision between
the West and North Australian Cratons at
1800–1765 Ma. Zircons within granitic rocks
related to this event indicate crustal residence
ages of 3.4 – 2.4 Ga, which have similarity
to crustal sources with the basement of the
Capricorn Orogen. Additionally, the Hf
isotopic signature of the Rudall Province has similarity to components
of the c. 1800 Ma Bridget Suite, which has a clear association to
the Pilbara Craton. Hence, sources for most isotopic compositions
preserved within the Rudall Province are present within the proximal
West Australian Craton and an exotic origin for the Rudall Province is
unlikely. A distinctive phase of crust formation at 1.9 Ga in the Talbot
Terrane implies an affinity to a major deep lithospheric source of
similar age in the Musgrave Province and could indicate a regional
underplate of this age.
Further details of geological products and maps produced by the
Geological Survey of Western Australia are available from:
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Phone: (08) 9222 3459 Fax: (08) 9222 3444
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