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Precambrian Research 187 (2011) 223–247

Contents lists available at ScienceDirect

Precambrian Research

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n the edge: U–Pb, Lu–Hf, and Sm–Nd data suggests reworking of the Yilgarnraton margin during formation of the Albany-Fraser Orogen

.L. Kirklanda,∗, C.V. Spaggiari a, M.J. Pawleya, M.T.D. Wingatea, R.H. Smithiesa, H.M. Howarda,.M. Tylera, E.A. Belousovab, M. Poujol c

Geological Survey of Western Australia, 100 Plain Street, East Perth, WA 6004, AustraliaGEMOC, Macquarie University, Sydney, NSW 2109, AustraliaGéosciences Rennes UMR CNRS 6118, Université Rennes 1, 35042 Rennes Cedex, France

r t i c l e i n f o

rticle history:eceived 25 July 2010eceived in revised form 23 February 2011ccepted 2 March 2011vailable online 22 March 2011

eywords:–Pbu–Hfm–Ndirconaddeleyitelbany-Fraser Orogeniranup Zoneraser Zone

a b s t r a c t

The Albany-Fraser Orogen is considered to be a response to Mesoproterozoic continent–continent col-lision between the combined North and West Australian Cratons and the combined East Antarctic andSouth Australian Cratons. However, the tectonic history of the orogen and its components remain enig-matic. Recently, the Kepa Kurl Booya Province has been defined as the crystalline basement of theorogen and divided into the Fraser, Biranup, and Nornalup Zones. New geochronology shows that theBiranup Zone includes 1710–1650 Ma granitic to gabbroic intrusions and is a substantial crustal com-ponent extending at least 1200 km along the southern and southeastern margins of the Yilgarn Craton.Previous models interpreted the Biranup Zone as an exotic terrane accreted to the Yilgarn Craton duringMesoproterozoic collision, but new data presented here indicate a strong link to the craton margin duringthe Paleoproterozoic.

Proterozoic magmatism commenced in the Biranup Zone at 1708 ± 15 Ma with metasyenograniteemplacement. This granite has εHf values of −10 to −8 and whole rock εNd of −15, consistent with areworked Archean Yilgarn source. Volcaniclastic deposition in the Biranup Zone occurred at 1689 ± 6 Ma,and was rapidly followed by granitic intrusion at 1686 ± 8 Ma. Deformation during the Zanthus Event isconstrained by 1676 ± 6 Ma folded migmatitic leucosomes and 1679 ± 6 Ma cross-cutting axial planar leu-cosomes. A younger suite of granitic and gabbroic rocks, which exhibit distinct mingling and hybridizationtextures, is dated at 1665 ± 4 Ma. Magmatism in the eastern Biranup Zone displays high-K, calc-alkalinechemistry and a trend towards more juvenile compositions from 1710 to 1650 Ma. Based on the rapidlyevolving tectonomagmatic history, modification of the original Yilgarn-like source by juvenile material,and the geochemical evolution of the melts, a feasible tectonic scenario for the Biranup Zone is an arcto back-arc setting on the active Yilgarn Craton margin. Such a model is supported by the 2684 ± 11 Mamagmatic crystallization age of an isolated Archean fragment, which has clear Yilgarn affinity, within theBiranup Zone.

The region was subsequently compressed and tectonically dismembered during Stages I(1345–1260 Ma) and II (1215–1140 Ma) of the Albany-Fraser Orogeny. Stage I was dominated by volu-

minous mafic and granitic magmatism, represented by the Fraser Zone intrusions and the RechercheSupersuite. Two granites from the Fraser Zone, dated at 1298 ± 4 Ma, have εHf values overlapping BiranupZone compositions, indicative of a reworked Biranup source. The Biranup Zone was dominated by gran-ulite facies metamorphism during Stage II. Zircons from the northeastern edge of the Fraser Zone areovergrown by two generations of zircon rims. The earlier rims, at c. 1270 ± 11 Ma, are broken andovergrown by a low-uranium fracture-filling phase at 1193 ± 26 Ma. This indicates uplift and brittle

ges I

deformation between Sta

∗ Corresponding author.E-mail addresses: kris.kirkland@gmail.com, Chris.KIRKLAND@dmp.wa.gov.au

C.L. Kirkland).

301-9268/$ – see front matter. Crown Copyright © 2011 Published by Elsevier B.V. All rioi:10.1016/j.precamres.2011.03.002

and II.Crown Copyright © 2011 Published by Elsevier B.V. All rights reserved.

1. Introduction

The recognition, on craton margins, of allochthonous (exotic)terranes (e.g. Thomas and Astini, 1996; Daly et al., 1991) as opposedto autochthonous units (e.g. Tanner and Sutherland, 2007) is fun-damental in understanding the geological evolution of a region.

ghts reserved.

224 C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247

F 3; Tyla ills; CC es (unW

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ig. 1. Crustal elements of easternmost Gondwana (modified from Fitzsimons, 200reas with or without outcrop. AG, Terre Adélie–King George V Land; BH, Bunger Hraton; DG, Denman Glacier region; M–F–W, Madura, Forrest, and Waigen Complexindmill Islands.

ot only does this distinction have a bearing on the displacementagnitudes that must be invoked to transport lithological units to

heir current locations, but most importantly reflects the tectonicnvironment. For example, large compressional or transpressionalinematics, usually in subduction-related accretionary settings, areequired to juxtapose exotic fragments, whereas suspect terranesre less likely to be found in extensional settings where marginifting occurs.

Initial models for the Proterozoic evolution of Australia empha-ised intracratonic deformation involving a single plate (e.g.nsialic model of Etheridge et al., 1987). However, more recentork favours plate tectonic processes in which Proterozoicustralia is made up of three major, distinct cratons: the Westustralian Craton, the North Australian Craton, and the South Aus-

ralian Craton (Myers et al., 1996; Tyler, 2005; Fig. 1). Proterozoic

rogens on the extremities of these cratons have been proposeds subduction-related convergent margins, which added to andventually amalgamated the three cratons. Examples of regions ofroterozoic convergent margin tectonism include the Halls Creekrogen (Sheppard et al., 2001), the Rudall Complex (Smithies and

er, 2005; Spaggiari et al., 2009). Paler and darker shades of the same pattern reflectC, Coompana Complex (concealed by the Officer and Eucla Basins); CC, Curnamonadivided; concealed by the Gunbarrel, Officer, and Eucla Basins); PB, Prydz Bay; WI,

Bagas, 1997), the Capricorn Orogen (Occhipinti et al., 1999), theArunta Orogen (Collins and Shaw, 1995; Scrimgeour, 2003), partsof the Gawler Craton (Betts and Giles, 2006), the Musgrave Provinceand the Albany-Fraser Orogen (Myers et al., 1996; Bodorkos andClark, 2004). In the recent literature, there is growing consensusthat Proterozoic Australia involved protracted subduction, accre-tion, crustal reworking, and episodic continental back-arc basindevelopment in interior regions (e.g. Betts and Giles, 2006; Korschet al., 2010). However, the specific details of recent models forProterozoic Australia, such as subduction zone location, polarity,and orientation of juxtaposed blocks, is diverse (Betts and Giles,2006; Betts et al., 2002; Dawson et al., 2002; Fitzsimons, 2003;Giles et al., 2002, 2004; Myers et al., 1996; Payne et al., 2009; Wadeet al., 2008; Howard et al., 2010). One of the lesser known cra-tonic margins is the southeastern West Australian Craton, which

contains the Albany-Fraser Orogen. Understanding the evolution ofthis orogen will help chart both the development of the West Aus-tralian Craton and, in turn, its relationship to the other Proterozoiccratons and their margins. Specifically, using geochronology, iso-tope ratio measurements, major- and trace-element geochemistry,

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 225

Fig. 2. Simplified interpreted bedrock geology map of the eastern Albany-Fraser Orogen and eastern Yilgarn Craton (adapted from Spaggiari et al., 2009), showing locations ofthe geochronology samples. The map shows only basement geology and no basin cover. MBG, Mount Barren Group; MRF, Mount Ragged Formation; WF, Woodline Formation.Inset shows the location of Mesoproterozoic tectonic units of Australia; MP, Musgrave Province; PO, Paterson Orogen; N, Northampton Complex; L, Leeuwin Complex; AFO,Albany-Fraser Orogen. Sample ids maybe truncated to the last two digits where multiple samples have similar initial digits.

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nd field and geophysical observations, we argue that it is possi-le to ascribe the development of this margin to autochthonousrocesses, with tectonic modification due to the Mesoproterozoicontinent–continent collision of the combined North and Westustralian Cratons with the combined East Antarctic and Southustralian Cratons (Myers et al., 1996; Bodorkos and Clark, 2004).

. Regional geology

The Albany-Fraser Orogen is an arcuate orogenic belt adjacento the southern and southeastern margins of the Archean Yilgarnraton in Western Australia (Fig. 2). The predominant tectonic andetamorphic features of the belt are generally considered to have

eveloped during the Mesoproterozoic Albany-Fraser Orogeny,hich is thought to have occurred in two stages (Clark et al.,

000): continental collision during Stage I (c. 1345–1260 Ma), andntracratonic reactivation during Stage II (c. 1215–1140 Ma). Bothtages have been interpreted to involve oblique dextral movementnd the northwestward transport of thrust slices (Myers, 1993,995; Bodorkos and Clark, 2004). Giles et al. (2004) proposed thathe orogeny was a response to Mesoproterozoic rotation of the

awson Craton onto the West Australian Craton.The dominant lithologies of the Albany-Fraser Orogen are

mphibolite to granulite facies paragneiss and orthogneiss,ntruded by late-tectonic granite plutons. The nomenclature ofhe tectonic units of the orogen has evolved from the initial cat-gorization of Myers (1990, 1995) to Spaggiari et al. (2009). Thelbany-Fraser Orogen is divided into a series of mostly fault-ounded zones, each with distinct lithotectonic character (Myers,990, 1995; Spaggiari et al., 2009). These lithotectonic units

nclude the Northern Foreland, the Kepa Kurl Booya Province (are-collisonal Stage I basement component), the Recherche andsperance Supersuites, and various Mesoproterozoic cover rocks.he Kepa Kurl Booya Province is further divided into the Biranupone, the Fraser Zone (formerly the Fraser Complex of Myers1985)), and the Nornalup Zone (Myers, 1990, 1995; Spaggiarit al., 2009). The Kepa Kurl Booya Province is in fault contactith the Archean Yilgarn Craton to the northwest. To the east, therovince is obscured by the Eucla Basin, and its relationship withhe Madura, Forrest, Waigen, and Coompana Complexes and theestern Gawler Craton is unknown (Fig. 1).

.1. Northern Foreland

The Northern Foreland comprises the component of the Archeanilgarn Craton that was reworked to produce mostly amphibo-

ite to granulite facies rocks during the Albany-Fraser OrogenyFig. 2). It consists of 3000–2600 Ma gneisses and granites, fault-ounded packages of metasedimentary rocks, and younger doleriteykes (Spaggiari et al., 2009). The Munglinup Gneiss was origi-ally defined by Myers (1993, 1995) as an allochthonous Archeannit within the Biranup Zone (formerly Biranup Complex). How-ver, recent geochronology from the Munglinup Gneiss indicateshat it represents overprinted Archean Yilgarn Craton rocks (c.660 Ma) and it is now considered part of the Northern ForelandGSWA, 2007; Spaggiari et al., 2009). Hf isotopes from the Northernoreland yield model ages clustering at c. 3.2 Ga, which implies aeworked Archean Hf source similar to many intrusive rocks withinhe Eastern Goldfields Superterrane (GSWA, unpublished data).

Paleoproterozoic sedimentary rocks of the Woodline Forma-

ion (Hall and Jones, 2005; Hall et al., 2008), Mount Barren GroupNelson, 1996; Dawson et al., 2002; Vallini et al., 2005), and Stir-ing Range Formation (Rasmussen et al., 2002) are part of theorthern Foreland and are interpreted to represent unconformable

equences on the Yilgarn Craton (Hall et al., 2008; Spaggiari et al.,

esearch 187 (2011) 223–247

2009). These rocks were deformed during the MesoproterozoicAlbany-Fraser Orogeny, including substantial north- to northwest-directed thrusting of the Stirling Range Formation and MountBarren Group (Myers, 1990; Dawson et al., 2002; Jones, 2006;Griffin, 1989).

2.2. Biranup Zone

The Biranup Zone is a belt of mid-crustal rocks that gir-dles the southern and southeastern margin of the Yilgarn Craton(Fig. 2; Myers, 1990; Spaggiari et al., 2009). The zone is dominatedby intensely deformed orthogneiss, paragneiss, and metagabbro,with ages of c. 1710–1620 Ma. The central Biranup Zone con-tains reworked 1690–1660 Ma orthogneiss, minor paragneiss, andMesoproterozoic granitic intrusions (Nelson et al., 1995; Spaggiariet al., 2009). It includes the Dalyup and Coramup Gneisses (Myers,1995), although both lithological units are chiefly composed ofgranitic rocks with similar crustal histories and hence the distinc-tion between Dalyup and Coramup Gneisses may not be meaningful(Bodorkos and Clark, 2004). The lack of evidence for a similar Pale-oproterozoic magmatic or tectonothermal event in the southernYilgarn Craton at this time has led to the suggestion that the BiranupZone was an exotic terrane accreted to the Yilgarn Craton marginduring Stage I of the Albany-Fraser Orogeny (Nelson et al., 1995;Clark et al., 2000; Spaggiari et al., 2009). A potential link has beensuggested between the Biranup Zone and the Warumpi Province ofthe southern Arunta Orogen (Spaggiari et al., 2009).

2.3. Nornalup Zone

To the south and east of the Biranup Zone, a different group ofProterozoic granitic and sedimentary gneisses, intruded by youngergranites, has been defined as the Nornalup Zone (Fig. 2; Myers,1990). In the Nornalup Zone, pre-orogenic basement rocks aresolely represented by the Malcolm Gneiss, which comprises parag-neiss intruded by both mafic and felsic rocks, all of which areintruded by granites of the 1330–1280 Ma Recherche Supersuite(Clark et al., 1999, 2000). Detrital zircons from the Malcolm Gneisshave yielded a maximum depositional age of 1560 ± 40 Ma (GSWA112128; Nelson, 1995g) with other detritus dated at 1807 Ma andminor age components at 2033 to 2734 Ma. The detrital zirconage spectrum of the Malcolm Gneiss indicates age componentsunrecognised within the Albany-Fraser Orogen (Kositcin, 2007).

2.4. Fraser Zone

The northeasterly trending Fraser Zone contains the c. 1300 MaFraser Range Metamorphics (Spaggiari et al., 2009), a suite of inter-leaved thin slivers of granitic gneiss, metasedimentary rocks, andmafic rocks, that are now mostly pyroxene granulites or maficamphibolites (Fig. 2; Myers, 1985; Clark et al., 1999; De Waeleand Pisarevsky, 2008; Spaggiari et al., 2009). Myers (1985) inter-preted the mafic rocks in the Fraser Zone as part of a large layeredmafic intrusion, whereas Condie and Myers (1999) argued thatthey represent remnants of multiple magmatic arcs. Doepel (1975)interpreted both the metagranitic and metamafic components ofthe Fraser Zone as an exhumed block of lower crust.

The Fraser Range Metamorphics are dominated by a northeast-erly trending, steeply dipping foliation (Myers, 1985; Clark et al.,1999). Boundaries between the rock units were previously inter-preted to be major thrust faults that interleaved slivers of older

‘basement’ gneiss and metasedimentary rocks with the mafic rocks(Myers, 1985). However, it is now known that the granitic andmetasedimentary rocks previously interpreted as ‘basement’ aresimilar in age to the mafic rocks (Clark et al., 1999; De Waele andPisarevsky, 2008; this study). Kinematic indicators and aeromag-

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etic data indicate a significant dextral shear component along theorthwestern edge of the Fraser Zone, defined by the Fraser Fault,hich separates the Biranup Zone from Fraser Zone rocks (Fig. 2).

Crystallization of gabbro within the Fraser Zone is datedt 1291 ± 8 Ma (De Waele and Pisarevsky, 2008) by U–Pb onircon and at 1291 ± 21 Ma by a whole-rock Sm–Nd isochronMSWD = 0.25; (Fletcher et al., 1991). A minimum age constraint onhe mafic rocks is provided by an intrusive charnockitic orthogneissutting the gabbros at 1301 ± 6 Ma (Clark et al., 1999). Early meta-orphism in the Fraser Zone at 1304 ± 7 Ma is recorded by zircon

ims developed within a quartz metasandstone interlayered withmphibolite and pyroxene granulite with a maximum deposi-ional age of 1466 ± 17 Ma (Wingate and Bodorkos, 2007b). Aiotite–whole-rock Rb–Sr isochron date of 1268 ± 20 Ma is inter-reted to reflect the time of cooling below the isotopic closureemperature for biotite in this rock (Fletcher et al., 1991). All iso-opic results from the Fraser Zone indicate a short time intervalor igneous crystallization at c. 1300 Ma, and essentially coevalranulite-facies metamorphism. Retrogression, cooling, and upliftccurred shortly after metamorphism (Fletcher et al., 1991; Clarkt al., 1999; De Waele and Pisarevsky, 2008).

.5. Mesoproterozoic reworking and the Recherche andsperance Supersuites

The Mesoproterozoic Albany-Fraser Orogeny is the principalvent that amalgamated the Biranup, Nornalup, and Fraser Zones,nd reworked the margin of the Yilgarn Craton to produce theorthern Foreland. The Biranup and Nornalup Zones were intrudedy granitic rocks of the c. 1330–1280 Ma Recherche Supersuiteformerly Recherche Granite of Myers, 1995), which is associ-ted with Stage I tectonism (Nelson, 1995a; Clark et al., 1999,000; Bodorkos and Wingate, 2008a). Metagranitic rocks datedt c. 1330–1280 Ma are also found in the Fraser Range Metamor-hics (Wingate and Bodorkos, 2007a; De Waele and Pisarevsky,008). Following Stage I uplift, erosion of the Nornalup Zone andecherche Supersuite granitic rocks produced massive quartzitesnd thin pelitic layers of the Mount Ragged Formation (Fig. 2; Clarkt al., 2000). The Mount Ragged Formation contains 1154 ± 15 Mautile, indicating burial and metamorphism during Stage II (Clarkt al., 2000). Stage II is thought to have taken place in an intra-ontinental setting (Bodorkos and Clark, 2004). Minor extensionccurred during Stage II during intrusion of the margin-parallelnowangerup–Fraser Dyke Suite at c. 1210 Ma (Wingate et al.,000), which was associated with a regionally elevated geothermalradient (Dawson et al., 2003). There is also evidence of alternat-ng extension and contraction during Stage II at c. 1180 Ma in theentral Biranup Zone, which produced several phases of boudi-age and folding (Barquero-Molina, 2009; Spaggiari et al., 2009).he c. 1330–1280 Ma Recherche Supersuite (Clark et al., 1999) andhe c. 1140 Ma Esperance Supersuite (Myers, 1995; Nelson, 1995c;elson et al., 1995) mark two major magmatic events that coin-ided with Stages I and II of the Albany-Fraser Orogeny, respectivelyClark et al., 2000).

. Ion microprobe (SHRIMP) U–Th–Pb geochronology

We present U–Th–Pb results from fifteen samples, which spanhe entire eastern portion of the Albany-Fraser Orogen (eastiranup Zone and Fraser Range Metamorphics; Fig. 2). The locations

f all samples are shown in Fig. 2, and a summary of the location,etrography, and U–Pb date for each sample is given in Table 1.–Pb data tables, together with external and internal uncertain-

ies from replicate analyses of standards, are available online asupplementary material (Table A). Details of the analytical method-

search 187 (2011) 223–247 227

ology are given in Appendix A. All geochronology results are shownin a stacked Tera-Wasserburg concordia diagram (Fig. 3). Groupletters ascribed to zircon analyses refer to the interpretation of theresult and correspond to those listed in the Supplementary materialTable. Representative cathodoluminescence images of all zirconsamples are provided as online Supplementary material.

3.1. Magmatism at c. 1700 Ma in the eastern Biranup Zone

The Bobbie Point Metasyenogranite, of which sample 194737is representative, is an extensive granitic intrusion that cropsout about 30 km northeast of the Tropicana-Havana gold deposit(Fig. 2). The metasyenogranite is seriate-textured to locally por-phyritic, with deep pink to red K-feldspar phenocrysts. Locally,the metasyenogranite contains xenoliths or enclaves of gab-broic rocks. The metasyenogranite exhibits a weak, northeasterlytrending, solid-state foliation, which is locally mylonitic, with well-developed strain gradients. Numerous thin quartz veins are alignedsub-parallel to the foliation (Fig. 4a).

3.1.1. 194737Zircons recovered from this sample are subhedral to euhedral,

yellow to brown, up to 200 �m long, and have aspect ratios up to4:1. Cathodoluminescence (CL) images reveal idiomorphic zoning.Three analyses are >5% discordant and are not considered geolog-ically significant. The remaining 14 analyses define one coherentgroup (Group I), which yields a weighted mean 207Pb*/206Pb* dateof 1708 ± 15 Ma (MSWD = 1.8). The analyses have low to moder-ate U contents (36–164 ppm) and moderate to high Th/U ratios(0.73–1.23). The date of 1708 Ma is interpreted as the age of mag-matic crystallization of the metasyenogranite.

3.2. Volcaniclastic sediment deposition at c. 1680 Ma in theeastern Biranup Zone

A package of north-northwesterly trending, southwesterly dip-ping metasedimentary rocks, belonging to the Biranup Zone, areexposed along Ponton Creek, about 15–20 km north of Zanthus andthe transcontinental railway. These rocks, of which sample 194731is representative, are mostly psammitic gneisses with sparse gar-net and, locally, thin leucosomes. Fine bedding laminations andcross-bedding are preserved and indicate younging to the west-southwest (Fig. 4b). The foliation, defined by biotite and quartz,is sub-parallel to bedding, and contains a mineral lineation thatplunges shallowly to the southwest. Locally, the psammitic gneisshas been intruded by metagranite and coarse pegmatite (neitherof which is present in the sample), and is flanked by migmatiticgranite gneiss and foliated metagranodiorite that exhibit the samefoliation and lineation.

3.2.1. 194731Zircons isolated from sample 194731 are subhedral and slightly

rounded. They are mainly colourless, up to 400 �m long, and haveaspect ratios up to 4:1. CL images reveal a range of textures includ-ing oscillatory zoning and homogenous domains. Eight analyses arecharacterized by >10% discordance. The dates obtained from theseeight analyses (Group D) are not considered geologically significant.The remaining 32 analyses of 32 zircons (Group Y) yield a weightedmean 207Pb*/206Pb* date of 1689 ± 6 Ma (MSWD = 1.5), interpretedas the age of magmatic crystallization of the igneous source of thisdetritus and also the maximum age of deposition.

3.3. Deformation at c. 1680 Ma; the Zanthus Event

Migmatitic, hornblende-biotite-garnet granitic gneiss exposedalong Ponton Creek belong to the eastern Biranup Zone. Outcrops of

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187 (2011) 223–247

Table 1Zircon U–Th–Pb ages of samples in the eastern Albany Fraser Orogen. Easting and Northing uses WGS84 datum, MGA Zone 51. Abbreviations of mineral names after Kretz (1983). All uncertainties are at the 95% confidence level.Type refers to material crushed for zircon extraction.

Sample Type Location (100 K map) Lithology (petrology) Magmatism Metamorphism Inheritance

Archean remnant194709 Whole rock 492878 E 6392895 S

(MOUNT ANDREW)Metasyenogranite (Fsp, Qtz, Hbl, Pl, Px, Bt, Zrn, Ttn) 2684 ± 11 Ma 1171 ± 30 Ma –

Biranup Zone194737 Whole rock 662415 E 6792732 S

(SCHERK RANGE)Metasyenogranite (Or, Qtz, Ms, Mag, Ttn, Py, Zrn) 1708 ± 15 Ma – –

194731 Whole rock 561726 E 6579780 S(YANDALLAH)

Psammitic gneiss (Qtz, Kfs,Grt, Py, Bt, Zrn) 1689 ± 6 Ma – –

194730 Leucosomedominant

562765 E 6582098 S(YANDALLAH)

Migmatitic metamonzogranite with folded leucosomes(Qtz, Pl, Kfs, Bt, Hbl, Ttn, Aln, Zrn, Ap)

1676 ± 6 Ma – –

194729 Leucosome only 562765 E 6582098 S(YANDALLAH)

Axial planar leucosome inmigmatiticmetamonzogranite (Qtz, Pl, Kfs, Bt, Ttn, Aln,Zrn, Ap)

1679 ± 6 Ma – –

194720 Whole rock 546153 E 6534950 S(COONANA)

Metadiorite (Pl, Qtz, Mc, Bt, Grt, Hbl, Ep, Ap, Zrn) 1665 ± 6 Ma – –

194721 Whole rock 546142 E 6535047 S(COONANA)

Metagabbronorite (Pl, Opx, Cpx, Bt, Ol, Mag, Spl, Hbl) 1664 ± 7 Ma – –

Biranup Zone (retaining evidence of overprinting)194701 Whole rock 419829 E 6330456 S

(BURDETT)Orthogneiss (Pl, Qtz, Bt, Mc, Ms, Ttn, Zrn, Aln) 1686 ± 8 Ma 1203 ± 11 Ma 1749, 1766 and 1809Ma

194725 Whole rock 540851 E 6541647 S(COONANA)

Orthogneiss (Qtz, Pl, Kfs, Grt, Bt, Mc, Ttn, Zrn, Hbl) 1671 ± 7 Ma 1205 ± 20 Ma –

194726 Whole rock 540239 E 6549701 S(COONANA)

Orthogneiss (Qtz, Pl, Kfs, Bt, Grt, Hbl, Ttn, Zrn) 1666 ± 11 Ma 1162 ± 39 Ma –

194734 Whole rock 561862 E 6579939 S(YANDALLAH)

Orthogneiss (Or, Qtz, Pl, Bt, Grt, Ap, Zrn) 1675 ± 9 Ma 1193 ± 9 1780Ma, ≥ 2340 Ma

194728 Melanosome only 560358 E 6583678 S(YANDALLAH)

Orthogneiss (Mc, Qtz, Pl, Grt, Ttn, Bt, Zrn) 1683 ± 8 Ma 1201 ± 15 Ma –

Gwynne Creek Gneiss194735 Whole rock 492904 E 6418535 S

(FRASER RANGE)Migmatitic gneiss (Pl, Qtz, Mc, Bt, Ep, Ttn, Ms, Ap, Zrn) 1657 ± 5 Ma 1270 ± 11 Ma and

1193 ± 26 Ma–

Fraser Zone194711 Whole rock 492904 E 6418535 S

(FRASER RANGE)Monzogranite (Qtz, Mc, Pl, Bt, Grt, Hbl, Ap, Zrn) 1297 ± 8 Ma – 1701–1684Ma

194719 Whole rock 503090 E 6475794 S(SYMONS HILL)

Banded orthogneiss with mafic schlieren (Qtz, Kfs, Afs,Bt, Pl, Zrn, Ttn)

1298 ± 5 Ma – 1770 Ma

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 229

Fig. 3. Stacked Tera-Wasserburg concordia diagrams for zircons and baddeleyites analysed by ion microprobe. Error crosses are 2�. Data are arranged according to geographiclocation: southwest at the bottom to northeast at the top. Those data points not lying within the concordia space for that sample are shown with an arrow to their respectivesample. The Fraser Zone data is shown on a grey background. Inset lower right shows Th/U versus 207Pb/206Pb age for selected samples with metamorphic zircon overgrowthsfrom the Biranup Zone and magmatic zircon from the Fraser Zone. Inset upper left shows concordia diagram for Archean remnant 194709.

230 C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247

Fig. 4. (a) Bobbie Point Metasyenogranite (194737) showing quartz veining. (b) Ponton Creek psammitic gneiss (194731) showing fine laminations and cross bedding. (c)Migmatitic, hornblende-biotite granitic gneiss at Ponton Creek, with early layer-parallel folded leucosomes (194730). (d) Axial planar leucosomes (194729), which themselvesare folded. (e) View of platform showing the axial planar parallel lensoid leucosomes that were sampled. Hammer head is to the north. (f and g) Eddy Suite of rapakivi-textured metagranodiorite extensively mingled with metagabbronoritic rocks. (h) Coarse-grained strongly foliated monzogranitic gneiss (194711) with sinistral shear bands.(i) Asymmetrically ponded leucosome (host rock is sample 194734). (j) Asymmetric deformed pegmatite (host rock is Gwynne Creek Gneiss sample 194735).

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he gneiss in this area are characterised by a northwesterly trend-ng gneissosity, consistent with aeromagnetic data, which indicateshat this is a widespread regional trend within the eastern Biranupone. This fabric is truncated by the northeasterly trending fabric ofhe Fraser Zone to the southeast (Fig. 2). The gneisses along Pontonreek contain an early gneissic fabric with centimetre-scale, layer-arallel leucosomes, (Fig. 4c), folded into northwesterly trending

soclinal folds with an axial planar foliation. These rocks are rep-esented by sample 194730. A second generation of leucosomes,epresented by sample 194729, was intruded parallel to the axiallanes of the folds, and was sampled by chiseling out leucosomeaterial from the axial plane (Fig. 4d and e). At several nearby

utcrops, the northwesterly trending gneissosity and layer-paralleleucosomes are overprinted by centimetre-scale, north-northeastrending, melt-filled, dextral shears. In one case, the outcrop alsoontains an east-southeast-trending, melt-filled, sinistral shearone that is along-strike from a dextral shear, indicating a conju-ate pair. Significantly, the second-generation leucosomes in thehear zones are texturally continuous with the first-generationneissosity-parallel leucosomes, indicating that the two genera-ions formed during a single event. These observations also indicatehat leucosome injection occurred during a period of northeast-outhwest directed shortening, the age of which is constrained byhe zircon U–Pb results from these samples.

.3.1. 194728Sample 194728 is a quartzofeldspathic gneiss of the eastern

iranup Zone and was recovered from an east-west track closeo Ponton Creek (Fig. 2). Both melanosome and leucosome con-ain garnet. Zircons separated from the melanosome are euhedral,p to 300 �m long, with generally high aspect ratios up to 6:1,nd are colourless to black. CL images display oscillatory zoning,hich in places is contorted. Older cores are present within some

rains, and thin homogeneous overgrowths mantle many crystals.wenty analyses are >5% discordant, but appear to have only beenffected by recent radiogenic-Pb loss. Twenty-two analyses of zir-on rims (Group M), with generally low Th/U ratios of c. 0.05, yield aeighted mean 207Pb*/206Pb* date of 1201 ± 15 Ma (MSWD = 1.6),

nterpreted as the timing of a high-grade metamorphic overprint.wenty-four analyses of oscillatory zoned zircons (Group I) yieldweighted mean 207Pb*/206Pb* date of 1683 ± 8 Ma (MSWD = 2.2),

nterpreted as the crystallization age of the granitic protolith to theneiss. One analysis (Group P) located on a homogeneous zirconore yields a 207Pb*/206Pb* date of 1610 Ma. This crystal is inter-reted to have been subject to ancient radiogenic-Pb loss.

.3.2. 194730Zircons from sample 194730, a migmatitic metamonzogran-

te with folded coarse-grained leucosomes, are euhedral, yellowo dark brown, up to 700 �m long, and have aspect ratios up to:1. CL images reveal ubiquitous oscillatory zoning. Seven analy-es are characterized by >5% discordance, and are not consideredeologically significant. Sixteen zircons (Group I) yield a weightedean 207Pb*/206Pb* date of 1676 ± 6 Ma (MSWD = 2.0), interpreted

s the age of the layer-parallel leucosomes formed during migma-ization of the monzogranite. The alternative interpretation –hat the date reflects the age of initial granitic magmatism – isegarded as unlikely, because the grain morphology and crys-al size are consistent with growth in a pegmatite. Furthermore,he date is apparently younger, though within uncertainty, of

elanosome material from a less-migmatized quartzofeldspathic

neiss (194728) in the same area, and is also consistent with theesult from leucosome-only material (sample 194729) separatedrom the host rock (see below). Two analyses (Group P) yield07Pb*/206Pb* dates of 1645 and 1596 Ma and are interpreted toeflect ancient radiogenic-Pb loss. A single analysis (10.1; Group

search 187 (2011) 223–247 231

M), which yields a 207Pb*/206Pb* date of 1247 ± 18 Ma (1�) andindicates a low Th/U ratio (0.02; Fig. 3), is interpreted to reflectthe timing of high-grade metamorphism that caused either meta-morphic zircon growth or near-complete radiogenic-Pb loss froma pre-existing zircon.

3.3.3. 194729Sample 194729 is from a leucosome injected into the axial

planes of the folds in the same outcrop from which sample 194730was collected. Both the gneissosity and also the early generation oflayer-parallel leucosomes (as dated by sample 194730) are folded,whereas these late-generation leucosomes post-date some foldingin this outcrop. Other examples of this axial planar set of leuco-somes are themselves folded in a similar orientation to those thathave affected the gneissic foliation and early leucosomes (Fig. 4d).This implies either that deformation outlasted crystallization ofthe younger leucosomes or that there was a period of folding sub-sequent to the initial deformation event. Zircons separated fromthe granitic leucosome are euhedral, yellow to dark brown, up to700 �m long, and have aspect ratios up to 6:1. CL images revealubiquitous oscillatory zoning. The grain morphology is very sim-ilar to crystals from sample 194730, and is consistent with bothcrystallizing from similar fluids. All analyses are <5% discordantand define a single group of 18 analyses (Group I), which yield aweighted mean 207Pb*/206Pb* date of 1679 ± 6 Ma (MSWD = 2.0),interpreted as the age of crystallization of the axial planar leuco-some. As with 194730, these zircons are unlikely to date inheritedmaterial from the enclosing host rock because the large euhe-dral crystals are more consistent with growth in a pegmatiticleucosome.

3.4. Mingled norite and granodiorite emplacement at c. 1665 inthe eastern Biranup Zone: the Eddy Suite

The Eddy Suite, which ranges from megacrystic metamonzo-granite and equigranular metasyenogranitic gneiss to rapakivi-textured metagranodiorite and metagabbronoritic rocks, occursin the eastern Biranup Zone, and is well exposed west of HarrisLake. The metagranodiorite contains ovoid K-feldspars, up to 3 cmlong with a mm-wide mantle of more calcic feldspar, and roundedquartz phenocrysts up to 6 mm in diameter, in a medium-grainedgroundmass. These textures are typical of magma mingling, andsuggest that the metagranodiorite is a hybrid of the megacrysticmetamonozogranite and a mafic end-member, likely the metagab-bronorite. The metagabbronorite is fine- to medium-grained, andforms irregular enclaves that have lobate, commonly gradational,boundaries with the metagranodiorite, suggesting the two phasesare comagmatic. These rocks are heterogeneously deformed, suchthat mingling textures are preserved in some areas (Fig. 4f andg), although most exposures exhibit a pervasive gneissosity andlocalised mylonite zones. The magmatic rocks are interpreted tointrude metasedimentary rocks that are probably part of the samesuccession as the psammitic gneiss in the Ponton Creek areadescribed above (sample 194731).

3.4.1. 194720Sample 194720 is a metadiorite from the Eddy Suite, sampled

about 6 km southeast of Harris Lake. Zircons isolated from this sam-ple are subhedral to euhedral, colourless to brown, up to 300 �m

long, and have aspect ratios up to 5:1. CL images reveal oscilla-tory zoning. The analyses are concordant and define one coherentgroup. Twenty-three analyses (Group I) yield a concordia age of1665 ± 6 Ma (MSWD = 1.7), interpreted as the age of magmatic crys-tallization of the diorite.

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.4.2. 194721Sample 194721 is a metagabbronorite from the Biranup Zone,

ollected c. 100 m north of 194720. The rock has an ophitic texture.addeleyites isolated from this sample are subhedral to euhedral,rown to black, up to 300 �m long, and have aspect ratios upo 3:1. The analyses are concordant to slightly discordant, owingn part to orientation-related bias in 238U/206Pb* (Wingate andompston, 2000). Five analyses affected by instrument instabil-

ty (Group D) are unreliable, and are not considered geologicallyignificant. Twenty-two analyses of 19 crystals (Group I) yield aeighted mean 207Pb*/206Pb* date of 1664 ± 7 Ma (MSWD = 0.74),

nterpreted as the age of magmatic crystallization. Four analy-es of three grains (Group P) yield younger 207Pb*/206Pb* datesf 1599–1548 Ma and are interpreted to have lost radiogenic Pb.he date of 1664 ± 7 Ma is essentially identical to the age of theetadiorite (194720) that mingled with this rock.

.5. Rifted fragment of Yilgarn Craton within the Biranup Zone

Within the Biranup Zone, a north- to northeast-trending meta-yenogranitic body, approximately 12 km long and 4 km wide, isistinct in being garnet-absent, weakly to locally strongly foliated,nd has only minor occurrences of leucosome cross-cutting theoliation. The contact with strongly migmatised orthogneiss of theiranup Zone is not exposed, but dated Biranup Zone orthogneiss

ies directly to the northwest (Nelson, 1995h), on the inboard side ofhe orogen. Outcrop observations and aeromagnetic data indicatehat the metasyenogranite, of which sample 194709 is represen-ative, is an isolated fragment surrounded by orthogneisses of theiranup Zone.

.5.1. 194709Sample 194709 is from weakly foliated metasyenogranite near

ave Rock, about 8 km north of Mount Andrew (Fig. 2). This sampleielded colourless to dark brown, subhedral to euhedral zircons.uhedral growth zoning is common, and many crystals are over-rown by homogeneous rims with low CL response. Eight analysesf zircon rims (Group M) yield a weighted mean 207Pb*/206Pb*ate of 1163 ± 14 Ma (MSWD = 2.0), interpreted as the age of meta-orphism. Eighteen analyses (Group I) define a discordia which

ntersects concordia at 2684 ± 11 and 1171 ± 30 (MSWD = 1.4).he upper intercept is interpreted as the age of igneous crystal-ization of the granite, the lower intercept is within uncertaintyf the age of the zircon rims and is interpreted as the age ofadiogenic-Pb loss during metamorphism. Four analyses (Group P)ndicate 207Pb*/206Pb* dates of 2585–1587 Ma, and are interpretedo have undergone multiple phases of radiogenic-Pb loss. Groupsand P together define a discordia which intersects concordia at669 ± 24 and 1137 ± 45 (MSWD = 3.4). However, the high MSWD

s interpreted to reflect the combined effects of ancient and recentadiogenic-Pb loss.

.5.2. Magmatism at c. 1300 Ma in the Fraser ZoneMetagranitic rocks exposed in the Fraser Zone vary from

etamonzogranite to metasyenogranite, and occur as sheets inter-ayered with metagabbros and metasedimentary rocks. Rocks ofhe Fraser Zone are typically metamorphosed to amphibolite orranulite facies and strongly foliated, although massive rocks canocally be found in the centre of the zone. The zone is bounded by

ajor structures, including the Fraser Fault along the northwest-rn margin, and a large shear zone (Newman Shear Zone) along its

outheastern boundary. The southeastern tip of the Newman Shearone contains strongly deformed, coarse-grained, garnet-bearingonzogranitic gneiss, represented by sample 194711. The mon-

ogranitic gneiss varies between an L- and S-tectonite and has atrong, northeasterly trending, subvertical solid-state foliation and

esearch 187 (2011) 223–247

a mineral lineation that plunges shallowly to the northeast. Locallydeveloped C–S planes and extensional shear bands indicate a sinis-tral sense of shear (Fig. 4h). In the southern part of the Fraser Zone,east of the Fraser Fault (Fig. 2), metasyenogranitic gneisses, rep-resented by sample 194719, are typically compositionally banded,contain mafic schleiren, and are interlayered with metagabbroicrocks.

3.5.3. 194711Sample 194711 is a coarse-grained, strongly foliated monzo-

granitic gneiss from the Newman Shear Zone. Zircons from thissample are euhedral, up to 400 �m long, with moderate to highaspect ratios, and are pale brown to black. CL images display oscil-latory zoning which in places is contorted. Older cores are presentwithin some grains. Ten analyses >5% discordant are not consid-ered further. Sixteen analyses (Group I) yield a weighted mean207Pb*/206Pb* date of 1297 ± 8 Ma (MSWD = 1.15), interpreted asthe timing of magmatic crystallization of this granite. Four analy-ses of cores (Group X) yield 207Pb*/206Pb* dates of 1701–1684 Ma,interpreted as the ages of inherited material incorporated into thisgranite.

3.5.4. 194719Sample 194719 is a foliated, medium- to coarse-grained, seriate-

textured, metasyenogranitic gneiss collected from the same localityas sample FR21of De Waele and Pisarevsky (2008), south of SymonsWell. The zircon crystals are euhedral, up to 500 �m long, withgenerally high aspect ratios, and are dark brown to black. CLimages display faded oscillatory zoning with convoluted texturesindicative of dissolution–reprecipitation (Vavra et al., 1996). Sevenanalyses (Group D) are >5% discordant, are imprecise or unre-liable, and are not considered geologically significant. Thirteenanalyses (Group I) yield a weighted mean 207Pb*/206Pb* date of1298 ± 5 Ma (MSWD = 1.9), interpreted as the age of magmaticcrystallization. Uranium content is variable but also generallyhigh (312–2307 ppm). Seven analyses (Group P) which indicate207Pb*/206Pb* dates of 1283–1278 Ma are interpreted to haveundergone ancient Pb loss. Uranium content indicated by theseanalyses is also high (815–1995 ppm). Radiogenic Pb-loss is the pre-ferred interpretation for Group P based on the high degree of crystaldamage estimated from the calculated alpha radiation dosage forall zircons in this rock (Murakami et al., 1991). One core anal-ysis (Group X) yields a 207Pb*/206Pb* date of 1770 ± 13 Ma (1�),interpreted as the age of a xenocrystic component. Some modern-day Pb-loss is also evident within these results. De Waele andPisarevsky (2008) reported an age of 1296 ± 7 Ma (plus one inher-ited grain at 1665 Ma) for this rock.

3.6. Zircon growth during metamorphism at c. 1200 Ma in theeastern Biranup Zone

Many orthogneisses in the eastern Biranup Zone contain zirconsthat have distinctly younger overgrowths, reflecting mobility ofzirconium-bearing fluids after magmatic crystallization. The sam-ples listed in the following section show evidence of metamorphiczircon growth onto pre-existing zircon crystals.

3.6.1. 194734Sample 194734 is a garnet-biotite gneiss of the Biranup Zone

from Ponton Creek, close to sample localities 194731, 194729, and194730, described above (Fig. 2). The rock contains coarse- to very

coarse-grained leucosomes composed of quartz and K-feldsparthat are typically aligned parallel to the northwesterly trendinggneissosity to form continuous layers or short lenses. Locally, theleucosome material has asymmetrically ponded in the necks ofboudinaged layers (Fig. 4i), suggesting that the ‘way-up’ direction

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as to the southwest during migmatization, and consistent withhe dip of overlying units. The zircons are generally euhedral, up to00 �m long, and colourless to brown. CL images display oscillatoryoning with low-CL-response rims developed on some crystals. Sixnalyses are >5% discordant and one analysis (5.1) is interpreteds a core-rim mixture (Group D). These seven analyses are notonsidered geologically significant. Sixteen analyses of 16 zirconsGroup I) yield a weighted mean 207Pb*/206Pb* date of 1675 ± 9 MaMSWD = 1.7), interpreted as the age of magmatic crystallizationf the granitic protolith to the gneiss. Uranium contents indi-ated by these analyses are low to moderate (781–74 ppm). Twonalyses (Group P), which yield 207Pb*/206Pb* dates of 1641 and613 Ma, are interpreted to have undergone ancient radiogenic-b loss. One core analysis (Group X) yields a 207Pb*/206Pb* datef 1780 ± 9 Ma (1�), which is interpreted as the age of an inher-ted component. Four analyses of four rims yield a concordia agef 1193 ± 9 (MSWD = 1.4), interpreted as the age of a metamor-hic overprint. One discordant analysis (18.1) has a 207Pb*/206Pb*ate of c. 2340 Ma, which is a minimum age, indicating an inheritedomponent of probable Archean age.

.6.2. 194701Sample 194701 is a compositionally banded orthogneiss pre-

iously mapped as Munglinup Gneiss (GSWA, 2007), southwestf the Fraser Zone (Fig. 2). However, the U–Pb data indicate thatt belongs to the Biranup Zone. The orthogneiss exhibits a well-eveloped gneissosity and layer-parallel leucosomes, and containsarasitic folds to a large-scale southwesterly plunging antiform,hich forms part of a northeasterly trending, elongate dome struc-

ure. The zircons are euhedral, up to 300 �m long, with generallyigh aspect ratios up to 6:1, and are colourless to pale brown. CL

mages display oscillatory zoning, which in places is contorted.lder cores are present within some grains, and thin homoge-eous overgrowths mantle many crystals. Sixteen analyses (Group) are greater than 5% discordant, and are not considered geologi-ally significant. Four analyses of zircon rims (Group M), with lowh/U ratios of 0.004–0.12, yield a concordia age of 1203 ± 11 MaMSWD = 1.05), interpreted as the timing of a high-grade metamor-hic overprint. Twenty-three analyses (Group I) indicate moderateh/U ratios of 0.21–1.25, and yield a weighted mean 207Pb*/206Pb*ate of 1686 ± 8 Ma (MSWD = 1.9), interpreted as the crystalliza-ion age of the granitic protolith. Some of these analyses areocated on grains with disrupted internal textures, which mayeflect dissolution and reprecipitation of inherited zircon during a. 1686 Ma melting event. Three analyses of zircon cores (Group X)ield 207Pb*/206Pb* dates of 1749, 1766, and 1809 Ma, interpretedo reflect the ages of inherited material, although these crystals

ay have undergone some radiogenic-Pb loss during the 1680 Maelting event. Three analyses (Group P) yield 207Pb*/206Pb* dates

etween 1626 and 1657 Ma and are interpreted to have undergonencient radiogenic-Pb loss.

.6.3. 194725Sample 194725 is a coarse-grained, garnet-rich orthogneiss

rom approximately 8 km south of Uraryie Rock in the easterniranup Zone (Fig. 2). The orthogneiss contains K-feldspar phe-ocrysts and has a strong, northeasterly trending gneissic foliationnd well-developed lineation. On a regional scale, the outcropccurs in an area of large-scale, easterly trending, refolded folds,djacent to a major northerly trending shear zone. Zircon grainsrom this sample are euhedral, up to 400 �m long, with high aspect

atios, and are colourless to brown. CL images display cores withscillatory zoning which are overgrown by high-CL-response rims.even analyses >5% discordant are not considered further. Nine-een analyses of zircon rims (Group M), have low U contents40–108 ppm), and yield a strong negative correlation between

search 187 (2011) 223–247 233

common-Pb corrected 207Pb*/206Pb* dates and f204, implying a sys-tematic error in the 204Pb corrected dates. This issue is commonin ion microprobe analyses where average 204Pb counts are closeto or below the background levels. A regression through GroupM data onto concordia from the assumed common Pb composi-tion (207Pb/206Pb = 0.925 at 1200 Ma; Stacey and Kramers, 1975)yields an intercept date of 1205 ± 20 Ma (MSWD = 1.7). This result isinterpreted as the time of high-grade metamorphism. Because thecommon Pb content is low and the analyses are near-concordant,neither the form of the common-Pb correction nor its applicationhas significant effect on the calculated age. Nineteen analyses ofzircon cores (Group I) yield a weighted mean 207Pb*/206Pb* dateof 1671 ± 7 Ma (MSWD = 1.8), interpreted as the age of magmaticcrystallization of this granite.

3.6.4. 194726Sample 194726 is a medium to coarse-grained, garnet- and

biotite-rich equigranular orthogneiss of the eastern Biranup Zone,from Uraryie Rock (Fig. 2). This sample yielded colourless to yel-low zircons, which are euhedral and elongate. The grains exhibitidiomorphic zoning, and have homogeneous high-CL-responserims. One analysis >5% discordant and one analysis indicating highwithin-analysis variation in isotope ratios are not considered fur-ther (Group D). Four analyses (Group P) indicating 207Pb*/206Pb*dates of 1553–1386 Ma are interpreted to reflect loss of radio-genic Pb. Nineteen analyses (Group I) yield a weighted mean207Pb*/206Pb* date of 1666 ± 11 Ma (MSWD = 2.1), interpreted asthe age of magmatic crystallization of the granitic protolith. Sixrim analyses (Group M) yield a weighted mean 238U/206Pb* age of1162 ± 39 Ma (MSWD = 0.84). These analyses indicate very low Ucontents and consequently have elevated analytical uncertainties.Nevertheless, this date serves as the best estimate of the age of ametamorphic overprint on this rock.

3.6.5. 194735Sample 194735 is a garnet-biotite, quartzofeldspathic

migmatitic gneiss (Gwynne Creek Gneiss), taken from thewestern side of Gwynne Creek near Plumridge Lakes, east of theTropicana-Havana deposit (Fig. 2). The Gwynne Creek Gneissis a Mesoproterozoic cover sequence that outcrops along thefar northeastern edge of the Fraser Zone, and is dominated bypsammitic and semi-pelitic gneiss. It has a maximum depositionalage of 1483 ± 12 Ma and a significant 1675 Ma detrital component(Kirkland et al., 2011). The sampled outcrop consists of layered,finely laminated quartzofeldspathic gneiss with layer-parallelleucosomes, and semi-pelitic schist, all intruded by K-feldspar-richpegmatite veins, which are locally boudinaged and have dextralasymmetry (Fig. 4j). The zircons are euhedral, up to 400 �mlong, and colourless to pale brown. CL images display cores withoscillatory zoning which are overgrown by low-CL-response,homogeneous overgrowths (“dark overgrowth”). The dark over-growths are rimmed by homogeneous, high-CL-response zircon(“bright rims”) which are typically <5 �m thick (but in places upto 20 �m thick). The “bright rims” are found on all grains andheal brittle fractures that dislocate both oscillatory zoned coresand “dark overgrowths” (Fig. 5). Twelve analyses (Group D) thatare >1300 Ma and >5% discordant or core-rim mixtures are notconsidered further. Eight analyses (Group P) yield 207Pb*/206Pb*dates from 1634 to 1605 Ma and are interpreted to have lostminor amounts of radiogenic Pb. Thirty-four analyses of 34 oscil-

latory zircon cores (Group I) yield a concordia age of 1657 ± 5 Ma(MSWD = 1.3), interpreted as the age of magmatic crystallization ofthe igneous source of this detritus. The CL-bright rims (Group M2;see below) have very low U and Th concentrations consistent withprecipitation from metamorphic solutions (e.g. Pettke et al., 2005).

234 C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247

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wo analyses of “dark overgrowths” in two grains (Group M)ield a concordia age of 1270 ± 11 Ma (MSWD = 0.43), interpretedo date zircon growth during metamorphism. Three analyses, inhree grains, of “bright rims” (Group M2) that were large enougho analyse, yield a concordia age of 1193 ± 26 Ma (MSWD = 0.43).hese analyses indicate very low U contents and consequentlyave low precision. This date is interpreted to reflect the timingf zircon growth from hydrothermal fluids. The “bright rims” healrittle fractures that transect entire zircon crystals, including thedark overgrowths”. Brittle deformation in this rock occurred afterormation of “dark overgrowths” and prior to crystallization ofbright rims”, and is therefore constrained between 1270 and193 Ma.

. Lu–Hf and Sm–Nd

Values of εHf in zircon and baddeleyite crystals in the Biranupone range between evolved values of −12.2 to weakly depletedalues of 2.2, which are just slightly more radiogenic than CHURTable 2; Fig. 6). Two-stage model ages range from 2.2 to 3.2 Ga.here is a distinct temporal trend within the Biranup Zone Hf data,ith younger intrusions indicating more juvenile values. εHf values

rom zircon in two Fraser Zone granites plot near CHUR (−2.86 to0.06), with only one analysis (in 194711) more depleted, withn �Hf value of +6. TDM

C model ages in these granites average c.

.2 Ga. The most unradiogenic components of the Fraser Zone couldave sourced the most radiogenic components of the Biranup Zone.owever, a more likely scenario is a heterogeneous source for theraser Zone granites, of Biranup Zone Hf mixed with an additionaluvenile component added during Stage I.

(for location see Fig. 2). Ellipses indicate analysed regions labelled with the spot

Ten whole-rock Sm–Nd samples of Biranup Zone intrusionsyield εNdi values ranging from −15.24 to −1.11 (Table 3; Fig. 7),with a distinct temporal trend towards more juvenile valuesthrough time (Fig. 8). Most of the Sm/Nd ratios are fractionated andhigher than normal crustal values. This implies multiple remelting,or segregation of strongly LREE-enriched mineral phases (either byfractional crystallization or by retention as a residue in the sourceregion after partial melting) to produce a complementary LREE-depleted source. Two-stage model ages from Biranup Zone sampleswith unfractionated Sm/Nd ratios range from 2.3 to 2.6 Ga. Twosamples from the Fraser Zone yield εNdi values of −4.1 and −3.97and one of these samples, which is unfractionated, yields a two-stage model age of 2.1 Ga (Table 3).

5. Geochemistry of eastern Biranup Zone intrusive rocks

The c. 1710 Ma Bobbie Point Metasyenogranite (194737) isperaluminous and plots in the “within-plate” field on tectonicdiscrimination diagrams (Pearce et al., 1984; Fig. 8a; Table 4).The c. 1680 Ma granites (194728 and 194730) are peraluminousand overlap fields for “within-plate” and “volcanic arc” (Fig. 8a).The felsic members of the c. 1665 Ma mingled mafic-felsic rocks(the Eddy Suite; 194720, 194725, 194726, 194734, and 194735)are peraluminous to metaluminous ranging in composition fromgranite to granodiorite, and either overlap the “volcanic arc” and

“within-plate” fields, or lie within the “volcanic arc” field on vari-ous tectonic discrimination diagrams (Fig. 8a; Pearce et al., 1984).A REE plot for the 1710 Ma Bobbie Point Metasyenogranite showsheavy REE enrichment and a very distinctive negative Eu anomaly(Fig. 8b), defining a distinct “wing shape” profile. Similar patterns

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 235

Table 2Lu–Hf isotopic analysis of zircon and baddeleyite grains from the Fraser and Biranup Zones.

Sample no–grain no. spot no 207Pb*/206Pb* age (Ma) 176Hf/177Hf ± 1SE 176Lu/177Hf 176Yb/177Hf 176Hf/177Hf(i)a εHfa ±1SE TDM (crustal)b

Biranup Zone194720–2.1R 1658 0.281729 0.000010 0.000541 0.026571 0.281712 −0.6 0.4 2.42194720–2.1C 1658 0.281729 0.000016 0.001121 0.060132 0.281694 −1.3 0.6 2.46194720–4.1C 1646 0.281736 0.000012 0.001254 0.059127 0.281697 −1.4 0.4 2.46194720–4.1R 1646 0.281817 0.000016 0.001154 0.061642 0.281781 1.6 0.6 2.27194720–6.1C 1698 0.281754 0.000012 0.001013 0.050982 0.281721 0.6 0.4 2.37194720–6.1R 1698 0.281696 0.000023 0.000676 0.033322 0.281674 −1.1 0.8 2.47194720–7.1C 1663 0.281703 0.000008 0.000894 0.043890 0.281675 −1.8 0.3 2.50194720–7.1R 1663 0.281682 0.000012 0.000814 0.035869 0.281656 −2.5 0.4 2.54194720–9.1C 1647 0.281730 0.000015 0.001514 0.075555 0.281683 −1.9 0.5 2.49194720–9.1R 1647 0.281684 0.000014 0.000967 0.041971 0.281654 −2.9 0.5 2.55194720–11.1C 1640 0.281669 0.000012 0.000829 0.040970 0.281643 −3.5 0.4 2.58194720–11.1R 1640 0.281709 0.000011 0.000605 0.030297 0.281690 −1.8 0.4 2.48194720–14.1C 1623 0.281642 0.000011 0.000974 0.046985 0.281612 −5.0 0.4 2.66194720–14.1R 1623 0.281682 0.000006 0.000699 0.034641 0.281661 −3.2 0.2 2.56194720–17.1C 1670 0.281659 0.000010 0.000966 0.046717 0.281628 −3.3 0.3 2.60194720–17.1R 1670 0.281750 0.000035 0.001609 0.057272 0.281699 −0.8 1.2 2.44194720–19.1C 1640 0.281663 0.000021 0.000949 0.042558 0.281634 −3.8 0.7 2.60194720–19.1R 1640 0.281686 0.000014 0.000637 0.029926 0.281666 −2.6 0.5 2.53194731–02.1 1660 0.281705 0.000015 0.001086 0.055526 0.281671 −2.0 0.5 2.51194731–03.1 1697 0.281676 0.000009 0.001619 0.065196 0.281624 −2.9 0.3 2.59194731–06.1 1732 0.281720 0.000015 0.001003 0.053659 0.281687 0.2 0.5 2.42194731–09.1 1697 0.281449 0.000028 0.002715 0.097947 0.281362 −12.2 1.0 3.18194731–13.1 1666 0.281639 0.000021 0.002373 0.084676 0.281564 −5.7 0.7 2.74194731–22.1 1701 0.281603 0.000020 0.001605 0.056943 0.281551 −5.3 0.7 2.75194731–28.1 1677 0.281704 0.000029 0.001789 0.079816 0.281647 −2.5 1.0 2.55194731–30.1 1717 0.281679 0.000016 0.001056 0.056658 0.281645 −1.7 0.6 2.53194721–1.1 1668 0.281767 0.000009 0.000123 0.006396 0.281763 1.4 0.3 2.29194721–2.1 1657 0.281746 0.000009 0.000195 0.009103 0.281740 0.3 0.3 2.35194721–3.1 1688 0.281775 0.000010 0.000068 0.004378 0.281773 2.2 0.4 2.26194721–4.1 1657 0.281757 0.000007 0.000096 0.005368 0.281754 0.8 0.3 2.32194721–7.2 1665 0.281763 0.000011 0.000087 0.004925 0.281760 1.2 0.4 2.30194721–8.2 1639 0.281764 0.000012 0.000080 0.005014 0.281762 0.7 0.4 2.32194721–11.2 1666 0.281782 0.000008 0.000089 0.005457 0.281779 1.9 0.3 2.26194721–14.2 1662 0.281755 0.000015 0.000138 0.005759 0.281751 0.9 0.5 2.33194721–15.2 1652 0.281798 0.000012 0.000110 0.004932 0.281795 2.2 0.4 2.23194721–20.2 1660 0.281768 0.000008 0.000054 0.003085 0.281766 1.4 0.3 2.29194701–3.1 1661 0.281577 0.000005 0.000399 0.020482 0.281564 −5.8 0.2 2.75194701–14.1 1707 0.281585 0.000010 0.000639 0.034387 0.281564 −4.7 0.3 2.72194701–33.1 1658 0.281649 0.000007 0.000662 0.034189 0.281628 −3.6 0.2 2.60194701–34.1 1686 0.281652 0.000011 0.000703 0.039937 0.281630 −2.9 0.4 2.58194701–36.1 1724 0.281623 0.000007 0.001293 0.071678 0.281581 −3.8 0.2 2.67194701–37.1 1680 0.281607 0.000009 0.000738 0.040770 0.281584 −4.7 0.3 2.69194701–41.1 1659 0.281635 0.000010 0.000632 0.033813 0.281615 −4.0 0.3 2.63194701–43.1 1661 0.281640 0.000011 0.001322 0.071950 0.281598 −4.6 0.4 2.67194737–1.1 1766 0.281477 0.000010 0.001359 0.067403 0.281432 −8.1 0.3 2.98194737–2.1 1719 0.281543 0.000011 0.002426 0.135297 0.281464 −8.0 0.4 2.93194737–10.1 1721 0.281494 0.000009 0.001204 0.060559 0.281455 −8.3 0.3 2.95194737–11.1 1700 0.281483 0.000013 0.000997 0.048376 0.281451 −8.9 0.5 2.97194737–14.1 1715 0.281441 0.000012 0.001201 0.061876 0.281402 −10.3 0.4 3.07Fraser Zone194719–9.1 1303 0.281942 0.000010 0.001073 0.056821 0.281916 −1.4 0.3 2.19194719–11.1 1307 0.281970 0.000009 0.000770 0.039308 0.281951 −0.1 0.3 2.11194719–15.1 1285 0.281992 0.000010 0.001156 0.064973 0.281964 −0.1 0.3 2.09194719–16.1 1302 0.281921 0.000009 0.001120 0.054905 0.281893 −2.2 0.3 2.24194719–20.1 1299 0.281984 0.000009 0.001450 0.095077 0.281948 −0.3 0.3 2.12194719–22.1 1295 0.281910 0.000006 0.001015 0.053009 0.281885 −2.7 0.2 2.26194719–24.1 1313 0.281966 0.000011 0.002514 0.130979 0.281904 −1.6 0.4 2.21194711–4.1 1306 0.282139 0.000016 0.000736 0.040547 0.282121 5.9 0.6 1.72194711–8.1 1279 0.281960 0.000009 0.000671 0.036225 0.281944 −1.0 0.3 2.14194711–10.1 1318 0.281881 0.000009 0.000641 0.034756 0.281865 −2.9 0.3 2.29194711–11.1 1300 0.281929 0.000008 0.000637 0.034203 0.281913 −1.5 0.3 2.20194711–16.1 1283 0.281963 0.000007 0.000815 0.045173 0.281943 −0.9 0.2 2.14194711–19.1 1317 0.281902 0.000008 0.000989 0.040880 0.281877 −2.5 0.3 2.27194711–21.1 1261 0.281965 0.000011 0.000738 0.040665 0.281947 −1.2 0.4 2.15194711–26.1 1321 0.281882 0.000010 0.000546 0.029657 0.281868 −2.7 0.3 2.29

Cain.77Hf r

hoii

and R, appended to the spot number refer to grain centre and edge, respectively.a 176Hf/177Hfi(i), εHf(t) and T(DM) are calculated using the 207Pb/206Pb age of the grb T(DM) crustal is calculated using a two-stage evolution assuming a mean 176Lu/1

ave been recognised within two-mica granites and leucogranitesf the European Hercynides (Webb et al., 1985), and leucogran-tes in the Central Alps (Schaltegger and Krähenbühl, 1990), andnterpreted as magmatic enrichment in a high-silica melt with frac-

atio of crust = 0.015.

tional crystallization dominated by feldspars. Elevated levels ofHREE are not consistent with fractionation of a HREE-rich phasesuch as hornblende or garnet and likely reflect paragenesis atmoderate to low pressure. The HREE enrichment trend cannot be

236 C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247

Table 3Whole rock Nd isotopic data for samples from the Fraser and Biranup Zones.

Samples Unit Age Sm Nd 147Sm/144Nda 143Nd/144Ndb Error (×10−6) 143Nd/144Ndi �Ndi TDM TDM·2stg

194701 Biranup 1686 2.43 12.41 0.118122 0.511445 5 0.510134 −6.36 2.57 2.59194720 Biranup 1665 5.29 27.68 0.115566 0.511573 4 0.510308 −3.45 2.31 2.34194721 Biranup 1664 2.08 9.24 0.136198 0.511918 5 0.510429 −1.11 2.26 2.16194725 Biranup 1671 6.41 28.42 0.136285 0.511582 5 0.510085 −7.67 2.87 2.68194726 Biranup 1666 9.46 42.00 0.136106 0.511639 5 0.510149 −6.55 2.76 2.59194728 Biranup 1683 9.18 51.01 0.108752 0.511436 4 0.510233 −4.46 2.36 2.44194730 Biranup 1676 9.83 46.88 0.126786 0.511627 5 0.510230 −4.70 2.51 2.45194731 Biranup 1689 3.00 18.87 0.096131 0.511257 5 0.510190 −5.16 2.34 2.50194737 Biranup 1708 1.83 6.48 0.170506 0.511567 5 0.509651 −15.24 4.93 3.29194735 Gwynne Creek 1657 5.95 35.67 0.100817 0.511444 4 0.510346 −2.92 2.19 2.30194711 Fraser 1297 5.85 32.31 0.109429 0.511685 5 0.510753 −4.10 2.03 2.11

0.5

f 0.511

awzruhf

as11ritmo

(htmTofeds(ZfoewLTghgtoa

6

6

e

194719 Fraser 1298 13.72 59.04 0.140508

a 1 Sigma uncertainty of 0.5%.b Uncertainties are 2 sigma within run precision. Normalized to a La Jolla value o

scribed to addition during post-magmatic fluid–rock interactionith F-bearing fluids (e.g. Webb et al., 1985), because the mean

ircon �Hf is decoupled from whole-rock εNd. Zircon εHf is moreadiogenic than predicted from whole-rock εNd, indicating thatnaltered c. 1710 Ma zircon crystallized through a reservoir withigh Lu/Hf decoupled from Sm/Nd. Therefore, elevated HREE is a

eature acquired during zircon crystallization.Both 1680 and 1665 Ma magmatic rocks show LREE enrichment

nd more subdued Eu anomalies (Fig. 8b). Biranup Zone intru-ive rocks have increasing Mg# with decreasing age from 1710 to665 Ma (Fig. 8c). The rocks also display decreasing Eu/Eu* from710 Ma to 1665 Ma (with coefficient of determination for a linearegression of 0.61) consistent with increasing fO2 and/or increas-ng temperature with time (Drake and Weill, 1975; Fig. 8d). Theserends are compatible with a mixing process that had an increasing

antle component (and/or progressively decreasing contributionf evolved crust) in the felsic magmatism through time.

A dataset of all eastern Biranup Zone intrusive rocksthis work and GSWA online geochemisty database –ttp://geochem.doir.wa.gov.au/geochem) indicates a calc-alkalineo predominant high-K calc-alkaline trend, which ranges from

etaluminous to weakly peraluminous (Fig. 8e). A Ta/Yb versush/Yb plot is useful because these ratios are largely independentf variations caused by the degree of partial melting and crystalractionation (Fig. 8f). Ta/Yb is a measure of the degree of mantlenrichment or depletion relative to N-MORB. Addition of a sub-uction component such as hydrous fluid from dewatering of thelab, results in the addition of Th, but not Ta, to the mantle sourceproducing a vertical trend). Plot 8f indicates that the Biranupone gabbros have an active continental margin affinity with theelsic rocks of the zone influenced by subduction zone enrichmentr crustal contamination, or both. In MORB-normalized trace-lement diagrams, the most primitive plutonic rocks (gabbrosith Mg# = 51–60; Ni = 12–176 ppm; Cr = 149–374 ppm) show

ILE and LREE enriched patterns with troughs at Nb–Ta andi, consistent with subduction-related magmas (GSWA onlineeochemisty database; samples 183685, 183683, 183681, 183678;ttp://geochem.doir.wa.gov.au/geochem). Field, petrographic,eochemical, and isotopic evidence (initial εNd values from −3o −15) support a hybrid nature for the c. 1665 Ma magmas,riginating through interaction between mantle-derived magmasnd crustal materials.

. Discussion

.1. Provenance of the Biranup Zone

Previous studies of the Albany-Fraser Orogen have favoured anxotic setting for the Biranup Zone, outboard of the Yilgarn Craton

11955 5 0.510758 −3.97 2.31 2.10

850. Single and two stage model ages are after Liew and Hofmann (1988).

margin, based on the absence of Archean zircon inheritance and thelack of late Paleoproterozoic magmatism within the Yilgarn Cra-ton (Nelson et al., 1995; Spaggiari et al., 2009). Correlations havebeen suggested between the Biranup Zone and the western GawlerCraton and the Warumpi Province of the southern Arunta Oro-gen (Spaggiari et al., 2009). The Warumpi Province initially formedas a magmatic arc between 1690–1670 Ma during the ArgilkeIgneous Event, associated with high-K calc-alkaline magmatism(Scrimgeour et al., 2005a,b). Further magmatism and accretionof the arc to the Aileron Province (North Australian Craton)occurred during the 1640–1635 Ma Liebig Orogeny (Scrimgeouret al., 2005b). On a continent scale the Biranup Zone may have a con-nection to the Warumpi Province, for example as part of the sameextensive magmatic arc system and plate margin (e.g. Betts et al.,2008), although the Lu–Hf and Sm–Nd data presented here suggestthat it was not exotic and evolved in proximity to the Yilgarn Craton,rather than to the Warumpi Province or the Gawler Craton. Further-more, the existence of an Archean fragment with a typical Yilgarngranite age of 2684 ± 11 Ma (metasyengranite sample 194709), sur-rounded by Biranup Zone rocks, supports the interpretation that theBiranup Zone was not exotic.

The Hf isotopic data from the oldest eastern Biranup Zone intru-sive rock (Bobbie Point Metasyenogranite) spans a range of initialHf isotopic values that encompass Yilgarn Craton-like values tothose representative of more juvenile crust. The psammitic gneisssample (194731) containing a significant c. 1689 Ma detrital zirconage component also displays Hf values that are only slightly moredepleted than Yilgarn Craton crust. Younger magmatism in theBiranup Zone becomes increasingly dominated by more depletedvalues. This pattern suggests melt production from mixed sources:a component with crustal residence ages of > c. 3100 Ma, and anadditional juvenile component. This juvenile input progressively,and thoroughly, diluted the isotopic signal from the basementthrough time and reflects the influence of Paleoproterozoic juvenileinput into non-radiogenic Archean sources (Fig. 6).

Such a temporal trend can also be seen within individualintrusions. For example, zircon rims in metagranodiorite sample194720, when outside of analytical uncertainty, always indicatehigher εHf values than zircon cores (Fig. 9), implying incorporationof material with a higher Lu/Hf ratio through time. Such a tem-poral trend towards more juvenile values is also replicated in thewhole-rock Nd data, with the most juvenile melts having epsilonvalues around −1. The most evolved granite in the Biranup Zone,the Bobbie Point Metasyenogranite, has a εNdi value of −15.24,

which is within the range of Yilgarn felsic melts at c. 1700 Ma(Champion et al., 2006; Champion and Cassidy, 2007). It is alsovery similar to the Nd isotopic composition at 1700 Ma of theMunglinup Gneiss, which reflects reworked Yilgarn crust (Spaggiariet al., 2009). The majority of the eastern Biranup Zone and all central

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 237

Table 4Whole-rock analyses of Fraser and Biranup Zone geochronology samples.

Fraser Biranup

194711 194719 194728 194730 194737 194720 194725 194726 194734 194735 194721Age (Ma) 1297 1298 1683 1676 1708 1665 1671 1666 1675 1657 1664

Weight percentSiO2 69.69 72.44 73.63 69.34 75.96 66.25 66.10 64.93 68.82 69.97 47.64Al2O3 14.12 12.42 12.67 13.18 11.90 14.59 14.42 14.37 13.36 14.12 15.76Fe2O3(t) 4.45 4.25 2.17 4.71 0.91 5.89 6.32 6.87 5.66 3.25 11.21FeO 3.10 2.55 1.07 3.12 0.69 3.88 3.49 4.14 3.57 2.19 8.39MgO 0.71 0.62 0.30 0.77 0.10 1.15 1.53 1.17 1.04 0.59 13.02CaO 2.36 1.46 1.46 1.88 0.03 3.38 3.90 4.03 2.36 2.10 9.04Na2O 2.61 2.86 2.50 2.82 2.95 2.51 2.37 2.73 2.20 2.85 1.74K2O 4.86 4.07 5.11 4.70 5.57 4.14 3.56 3.33 4.10 4.45 0.51TiO2 0.524 0.48 0.33 0.56 0.109 0.792 0.82 0.86 0.73 0.33 0.80P2O5 0.14 0.17 0.06 0.32 0.02 0.16 0.21 0.22 0.18 0.13 0.12MnO 0.11 0.18 0.04 0.07 0.00 0.10 0.11 0.12 0.11 0.05 0.16LOI 0.24 0.92 1.54 1.44 2.37 0.82 0.46 1.12 1.26 1.98 −0.01

Parts per millionCs 5.83 7.25 5.44 7.22 0.32 2.17 6.69 5.00 8.00 1.94 0.69Rb 178.0 295.7 238.4 279.6 181.2 129.9 163.8 130.6 196.1 161.5 14.2Ba 967 260 989 804 115 1041 887 1128 739 905 190Sr 141.0 51.9 115.4 130.2 11.2 164.1 222.0 253.7 131.6 175.9 253.3Pb 32.0 41.0 31.0 19.0 6.0 22.2 19.2 18.1 29.0 27.0 6.0Th 14.7 15.0 21.6 32.3 13.2 4.3 15.5 8.5 18.6 11.3 1.6U 2.0 3.7 4.3 7.7 3.2 1.1 1.9 1.8 4.0 1.0 0.3Zr 222 229 308 434 218 262 299 604 309 185 63Hf 6.2 6.9 8.2 11.5 8.1 6.7 7.8 13.5 8.1 4.8 1.7Ta 0.7 1.5 0.8 1.3 1.2 0.7 0.9 0.9 1.1 0.6 0.4Y 32.0 107.3 54.1 71.0 64.0 29.0 40.6 51.6 42.9 30.5 17.0Nb 10.7 23.4 11.0 23.3 29.2 12.0 14.3 18.2 12.6 8.8 2.9Sc 12 17 8 13 2 17 18 22 16 7 26Cr 11 10 2 12 24 44 21 30 3 843Ni 6 5 2 7 3 11 10 10 12 2 572V 33 25 11 35 76 69 63 58 16 130Ga 18.0 19.8 17.1 21.7 20.1 20.7 19.9 19.5 19.3 18.1 15.8Zn 59 93 35 56 13 75 81 91 78 43 82Cu 9 17 14 8 18 14 17 17 2 126

La 42.50 59.36 70.57 48.96 7.38 33.45 25.53 31.23 24.02 51.53 8.84Ce 84.60 131.20 132.80 186.70 17.40 64.97 94.36 94.40 95.03 94.03 19.16Pr 10.35 18.17 14.85 13.46 1.83 8.26 7.69 11.01 7.25 9.85 2.28Nd 36.80 66.50 55.98 54.80 6.90 27.59 31.97 52.60 28.40 37.80 10.58Sm 7.04 16.08 10.65 11.40 1.90 5.44 7.46 10.90 6.25 6.10 2.45Eu 1.62 0.72 1.58 1.53 0.08 1.93 1.65 2.69 1.15 1.05 0.96Gd 6.07 16.24 9.27 10.62 3.64 5.84 6.97 10.06 5.92 5.32 2.66Tb 0.90 2.72 1.42 1.78 0.97 0.89 1.07 1.46 1.02 0.78 0.43Dy 5.17 16.79 8.48 11.01 8.03 4.89 6.53 8.64 6.92 4.74 2.63Ho 1.01 3.50 1.69 2.31 1.95 0.97 1.33 1.70 1.44 0.97 0.56Er 2.94 9.86 4.69 6.81 6.42 2.72 3.81 4.74 4.29 2.67 1.56Tm 0.42 1.45 0.39 0.53 0.24Yb 2.70 9.04 4.19 7.00 7.00 2.35 3.44 4.25 4.10 2.38 1.61Lu 0.43 1.42 0.61 1.06 1.05 0.40 0.56 0.63 0.68 0.34 0.24

Eu/Eu* 0.755 0.136 0.486 0.423 0.095 1.046 0.697 0.785 0.578 0.561 1.147Mg# 24.10 22.50 21.60 26.90 17.80 27.90 32.40 25.20 26.70 26.50 69.70

La/Nb 4.0 2.5 6.4 2.1 0.3 2.8 1.8 1.7 1.9 5.9 3.0La/Yb 15.74 6.57 16.84 6.99 1.05 14.23 7.42 7.35 5.86 21.65 5.49La/Sm 6.04 3.69 6.63 4.29 3.88 6.15 3.42 2.87 3.84 8.45 3.61Sr/Ba 0.15 0.20 0.12 0.16 0.10 0.16 0.25 0.22 0.18 0.19 1.33

Major elements were determined by wavelength-dispersive XRF on fused disks, precision is better than ±1%. Loss on Ignition (LOI) was determined by gravimetry aftercombustion. Iron abundances were determined by digestion and electrochemical titration (Shapiro and Brannock, 1962). Trace elements (Ba, Cr, Cu, Ni, Sc, V, Zn, and Zr)w happe( r thanM

BGtnovrt

ere determined by wavelength-dispersive XRF on a pressed pellet (Norrish and CEggins et al., 1997; as modified by Pyke, 2000). Precision for trace elements is bette

orris and Pirajno (2005).

iranup Zone samples are more depleted relative to typical Easternoldfields Superterrane (Yilgarn Craton) felsic crust. According to

he Liew and Hofmann (1988) depleted-mantle model, uncontami-143 144

ated depleted mantle at 1665 Ma should have a Nd/ Nd value

f 0.506610, whereas the most juvenile sample has a 143Nd/144Ndalue of 0.510429, and is evidently still affected by crustal mate-ial. Assuming an initial Nd isotope composition similar to that ofhe Bobbie Point Metasyenogranite, about 70% of depleted mantle

ll, 1977), Cs, Ga, Nb, Pb, Rb, Sr, Ta, Th, U, Y, and the REEs were analysed by ICP-MS±10%. Details of standards used for major and trace element analysis are given in

input is required to explain the most juvenile melts of the BiranupZone.

Only one eastern Biranup Zone sample (194734) retains an

inherited zircon as evidence of an earliest Paleoproterozoic orArchean source component (in the form of a single discordant anal-ysis). Magmatic temperatures at which the intrusive rocks of theeastern Biranup Zone were emplaced can be estimated using theZr-saturation thermometer (Watson and Harrison, 1983). Calcu-

238 C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247

FF(t

l8xmpqi

6

lz

Fig. 7. εNdi evolution diagram for the Albany-Fraser Orogen, compared to thefield (shaded) for Eastern Goldfields Superterrane. The Eastern Goldfields Supert-errane field is based on felsic samples with normal crustal ratios from thecompilation in the Geological Survey of Western Australia’s online geochemi-

ig. 6. (a) Initial 176Hf/177Hf evolution diagram for seven samples from the Albany-raser Orogen. (b) Event signature plot which shows the general trend of reworkingdownwards), mixing (horizontal), or juvenile input (upwards). (c) Stacked his-ograms for juvenile (>0), intermediate (0 to −5) and evolved εHf (<−5).

ated temperatures fall in the range 797–882 ◦C, with an average of28 ◦C. These are minimum estimates because the general lack ofenocrystic zircons in these rocks suggests that the primary mag-as were undersaturated with respect to Zr. It appears likely that

re-existing zircon has been completely reabsorbed during subse-uent melting events, hence essentially no record of Archean zircon

nheritance has been found.

.2. The Zanthus Event

In the Ponton Creek area of the eastern Biranup Zone, foldedeucosomes in a migmatitic monzogranite (194730) yield a U–Pbircon date of 1676 ± 6 Ma, which is within uncertainty of the crys-

cal database (GeoChem Extract; http://geochem.doir.wa.gov.au/geochem/). CentralBiranup Zone, Recherche Supersuite, and Munglinup Gneiss samples are fromSpaggiari et al. (2009). The depleted mantle (DM) model is from Goldstein et al.(1984).

tallization age of cross-cutting axial planar leucosomes (Fig. 4d),dated at 1679 ± 6 Ma (194729). Migmatization must have immedi-ately preceded folding, with subsequent leucosome injection alongthe axial planes of the folds. Although the younger leucosomes yieldan older isotopic age, the two results agree to within uncertaintyand imply deformation at 1678 ± 4 Ma.

These data, and the outcrop relationships, thus define a pre-viously unrecognised deformation and high-grade metamorphicevent, here named the Zanthus Event. The rocks that retain evi-dence of this event in the Ponton Creek area occur within the centreof a geophysically anomalous zone that is about 85 km long and25 km wide, and is interpreted as a tectonic slice within the oro-gen. The slice is characterized by a northwest-trending magneticfabric, whereas the dominant regional trend of the eastern Albany-Fraser Orogen is to the northeast. This northwesterly fabric matchesthe northwesterly trend of folds in outcrop. The slice has a distinc-tive aeromagnetic pattern with open to tight, non-cylindrical folds.This suggests that the Zanthus Event was not a local occurrence,but affected at least the entire tectonic slice. The orientation ofthe fabric, folds, axial planar leucosomes, and melt-filled dextralshears, implies northeast–southwest directed (present orienta-tion) shortening during the Zanthus Event. The Zanthus Event wasfollowed by intrusion of the Eddy Suite of peraluminous to met-aluminous, granitic to gabbroic rocks, with distinct mingling andhybridisation textures. These mingled mafic and felsic rocks crys-tallized at 1665 ± 4 Ma (weighted mean date for samples 194720and 194721).

6.3. A tectonic model for the Biranup Zone

A tectonic model for the Biranup Zone must account for thefollowing: (1) metaluminous, to weakly peraluminous magmatismshowing mineralogical, petrographic and chemical characteristics

of high-K calc-alkaline suites, (2) Hf and Nd isotopic signatures thatindicate a progressive increase of juvenile material into Archeanunradiogenic crust, and (3) chemistry that implies progressiveincreases in the Fe and Mg content of felsic magmas and a decreasein the Eu/Eu* through time.

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 239

Fig. 8. Geochemical plots for Albany-Fraser rocks. (a) Rb versus Y + Nb tectonic discrimination diagram, syn-COLG = syn-collisional granite; VAG = volcanic arc granite;WPG = within plate granite; ORG = orogenic granite (Pearce et al., 1984). Symbols as in part b. (b) chondrite-normalised trace-element plot for the various magmatic rocks ofthe Albany-Fraser Orogen (Boynton, 1984). (c and d) geochemical trends with age for felsic rocks within the Biranup Zone. (e) K O versus SiO plot for all magmatic rocksi geochs up Zo( arateA 2004)

emcadi

n the Biranup Zone (GSWA online geochemical database; GeoChem Extract; http://ample numbers. (f) Th/Yb–Ta/Yb discrimination diagram (Pearce, 1982) for all BiranC), within plate enrichment (W) and fractional crystallization (F). Dashed lines sepctive continental margin and oceanic island arc fields modified after Schulz et al. (

A post-orogenic lithospheric extensional setting influenced byxtensive crustal contamination of basaltic magmas derived from

antle source(s) (e.g. Permian magmatism in the European Her-

ynian belt; Rottura et al., 1998) is consistent with the chemicalnd isotopic signatures of the magmas. However, an active sub-uction margin is more favourable because it not only explains the

sotopes and chemistry, but also accounts for the regional compres-

2 2

em.doir.wa.gov.au/geochem/). Those specimens from this work are indicated withne magmas. Vectors indicate the influence of subduction (S), crustal contaminationthe boundaries of the tholeiitic (TH), calc-alkaline (CA) and shoshonitic (SH) field..

sional deformation under granulite facies conditions, and the rapidbasin formation, infill, and intrusion by near-contemporaneous fel-

sic magmas.

The presence of fragments of Archean crust in the BiranupZone, and a Yilgarn-like source for these Paleoproterozoic magmas,favours a Yilgarn Craton margin subduction model with a vol-canic arc to back-arc system. An active margin model is presented

240 C.L. Kirkland et al. / Precambrian R

F1

ddwSsmapciscaEtwTpεc

AgSiri2YtBmws

6e

iwR(To

ig. 9. εHf values for centre and edge analyses on the same grains from sample94720.

iagrammatically in Fig. 10. At c. 1710 Ma, westward-dipping sub-uction (present-day coordinates) produced an early suite of melts,hich crystallized in the shallow crust of the Yilgarn Craton margin.

ubsequent slab roll-back outboard of the margin led to back-arcpreading and a greater influence of the asthenosphere on the mag-as. The associated basin was filled by sediments from c. 1710 Ma

rc magmatism and parts of this sedimentary pile underwentrogressive dehydration-related melting and deformation due torustal thickening. Later melts produced within the back-arc regionncorporated a greater mantle component, due to increasing exten-ion which allowed greater asthenospheric upwelling. These meltsrystallized at c. 1680 Ma and the rocks were rapidly migmatizednd deformed during the Zanthus Event at 1678 Ma. The Zanthusvent was associated with northeast–southwest (present orienta-ion) compression that may represent a period of tectonic switchinghen slab roll-back stalled, possibly driven by seamount arrival.

he youngest suite of intrusive rocks (c. 1665 Ma Eddy Suite) showrogressively more juvenile influence, through an increase in Mg#,Hf, and εNd, with decreasing age. This implies a return to signifi-ant back-arc extension.

The effect of back-arc extension and slab roll-back was to riftrchean fragments from their original locations on the Yilgarn mar-in and isolate them within Paleoproterozoic Biranup Zone rocks.ample 194709 dates the magmatic crystallization of one of thesesolated Archean fragments at 2684 ± 11 Ma. Such ages are widelyecognised within the Yilgarn Craton, including the high-Ca gran-tes of the Eastern Goldfields Superterrane (Cassidy and Champion,004; Cassidy et al., 2006), the Southern Cross Domain of theouanmi Terrane (e.g. GSWA 168963; Nelson, 2001), and withinhe Northern Foreland of the Albany-Fraser Orogen (GSWA 184120;odorkos and Wingate, 2008b). The location of this Archean frag-ent implies that much of the Biranup Zone must have formedithin the back-arc region of a Paleoproterozoic subduction zone

ystem.

.4. Mesoproterozoic overprinting of the Biranup Zone andmplacement of the Fraser Zone

The c. 1305–1290 Ma Fraser Zone represents a structurally mod-fied, thick piece of hot mafic crust presently in fault contact

ith the Biranup Zone. Two granitic samples within the Fraserange Metamorphics yield a weighted mean date of 1298 ± 4 MaMSWD = 0.045), interpreted as the age of magmatic crystallization.his result refines the date of 1293 ± 9 Ma for the crystallizationf post-D1 granites (Clark et al., 1999). The foliation within these

esearch 187 (2011) 223–247

two samples most likely formed shortly after their emplacement,consistent with dates from disturbed zircon grains, which suggesta radiogenic-Pb loss event soon after crystallization (Clark et al.,1999; De Waele and Pisarevsky, 2008). Hf isotopic data from thesegranites imply reworking of an isotopically similar Hf source tothe Biranup Zone, but with some indication of additional juvenilematerial.

Within the eastern Albany-Fraser Orogen, 1298 ± 4 Ma oscilla-tory zoned zircons, indicating Mesoproterozoic magmatism, arerestricted to the Fraser Zone and Recherche Supersuite. In the east-ern Biranup Zone, the crystallization mechanism and timing ofzircon growth was distinctly different, with younger metamorphicrims that mantle inherited zircon cores. No evidence of RechercheSupersuite intrusive rocks or Stage I metamorphism resultingin significant zircon growth has been found within the easternBiranup Zone. However, Stage II zircon overgrowth is recorded at1197 ± 8 Ma (weighted mean of six samples; MSWD = 1.2) in theeastern Biranup Zone. These zircon overgrowths show a range ofTh/U ratios, from values similar to those in magmatic crystals tolower values of around 0.001 (Fig. 3). The Stage I events responsiblefor zircon growth within the Fraser Zone and Recherche Supersuitegranites do not appear to have produced a significant volume ofsilicate melt in the eastern Biranup Zone.

The central Biranup Zone contains 1690–1660 Ma metagraniticand metasedimentary rocks that yield identical Paleoprotero-zoic magmatic and depositional ages to the eastern BiranupZone (Spaggiari et al., 2009). In contrast to the eastern BiranupZone, Recherche Supersuite granitic rocks that intruded centralBiranup Zone rocks include Coramup Hill (1283 ± 13 Ma; Nelson,1995f), Mount Burdett (1299 ± 18; Nelson, 1995e), and ObservatoryPoint (1322 ± 11 Ma; Bodorkos and Wingate, 2008a; 1288 ± 12 Ma;Nelson, 1995d; Fig. 2). Subsequent high-temperature metamor-phism during Stage II, predominantly between 1200 and 1180 Ma,is recorded by metamorphic rims on zircons from orthogneisses,and partial melts and intrusions of felsic and pegmatitic materialinto orthogneisses (Nelson, 1995b; Spaggiari et al., 2009).

A feasible explanation for the apparent lack of Stage I ages inthe eastern Biranup Zone is provided by the crustal architecture(Fig. 2), where exhumed fault-bounded slices of eastern BiranupZone rocks may not have been in the vicinty of Stage I events. Thecentral Biranup Zone rocks that are intruded by Recherche Super-suite granitic rocks are further outboard than the eastern BiranupZone fault slices (Fig. 2), and hence may have been broadly along-stike from the Fraser Zone intrusions.

Zircon overgrowths provide a detailed picture of the Meso-proterozoic evolution of the eastern Albany-Fraser orogen. At1270 ± 11 Ma, high-U homogenous zircon overgrowths developedon 1657 ± 5 Ma oscillatory zoned detrital zircon cores (sample194735; Fig. 5) in the Gwynne Creek Gneiss. These crystals werethen fractured and mantled by 1193 ± 26 Ma, homogeneous, low-Urims which in-filled the fractures. The oscillatory zoned fragmentsare not rotated and zoning is continuous although displaced bythe fracture-filling zircon. Both the internal structure of the frac-tured zircons and the very low Th content (below detection) ofthe in-filling zircon suggest that the fractures were sealed by c.1193 Ma zircon precipitated from hydrothermal fluids. Very similarfracture-fill features in zircon have been reported from migmatiticrocks elsewhere (Rimsa et al., 2007). Fractures transecting the zir-con crystals are thus bracketed between c. 1270 Ma zircon growthand 1197 Ma zircon rims, implying a period of brittle deformationrelating to crustal uplift and cooling between these zircon growth

phases. The timing of this uplift is consistent with that in the FraserRange Metamorphics, which were uplifted to less than ∼400 MPasome time between 1288 and 1260 Ma (Fletcher et al., 1991; Clarket al., 1999). Uplift at this time is also consistent with the pres-ence of Stage I basement-derived detrital zircons within the Mount

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 241

Fig. 10. Schematic diagrams showing the evolution of the Biranup Zone. (a) At c. 1710 Ma subduction under the Yilgarn Craton produced a magmatic arc on its margin. (b)During the period 1700–1690 Ma, continued convergence and slab roll-back with voluminous felsic magmatism produced the accommodation space for a back-arc basin,which was filled with near-coeval volcanic detritus. (c) Tectonic switching during the Zanthus Event, possibly driven by seamount arrival, compressed and deformed theback-arc region. (d) Renewed slab roll-back and continued attenuation of the Yilgarn margin resulted in asthenospheric upwelling, bimodal magmatism, and formation of amingled norite and granodiorite suite of intrusive rocks. This process resulted in Archean remnants becoming isolated from their ancestral home on the Yilgarn Craton byadditions of predominantly juvenile crust.

2 rian R

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42 C.L. Kirkland et al. / Precamb

agged Formation, which overlies the eastern Nornalup Zone, andas interpreted to reflect extension and uplift prior to Stage II. Thisrovided key evidence for division of the Albany-Fraser Orogeny

nto two stages (Clark et al., 2000). These results show that thewynne Creek Gneiss, the Fraser Zone, and the Mount Ragged For-ation, shared a widespread uplift and cooling event, some time

etween Stages I and II. This could, therefore, also mark a time ofajor structural modification of the eastern part of the orogen.There is no evidence of Stage II events within the Fraser Zone,

lthough Stage II ages are prolific across the entire Biranup Zone.reservation of pre-1250 Ma Rb–Sr cooling ages in the Fraser Rangeetamorphics also indicates a lack of Stage II resetting in that area

Fletcher et al., 1991). Nonetheless, an earlier connection betweenhe Fraser and Biranup Zones is implied from inherited zircon agesithin intrusive units of the Fraser Range Metamorphics which,

lthough limited, are similar to the ages of intrusions within theiranup Zone, and inherited Paleoproterozoic material within it.his is compatible with the Fraser Range intrusions being emplacedhrough rocks of similar age to the Biranup Zone. Furthermore, thef isotope signature of the Fraser Range Metamorphics is consis-

ent with the Fraser Zone rocks containing recycled Biranup Zonerust. However, as outlined above, there is no evidence for pro-ific zircon growth during Stage I thermal events in the easterniranup Zone. The earliest growth of zircon rims in the easternlbany-Fraser Orogen, inboard of the Fraser Zone, is restricted to

he Gwynne Creek Gneiss, at c. 1270 Ma, and is at least 10 millionears younger than the emplacement of granites in the Fraser Zonend the Recherche Supersuite. These features suggest juxtaposi-ion of the zones, along major structures, some time after Stage I

agmatism.The Fraser Fault represents a major structural boundary

etween the eastern Biranup and Fraser Zones. A tectonic scenariohat could explain the absence of Stage I events in the easterniranup Zone and lack of Stage II metamorphism in the Fraser Zone

s the emplacement of the Fraser Zone by thrusting and extru-ion during the uplift event recorded by fractured zircon grains inhe Gwynne Creek Gneiss. This event may have placed the Fraserone at shallow crustal levels, which was less conducive to zir-on growth or regrowth during Stage II. In contrast, the easterniranup Zone must have remained in a favourable position for high-emperature metamorphism and zircon growth during Stage IITable 4).

.5. Mesoproterozoic tectonic setting and comparison with theusgrave Province

The Mesoproterozoic to Neoproterozoic Musgrave Province liest the convergence of central Australia’s main Proterozoic struc-ural trends and shares certain chronological similarities withhe Albany-Fraser Orogen (Myers et al., 1996; Wade et al., 2008;ig. 11). The aim of this section is to highlight these similarities.

Intrusive rocks with protolith ages between 1345 Ma and293 Ma form a significant component within the western Mus-rave Province (Howard et al., 2007; Smithies et al., 2009; Fig. 11).he crustal event that produced these melts has been termed theount West Orogeny. The age of this event is similar to that of Stage

of the Albany-Fraser Orogeny and specifically overlaps with themplacement of mafic to felsic components within the Fraser Zonend with emplacement of the Recherche Supersuite. Several studiesave suggested that the 1350–1290 Ma events in the Albany-Fraserrogen involved convergence and suturing of the West Australian

raton and Mawson Craton, with the subducting oceanic slab dip-ing to the southeast, away from the West Australian Craton (Clarkt al., 2000; Bodorkos and Clark, 2004). The tectonic setting ofount West granites is unclear, although they retain subduction-

ike geochemistry similar to Andean-style continental arc magmas

esearch 187 (2011) 223–247

(Smithies et al., 2010). Mount West Orogeny granites also havejuvenile Nd and Hf isotopic compositions consistent with a con-tinental arc setting (Smithies et al., 2009). Such a correlation leadsto wider associations of the Musgrave Province and Albany-FraserOrogen with other Mesoproterozoic (Grenvillian) orogenic belts.No evidence for a subduction-related suture in the west MusgraveProvince exists. This therefore implies a north-dipping slab and anunexposed suture to the south.

The Hf isotopic signal from Stage I Fraser Zone granites(1298 ± 4 Ma) is predominantly near CHUR and consistent withreworking of material with 2.0–2.5 Ga crustal residence (Fig. 6a).This is compatible with c. 1300 Ma extensive magmatic reworkingof Biranup Zone material, which itself reflects the heavily modifiedYilgarn Craton margin. A feasible tectonic setting for Stage I is asubduction zone outboard of the Biranup Zone, which compressedthis margin and uplifted a deep lower-crustal segment representednow by the Fraser Zone. If Biranup Zone rocks were the basementfor the Fraser Zone there is no necessity for the Fraser Zone to haveoriginated from a position substantially outboard of the craton mar-gin. Clark et al. (2000) and Bodorkos and Clark (2004) favouredsoutheast-directed Mesoproterozoic subduction during early StageI, based on pre-1313 Ma magmatism and tectonic activity beingrestricted to the Nornalup Zone. This included deformation thatproduced folds with northeast-trending, steeply southeast-dippingaxial surfaces, which are bracketed in time by 1330 ± 14 Ma and1313 ± 16 Ma granitoids (Clark et al., 2000). A significant pressureincrease (2–4 kbar) is recognised in the Fraser Zone and centralBiranup Zone (Coramup Gneiss) between 1290 and 1280 Ma (Clarket al., 1999; Bodorkos and Clark, 2004), and implies over-thrustingrelated to west-northwest to northwest convergence of the com-bined South Australian and Mawson Cratons during Stage I (Myerset al., 1996; Bodorkos and Clark, 2004; Giles et al., 2004). This indi-cates that the southeastern margin of the West Australian Cratonwas active in the Mesoproterzoic, which resulted in closure of anocean basin by the arrival and docking of the combined South Aus-tralian and Mawson Cratons (Bodorkos and Clark, 2004; Giles et al.,2004).

The Musgrave Orogeny (1220–1150 Ma) is interpreted to reflecta period of intracratonic extension and is synchronous with StageII tectonothermal activity in the Albany-Fraser Orogen (Fig. 11).Stage II commenced with high-temperature metamorphism of theeastern Nornalup Zone and the Biranup Zone between 1225 and1215 Ma (Clark et al., 2000; Spaggiari et al., 2009). This was followedby emplacement of the c. 1210 Ma Gnowangerup–Fraser Dyke Suite(Wingate et al., 2000, 2005). Stage II events recorded in the Albany-Fraser Orogen are widespread in the Northern Foreland, Biranup,and Nornalup Zones, and include pluton emplacement (EsperanceSupersuite) as well as prolific metamorphic zircon growth (Nelsonet al., 1995; Spaggiari et al., 2009; Kirkland et al., 2010). In thecentral Biranup Zone, granulite facies metamorphism took placeat c. 1180 Ma and again between 1170 and 1150 Ma (Spaggiariet al., 2009), or was a prolonged event throughout this period. Inthe eastern Biranup Zone, metamorphic zircon growth is definedat 1197 ± 6 Ma (Fig. 11). Significant extension during Stage II ofthe Albany-Fraser Orogeny is evident in central Biranup Zoneorthogneisses at Bremer Bay, where leucosomes formed in thenecks of boudins at c. 1180 Ma (Barquero-Molina, 2009; Spaggiariet al., 2009). The range of Stage II ages throughout the Biranup Zoneappears to reflect metamorphism in a predominantly extensionalregime within an intracratonic setting. Protracted extension is con-sistent with the tectonic scenario proposed for the west Musgrave

Province, where repeated or continuous ultrahigh-temperaturemetamorphism appears to have spanned the interval encompass-ing both the c. 1200 Ma and c. 1180 Ma events recognized in theAlbany-Fraser Orogen. However, the Musgrave Province shows noevidence of the c. 1680 Ma Zanthus tectonomagmatic event imply-

C.L. Kirkland et al. / Precambrian Research 187 (2011) 223–247 243

Fig. 11. Time-space diagram for the Albany-Fraser Orogen and the west Musgrave Province. The diagram includes all ion microprobe (SHRIMP) U–Pb zircon and baddeleyiteages determined by the Geological Survey of Western Australia within the region. Within each major lithostratigraphic domain (Recherche Supersuite, Fraser Zone, easternand central Biranup Zone) the data are arranged in geographic order from southwest at the bottom to northeast at the top. n = Number of analyses. All data can be downloadedfrom http://www.dmp.wa.gov.au/geochron. The region names for the Musgrave Province are after Smithies et al. (2010).

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44 C.L. Kirkland et al. / Precamb

ng that the Paleoproterozoic active Yilgarn margin was not inroximity to this region (Fig. 11).

. Conclusions

The eastern Biranup Zone is composed of 1710–1650 Maranitic to gabbroic intrusions and metasedimentary rocks, andies adjacent to the entire southern and southeastern marginsf the Yilgarn Craton over a distance of about 1200 km. The708 ± 15 Ma Bobbie Point metasyenogranite has a Hf isotopicignature indicating predominately a reworked Archean Yilgarnource. Volcaniclastic deposition in the Biranup Zone is datedt 1689 ± 6 Ma. These volcanogenic sediments were intruded byranitic rocks at 1686 ± 8 Ma, very soon after deposition. The Hfsotopic signature of detrital zircons from the volcaniclastic rockss consistent with a source incorporating both Yilgarn crust anduvenile material. A suite of granitic and gabbroic rocks, the Eddyuite, with distinct mingling and hybridisation textures, is datedt 1665 ± 4 Ma. In this suite, younger igneous rocks incorporated areater juvenile mantle-derived component, as indicated by bothhe whole-rock chemistry and Hf isotopes. The isotopic featuresf the Biranup Zone indicate it is not exotic to the margin of theilgarn Craton, but instead represents a Paleoproterozoic activeargin. On this margin back-arc processes isolated Archean frag-ents, dated at 2684 ± 11 Ma, in a Paleoproterozoic magmatic

rc.In the eastern Biranup Zone, folded leucosomes in a migmatitic

onzogranite yield a U–Pb zircon date of 1676 ± 6 Ma, whichs identical to that for crystallization of cross-cutting axial pla-ar leucosomes at 1679 ± 6 Ma. This indicates high-temperatureetamorphism and deformation, including isoclinal folding, in the

astern Biranup Zone at c. 1680 Ma. This event is here named theanthus Event. Based on the rapidly evolving tectonomagmatic his-ory, the original Yilgarn-like Hf isotopic signature modified byuvenile material, and the geochemical evolution of high-K calc-lkaline magmas, a feasible tectonic scenario for the Biranup Zones an evolving arc to back-arc within an active margin on the Yilgarnraton. This region was subsequently compressed and tectonicallyismembered during Stages I and II of the Albany-Fraser Orogeny.

Two strongly foliated granite samples within the Fraser Rangeetamorphics yield a weighted mean date of 1298 ± 4 Ma, inter-

reted as the age of magmatic crystallization during Stage I of thelbany-Fraser Orogeny. A major foliation-forming event within theraser Zone must have occurred after c. 1300 Ma. These Fraser Zoneranites have initial Hf isotopic ratios compatible with juvenilenput into a Biranup Zone source, implying a Biranup Zone base-

ent to the Fraser Zone. The eastern Biranup Zone preserves novidence of Stage I intrusive activity, suggesting it was structurallymplaced to its present position after Stage I. However, evidence oftage II metamorphic overprinting is indicated by the widespreadevelopment of low-uranium zircon overgrowths at 1197 ± 6 Ma.ithin the Gwynne Creek Gneiss, high-U zircon overgrowths are

ractured and then overgrown by a younger phase of metamorphicircon. This indicates a period of crustal uplift and cooling between270 and 1197 Ma. The timing of this uplift is comparable with that

n the Fraser Zone and Mount Ragged Formation.The Mount West Orogeny of the Musgrave Province and Stage I

f the Albany-Fraser Orogeny, at c. 1300 Ma, share a similar timingnd may reflect development of an arc system and its compressiongainst the craton margin. In the case of the Fraser Zone, it was

riginally rooted on the outer Biranup Zone, and reflects the up-hrusting and juxtaposition of lower crustal rocks. Stage II of thelbany-Fraser Orogeny was contemporaneous with the Musgraverogeny and likely reflects predominant intracratonic extensionlong pre-existing sutured craton edges.

esearch 187 (2011) 223–247

Acknowledgements

Zircon and baddeleyite analyses were conducted using theSHRIMP II ion microprobes at the John de Laeter Centre for MassSpectrometry at Curtin University, in Perth, Australia. GeologicalSurvey of Western Australia’s Carlisle laboratory staff are thankedfor their diligent efforts in mineral separation. M. Prause is thankedfor assistance in drafting the figures. D. Vilbert is thanked for per-forming the Nd analyses. C. Forbes is thanked for a constructivereview. P. Cawood is thanked for efficient editorial handling. Theauthors publish with permission of the Executive Director of theGeological Survey of Western Australia.

Appendix A.

U–Pb

Zircon and baddeleyite separation was performed by crushingand elutriation, followed by heavy-liquid and magnetic separa-tion. The resulting hand-picked zircon or baddeleyite crystals weremounted with zircon standards (CZ3, OG1, and BR266 or Temora2)or baddeleyite (PBR2) in epoxy and ground to half grain thickness toexpose crystal interiors. Transmitted and reflected-light images ofall grains were produced. After applying a 40 nm-thick gold coating,cathodoluminescence (CL) imaging of all zircons was performed.Operating procedures for U, Th, and Pb isotopic measurementsusing the SHRIMP ion microprobes are detailed in Wingate andKirkland (2009). The zircon standard CZ3 was used for concen-tration calibration (551 ppm 238U; Claoué-Long et al., 1995) andeither Temora2 (Black et al., 2004) or BR266 (Stern, 2001) was usedas the zircon U–Pb calibration standard whereas PBR2 was usedfor baddeleyite (Wingate and Kirkland, 2009). All mounts had theaccuracy of 207Pb*/206Pb* ratios verified by comparison with theArchean OG1 zircon standard (Stern et al., 2009). No correction for207Pb*/206Pb* fractionation is deemed necessary.

Lu–Hf

Hafnium isotope analyses were conducted on previously datedzircons mounted in epoxy resin using a New Wave/MerchantekLUV213 laser-ablation microprobe, attached to a Nu Plasmamulti-collector inductively coupled plasma mass spectrometer(LA-MC-ICPMS). The analyses employed a beam diameter of∼55 �m and a 5 Hz repetition rate which resulted in ablation pitstypically 40–60 �m deep. The ablated sample material was trans-ported from the laser cell to the ICP-MS torch by a helium carriergas. Interference of 176Lu on 176Hf was corrected by measurementof interference-free 175Lu, and using the invariant 176Lu/175Lu cor-rection factor 1/40.02669 (DeBievre and Taylor, 1993). Interferenceof 176Yb on 176Hf was corrected by measuring the interference-free 172Yb isotope, and using the 176Yb/172Yb ratio to obtainthe interference-free 176Yb/177Hf ratio. The appropriate valueof 176Yb/172Yb was determined through spiking of the JMC475hafnium standard solution with ytterbium, and finding the valueof 176Yb/172Yb (0.58669) required to yield the 176Hf/177Hf value forthe un-spiked solution. The typical 2� precision of the 176Hf/177Hfratios is +0.00002, equivalent to +0.7 εHf unit.

Thirty zircons from the Mud Tank carbonatite locality were anal-ysed, together with the samples, as a measure of the accuracyof the results. Most of the data and the mean 176Hf/177Hf value

(0.282522 ± 0.000015; n = 30) are within 2 standard deviations ofthe recommended value (0.282522 ± 0.000042 (2�); Griffin et al.,2007). Six analyses of the 91500 zircon standard analysed duringthis study indicated 176Hf/177Hf = 0.282320 ± 0.000021 (2�), whichis well within the range of values reported by Griffin et al. (2006).

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Calculation of initial 176Hf/177Hf is based on the 176Lu decayonstant of Scherer et al. (2001; 1.867 × 10−11 y−1) and �Hf valuesmployed the present day chondritic measurement of Blichert-Toftnd Albarède, (1997; 0.282772). Calculation of model ages (TDM) isased on a depleted-mantle source with (176Hf/177Hf)i = 0.279718t 4.56 Ga and 176Lu/177Hf = 0.0384 (Griffin et al., 2004). TDMcrustal) ages were calculated assuming that the Hf within eachircon resided within a reservoir with 176Lu/177Hf ratio of 0.015,orresponding to an average Continental Crust (Griffin et al., 2002,004).

m–Nd

Sm–Nd isotopic values where determined on crushed whole-ock samples by isotope dilution. All analyses were carried out athe Géosciences Rennes Laboratory at the University of Rennes 1.amples were spiked with a 150Nd–149Sm mixed solution and dis-olved in HF-HNO3. REE elements were separated using BioRad AG0W × 8 H + 200–400 mesh cationic resin. Sm and Nd were sepa-ated and collected by passing the solution through a further setf ion exchange columns loaded with Ln spec Eichrom resin. Smnd Nd were loaded with HNO3 reagent on to double Re filamentsnd analysed in a Finnigan MAT262 multicollector mass spectrom-ter in static mode. In each analytical session, the unknowns werenalysed together with the Ames nNd-1 Nd standard, which duringhe course of this study yielded an average of 0.511964 (standardeviation = 7.23 × 10−6). All analyses of the unknowns are adjustedo a nominal 143Nd/144Nd value of 0.511850 for the La Jolla stan-ard. Mass fractionation was monitored and corrected using thealue 146Nd/144Nd = 0.7219. Procedural blanks analysed during theeriod of these analyses were ∼190 pg and are considered to beegligible compared to the total quantity of Nd in the samples.

ppendix B. Supplementary data

Supplementary data associated with this article can be found, inhe online version, at doi:10.1016/j.precamres.2011.03.002.

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