Detrital zircon U–Pb–Hf and O isotope character of the Cahill Formation and Nourlangie Schist, Pine Creek Orogen: Implications for the tectonic correlation and evolution of the

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Precambrian Research 246 (2014) 35–53

Contents lists available at ScienceDirect

Precambrian Research

jo ur nal homep ag e: www.elsev ier .com/ locate /precamres

etrital zircon U–Pb–Hf and O isotope character of the Cahillormation and Nourlangie Schist, Pine Creek Orogen: Implications forhe tectonic correlation and evolution of the North Australian Craton

.A. Hollisa,∗, C.J. Carsonb, L.M. Glassa,1, N. Kositcinb, A. Schersténc,.E. Wordend, R.A. Armstronge, G.M. Yaxley f, A.I.S. Kempg, EIMFh

Northern Territory Geological Survey, PO Box 3000, Darwin, NT 0801, AustraliaGeoscience Australia, PO Box 378, Canberra, ACT 2601, AustraliaDepartment of Geology, Lund University, Sölvegatan 12, S-223 62 Lund, SwedenBBY Ltd., 17/60 Margaret Street, Sydney, NSW 2000, AustraliaPRISE, The Australian National University, Research School of Earth Sciences, Building 61, Mills Road, Acton, ACT 0200, AustraliaThe Australian National University, Research School of Earth Sciences, Building 61, Mills Road, Acton, ACT 0200, AustraliaCentre for Exploration Targeting, School of Earth and Environment, The University of Western Australia M006, 35 Stirling Highway, Crawley, WA 6009,ustraliaEdinburgh Ion Microprobe Facility, University of Edinburgh, Edinburgh, UK

r t i c l e i n f o

rticle history:eceived 8 May 2013eceived in revised form 21 January 2014ccepted 26 February 2014vailable online 12 March 2014

eywords:ine Creekorth Australian Cratonawler Cratonharwar Cratonetrital zirconranium

a b s t r a c t

Detrital zircon age and Hf isotope patterns for the Cahill Formation and Nourlangie Schist are distinctlydifferent from other Paleoproterozoic successions in the North Australian Craton. The Cahill Formationand Nourlangie Schist comprise the bulk of the Paleoproterozoic strata in the Nimbuwah Domain, theeasternmost part of the Pine Creek Orogen on the northern margin of the North Australian Craton. Theycomprise micaceous and quartzofeldspathic schist, carbonaceous schist, calc-silicate rock, amphiboliteand quartzite, deformed and metamorphosed during emplacement of the granitic to dioritic NimbuwahComplex at 1867–1857 Ma. The Cahill Formation hosts several world-class uranium deposits includingRanger, Jabiluka and Nabarlek. U–Pb SHRIMP and LA-SF-ICPMS detrital zircon spectra for four samplesof the Cahill Formation and six samples of the Nourlangie Schist show a similar broad spectrum of agesmainly in the range 3300–1900 Ma. A ubiquitous dominant peak at 2530–2470 Ma matches the age ofunderlying Neoarchean basement, but is distinct in its dominantly mantle-like Hf and O zircon isotopiccharacter, which shows closer similarity with possible source rocks from the Gawler Craton or alterna-tively from the Dharwar Craton. Common smaller age peaks occur at 2180 Ma, 2080 Ma and 2020 Ma.The first two have no known magmatic age correlatives in the North Australian Craton. Zircons of the2020 Ma peak have distinctively unradiogenic Hf and elevated �18O, at variance with local rocks of thisage but similar to detrital zircon of the same age from the Gawler Craton. In contrast to younger Pro-terozoic sedimentary successions within the Pine Creek Orogen, which contain ubiquitous ca. 1870 Madetritus, the detrital spectra for the Cahill Formation and Nourlangie Schist contain almost no ca. 1870 Madetritus. A maximum deposition age of ca. 1866 Ma indicates deposition within error of intrusion of the
Nimbuwah Complex. We propose that the Cahill Formation and Nourlangie Schist were deposited at aplate margin immediately prior to convergent tectonism. This resulted in their burial, deformation andamphibolite facies metamorphism during orogenesis associated with the Nimbuwah Event. These find-ings have implications for understanding the Paleoproterozoic evolution of the Pine Creek Orogen within the context of northern Australia.
∗ Corresponding author at: Geological Survey of Western Australia, Mineral House, 100E-mail address: [email protected] (J.A. Hollis).

1 Current address: Territory Iron Pty Ltd, 23 Ventnor Avenue, West Perth, WA 6005, Au

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. Introduction

Detrital zircon age spectra are a powerful tool for interpretinghe provenance of sedimentary rocks and, coupled with litholog-cal and tectonostratigraphic constraints, for making correlationsetween sedimentary successions (e.g. Fedo et al., 2003; Cawoodt al., 2012). In addition, the youngest detrital zircon populationonstrains the maximum age of deposition (e.g. Fedo et al., 2003).orrelation with possible source regions and the change in pro-enance through time can also provide valuable information onhe nature and timing of tectonic processes, such as depositionlong active margins, or the arrival of allochthonous terranes atontinental margins, or the opening of intracratonic basins (e.g.arr et al., 2003; Bingen et al., 2001; Goodge et al., 2002; Rojas-gramonte et al., 2011; Cawood et al., 2012). Combined with otheronstraints, such as the nature and age of regional magmatism,olcanism, metamorphism, and deformation, together with wholeock and mineral isotopic data, this information can be used to aidaleogeographic reconstructions and tectonic models (e.g. Cawoodt al., 2007, 2012).

The O and Lu–Hf isotope composition of detrital zircon providesurther information on the nature and evolution of protoliths fromhich the zircons were sourced. This provides a window into crust

nd mantle processes important in formation of the original mag-atic rocks from which the zircons crystallised, subsequent to their

elease during erosion and deposition (e.g. Valley, 2003; Kinney andaas, 2003; Griffin et al., 2004; Kemp et al., 2006; Pietranik et al.,

008). O and Lu–Hf data can also provide further insight on possibleource regions or further develop or refine stratigraphic correla-ions made solely, or largely, on the basis of detrital age data (e.g.eevers et al., 2005; Howard et al., 2009).

In the North Australian Craton, many Paleo- to Mesoprotero-oic sedimentary and metasedimentary rocks have detrital spectraharacterised by a dominant ca. 1870 Ma peak with a small ca.500 Ma peak (e.g. Neumann et al., 2006; Cross and Crispe, 2007;laoué-Long et al., 2008a, 2008b; Wade et al., 2008; Worden et al.,008a; Carson, 2013). Marked exceptions are the 2020 Ma Wood-utters Supergroup, the oldest known succession in the Pine Creekrogen, and the Ferdies Member of the Dead Bullock Formation in

he Tanami region, which have detrital zircon spectra dominatedy Neoarchean sources (Cross et al., 2005aCross and Crispe, 2007).

Although the Paleoproterozoic stratigraphy of parts of the Pinereek Orogen are well characterised (e.g. the Central Domain,orden et al., 2008b), this is not the case for the amphibolite

acies Cahill Formation and Nourlangie Schist that dominate thealeoproterozoic stratigraphy in the eastern-most part of the Pinereek Orogen, the Nimbuwah Domain. The relative stratigraphicosition and possible correlative units of the Cahill Formation andourlangie Schist are not well understood because these units (a)ave no known volcanic rocks, tuffs, or dykes that can be used toirectly determine ages of deposition, (b) are strongly deformed inight to isoclinal folds and thrusts, (c) are only locally well exposednd, (d) relative to strata to the west, are more strongly meta-orphosed to amphibolite facies conditions. Nonetheless several

uthors (Needham and Stuart-Smith, 1976, 1985; Needham et al.,980; Needham, 1988; Ferenczi and Sweet, 2005) have suggestedorrelations with a number of stratigraphic units of distinct ages inifferent parts of the orogen. The Cahill Formation and Nourlangiechist locally host large uranium deposits, including Ranger, Nabar-ek and Koongarra, therefore correct stratigraphic correlation hasmportant implications for uranium exploration strategies.

In this contribution we present U–Pb SHRIMP and LA-SF-ICPMS
etrital zircon data for four samples of the Cahill Formation andix samples of the Nourlangie Schist from across a wide area ofhe Nimbuwah Domain in the Pine Creek Orogen. The data showtrong consistency between samples and distinct detrital spectra
search 246 (2014) 35–53

from all other strata for which detrital zircon data are availablefrom the Pine Creek Orogen and from the North Australian Cratonin general. We also present zircon O (SIMS) isotope and Hf (LA-MC-ICPMS) isotope zircon data for two, geographically widely spaced,samples of the Cahill Formation and one sample of the NourlangieSchist. These provide possible constraints on the origins and natureof the Archean to Paleoproterozoic source rocks for the sedimentaryprecursors to these units. The results have significant implicationsfor stratigraphic correlations across the Pine Creek Orogen, and tec-tonic and crustal evolution models for the North Australian Craton.

2. Regional geology

The Pine Creek Orogen is exposed over 47,500 km2 on the north-ern margin of the North Australian Craton (Fig. 1). It comprises thicksuccessions of Paleoproterozoic clastic and carbonaceous sedimen-tary rocks and volcanics, unconformably overlying Neoarchaeangranitic and gneissic basement (ca. 2670–2500 Ma). The marginsof the Pine Creek Orogen are concealed by younger, unmetamor-phosed strata, hence the total extent is unknown.

The Pine Creek Orogen is subdivided from west to east into threedomains: the Litchfield, Central and Nimbuwah Domains (Fig. 1),based on distinct Paleoproterozoic tectonometamorphic historiesand the nature and timing of the main phases of magmatism (e.g.Walpole et al., 1968; Needham et al., 1980, 1988; Ahmad et al.,1993; Worden et al., 2008b). The boundaries between the terranesalso broadly correlate with Neoarchean basement highs (Lewiset al., 1995).

Rifting of Neoarchean basement at ca. 2020 Ma (Worden et al.,2008a, 2008b) is thought to have led to the deposition of clastic,carbonate, and carbonaceous sedimentary and volcanic rocks of theWoodcutters Supergroup in a shallow marine basin across the Cen-tral and Nimbuwah Domains (e.g. Stuart-Smith et al., 1984). Theserocks comprise iron-rich sedimentary rocks, conglomerate, sand-stone, quartzite, carbonate, pyritic and dolomitic shale, siltstone,tuff basaltic to andesitic lava and agglomerate.

In the Nimbuwah Domain, the Woodcutters Supergroup andequivalents were overlain by the sedimentary precursors to theCahill Formation, which now comprises mica schist, carbonaceousschist, calc-silicate rock, para-amphibolite, and quartzite, grad-ing upwards into quartzofeldspathic mica schist of the NourlangieSchist (Needham, 1988). These were intruded at depth by mainlydioritic to granodioritic magmas of the Nimbuwah Complex atca. 1867–1857 Ma (Page et al., 1980; Worden et al., 2008b;Carson et al., 20103) during amphibolite-facies metamorphism(ca. 1865–1855 Ma, Ferguson, 1980; Kositcin et al., 2013Hollis andGlass, 2012). Deep crustal Nimbuwah magmatism coincided withsedimentation and volcanism (Cosmo Supergroup and equivalents)in the Central Domain and the Litchfield Domain at ca. 1863 Ma(Fig. 2, Worden et al., 2006a; Worden et al., 2008a; Worden et al.,2008b; Worden et al., 2006a, 2008a,b; Beyer et al., 2013; Kositcinet al., 2013). The Cosmo Supergroup comprises iron-rich sedimen-tary rocks, tuff, carbonate rocks, shale, greywacke and siltstone ofthe South Alligator Group deposited in a low-energy environment,overlain by a thick succession of deeper water turbiditic shale andsiltstone and interbedded felsic volcanic rocks and tuff of the FinnissRiver Group (Fig. 2; Needham et al., 1988).

Sedimentation in the Central and Litchfield Domains wasfollowed by extensional high-temperature, low-pressure meta-morphism (ca. 1855 Ma, Carson et al., 2008) and associated felsicand back-arc basin mafic magmatism in the Litchfield Domain (ca.1862–1850 Ma, Glass, 2007, 2011; Worden et al., 2008a). At or after
this time, greenschist-facies metamorphism and north-strikingupright folding and shearing occurred at upper crustal levels inthe Central Domain. Late to post-orogenic, I-type Cullen Supersuite(mainly in the period 1835–1820 Ma, Stuart-Smith et al., 1993;

J.A. Hollis et al. / Precambrian Research 246 (2014) 35–53 37

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ig. 1. Location of the Pine Creek Orogen within the North Australia Craton (inset) aomains: the Litchfield Domain; Central Domain; and Nimbuwah Domain.

orden et al., 2008a) and Jim Jim Suite granites (1847–1818 Ma,orden et al., 2008a; Beyer et al., 2013) were broadly coevalith intracratonic rift-related volcanism and sedimentation in the

outh Alligator Valley (Needham et al., 1988; Needham and Stuart-mith, 1985; Freidmann and Grotzinger, 1994; Kruse et al., 1994;agodzinski, 1999). Unconformably overlying Paleo- to Mesopro-erozoic platform clastic sediments and volcanics of the Katherineiver Group were deposited in braided rivers across and well to theoutheast of the Pine Creek Orogen (e.g. Kruse et al., 1994; Carsont al., 1999; Rawlings, 1999).

.1. Cahill Formation and Nourlangie Schist

The Cahill Formation and Nourlangie Schist are inferred toe a largely conformable succession that crops out sporadi-ally within incised Cenozoic cover and as inliers within the

neralised geology of the Pine Creek Orogen showing the three tectonostratigraphic

Kombolgie Subgroup. They are also known from drill core beneaththe unconformably overlying Kombolgie Subgroup. The CahillFormation is inferred to conformably overlie the KudjumarndiQuartzite, although lithological contacts are rarely exposed andusually tectonised. The contact between the Cahill Formation andNourlangie Schist is usually concealed and contact relationships arealso complicated by thrust and fold repetition.

The lower member of the Cahill Formation comprises mar-ble, calc-silicate rock, pyritic, garnetiferous and carbonaceousschist, minor amphibolite, micaceous schist and quartzite. Theupper member of the Cahill Formation comprises quartzofelds-pathic schist, feldspathic quartzite, mica schist, magnetite-bearing
schist and amphibolite. The mica schists are commonly hematite-bearing and locally garnet ± staurolite ± kyanite-bearing. Thecontact between the two members, marked by an increase in theproportion of mica schist, is gradational and can be difficult to

38 J.A. Hollis et al. / Precambrian Research 246 (2014) 35–53

Fig. 2. Simplified stratigraphic column for the Pine Creek Orogen modified from Worden et al., 2008b. 1Page, 1996, 2Jagodzinski, 1998, 3Annesley et al., 2002, 4Worden et al.,2 010, 9

1 Sands

drptsmtc

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008a, 5Page et al., 1985, 6Worden et al., 2008b, 7Carson et al., 2009, 8Carson et al., 23Glass et al., 2010, 14McAndrew et al., 1985, 15Hollis et al., 2009a, Ck = Creek; Sst =

istinguish because outcrop is limited and typically heavily ret-ogressed and weathered. However, the boundary is marked, inlaces, by a change in magnetic response, with the upper part ofhe lower member containing magnetic amphibolites or magnetitechist (Hollis and Glass, 2012). Magnetic units within the Cahill For-ation that contrast with surrounding less magnetic units can be

raced over hundreds of kilometres under Cenozoic and Cretaceousover through west Arnhem Land (Hollis and Glass, 2012).

The contact of the upper Cahill Formation with the Nourlangie
chist appears to be gradational. The Nourlangie Schist comprises
monotonous succession of pelitic and psammitic layered, crenu-ated sericite-biotite/chlorite-quartz-muscovite, muscovite-quartzchist and quartzofeldspathic schist with minor quartzite and

Hollis et al., 2009b, 10Page et al., 1980, 11Kositcin et al. (2013), 12Cross et al., 2005a,tone; Metms = Metamorphics; Volc = Volcanic; Volcs = Volcanics.

amphibolite. In some cases mica schists are garnet- ± staurolite-and, rarely, kyanite-bearing but more typically they are stronglyretrogressed to sericite-chlorite schist and are heavily weathered.Chloritic, sericitic and hematitic alteration assemblages are per-vasive in the Cahill Formation and Nourlangie Schist, particularlyin proximity to the contact with the basal unconformity with theoverlying Mamadawerre Sandstone, the basal unit of the KombolgieSubgroup.

Needham and Stuart-Smith, 1976 inferred that deposition of the
Cahill Formation occurred in a shallow near-shore shelf environ-ment based on the carbonate and carbonaceous lithologies, withadmixing of terrigenous material accounting for the predominantquartzofeldspathic metasedimentary rocks.

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Quartzofeldspathic schist of the upper Cahill Formation haseen proposed as a possible correlative of the ca. 2020 Ma Mundo-ie Sandstone and the Crater Formation of the Mount Partridgeroup (Woodcutters Supergroup) in the Central Domain (Needhamt al., 1980; Needham, 1988). Similarly the Nourlangie Schist haseen interpreted as a metamorphosed equivalent of the ca. 2020 Maildman Siltstone of the Mount Partridge Group (Fig. 2; Needham

nd Stuart-Smith, 1985; Needham, 1988; Worden et al., 2008a,008b). Ferenczi and Sweet, 2005 correlated the Cahill Formationith the ca. 2020 Ma Namoona Group (Fig. 2). In contrast, Needham

nd Stuart-Smith, 1976 proposed the Cahill Formation as a faciesquivalent of the 1863 Ma Koolpin Formation of the South Alligatorroup, Central Domain, which is host to uranium mineralisation in

he South Alligator Valley, separated by a basement high of Mountartridge Formation.

. Methods

The U–Pb zircon data presented here were collected usingensitive High Resolution Ion MicroProbe (SHRIMP) and Laserblation-Sector Field-Inductively Coupled Plasma Mass Spec-

rometry (LA-SF-ICPMS). Sample locations are listed in Table 1.ethodologies specific to each technique and all data tables are

ocated in the Supplementary data. A summary of analytical sessionetails is shown in Table S2 (Supplementary data). Age data in theext and plotted in figures are at 95% confidence level. Age data inables are quoted at 1� uncertainty (Tables S3–S12, Supplementaryata). Sample numbers are listed in the text in Northern Territoryeological Survey (NTGS) format, whereas in Tables S3–S12 bothTGS and Geoscience Australia (GA) sample numbers are given.

. Samples analysed

Ten micaceous pelitic and psammitic samples of the Cahillormation and Nourlangie Schist were collected from outcropnd drill core over a wide area of west Arnhem Land, includingrill core samples from beneath a thick (up to 1000 m) cover ofombolgie Subgroup sandstone (Fig. 3, Table 1). Samples were

nterpreted as Cahill Formation only where reasonable litholog-cal associations (e.g. calc-silicates, magnetic metasedimentaryocks, graphitic intervals) and tectonostratigraphy (e.g. proximityo structurally underlying Kakadu Group) could be established. Inther cases, where samples were collected from thick packages ofonotonous mica schists interpreted to be relatively high in the

uccession, these were assigned to the Nourlangie Schist.

. Geochronology results

.1. SHRIMP

.1.1. Sample AL07JHO244 – upper Cahill FormationSample AL07JHO244 was collected from Energy Resources

ustralia drill core from the upper mine sequence of the Rangerine (drill hole GT07P210, 54.3–55.8 m, Figs. 3 and 4), where

he stratigraphy of the Cahill Formation is well constrained. Its a muscovite-bearing semi-pelitic schist with a spaced cleav-ge defined by muscovite stringers and microlithons of polygonaluartz, plagioclase and minor muscovite.

The majority of zircons are subhedral, equant to elongate pris-atic grains, commonly with rounded, scalloped and resorbed

dges and facets. Rounded subhedral grains and fragmented grains
re also common. Zircons vary from clear light yellow to faint redcommon) to deep reddish brown (<10%). Width to length aspectatios are typically 1:3. Elongate grains are generally 100–150 �mong but range up to 230 �m. Equant rounded grains range from
search 246 (2014) 35–53 39

40 to 100 �m diameter. In cathodoluminescence (CL) images, mostgrains exhibit well-defined concentric oscillatory zoning, with asubordinate number of bright to dull homogeneous or weaklystructured grains (Fig. 5a). Approximately half have narrow bright,discontinuous rims (typically <10 �m) that truncate internal zones(Fig. 5a).

Seventy-seven zircons were analysed. Sixteen analyses wereexcessively discordant (>10%). The remaining 61 define an agedistribution that spans 3062–2007 Ma (Fig. 6 and Figs. 6a and 7aTable S3). The spectrum comprises a dominant peak at ca.2520–2490 Ma (20%) with smaller peaks at 2460–2440 Ma (8%),2360–2350 Ma (8%), 2190–2170 Ma (10%) and 2030–2000 Ma (10%,Fig. 7a). The youngest peak comprising the seven youngest grainsgives a conservative maximum age of deposition of 2019 ± 11 Ma(MSWD = 0.91). It is also within error of the youngest analysis(2007 ± 22 Ma, 2�).

5.1.2. Sample AL09CJC054 – Cahill FormationSample AL09CJC054 is a retrogressed micaceous schist from the

Beatrice Inlier (Figs. 3 and 4b). It is interpreted as Cahill Formationbased on its tectonostratigraphic position, immediately beneaththe unconformity with the overlying Mamadawerre Sandstone(Kombolgie Subgroup) and proximal to Kudjumarndi Quartzite(Kakadu Group, Fig. 3). It contains distinct psammitic and peliticlayers and prominent knobs (up to 3 cm) of a retrogressed phasethat was possibly cordierite or andalusite.

Zircons are predominantly subrounded and subhedral, mostwith surficial scouring, pitting and frosting. Colour ranges fromclear and colourless, to pale yellow-brown to orange. There are sev-eral highly fractured metamict dark brown grains. Grain size variesfrom 60 to 200 �m long, with aspect ratios typically 1:1 to 1:3. Mostgrains exhibit fine-scale oscillatory zoning ranging from subduedto very bright CL (Fig. 5b). A few grains have incipient sector zoningand several have a very bright CL, or very dark CL response, with nodiscernable zoning. In a few cases oscillatory zones are truncatedat rounded grain edges.

One hundred and nine grains were analysed (Fig. 6b, Fig 7b,Table S4). One grain was rejected due to excess discordance andanother on the basis of poor precision. The remaining 107 analy-ses define an age distribution of ca. 3231–1853 Ma. The spectrumcomprises a dominant peak at ca. 2540–2460 Ma (28%) from whichcan be distinguished three individual overlapping peaks at ca.2540–2520 Ma (8%), ca. 2510–2490 Ma (11%) and ca. 2475–2460 Ma(9%, Fig. 7b), with subordinate peaks at ca. 2430–2400 Ma (5%),ca. 2365–2345 Ma (4%), ca. 2190–2170 Ma (5%), ca. 2090–2070 Ma(6%), ca. 2030–2000 Ma (7%) and ca. 1990–1975 Ma (6%). There areseveral other poorly defined irregular peaks and scattered individ-ual analyses. The oldest three analyses at 3231 Ma, 3150 Ma, and2907 Ma are distinctly older than all other analyses. The youngestfour analyses, which are not morphologically distinct from othergrains, combine to give a weighted mean age of 1866 ± 11 Ma(MSWD = 0.93), which is interpreted as a maximum depositionalage.

5.1.3. Sample AL04NJD007 – Nourlangie SchistSample AL04NJD007 is a garnet-biotite-sillimanite-staurolite-

quartz schist collected from Cameco Australia drill core (Drill holeALG002, 271.1–271.9 m) from the Algodo uranium prospect in theBeatrice Inlier (Fig. 3).

Zircons range from anhedral with pitted surfaces to euhedral,prismatic grains. Acicular and ovoid inclusions are present, andfracturing varies from absent to intense. Zircons are transparent to
translucent and typically colourless. Euhedral grains have aspectratios typically 1:4. They are up to 250 �m in length, most aver-aging 100 �m. Euhedral grains exhibit distinct concentric zoning,as revealed by CL imaging (Fig. 5c). Structureless grains are also


Table 1Geochronology sample location data. All coordinates use the GDA94 datum zone 53 projection.

Unit NTGS Sample No Rock type Easting (m) Northing (m)

Upper Cahill Formation AL07JHO244 Muscovite semi-pelitic schist 274,471 8,597,670Cahill Formation AL09CJC054 Retrogressed micaceous schist 313,488 8,607,849Nourlangie Schist AL07NJD007 Garnet-sillimanite-staurolite pelitic schist 290,308 8,607,903Nourlangie Schist ME03JHL005 Possible tuffaceous bed within graphitic mica-quartz schist 293,170 8,517,620Cahill Formation CP07JHO009 Garnet-staurolite-biotite schist 284,695 8,711,938Nourlangie Schist AL07JHO242B Micaceous laminated psammitic schist 272,820 8,656,417Cahill Formation AL07JHO088 Pelitic biotite schist 294,859 8,616,521

samm psam

schis

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Nourlangie Schist AL07JHO025 Muscovite-biotite pNourlangie Schist AL07JHO120 Sillimanite-bearingNourlangie Schist AL07JHO266 Chlorite-muscovite

resent. Minor morphologically discordant cores are observed andruncation of patterns by rounding at grain boundaries is common.ecrystallisation along cracks is common in intensely fracturedrains, which typically display dark-CL responses consistent withetamictisation. Rare CL-bright zircons are present.Sixty-nine grains were analysed. Three analyses were rejected

n the basis of excess discordance and two on the basis of excessommon lead (>0.5%). Another was rejected due to transientnstable analytical conditions (analysis A69.1). The remaining
3 analyses define an age distribution that spans 3239–1868 MaFigs. 6c, 7c, Table S5). The dominant population occurs at530–2470 Ma (33%), with smaller peaks at 2440–2430 Ma (5%),230–2210 Ma (6%), 2195–2160 Ma (10%) and 2090–2070 Ma (11%,
Fig. 3. Location of analysed samples of the Cahill Formation

itic schist 307,552 8,626,635mitc schist 335,278 8,641,466t 266,571 8,649,704

Fig. 7c). There are also several smaller, less well-defined peaks andscattered individual analyses. The youngest individual grain hasa 207Pb/206Pb age of 1868 ± 58 Ma (2�). The large uncertainty isprobably a consequence of the relatively low U content (84 ppm). Aweighted mean of the next youngest five grains yields a 207Pb/206Pbage of 1955 ± 10 Ma (MSWD = 1.15), which is interpreted as amaximum deposition age of the sedimentary protolith.

5.1.4. Sample ME03JHL005 – Nourlangie Schist
Sample ME03JHL005 was collected from a deep drill hole (drill
hole DAD008, 1060.1–1061.9 m) beneath the Kombolgie Subgroup(Fig. 3). The sample comprises a possible tuffaceous bed withingraphitic mica-quartz schist.

and Nourlangie Schist. See Table 1 for sample details.


Fig. 4. Outcrop photos of analysed samples of Cahill Formation and Nourlangie Schist. (a) Sample AL07JHO244, upper Cahill Formation, Ranger Mine; (b) sample AL09CJC054,Cahill Formation, Beatrice Inlier; (c) sample CP07JHO009, Cahill Formation, Wellington Range drill core, (d) sample AL07JHO088, Cahill Formation, Myra Falls Inlier; (e)sample AL07JHO025, Nourlangie Schist, Myra Falls Inlier; (f) sample AL07JHO266, Nourlangie Schist, Arrarra prospect, ca. 14 km NE of Oenpelli. Photographs of the remainingsamples are not available.

Fig. 5. Cathodoluminescence images of representative zircon grains from samples of the Cahill Formation and Nourlangie Schist; (a) sample AL07JHO244, upper CahillFormation; (b) sample AL09CJC054, Cahill Formation; (c) sample AL04NJD007, Nourlangie Schist; (d) sample ME03JHL005, Nourlangie Schist; (e) sample CP07JHO009, CahillFormation, (f) sample AL07JHO088, Cahill Formation; (g) sample AL07JHO242B, Nourlangie Schist; (h) sample AL07JHO025, Nourlangie Schist; (i) sample AL07JHO120,Nourlangie Schist; (j) sample AL07JHO266, Nourlangie Schist. Scale is the same for each image.


Fig. 6. Wetherill concordia diagrams showing U–Pb zircon isotope data from: (a) sample AL07JHO244, upper Cahill Formation; (b) sample AL09CJC054, Cahill Formation; (c)sample AL04NJD007, Nourlangie Schist; (d) sample ME03JHL005, Nourlangie Schist; (e) sample CP07JHO009, Cahill Formation, (f) sample AL07JHO088, Cahill Formation; (g)sample AL07JHO242B, Nourlangie Schist; (h) sample AL07JHO025, Nourlangie Schist; (i) sample AL07JHO120, Nourlangie Schist; (j) sample AL07JHO266, Nourlangie Schist.Grey shaded ellipses are < 10% discordant and unfilled ellipses are >10% discordant.


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2000 220 0 240 0 260 0 280 0 300 0 320 0 340 0 36001800 200 0 2200 2400 260 0 280 0 300 0 3200 3400 3600

(a) (b)

(c ) (d)

(e) (f)

(g) (h)

AL07JHO244Cahill Formationn = 61/77

AL09CJC054Cahill Formationn = 107/109

AL04NJD007Nourlangie Schistn = 63/69

ME03JHL005Nourlangie Schistn = 88/93

CP07JHO009Cahill Formationn = 52/97

AL07JHO088Cahill Formationn = 46/70

AL07JHO242bNourlangie Schistn = 54/61

AL07JHO025Nourlangie Schistn = 42/64



ytilibaborP

Age (Ma) Age (Ma)

(j)(i)

Fig. 7. Cumulative probability diagrams of <10% discordant isotopic data from: (a) sample AL07JHO244, upper Cahill Formation; (b) sample AL09CJC054, Cahill Formation; (c)sample AL04NJD007, Nourlangie Schist; (d) sample ME03JHL005, Nourlangie Schist; (e) sample CP07JHO009, Cahill Formation, (f) sample AL07JHO088, Cahill Formation; (g)sample AL07JHO242B, Nourlangie Schist; (h) sample AL07JHO025, Nourlangie Schist; (i) sample AL07JHO120, Nourlangie Schist; (j) sample AL07JHO266, Nourlangie Schist.Probability diagrams have been normalised based on number of analyses. The grey shaded bands at 2530–2470 Ma and at 2180, 2080 and 2020 Ma are shown for comparisonbetween spectra.

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The majority of grains are subhedral or anhedral, elongate andounded. Equant rounded grains are also common. Many grainsre broken fragments and localised pitting of surfaces is evident.

few euhedral grains and grain fragments are also present. Zir-ons are predominantly colourless and transparent to translucent.spect ratios are typically 1:1 to 1:3 and 50–200 �m long, aver-ging 150 �m. The majority of grains exhibit oscillatory zoningn CL images (Fig. 5d). Homogeneous bright-CL and sector-zonedrains are also common. There are also a few homogeneous, asell as irregularly zoned and metamict grains that exhibit resorp-

ion and recrystallisation textures. Around 15% of grains have rimshat truncate growth zones in older cores. These include bright-CL,ector-zoned and homogeneous-CL rims.

Ninety-three grains were analysed. Three were rejected on theasis of excess common lead and a further two on the basis ofxcess discordance. The remaining 88 analyses define an age dis-ribution that spans 3000–1972 Ma (Figs. 6d, 7d, Table S6). Thepectrum comprises a dominant peak at 2530–2450 Ma (36%),maller clusters at ca. 2340–2300 Ma (8%), 2200–2170 Ma (7%)nd 2030–2000 Ma (13%) and scattered individuals (Fig. 7d). Theoungest individuals at 1999 ± 46 Ma and 1972 ± 98 Ma (2�) havearge uncertainties, probably due to very low uranium contents95 ppm and 29 ppm respectively). A conservative maximum depo-itional age is given by the next youngest 13 analyses, which yield

weighted mean 207Pb/206Pb age of 2024 ± 7 Ma (MSWD = 1.15).

.2. LA-SF-ICPMS

.2.1. CP07JHO009 – Cahill FormationSample CP07JHO009 is a garnet-staurolite mica schist

ampled from Cameco Australia drill core (WRPD010,73.1–273.46 m) from Wellington Range (Figs. 3 and 4c). Theineral assemblage associated with the schistose fabric com-

rises garnet–staurolite–biotite–muscovite–plagioclase–quartz–ematite–pyrite.

Zircons are rounded and equant to elongate. Many preserve pris-atic grain shapes. They are transparent and colourless to very pale

ink. Typically they are 80–150 �m long with aspect ratios up to:4 but typically 1:1 to 1:2. Most grains are weakly cathodolumi-escent and show weakly to moderately well-defined oscillatoryoning, while a few grains are homogeneous (Fig. 5e).

The analytical data was collected in two sessions. In total,inety-seven analyses were made on 97 grains. Fourteen wereejected on the basis of high common lead (i.e. mass 204 signifi-antly above detection limit, see Supplementary data) and another1 on the basis of excess discordance. The discordant analyses falllong a discordia consistent with recent Pb loss. The large pro-ortion of discordant analyses may be related to the abundancef relatively small grains in this sample. The small grain size mayave allowed more pervasive infiltration of fluids to the cores ofrains along microfractures. The remaining 52 analyses form an ageistribution that spans 3028–1897 Ma (Figs. 6e, 7e, Table S7). Thepectrum comprises a dominant peak at ca. 2540–2470 Ma (50%)ith smaller clusters at 2450–2440 Ma (8%), 2400–2350 Ma (15%)

nd scattered individuals (Fig. 7e). Excluding the youngest fourcattered analyses (1897 Ma, 2179 Ma, 2297 Ma, 2304 Ma), the nextight youngest grains give a weighted mean age of 2384 ± 17 MaMSWD = 1.3), regarded as a conservative maximum depositionge.

.2.2. AL07JHO088 – Cahill Formation
Sample AL07JHO088, from the Myra Falls Inlier, is a pelitic
iotite schist with abundant flattened quartz lenses (Figs. 3 and 4d).t is unconformably overlain by the Kombolgie Sandstone immedi-tely adjacent to the sample location.

search 246 (2014) 35–53

Zircons are in low abundance in this sample. Grains are equantto elongate and rounded. They are transparent to translucent andcolourless to pale yellow to pale pink. They typically have aspectratios of 1:1 to 1:2 and are 100–200 �m long. The majority ofgrains have moderate CL responses and a minority have bright tovery bright responses. Most are oscillatory zoned (Fig. 5f). In a fewcases inner zones are truncated by outer zones. In several casesoscillatory zones are truncated at rounded grain edges. Patchy andhomogeneous grains are common and only a few grains are sectorzoned. A few have thin homogeneous rims with moderate to brightCL responses.

Seventy grains were analysed. Four were rejected on the basis ofhigh common lead and a further 20 analyses on the basis of excessdiscordance. The remaining 46 analyses define an age distribu-tion that spans 3715–2019 Ma (Figs. 6f, 7f, Table S8). The spectrumcomprises a dominant peak at 2520–2480 Ma (28%) and small clus-ters at 2470–2430 Ma (13%), 2200–2180 Ma (11%), 2080–2060 Ma(9%) and scattered individuals (Fig. 7f). The oldest five analyses at2823 Ma, 2912 Ma, 3173 Ma, 3253 Ma and 3715 Ma are distinctlyolder than all other analyses. Excluding the youngest analysis(2019 ± 30 Ma, 2�), the next five youngest grains give a conser-vative maximum age of deposition of 2078 ± 13 Ma (MSWD 1.1).

5.2.3. AL07JHO242B – Nourlangie SchistSample AL07JHO242B is an amphibolite facies biotite-

muscovite-bearing laminated psammitic schist collected fromdrill core from the Arrarra uranium prospect (Cameco Australiadrillhole AAD005, 43.63–44.14 m, Fig. 3).

The zircons are typically rounded and equant to elongate.Rounded fragments are common. They are transparent to translu-cent and colourless, very pale pink, or very pale orange. Aspectratios range from 1:1 to 1:3 and are typically 100–250 �m long.They show a range of CL responses, from dull to very bright(Fig. 5g). Most exhibit oscillatory zoning, a few with a very brightCL response. Many of the more bright-CL grains show very well-defined oscillatory and sector zoning. Some dark-CL grains arehomogeneous. A few relatively dark-CL grains show irregular zon-ing with relatively bright responses along fractures and oscillatoryzones.

Sixty-one grains were analysed. Four were rejected on the basisof high common lead and a further three on the basis of excess dis-cordance. The remaining 54 analyses define an age distribution thatspans 3212–1898 Ma (Figs. 6g, 7g, Table S9). The spectrum com-prises several significant age peaks including 2580–2510 Ma (19%),2400–2340 Ma (9%), 2250–2190 Ma (13%) and 2100–2010 Ma (19%)and scattered individuals (Fig. 7g). Excluding the two youngestgrains, the next 10 youngest grains give a conservative maximumage of deposition of 2006 ± 15 Ma (MSWD = 1.02).

5.2.4. AL07JHO025 – Nourlangie SchistSample AL07JHO025 is a medium-grained muscovite-biotite

psammitic schist from the Myra Falls Inlier. It forms part of apackage of monotonous widespread laminated pelitic and psam-mitic schists that crop out from the Myra Falls Inlier north throughthe Nabarlek uranium prospect to the Arrarra region (Figs. 3 and 4e).

Zircons are low in abundance in this sample. They range fromequant to highly elongate and are typically subhedral and rounded.They are translucent and range from colourless to pale yellow-brown to orange to pale pink. Aspect ratios are typically 1:1 to1:2.5 and 100–250 �m long. Grains have a moderate to strong CLresponse. The majority show well-defined oscillatory zoning, in a
few cases truncated at rounded grain edges (Fig. 5h). Patchy andhomogeneous grains are fairly common. Only a few grains are sec-tor zoned and a few have thin bright homogeneous rims that maybe metamorphic in origin.

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Sixty-four grains were analysed. Three analyses were rejectedn the basis of high common lead and a further 19 analyses on theasis of excess discordance. The remaining 42 analyses define ange distribution that spans 3290–1983 Ma (Fig. 6h, Fig. 7h, Table10). The spectrum comprises a dominant peak at 2520–2480 Ma48%) and a small cluster at 2190–2160 Ma (14%) with other scat-ered individuals (Fig. 7h). Excluding the four youngest grains,hich consist of a discontinuous series between 1983 Ma and

076 Ma, the next six youngest grains give a conservative maxi-um depositional age of 2172 ± 9 Ma (MSWD = 0.79).

.2.5. AL07JHO120 – Nourlangie SchistSample AL07JHO120 is a sillimanite-bearing metapsammitic

ock, which forms part of regionally extensive monotonous mica-eous and quartzitic schist of the Nourlangie Schist (Fig. 3). It wasollected from an area of isolated outcrops in a creek bed north ofhe Myra Falls Inlier.

Zircons are typically anhedral to subhedral, equant to slightlylongate rounded grains, though a few prismatic grains also occur.hey are colourless to pale orange and transparent to translucent.spect ratios are typically 1:1 to 1:2 and typically 80–150 �m long.ost have a weak to moderate CL response (Fig. 5i). A few have

ery bright CL cores or broad, very bright-CL oscillatory zones inhe core regions. Most others show weakly to moderately definedscillatory zoning, some weak sector zoning, and a few are almostompletely homogeneous.

Sixty-seven grains were analysed. Four analyses were rejectedn the basis of high common lead and a further 29 (43% of anal-ses) on the basis of excess discordance. The discordant analysesall along an array consistent with recent Pb loss. The remaining4 analyses define an age distribution that spans 3372–1865 MaFigs. 6i, 7i, Table S11). There is no single dominant age popula-ion, but rather a spread mainly from ca. 2700 Ma to 1865 Ma with

general decrease in proportion with decreasing age (Fig. 7i). Dis-egarding the six youngest individual analyses, which consist of

discontinuous series from 1865 Ma to 2136 Ma, the next threeoungest analyses yield a conservative maximum depositional agef 2217 ± 67 Ma (MSWD = 2.0).

.2.6. AL07JHO266 – Nourlangie SchistSample AL07JHO266 is a greenschist facies laminated fine-

rained chlorite-muscovite schist, collected from outcrop close tohe Arrarra uranium prospect (Figs. 3 and 4f). Zircons are in lowbundance in this sample. Grains are typically equant to slightlylongate and rounded. They are transparent and colourless to paleink. Aspect ratios are typically in the range 1:1 to 1:2.5, buteach up to 1:4, and are 100–150 �m long. The majority of grainsave a moderate-CL response, while only a few, particularly aci-ular grains, have a very bright-CL response. Almost half haveell-defined oscillatory zoning, in some cases with outer zones

runcating inner zones (Fig. 5j). In some cases, oscillatory zonesre truncated by rounded grain edges. Patchy-zoned and homoge-eous grains are also common. A few grains show irregular zoningnd have truncations consistent with zircon resorption and recrys-allisation. A few have thin bright or dark homogeneous rims, inome cases truncating inner zones.

Sixty-three grains were analysed. Twenty-five analyses wereejected on the basis of excess discordance. This relatively highroportion of discordant analyses may be the result of infiltrationf fluids along microfractures, however the discordant analyseso not have high 204, as would be expected. Alternatively theyay be the product of mixed analyses of distinct zones not visible

rom the CL images, during depth profile analysis of the sample.he remaining 38 analyses define an age distribution that spans319–2042 Ma (Figs. 6j, 7j, Table S12). There is a dominant ageeak at 2510–2490 Ma (34%) and a smaller cluster at 2460–2440 Ma

search 246 (2014) 35–53 45

(16%, Fig. 6j). The youngest four grains define a maximum deposi-tional age of 2059 ± 24 Ma (MSWD = 1.6).

5.3. Synopsis

The four Cahill Formation and six Nourlangie Schist samplesshow strong similarities in their detrital zircon spectra. All tensamples show a broad spectrum of ages, typically in the range ca.3300–1900 Ma, but in some samples extending to scattered olderages up to ca. 3700 Ma. All ten samples all have one or more dom-inant age peaks that fall in the range 2530–2470 Ma. There areother smaller common age peaks at 2460–2440 Ma, 2370–2340 Ma,2200–2160 Ma, 2090–2070 Ma and 2030–2000 Ma. These ages arenot represented in all samples, but all occur in at least five.

The four youngest grains in sample AL09CJC054 define a pop-ulation of 1866 ± 11 Ma (MSWD = 0.93), regarded as a maximumdeposition age. Four other samples have single isolated youngestgrains of 1868 ± 58 Ma (AL04NJD007), 1897 ± 68 Ma (CP07JHO009),1898 ± 24 Ma (AL07JHO242B) and 1865 ± 50 Ma (AL07JHO120).The occurrence of youngest grains in four samples of a similar ageto the youngest population in sample AL09CJC054 is interpreted toindicate the maximum deposition age.

6. Lutetium-Hafnium isotope results

6.1. Sample AL07JHO244 – upper Cahill Formation

Hf isotopic data were collected from 57 grains and results rangefrom very radiogenic (εHf +7.7) to very unradiogenic values (cor-responding εHf −14.2, Fig. 8a , Table S3). The majority of grains inthe dominant 2550–2490 Ma population (80%) have radiogenic Hfrelative to CHondritic Uniform Reservoir (CHUR, εHf +3.2 to +7.7),consistent with a dominantly Neoarchean mantle-derived source(TDM = 2.8–2.5 Ga). Five of six grains in the range 2026–2013 Ma(2020 ± 13 Ma, 95% conf., MSWD = 0.15) are strongly unradiogenic(εHf −8.2 to −13.2), consistent with 2020 Ma magmatic reworkingof a much older crustal source (TDM = 3.4–3.1 Ga).

6.2. Sample AL09CJC054 – Cahill Formation

Hf isotopic data were collected for 94 grains and results rangefrom very radiogenic (εHf +10.2), to very unradiogenic values(εHf −13.2, Fig. 8b, Table S4). The dominant 2540–2460 Ma pop-ulation shows a broad range in Hf isotopic ratios (εHf −13.2 to10.2), though the majority are radiogenic (εHf > 0, 61%), consistentwith their derivation from a Neoarchean mantle-derived source(TDM = 2.9–2.6 Ga). Seven of eight grains that form a population at2017 ± 9 Ma (95% conf., MSWD = 0.81) are strongly unradiogenic(εHf −6.7 to −12.9), again consistent with ca. 2020 Ma magmaticreworking of an older source (TDM = 3.4–2.7 Ga).

6.3. Sample AL04NJD007 – Nourlangie Schist

Hf isotopic data were collected for 34 grains and results rangefrom very radiogenic (εHf +6.0), to very unradiogenic values (εHf−11.9, Fig. 8c, Table S5). The dominant 2530–2470 Ma populationshows a range in Hf isotopic values spreading across CHUR towardsdepleted mantle compositions (εHf −5.8 to 6.0). Most of these (54%)are more radiogenic than CHUR, consistent with derivation from aNeoarchean mantle-derived source (TDM = 2.9–2.6 Ga). An outlier
at 2039 Ma is significantly more unradiogenic than all other grains(εHf −11.9), but similarly low εHf is shown by grains of the sameage in the other samples, consistent with derivation from the same,probably Meso- to Paleoarchean source.


0.28050

0.28070

0.28090

0.28110

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0.28130

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0.28190

176

/fH

177

laitini fH

Age (Ma)

(b)

(a)

0.28050

0.28070

0.28090

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0.28130

0.28150

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0.28190

1800 200 0 2200 2400 2600 280 0 3000 3200 3400

(c)

AL07JHO244Cahill Formationn = 57

AL09CJC054Cahill Formationn = 94

AL04NJD007Nourlangie Schistn = 34

DMCHUR

DMCHUR

DMCHUR

Fig. 8. Initial 176Hf/177Hf versus U–Pb age plot showing average crustal model agesfor detrital zircon from (a) Cahill Formation sample AL07JHO244, (b) Cahill Forma-tion sample AL09CJC054, (c) Nourlangie Schist sample AL04NJD007. Data are shownwCfi

7

7

vt(2�

fcwf

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Age (Ma)

1

2

3

4

5

6

7

8

9

10

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(a)

(b)

(c)

18O

(‰)

AL07JHO244Cahill Formationn = 59

AL09CJC054Cahill Formationn = 107

AL04NJD007Nourlangie Schistn = 35

Fig. 9. �18O versus age for detrital zircons from (a) Cahill Formation sampleAL07JHO244, (b) Cahill Formation sample AL09CJC054, (c) Nourlangie Schist sampleAL04NJD007. Data are shown with 2� error bars. Horizontal grey-filled bar showsthe range of values expected for zircon in equilibrium with mantle oxygen. Vertical

ith 1� error bars. DM is Depleted Mantle (Vervoort and Blichert-Toft, 1999) andHUR is CHondritic Uniform Reservoir (Blichert-Toft and Albaréde, 1997). Grey-lled bar from 2040 to 2000 Ma highlights a distinct unradiogenic Hf population.

. Oxygen isotope results

.1. Sample AL07JHO244 – upper Cahill Formation

Oxygen isotopic ratios were measured for 59 zircons and �18Oaries from 2.2 to 8.7‰ (Fig. 9a , Table S3). Forty of these (68%) fall inhe range expected for zircon in equilibrium with mantle oxygen4.7–6.5‰, Cavosie et al., 2005; Valley et al., 2005). Notably the550–2490 Ma population is dominated by grains with mantle-like18O (n = 13, 81%).

Eleven grains have �18O > 6.5‰, indicative of their derivationrom reworking of sources that have experienced a sedimentaryycle. Notably, from ca. 2300 Ma there is a broad increase in �18Oith decreasing age, consistent with an increasing contribution

rom reworked supracrustal sources from this time.There are also eight grains with �18O lower than that expected

or zircon formed in equilibrium with mantle oxygen (<4.7‰). Low
18O zircon has been explained as a result of crystallisation fromagmatic rocks produced by melting of crust previously altered by
igh-temperature meteoric fluids (e.g., Gregory and Taylor, 1981;illiam and Valley, 1997; King et al., 2000; Valley et al., 2005;

grey-filled bar from 2040 to 2000 Ma highlights a distinct elevated �18O populationand grey line at 2350 Ma highlights a distinct low �18O population.

Bindeman, 2008; Hiess et al., 2011). The low �18O grains cover aspectrum of ages from 3063 to 2186 Ma. They include a distinct agepeak at 2351 ± 10 Ma (95% conf., MSWD = 0.116) for three grainswith particularly low �18O of 2.2, 3.1, and 3.2‰.

7.2. Sample AL09CJC054 – Cahill Formation

Oxygen isotopic ratios were measured for one hundred andseven zircons and �18O results cover a very broad range from 0.9to 9.4‰ (Fig. 9b, Table S4). The 2550–2480 Ma population in thissample is dominated by zircon with �18O consistent with being in
equilibrium with mantle oxygen (73%, 5.4–6.5‰).
The seven (of eight) grains that form a population at 2017 ± 9 Mahave �18O in the range 4.9–8.2‰. Although this covers a broad

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pectrum, all but one fall in the range 6.3–8.2‰, consistent witherivation from reworked supracrustal sources.

This sample has five grains with �18O values lower than thatould be expected for zircon in equilibrium with mantle oxygen

4.7‰). Notably, a distinct population at 2341 ± 10 Ma (95% conf.,SWD = 0.55, n = 6), is dominated by the lowest �18O values of 0.9,

.2, 2.5, and 2.7‰ (n = 4 of 6).Thirty-eight grains have �18O > 6.5 up to 9.4‰, indicative of

heir derivation from sources that have experienced a sedimen-ary cycle. These grains have a broad spectrum of ages in the range231–1853 Ma. Notably, from ca. 2150 Ma, there is a general trendo higher �18O with decreasing age.

.3. Sample AL04NJD007 – Nourlangie Schist

Oxygen isotopic ratios were measured for 35 zircons and �18Oaries from 4.3 to 9.0‰ (Fig. 9c, Table S5). Twenty-six grains (in theange 3239–1952 Ma) fall in the range expected for zircon in equi-ibrium with mantle oxygen (<6.5‰). Of the 13 grains that formhe 2530–2470 Ma population, all but three have �18O in the range.7–6.5‰ (i.e. 77%), consistent with a dominant mantle-like oxygenource. Six grains have �18O > 6.5‰, indicative of their derivationrom reworking of sources that have experienced a sedimentaryycle. These grains have a broad spectrum of ages in the range487–1943 Ma. There are three grains with �18O < 4.7‰, with ages

n the range 2478–2300 Ma.

. Discussion

.1. Timing of deposition

The depositional age of the Cahill Formation and Nourlangiechist is well constrained by the detrital zircon data coupled withhe emplacement age of the Nimbuwah Complex, which intrudeshese units. A maximum age of deposition is given by the youngestopulation in Cahill Formation sample AL07CJC054 of 1866 ± 11 Mand is supported by similarly aged isolated youngest grains in onether Cahill Formation sample (CP07JHO009) and three Nourlangiechist samples (AL04NJD007, AL07JHO242B and AL07JHO120). Onhe basis of 1867–1857 Ma magmatic crystallisation ages for thentrusive Nimbuwah Complex (Page et al., 1980; Worden et al.,008a; Carson et al., 2010; Beyer et al., 2013; Kositcin et al., 2013),he maximum depositional age of 1866 ± 11 Ma for the Cahill For-

ation must be within error of the timing of deposition.

.2. Provenance

Similarities in the detrital spectra of the four Cahill Formationnd six Nourlangie Schist samples are consistent with the inter-retation of a transitional, conformable (meta)sedimentary suc-ession. The dominant detrital age peaks occur at 2530–2470 Ma,180 Ma, 2080 Ma and 2020 Ma.

Most of the detrital zircon in the Cahill Formation andourlangie Schist are derived from a relatively juvenile530–2470 Ma source or sources, indicated by mainly mantle-like18O values (Fig. 9) and corresponding mainly radiogenic HfFig. 8). Although there are proximal underlying granitic andneissic basement rocks of the same age (2527–2510 Ma Kukalakneiss, 2520 Ma Nanambu Complex, 2545–2521 Ma Rum Jungleomplex, Page et al., 1980; Cross et al., 2005aHollis et al., 2009a;arson et al., 2010), these are all characterised by unradiogenicf and heavy �18O zircon (typically εHf = 0 to −7 and �18O > 6.5‰,
ollis et al., 2010; Beyer et al., 2013). The implication is thateoarchean basement from the Pine Creek Orogen is probably not
he main source of 2530–2470 Ma detritus in the Cahill Formationnd Nourlangie Schist, unless there is considerable, currently

search 246 (2014) 35–53 47

unrecognised, isotopic heterogeneity in the basement. Anotherpossibility is that detritus of this age may have been derived frommagmatically reworked 2640 Ma Arrarra Gneiss, which crops outin the Nimbuwah Domain and which is has similarly radiogenicHf and mantle-like �18O (Hollis et al., 2010). However, if this isthe case, the magmatic sources for the detritus have not yet beenidentified in the Pine Creek Orogen.

Further afield, there are two possibilities based on (a) consistentage and isotopic compositions of potential source rocks and detritalzircons in the Cahill Formation and Nourlangie Schist and (b) suit-able geographic locations based on current tectonic reconstructionsof Columbia (Nuna) at ca. 1870 Ma. These two possibilities are theGawler Craton and the Dharwar Craton.

From the Gawler Craton, the 2520 Ma Coulta Granodiorite(Fanning et al., 2007; Howard et al., 2009) is a possible isotopicmatch for the 2530–2470 Ma detritus in the Cahill Formation andNourlangie Schist. The Coulta Granodiorite has magmatic zirconwith radiogenic Hf (εHf = +1.8 to +5.4, Howard et al., 2009). Similarly,detrital zircon Hf TerraneChron data for modern stream sedimentsfrom the Gawler Craton (Belousova et al., 2006) also indicate a sig-nificant phase of juvenile magmatism in the latest Neoarchean,consistent with Hf data for 2530–2470 Ma detrital zircon in theCahill Formation and Nourlangie Schist, which dominantly haveεHf > 0. Furthermore, a small but significant 2020 Ma age peakin the detrital spectra of the Cahill Formation and NourlangieSchist has a distinct isotopic signature that can also be matchedto possible sources in the Gawler Craton. These 2020 Ma zirconsin the Cahill Formation and Nourlangie Schist are characterisedby unradiogenic Hf and elevated �18O (Figs. 8 and 9, εHf = −6.7 to−14.2 and �18O = 5.9–8.7‰), indicative of a source derived fromreworking of much older supracrustal rocks. The magmatic ageis coincident with that of the Stag Creek Volcanics (NamoonaGroup) and tuff beds within the Wildman Siltstone (Mount Par-tridge Group, Worden et al., 2008a, 2008b) of the Central Zone ofthe Pine Creek Orogen. However, volcanic zircon from tuff in theWildman Siltstone have radiogenic Hf zircon (εHf = +0.1 to +6.8,Howard et al., 2009) and are thus unlikely to be the source forthis detritus. Detrital zircon TerraneChron data for modern streamsediments of the Gawler Craton (Belousova et al., 2006) include2035–2000 Ma zircon, ca. 18% of which have εHf < −7, consistentwith values observed from our detrital samples. Thus it is possi-ble that there is a source of this age and isotopic character withinthe Gawler Craton that may have fed detritus to the Cahill Forma-tion and Nourlangie Schist at ca. 1870 Ma. A recent, proto-SWEATtectonic reconstruction of the Mawson Continent (Payne et al.,2009) places the Gawler Craton east of the Arunta region along acommon eastern margin of the North Australian Craton with thePine Creek Orogen at ca. 1870 Ma. Although potentially still ca.1000 km distant from the Pine Creek Orogen at this time, along-margin transport of detritus from the Gawler Craton (or similar,now unexposed crust between the two) is possible in this sce-nario.

Links between the Pine Creek Orogen and the Gawler Cratonhave been made previously by several authors (Hand et al., 2007;Howard et al., 2009; Payne et al., 2009) based on similarities in theirlatest Neoarchean to Palaeoproterozoic magmatic and tectonicevolutions. Both regions experienced latest Neoarchean graniticmagmatism (2545–2510 Ma Rum Jungle and Nanambu complexesand Kukalak Gneiss in the Pine Creek Orogen, and 2550–2440 MaMulgathing and Sleaford complexes in the Gawler Craton; Pageet al., 1980; Daly and Fanning, 1993; Daly et al., 1998; Cross et al.,2005aFanning et al., 2007; Hollis et al., 2009a; Carson et al., 2010).
At ca. 2500–2470 Ma Neoarchaean granitic rocks in the Pine CreekOrogen record metamorphic zircon growth (Worden et al., 2006a;Hollis et al., 2009a; Carson et al., 2010), while metamorphism of the2480–2420 Ma Sleafordian Orogeny ensued in the Gawler Craton

4 ian Re

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Daly and Fanning, 1993; Daly et al., 1998). Both regions thennderwent ca. 400 Ma of tectonic quiescence prior to ca. 2020 Maelsic magmatism (granitic Miltalie Gneiss, Gawler Craton and

ildman Siltstone tuff and Stag Creek Volcanics, Pine Creekrogen; Fanning et al., 1998, 2007; Worden et al., 2008a, 2008b).oward et al., 2009 also noted that 2020 Ma detrital zircon with

trongly radiogenic Hf in the 1880–1870 Ma Corny Point Paragneissn the Gawler Craton have no known local source but are consistent

ith derivation from 2020 Ma zircon from tuff of the Wildmaniltstone in the Pine Creek Orogen, supporting a possible con-ection between the Gawler Craton and Pine Creek Orogen at ca.870 Ma. Both the Pine Creek Orogen and the Gawler Craton werehen emplaced by 1870–1850 Ma granites characterised by similar,nradiogenic Nd, during compressional tectonism (εNd = −2 to −4,imbuwah Complex in the Pine Creek Orogen, Donington Suite in

he Gawler Craton; Mortimer et al., 1988; Reid et al., 2008; Glasst al., 2009; Hollis and Glass, 2012). After this, the tectonothermalistories of the Pine Creek Orogen and the Gawler Craton diverge.

An alternative to sourcing Archean detritus from the Gawlerraton, is a source from the Dharwar Craton and northern Madu-ai Block of southern India. In this region 2560–2520 Ma granitesnd granitic orthogneiss (Krogstad et al., 1991, Friend and Nutman,992; Peucat et al., 1993; Jayananda et al., 1995, 2000; Anandt al., 2014; Mohan et al., 2014) have relatively juvenile whole rockd isotope compositions (εNd −2.8 to +1, Jayananda et al., 2000;lavsa et al., 2012). These granites and felsic volcanic rocks of theame age from the Dharwar Craton have heterogeneous Hf zirconompositions of εHf = −13.0 to +7.1, indicating both juvenile andlder reworked components, which have been interpreted as beingerived from heterogeneous mantle sources with variable contrib-tions from reworked older crust (Praveen et al., in press; Mohant al., 2014). Also, 2690 Ma and 2630–2610 Ma granites are knownrom the same area (Plavsa et al., 2012; Jayananda et al., 2000), simi-ar to the age of magmatism of the Njibinjibinj and Arrarra Gneissesn the Nimbuwah Domain (Hollis et al., 2009a) and which may indi-ate a common Archean history. A recent tectonic reconstructionf Columbia (Nuna) at ca. 1880–1800 Ma (Zhang et al., 2012) placesndia immediately to the north of the North Australian Craton at thisime, which may have allowed transport of detritus from southernndia to the Pine Creek Orogen at the time of deposition of the Cahillormation and Nourlangie Schist.

Sources for the remaining detrital ages in the range ca.700–1900 Ma in the Cahill Formation and Nourlangie Schist arenknown. Specifically, significant age peaks at ca. 2180 Ma anda. 2080 Ma are not ages that are known from magmatic rocks inhe North Australian Craton. It is possible that these zircons wereerived from recycling of older sedimentary rocks that are no longerxposed. Noteworthy is a very small population at ca. 2350 Maresent in several samples of the Cahill Formation and Nourlangiechist. In two of the three samples analysed for Hf and O, the fewrains of this age have very low �18O values ranging 0.9–5.2‰. Fivef those six grains have �18O < 3.2‰. Care is advised in placing toouch emphasis on these results, given the small number of analy-

es and given that analysis sites were not re-imaged after analysis tossess for cracks not apparent at surface. However, their occurrencen two samples and in zircons of the same age is consistent withheir derivation from a 2350 Ma source formed by melting of rockshat were altered by hydrothermal fluids or by meteoric water.lthough a minor detrital component, its distinct �18O signatureay prove useful in regional correlations.

.3. Regional correlations

The detrital zircon spectra of the Cahill Formation andourlangie Schist are distinct from both the ca. 2020 Ma Wood-utters Supergroup (exemplified by the Beestons Formation and

search 246 (2014) 35–53

Acacia Gap Quartzite Member, Fig. 10) and the ca. 1862 Ma CosmoSupergroup (Burrell Creek Formation, Fig. 10) of the Central Domainof the Pine Creek Orogen. Sandstone and quartzite units of theca. 2020 Ma Woodcutters Supergroup are characterised by a dom-inant ca. 2500 Ma detrital peak, in some cases with lesser ca.2670–2640 Ma peaks (Fig. 10). Aside from the marked differencein the overall detrital zircon spectra compared with the CahillFormation and Nourlangie Schist (Fig. 10), the 2020 Ma age ofconstituent volcanic units (Stag Creek Volcanics and Wildman Silt-stone) establish the Woodcutters Supergroup as much older thanthe ca. 1866 Ma Cahill Formation and Nourlangie Schist and thusthey cannot be correlative (cf. Needham et al., 1980; Needham,1988).

In contrast to the Woodcutters Supergroup, siltstones of the Bur-rell Creek Formation of the Cosmo Supergroup are characterisedby a dominant ca. 1870 Ma peak with a small ca. 2500 Ma peakand some older Archean grains (Fig. 10). Metasedimentary rocksof the Hermit Creek and Welltree Metamorphics in the LitchfieldDomain also show similar detrital zircon spectra and have beencorrelated with the Burrell Creek Formation (Pietsch and Edgoose,1988). Their detrital spectra are again quite distinct from the CahillFormation and Nourlangie Schist, which contain almost no ca.1870 Ma zircon. Furthermore the Burrell Creek Formation and cor-relatives were deposited at ca. 1862 Ma, based on the timing ofcrystallisation of the 1863 ± 2 Ma Gerowie Tuff (South AlligatorGroup), 1861 ± 4 Ma Berinka Volcanics and 1862 ± 3 Ma Warrs Vol-canic Member (Finniss River Group, Fig. 2; Worden et al., 2008a,2008b). Thus sedimentation of the Cosmo Supergroup in the Cen-tral Domain was occurring during emplacement of the NimbuwahComplex into, and amphibolite facies metamorphism of, the CahillFormation and Nourlangie Schist (see also Hollis and Glass, 2012),illustrating that the latter units must be older and most likelydeposited in a geographically distinct area.

8.4. Implications for Paleoproterozoic tectonism in the Pine CreekOrogen

The presence of the Woodcutters Supergroup in both the Nim-buwah (Kakadu Group) and Central Domains (Namoona Group,Masson Formation, Mount Partridge Group) overlying Neoarcheanbasement of similar age suggests a common tectonic history fromthe Neoarchean through to ca. 2020 Ma, when deposition of theWoodcutters Supergroup occurred, probably in a rift environment(Stuart-Smith et al., 1984). However, the distinct detrital spectraand timing of deposition of the Cahill Formation and NourlangieSchist and subsequent deformation and metamorphism,compared with the Cosmo Supergroup of the Central Domain,indicate that the depositional and tectonic environments of thetwo domains diverged after 2020 Ma.

A ca. 1870 Ma age peak dominates detrital zircon spectra fromnot only the Burrell Creek Formation of the Central Domain, butalso from most Paleoproterozoic (meta)sedimentary successions inthe North Australian Craton (e.g. Neumann et al., 2006; Cross andCrispe, 2007; Claoué-Long et al., 2008a, 2008b; Wade et al., 2008;Worden et al., 2008a; Carson, 2013). Examples from the Tanamiand Arunta regions are shown in Fig. 10. (The Ferdies Member,Tanami region, is an exception, being dominated by Neoarcheandetritus and showing some similarities with the detrital spectraof the Woodcutters Supergroup, Pine Creek Orogen.) The absenceof this dominant ca. 1870 Ma source or sources in the Cahill For-mation and Nourlangie Schist is consistent with their depositionshortly prior to 1865 Ma, which is also constrained by intrusion of
the 1867–1857 Ma Nimbuwah Complex (Page et al., 1980; Wordenet al., 2008b; Carson et al., 2010; Kositcin et al., 2013). Deposition,however, can only have been immediately prior to Nimbuwah mag-matism, given their maximum deposition age of 1866 ± 11 Ma. The


Ferdies Membern=86

Killi Killi Formationn=58

Wilson Formationn=75

Lander Rock Formationn=77

Delmore Metamorphicsn=49

Prickle Hill Sandstonen=84

Beestons Formationn=72

Acacia Gap Quartziten=71

Burrell Creek Formationn=69

n=584Cahill Formation andNourlangie Schist

Pine Creek Oroge n Tanami Regio n Arunta Region

1

1

2 3

3

3

4

5

6

1.8 2. 0 2. 2 2. 4 2. 6 2. 8 3. 0 3. 2 3. 4 3.6Age (Ga)

1.8 2. 0 2. 2 2. 4 2. 6 2. 8 3. 0 3. 2 3. 4 3.6Age (Ga)

1.8 2. 0 2. 2 2. 4 2. 6 2. 8 3. 0 3. 2 3. 4 3.6Age (Ga)

Fig. 10. Comparison of detrital zircon data from the combined data set for the Cahill Formation and Nourlangie Schist (this study) with data from other units in the PineC e vertr 0 Ma a( yer et

Nfrad

reek Orogen, Tanami and Arunta regions. Only <10% discordant data are shown. Thanges from 1800 Ma (left) to 3700 Ma (right) in each case with vertical lines at 1872008a), 3Cross and Crispe (2007), 4Worden et al. (2006b), 5Cross et al. (2005b), 6Be

imbuwah Complex, and/or volcanic equivalents, may indeed have
ormed part of the source for the ca. 1870 Ma detritus in the Bur-ell Creek Formation in the Central Domain. If so, this also impliesctive uplift and erosion of the Nimbuwah Domain shortly after oruring Nimbuwah – aged magmatism.
ical axis corresponds to interpreted relative time of deposition. The horizontal axisnd 2500 Ma for reference. Data are taken from 1 Cross et al. (2005a), 2Worden et al.

al. (2013).

The distinct provenance of the Cahill Formation and Nourlangie
Schist from the Cosmo Supergroup also suggests they weredeposited in geographically distinct areas. This is consistent withtheir current distribution on either side of a Neoarchean basementhigh known as the Nanambu Ridge, which is characterised by a

5 ian Research 246 (2014) 35–53

hiWfbztgmN

wgsrStoaa1ttoNtsfbaawcmfno2fluS(vb

8C

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0.000

0.001

0.002

0.003

0.004

0.005

400038003600340032003000280026002400220020001800

Pro

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lity

Age (Ma)

Fig. 11. Cumulative probability diagram (dark grey) of all <10% discordant detritalzircon ages for the Cahill Formation and Nourlangie Schist for which �18O was alsoobtained (samples AL07JHO244, AL09CJC054, AL04NJD007). Light grey shaded area


igh in Bouguer gravity data (Lewis et al., 1995). Based on changesn the structural style and metamorphic grade across this ridge (e.g.

orden et al., 2008b; Carson et al., 2008), which is also the criteriaor the boundary between the Central and Nimbuwah Domains, thisasement high likely represents a strongly tectonised boundaryone. Combined with the provenance data from the Cahill Forma-ion and Nourlangie Schist, which have a significant proportion ofrains derived from unknown oldest Paleoproterozoic sources, thisay also mark a transition into an allochthonous succession in theimbuwah Domain.

We propose that the Cahill Formation and Nourlangie Schistere deposited at a plate margin immediately prior to conver-

ent margin tectonism and crustal thickening. A continental marginetting is consistent with the near-shore shelf depositional envi-onment, based on interpretation of lithofacies (Needham andtuart-Smith, 1976). Subsequent inferred convergent margin tec-onism was responsible for burial, deformation and metamorphismf the succession during granitic to dioritic Nimbuwah magmatismt ca. 1867–1857 Ma. This is supported by evidence from zirconge data for rapid burial to mid-crustal depths in the period ca.870–1867 Ma, i.e. the time interval from sedimentary depositiono the earliest known emplacement of Nimbuwah Complex plu-ons, which in turn are linked to amphibolite facies metamorphismf the Cahill Formation and Nourlangie Schist (Ferguson, 1980;eedham et al., 1988; Hollis and Glass, 2012). We also propose

hat active uplift in the volcanic/magmatic zone resulted in depo-ition of dominantly ca. 1870 Ma detritus into the Central Domainorming the Burrell Creek Formation at ca. 1862 Ma (also suggestedy Ferguson, 1980). Also, limited geochemical data available formphibolites within the Cahill Formation and Nourlangie Schistre calc-alkaline to shoshonitic (Hollis and Glass, 2012), consistentith active margin magmatism. The dominance of zircon ages of

a. 1870 Ma, close to the depositional age of the Burrell Creek For-ation, is also consistent with detrital zircon age patterns typically

ound in convergent margin settings (e.g. Cawood et al., 2012). Sig-ificant uplift of the Nimbuwah Domain by 1820–1800 Ma (basedn isotopic age constraints of Polito et al., 2005 and Worden et al.,006b) is also indicated by the unconformable contact betweenuvial sediments of this age of the basal McArthur Group withnderlying amphibolite facies Cahill Formation and Nourlangiechist. Stratigraphically underlying (Gerowie Tuff) and interleavedBerinka Volcanics, Warrs Volcanic Member) ca. 1862 Ma felsicolcanics may represent high crustal level equivalents of the Nim-uwah Complex.

.5. Implications for the crustal evolution of the North Australianraton

Detrital zircon data presented here have implications for under-tanding the crustal evolution of the North Australian Craton inerms of the timing and nature of crustal growth processes. Theombination of Hf and O isotope data can be used to distinguishetween magmatic events that represent formation of new crustrom those that are the product of reworking of existing, olderrust (e.g. Hawkesworth and Kemp, 2006). This is illustrated forhe Cahill Formation and Nourlangie Schist in Fig. 11, which showsll age data for grains from which �18O data were collected, as wells Hf model ages for those grains with �18O < 6.5‰, i.e. those consis-ent with formation from sources with mantle-like oxygen. Thesef model ages therefore could correspond to periods of crustalrowth by addition of juvenile melt, if other assumptions in the
odel age formulation are satisfied. The data are dominated by Hfodel ages of ca. 2750–2550 Ma, suggesting a significant period of
uvenile crust formation in the Neoarchean. There are also smaller,ess well defined model age peaks in the range 3400–3000 Ma.

shows Hf model ages for those analyses with �18O < 6.5‰, reflecting ages of juvenilecrust formation.

The detrital zircon data for the Cahill Formation and NourlangieSchist also shed light on a period of the Australian Proterozoicthat is not well represented in the rock record. Australian Protero-zoic orogenic belts are typically characterised by Nd model agesin the range 2400–2000 Ma (e.g. McCulloch, 1987), though mag-matic rocks of this age in Australia are relatively rare. This suggeststhat either juvenile rocks of this age have simply not been iden-tified (or preserved) or that these Nd model ages reflect mixing ofyounger juvenile sources with older reworked crust. The Cahill For-mation and Nourlangie Schist are relatively unusual in preservinga significant proportion of detrital zircon derived from magmaticrocks in this age range (ca. 2400–1900 Ma). Notably, all of the detri-tal zircon from the Cahill Formation and Nourlangie Schist in therange 2400–1900 Ma is the product of reworking of older, mainlylatest Neoarchean crust, with no indication of juvenile magmatism(Fig. 11). This suggests that magmatic reworking of older crust,rather than juvenile crust formation, dominated this period. Thisconclusion is supported by zircon O data for the Cahill Formationand Nourlangie Schist, which shows a trend towards increasinglyelevated �18O with decreasing age for detrital grains <2300 Ma(Fig. 9). This trend is consistent with an increasing contributionfrom reworking of supracrustal source rocks through the Paleopro-terozoic and is similar to global trends for detrital zircon youngerthan ca. 2500 Ma (e.g. Valley et al., 2005).

9. Conclusions

Ten samples of the Cahill Formation and Nourlangie Schist havedetrital zircon spectra that are internally consistent but whichare distinct from other sedimentary successions in the Pine CreekOrogen and the North Australian Craton more generally. Previouslithostratigraphic correlations of these units with other parts of thePine Creek stratigraphy are invalid, which has implications for ura-nium exploration strategies in particular. Instead we interpret theCahill Formation and Nourlangie Schist as a probably allochthonoussuccession. A maximum age of deposition of 1866 ± 11 Ma forone sample of the Cahill Formation is consistent with ages ofisolated individual youngest grains in another four samples. Thescarcity of detrital zircon of this age is attributed to deposition ofthe Cahill Formation and Nourlangie Schist immediately prior toconvergent tectonism, which generated the voluminous intrusive1867–1857 Ma Nimbuwah Complex and probably also felsic vol-
canics of the same age in the Central Domain of the Pine CreekOrogen. By contrast, the dominance of ca. 1870 Ma detrital zir-con in sedimentary rocks of the slightly younger, 1862 Ma Cosmo

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upergroup is attributed to derivation from magmatic and/or vol-anic equivalents of the actively shedding Nimbuwah Complex.

Zircon isotope data shows that the sources that eroded toorm the sedimentary precursors to the Cahill Formation andourlangie Schist are largely unknown in the North Australian Cra-

on. The detrital spectra are largely dominated by 2530–2470 Maircon, which may be in part derived from the known underly-ng Neoarchean basement, but which is isotopically more similaro juvenile felsic basement rocks of this age in the Gawler Cra-on or the Dharwar Craton. These data and existing recognisedommonalities in their Neoarchean to Palaeoproterozoic historiesuggest that the Pine Creek Orogen and Gawler Craton, now sepa-ated by ca. 1500 km, may have shared a common history until ca.870–1850 Ma.

cknowledgements

The traditional owners are thanked for permission to workn Arnhem Land, and Peter Campbell (NTGS) and the Northernand Council for facilitating access. Cameco Australia Pty Ltd pro-ided field accommodation, mess facilities, access to field data andrill core samples. Energy Resources Australia Pty Ltd. providedccess to drill core. Field support from Niels Nielsen, Darryl Stacey,imon Fanning, Darren Carpenter, and Steen Rosenberg-Nielsen,rafting by Kathy Johnston, cartographic work by Russell Poolend editing by Tim Munson (all NTGS) are acknowledged. Patrickurke, Emma Chisholm, Simon Bodorkos, David DiBugnara, Chrisoudoulis, Stephen Ridgway, Keith Sircombe (all GA) and Dirk FreiGEUS) are thanked for their professionalism and skill in providingeochronology services. Masood Ahmad, Andrew Browne, Dorothylose, Andrew Cross, John Fabray, Subhash Jaireth, Gavin Otto, Paulelville, Jennifer Parks, Paul Polito, Ian Scrimgeour, Roger Skir-

ow and Jeremy Wykes are thanked for constructive discussions.K acknowledges receipt of an Australian Research Council fel-owship (DP0773029). Dave Huston and Andrew Cross providedonstructive reviews of an early version. Two anonymous review-rs are thanked for constructive comments. This contribution is aroduct of the National Geoscience Agreement and is publishedith the permission of the Directors, NTGS, GSWA, and the CEO ofeoscience Australia (Geocat 74927).

ppendix A. Supplementary data

Supplementary data associated with this article can be found,n the online version, at http://dx.doi.org/10.1016/j.precamres.014.02.013.

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Documents

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