Crustal Architecture of the Capricorn Orogen, Western Australia and Associated Metallogeny

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TAJE_A_826735.3d (TAJE) 09-10-2013 19:18

Australian Journal of Earth Sciences (2013) 60, 681–705, http://dx.doi.org/10.1080/08120099.2013.826735

Crustal architecture of the Capricorn Orogen, Western Australia and associated metallogeny

S. P. JOHNSON1*, A. M. THORNE1, I. M. TYLER1, R. J. KORSCH2, B. L. N. KENNETT3, H. N. CUTTEN1, J. GOODWIN2, O. BLAY1, R. S. BLEWETT2, A. JOLY4, M. C. DENTITH4, A. R. A. AITKEN4, J. HOLZSCHUH2, M. SALMON3, A. READING5, G. HEINSON6, G. BOREN6, J. ROSS6, R. D. COSTELLOE2 AND T. FOMIN2

1Geological Survey of Western Australia, Department of Mines and Petroleum, Mineral House, 100 Plain Street, East Perth, WA 6004, Australia 2Minerals and Natural Hazards Division, Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia 3Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia 4Centre for Exploration Targeting, School of Earth and Environment, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia 5School of Earth Sciences and CODES Centre of Excellence, University of Tasmania, Private Bag 79, Hobart, TAS 7001, Australia 6Centre for Tectonics, Resources and Exploration, University of Adelaide, Adelaide, SA 5005, Australia

A 581 km vibroseis-source, deep seismic reflection survey was acquired through the Capricorn Orogen of Western Australia and, for the first time, provides an unprecedented view of the deep crustal architecture of the West Australian Craton. The survey has imaged three principal suture zones, as well as several other lithospheric-scale faults. The suture zones separate four seismically distinct tectonic blocks, which include the Pilbara Craton, the Bandee Seismic Province (a previously unrecognised tectonic block), the Glenburgh Terrane of the Gascoyne Province and the Narryer Terrane of the Yilgarn Craton. In the upper crust, the survey imaged numerous Proterozoic granite batholiths as well as the architecture of the Mesoproterozoic Edmund and Collier basins. These features were formed during the punctuated reworking of the craton by the reactivation of the major crustal structures. The location and setting of gold, base metal and rare earth element deposits across the orogen are closely linked to the major lithospheric-scale structures, highlighting their importance to fluid flow within mineral systems by the transport of fluid and energy direct from the mantle into the upper crust.

KEYWORDS: Ashburton Basin, Capricorn Orogen, Collier Basin, Edmund Basin, Fortescue Basin, Gas- coyne Province, Glenburgh Orogeny, Glenburgh Terrane, Hamersley Basin, intracontinental reworking, mineralisation, Narryer Terrane, Ophthalmian Orogeny, Pilbara Craton, seismic reﬂection study, suture zone, West Australian Craton, Yilgarn Craton.

INTRODUCTION inaccessibility of the bedrock, up to 80% of which is cov-

Downloaded by [Australian National University] at 15:07 07 November 2013 ered by a thick layer of regolith, or is locally deeply Like most continental regions on Earth, the Australian weathered (Australian Academy of Science 2012). It also continent is particularly well endowed with several suffers from a lack of detailed geological knowledge in large, high-quality (or giant) orebodies including iron some underexplored (greenfields) parts of the continent. – ore in the Hamersley Ranges of the Pilbara, lead zinc at A variety of geological evidence has shown that the for- – – Broken Hill, uranium copper gold at Olympic Dam and mation of giant orebodies or deposit clusters in the – – – lead zinc copper gold at Mount Isa, as well as numerous upper crust, are directly related to specific tectonic set- high-quality gold and nickel deposits. The large range of tings (e.g. Groves et al. 2005; Kerrich et al. 2005;Begg commodities and abundance of deposits has been the et al. 2010; Hronsky et al. 2012), and that they commonly ’ main driver for Australia s recent economic success and occur above deep crustal structures that mark the edges stability; however, these resources are being depleted at of discrete continental blocks, such as fossil suture a rate greater than they are being discovered. The zones or the extended margins of rifted continents. decline in exploration success is due mostly to the

*Corresponding author: [email protected] Ó 2013 Crown Copyright TAJE_A_826735.3d (TAJE) 09-10-2013 19:18

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Regional-scale geophysical surveys, including aeromag- orientation of major crustal structures and craton edges, netic, gravity and a range of passive and active seismic as well as any island arc, or exotic accreted crustal techniques, provide a relatively rapid method for greatly material. increasing our geological understanding of deeply bur- In April and May 2010, 581 km of vibroseis-source, ied or weathered geological terranes, as well as provid- deep seismic reflection data were acquired along three ing critical first-order constraints on crustal traverses (10GA–CP1, 10GA–CP2, and 10GA–CP3) architecture (e.g. Golbey et al. 2006; Aitken & Betts 2009; through the well-exposed western part of the orogen. Cayley et al. 2011). When these geophysical methods are These data were interpreted in conjunction with 400 m- combined with some degree of geological knowledge, line-spaced aeromagnetic and 2.5 km-spaced regional regions of preferential mineral endowment can be iden- gravity data, as well as detailed gravity and magnetotel- tified, providing a locus for mineral exploration and luric data that were collected along the length of the sur- targeting. vey. The traverses started in the southern part of the The Capricorn Orogen of Western Australia is a Pilbara Craton, crossed the Gascoyne Province, and 1000 km long, 500 km wide region of variably deformed ended in the Narryer Terrane of the Yilgarn Craton rocks located between the Pilbara and Yilgarn Cratons (Figures 2, 3). The project was a collaboration between (Figure 1) and records the Paleoproterozoic assembly of the Geological Survey of Western Australia (GSWA), these cratons to form the West Australian Craton, as AuScope (a component of NCRIS, the National Collabora- well as over one billion years of subsequent intracra- tive Research Infrastructure Strategy), and Geoscience tonic reworking (Cawood & Tyler 2004; Sheppard et al. Australia. The seismic data were processed by the Seis- 2010a, b; Johnson et al. 2011a). Apart from the extensive mic Acquisition and Processing team of the Onshore high-grade iron-ore deposits along the southern Pilbara Energy and Minerals Division at Geoscience Australia margin, the region has few working mines and has had and interpreted by the authors of this paper during sev- little history of recent world-class orebody discovery. eral interpretation sessions. The seismic processing The western part of the orogen is particularly well steps, 2.5D geophysical forward modelling and geological exposed, and as a result the surface geology, geological interpretation of the seismic data are outlined in detail history and plate tectonic setting of the orogen is mostly in Johnson et al. (2011b) and in the Supplementary well understood (e.g. Sheppard et al. 2010b; Johnson Paper. This paper presents the results of that final inter- et al. 2011a). However, owing to extensive crustal rework- pretation in order to construct a rigid architectural and ing, the location of major crustal structures and broad geological framework for the orogen, and to better architecture of the orogen are poorly constrained. To understand the nature and geometry of events associ- improve the exploration potential of the region, a better ated with both the assembly and punctuated reactivation understanding of the crustal architecture across the oro- of the West Australian Craton. This improved and inte- gen is critical, especially identifying the location and grated geological dataset also provides critical Downloaded by [Australian National University] at 15:07 07 November 2013

Figure 1 Elements of the Capricorn Orogen and surrounding cratons and basins, showing the location of the Capricorn Oro- gen seismic transect. Modified from Martin & Thorne (2004). The thick grey lines delimit the northern and southern boundaries of the Capricorn Orogen. Inset shows location of the Capricorn Orogen and Paleoproterozoic crustal elements (KC, Kimberley Craton; NAC, North Australian Craton; SAC, South Australian Craton; WAC, West Australian Craton) and Archean cratons (YC, Yilgarn Craton; PC, Pilbara Craton; GC, Gawler Craton). Other abbreviations: MI, Marymia Inlier; YGC, Yarlar- weelor Gneiss Complex. TAJE_A_826735.3d (TAJE) 09-10-2013 19:18

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Figure 2 Geological map of the western Capricorn Orogen, showing the location of the Capricorn Orogen seismic lines 10GA– CP1, 10GA–CP2, and 10GA–CP3. TAJE_A_826735.3d (TAJE) 09-10-2013 19:18

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Figure 2 Continued.

geodynamic information that may be used to identify core of the orogen; and numerous, variably deformed regions of the upper crust that may contain a preferen- low-grade metasedimentary rocks—including the upper tial mineral endowment or be more prospective for par- Wyloo, Bresnahan, Mount Minnie, Padbury, Bryah, Yer- ticular commodities. rida, Earaheedy,Edmund and Collier Groups—that overlie the West Australian Craton (Figures 1–4; Cawood & Tyler 2004; Sheppard et al. 2010b). The geological data GEOLOGICAL SETTING are summarised in a time–space plot in Figure 4, and a detailed geotectonic history of the orogen, in the vicinity Early interpretations of the Capricorn Orogen (e.g. of the seismic traverse, is provided below. Horwitz & Smith 1978; Gee 1979) favoured an intracratonic setting. These were followed by plate tectonic models in which the Proterozoic orogeny was driven by collision between the hitherto unrelated Pilbara and Yil- The Pilbara Craton and Archean to Proterozoic garn Cratons (Muhling 1988; Tyler & Thorne 1990; Blake sedimentation in the northern Capricorn Orogen & Barley 1992; Powell & Horwitz 1994; Evans et al. 2003). Downloaded by [Australian National University] at 15:07 07 November 2013 More recent work, however, has highlighted the com- During the late Archean and Paleoproterozoic, prior to plexity of the Capricorn Orogen, which has now been the collision of the Pilbara Craton with the Glenburgh shown to record at least seven major orogenic events Terrane of the Gascoyne Province, the southern margin (Figure 4; e.g. Sheppard et al. 2010b), the oldest two of of the craton evolved from an intracontinental rift to a which, the 2215–2145 Ma Ophthalmian Orogeny and the passive margin, before being converted to an active mar- 2005–1950 Ma Glenburgh Orogeny, relate to the punctu- gin, and subsequently into a series of foreland basins ated assembly of the West Australian Craton (Blake & (Blake & Barley 1992; Krapez 1999; Martin et al. 2000; Barley 1992; Powell & Horwitz 1994; Occhipinti et al. Thorne & Trendall 2001; Trendall et al. 2004; Martin & 2004; Sheppard et al. 2004; Rasmussen et al. 2005; John- Morris 2010). This history is marked by the deposition of son et al. 2011a), while the younger five, record over one the Fortescue, Hamersley, Turee Creek, and lower Wyloo billion years of intracratonic reworking (Cawood & Groups. Following the assembly of the West Australian Tyler 2004; Sheppard et al. 2010b; Johnson et al. 2011a). Craton, Paleoproterozoic intracontinental reactivation The orogen includes the deformed margins of the Pil- resulted in the deposition of the upper Wyloo and Capri- bara and Yilgarn Cratons and associated deformed conti- corn Groups (Figures 4, 5) in a possible foreland basin nental margin rocks of the Fortescue, Hamersley, Turee setting. Based on the known stratigraphy, stacking of all Creek and lower Wyloo Groups in the Ophthalmia Fold the Archean and Paleoproterozoic supracrustal units Belt; medium to high-grade meta-igneous and metasedi- present in the northern Capricorn Orogen gives a maxi- mentary rocks of the Gascoyne Province that form the mum cumulative thickness of 26 km (Figure 5). TAJE_A_826735.3d (TAJE) 09-10-2013 19:18

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Figure 3 Regional geophysical data for the western Capricorn Orogen with 2.5 km bouguer anomaly gravity data (colour) draped over 300–500 m line-spaced TMI aeromagnetic data (black and white). The location of the structural-metamorphic zone boundaries of the Gascoyne Province, major fault and mineral deposits is also shown. TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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Figure 4 Time–space plot for the Capricorn Orogen. Abbreviations: AB, Ashburton Basin; BBZ, Boora Boora Zone; ESZ, Erra- biddy Shear Zone; HFTB, Hamersley, Fortescue and Turee Creek basins; LZ, Limejuice Zone; ManZ, Mangaroon Zone; MooZ, Mooloo Zone; MutZ, Mutherbukin Zone; NT, Narryer Terrane; PC, Pilbara Craton; PCS, Petter Calc-silicate; PWd, Paradise Well diatexite PZ, Paradise Zone; QP,Quartpot Pelite; YC, Yilgarn Craton; YGC, Yarlarweelor Gneiss Complex. Downloaded by [Australian National University] at 15:07 07 November 2013

PILBARA CRATON BASEMENT FORTESCUE GROUP: RIFTING OF THE PILBARA CRATON Within the northern Capricorn Orogen, granite–green- Granite–greenstone rocks are unconformably overlain stone basement rocks of the Pilbara Craton are exposed by mixed volcano-sedimentary rocks of the Fortescue in the Wyloo, Rocklea and Milli Milli Domes, and in the Group, formed during protracted rifting of the Pilbara Sylvania Inlier (Figures 1, 2). Greenstones are domi- Craton between ca 2775 and ca 2630 Ma (Blake 1993, 2001; nated by low-grade metamorphosed mafic volcanic and Thorne & Trendall 2001; Blake et al. 2004; Trendall et al. siliciclastic sedimentary rocks. The minimum age of the 2004). In the northwestern and northeastern Pilbara, granite–greenstones is fixed by the ca 2775 Ma age of the Fortescue Group sedimentation and volcanism was con- overlying basal Fortescue Group (Trendall et al. 2004). trolled by a northeast-striking extensional fault system Their maximum age is unknown, although comparison (Blake 2001), whereas in the southern Pilbara, Thorne & with similar granite–greenstone assemblages in the Trendall (2001) argued that the fault system was princi- northern Pilbara Craton (Van Kranendonk et al. 2007; pally oriented east-southeast. Hickman & Van Kranendonk 2008) suggests they proba- In the South Pilbara Sub-basin (Thorne & Trendall bly formed sometime between ca 3800 and ca 2830 Ma. 2001), the Fortescue Group is up to 6.5 km thick TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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Figure 5 Generalised stratigraphy and deformation history of the northern Capricorn Orogen. The tectonic interpretation is modified after Martin & Morris (2010).

(Figure 5), and is subdivided, into seven formations, are the Marra Mamba Iron Formation, Wittenoom For- which are grouped into four major tectono-stratigraphic mation, Mount Sylvia Formation, Mount McRae Shale, units. From the base upwards, Unit 1 consists of the Bel- Brockman Iron Formation, Weeli Wolli Formation, and lary Formation and Mount Roe Basalt; Unit 2 is the Boolgeeda Iron Formation (Trendall & Blockley 1970; Hardey Formation; Unit 3 consists of the Boongal, Pyra- Simonson et al. 1993; Trendall et al. 2004). die and Bunjinah formations; and Unit 4 is the Jeerinah Formation. Thick mafic to ultramafic sills intrude much of the succession above the Mount Roe Basalt. The origin TUREE CREEK GROUP AND LOWER WYLOO GROUP: of the four major tectono-stratigraphic units of the For- FORELAND BASIN SEDIMENTATION AND VOLCANISM DURING tescue Group are interpreted to result from deposition THE OPHTHALMIAN OROGENY in an extensional tectonic setting (Thorne & Trendall Deposition of the Turee Creek and lower Wyloo Groups,

Downloaded by [Australian National University] at 15:07 07 November 2013 2001). took place during the early foreland-basin stage of the 2215–2145 Ma Ophthalmian Orogeny, when the Pilbara Craton collided with the Glenburgh Terrane to the south HAMERSLEY GROUP: PASSIVE- TO ACTIVE-MARGIN (Blake & Barley 1992; Martin et al. 2000; Occhipinti et al. SEDIMENTATION AND IGNEOUS ACTIVITY 2004; Sheppard et al. 2004, 2010b; Rasmussen et al. 2005; The 2.5–3.0 km thick Hamersley Group conformably Johnson et al. 2010, 2011a; Martin & Morris 2010). An overlies the Fortescue Group (Figure 5), and was depos- alternative view by Krapez & McNaughton (1999), consid- ited between ca 2630 and ca 2450 Ma, when the southern ered the post-Turee Creek Group history in terms of two Pilbara evolved from a rift setting to a passive continen- mega-sequences that record the opening and closure of tal margin and finally to an active margin (Morris & an Atlantic-type ocean. Horwitz 1983; Blake & Barley 1992; Krapez 1999; Thorne Along the southern Pilbara margin, the Turee Creek & Trendall 2001; Trendall et al. 2004; Martin & Morris and lower Wyloo groups have maximum thicknesses of 2010). Rocks of the Hamersley Group reflect this largely about 4 and 3 km, respectively,although the Turee Creek deeper-marine distal setting, and are dominated by Group was not crossed during the survey. The upper banded iron-formation, shale, chert and fine-grained part of the lower Wyloo Group is dominated by the carbonate. 2 km thick, ca 2210 Ma Cheela Springs Basalt, and Seven major lithostratigraphic units are recognised both the Turee Creek and lower Wyloo Groups are within the Hamersley Group. In ascending order, these intruded by similar-aged dolerite sills and dykes (Martin TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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et al. 1998;Muller€ et al. 2005; Martin & Morris 2010). The extensive metamorphism and reworking during the two groups are separated by a significant angular uncon- 1820–1770 Ma Capricorn Orogeny and these strongly formity (Figure 5), and, together with another occurring deformed parts have been termed the Yarlarweelor within the upper Turee Creek Group, are interpreted to Gneiss Complex (Figures 1, 2; Sheppard et al. 2003). The reflect the northward propagation of the Ophthalmia Murchison Domain consists of granite–greenstones and fold-and-thrust belt into the foreland basin (Martin & contains rocks as old as ca 3000 Ma. All of the northern Morris 2010). Yilgarn Craton terranes were intruded by granitic rocks between ca 2800 and ca 2600 Ma. All of the northern Yil- garn Craton (super)terranes were intruded by high-Ca UPPER WYLOO AND CAPRICORN GROUPS: FORELAND-BASIN TTG granitic rocks between ca 2690 and ca 2660 Ma, and SEDIMENTATION AND VOLCANISM DURING THE CAPRICORN low-Ca granites between ca 2660 and ca 2620 Ma (Cassidy OROGENY et al. 2006; Champion & Cassidy 2007). The upper Wyloo Group (Figure 5) has an estimated thickness of about 7.5 km, and, in ascending order, con- The Glenburgh Terrane and assembly of the sists of the Mount McGrath Formation, Duck Creek West Australian Craton Dolomite, and Ashburton Formation (Thorne & Seymour 1991). A 120 m-thick, mixed mafic and felsic The Glenburgh Terrane of the Gascoyne Province repre- volcanic unit, the June Hill Volcanics, overlies the Duck sents a continental fragment, exotic to both the Pilbara Creek Dolomite north of the Wyloo Dome, although this and Yilgarn Cratons. The oldest component of the unit was not crossed during the survey. The Ashburton Glenburgh Terrane, the 2555–2430 Ma Halfway Gneiss Formation is unconformably overlain by siliciclastic, (Figures 2, 4), consists of heterogeneous granitic carbonate and felsic volcanic rocks of the Capricorn gneisses that contain abundant older inherited zircons, Group, deposited following the early deformation stage some of which are as old as ca 3447 Ma (Johnson et al. of the 1820–1770 Ma Capricorn Orogeny. 2011c). Although no older crust (>2555 Ma) is exposed, The age of the upper Wyloo Group is still poorly con- the Lu–Hf compositions and crustal model ages of both strained. Evans et al. (2003) obtained an age of ca magmatic and inherited zircons indicate a long crustal 1800 Ma for the June Hill Volcanics, whereas a tuffaceous history, ranging back to ca 3700 Ma. These isotopic data unit in the overlying Ashburton Formation has been also demonstrate that large parts of the unexposed ter- dated at ca 1829 Ma (Sircombe 2003). The apparent con- rane formed via juvenile crustal growth processes tradiction in these ages, coupled with the ca 1804 Ma age between ca 2730 and ca 2600 Ma. Formation of the 2555– of felsic volcanic rocks in the Capricorn Group (Hall 2430 Ma gneisses occurred mainly by the in situ rework- et al. 2001), has led Evans et al. (2003) to suggest that ing of these older crustal components (Johnson et al. deposition of the upper part of the upper Wyloo Group 2011c). A comparison of the U–Pb zircon ages and zircon- and of the Capricorn Group were strongly diachronous Hf isotopic compositions of the Halfway Gneiss with owing to oblique basin closure during the Capricorn those of the bounding Pilbara and Yilgarn cratons, indi- Orogeny. cates that the Halfway Gneiss (and thus the Glenburgh The tectonic setting of the upper Wyloo Group is con- Terrane) is exotic to, and evolved independently from, sidered to be a retro-foreland basin associated with the these cratons (Johnson et al. 2011c). The Glenburgh Ter- onset of the 1820–1770 Ma Capricorn Orogeny (Tyler & rane is interpreted to have collided with, and accreted Thorne 1990; Thorne & Seymour 1991; Evans et al. 2003), to, the Pilbara Craton during the 2215–2145 Ma Ophthal- although Blake & Barley (1992) and Martin & Morris mian Orogeny (Blake & Barley 1992; Powell & Horwitz (2010) suggest that the setting may have been extensional 1994; Occhipinti et al. 2004; Johnson et al. 2010, 2011a, c). in its early stages. The Moogie Metamorphics (Figures 2, 4) are dominated by psammitic schists, the protoliths to which were deposited across the Glenburgh Terrane in a time frame Downloaded by [Australian National University] at 15:07 07 November 2013 The Narryer Terrane of the Yilgarn Craton coincident with the 2215–2145 Ma Ophthalmian Orogeny. The Yilgarn Craton is an extensive region of Archean These rocks contain detrital zircon sourced from the continental crust dominated by granite–greenstone ter- southern Pilbara region, and are interpreted to have ranes. On the basis of recent geological mapping and a been deposited in a foreland basin that formed in re-evaluation of geological data at all scales (Cassidy response to uplift of the southern margin of the Pilbara et al. 2006), this craton has been divided into several dis- Craton during the collision of the Glenburgh Terrane tinct tectonic entities—the Narryer, Youanmi and South with the Pilbara Craton (Occhipinti et al. 2004; Johnson West Terranes, and the Eastern Goldfields Superterrane. et al. 2010, 2011a; Martin & Morris 2010). Deposition of The Narryer and South West Terranes are dominated by the Moogie Metamorphics occurred in a similar time granite and granitic gneiss with only minor supracrus- frame to the Beasley River Quartzite of the lower Wyloo tal greenstone inliers, whereas the Youanmi Terrane Group, which was also deposited in a foreland basin set- and the Eastern Goldfields Superterrane contain sub- ting during the Ophthalmian Orogeny (Martin & Morris stantial greenstone belts separated by granite and gra- 2010). nitic gneiss. The Narryer Terrane contains the oldest Sometime after the collision between the Glenburgh rocks in Australia—the ca 3730 Ma Manfred Complex— Terrane and the Pilbara Craton, continental-margin arc- as well as the oldest detrital zircons on Earth, at ca 4400 magmatic activity was initiated along the southern mar- Ma (Froude et al. 1983; Compston & Pidgeon 1986; Wilde gin of this newly amalgamated block (Sheppard et al. et al. 2001). Part of the Narryer Terrane was subject to 2004; Johnson et al. 2010, 2011a). The 2005–1975 Ma TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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Dalgaringa Supersuite is exposed in the southern part of accompanying 1820–1775 Ma Moorarie Supersuite, are the province (Figures 2, 4), and consists of granitic recognised across the province and in adjacent tectonic gneisses, which have major-, trace-, and rare earth ele- units such as the Ashburton Basin to the north, the Yar- ment concentrations consistent with formation in a larweelor Gneiss Complex and Errabiddy Shear Zone to supra-subduction zone setting (Sheppard et al. 2004). the south, and the Padbury, Bryah and Yerrida basins to Their whole-rock Sm–Nd, and magmatic zircon Lu–Hf, the east (Thorne & Seymour 1991; Occhipinti et al. 1998; isotopic signatures indicate the incorporation of Neo- Krapez & McNaughton 1999; Occhipinti & Myers 1999; archean granitic gneisses with isotopic compositions Sheppard & Swager 1999; Pirajno et al. 2000; Sheppard similar to those of the Halfway Gneiss (Sheppard et al. et al. 2003, 2010b; Martin et al. 2005; Muhling et al. 2012). 2004; Johnson et al. 2011a), suggesting that magmatism The orogeny is characterised by extensive compres- occurred in a continental-margin arc, the Dalgaringa sional and possibly strike-slip deformation at low- to Arc, which formed along the southern margin of the medium-metamorphic grades, and was accompanied by Glenburgh Terrane. This magmatic event records the the intrusion of voluminous, felsic magmatic stocks and progressive closure and northward subduction of oce- plutons of the Moorarie Supersuite, including the Min- anic crust under the combined Pilbara Craton–Glen- nie Creek and Landor batholiths (Figures 2, 4). Intense burgh Terrane. structural and magmatic reworking of the northern mar- Terminal ocean closure, the collision between the gin of the Narryer Terrane formed the Yarlarweelor amalgamated Pilbara Craton–Glenburgh Terrane and Gneiss Complex (Figures 1, 2; Sheppard et al. 2003). Sedi- the Yilgarn Craton, and the formation of the West mentation is recorded across the orogen with the deposi- Australian Craton, all took place during the 1965–1950 tion of the upper Wyloo and Capricorn groups in the Ma collisional phase of the Glenburgh Orogeny (Occhi- Ashburton Basin, and the Leake Spring Metamorphics pinti et al. 2004; Johnson et al. 2010, 2011a). The collision in the Gascoyne Province (Figure 4). resulted in the imbrication of the northern margin of the Yilgarn Craton with slices of the Glenburgh Terrane THE 1680–1620 MA MANGAROON OROGENY along the Errabiddy Shear Zone (Figure 2), and the high- grade tectonometamorphism of metasedimentary and The Mangaroon Orogeny encompasses complex defor- meta-igneous rocks along the southern margin of the mation, metamorphism, sedimentation and granite mag- Glenburgh Terrane. Substantial uplift and exhumation matism. Extensional-related faults and fold structures of the Narryer Terrane also occurred during this event and metamorphic assemblages related to the orogeny (Muhling et al. 2008). The collisional event was accompa- appear to be restricted entirely to the Mangaroon Zone nied by the intrusion of granitic stocks and dykes of the (Figures 2–4) in the northern part of the Gascoyne Prov- 1965–1945 Ma Bertibubba Supersuite, which are the first ince, although granite magmatism (the Durlacher Super- common magmatic element of the northern margin of suite) and sedimentation (the Pooranoo Metamorphics) the Yilgarn Craton, the Yarlarweelor Gneiss Complex, took place across the entire province (Figures 2, 4). the Errabiddy Shear Zone, and the Paradise Zone of the In the southern part of the Gascoyne Province, the Glenburgh Terrane (Figures 2, 4). Pooranoo Metamorphics consist of a lower fluvial succession of sandstones, which are overlain by shallow-marine sandstones. Farther north, in the Mangaroon Zone, deep- Intracratonic reworking, magmatism and water turbiditic sandstones dominate the succession. sedimentation Deformation and medium-grade metamorphism is Subsequent to the assembly of the West Australian Cra- restricted to the Mangaroon Zone of the Gascoyne Prov- ton during the Glenburgh Orogeny, the history of the ince, which records high-temperature–low-pressure meta- Capricorn Orogen is dominated by more than one billion morphism, presumably under extensional crustal regimes years of episodic intracontinental reworking and reacti- (Sheppard et al. 2005). Metamorphism was accompanied vation, including sedimentation, magmatism, metamor- by the intrusion of voluminous granitic stocks and plu- Downloaded by [Australian National University] at 15:07 07 November 2013 phism and deformation (Figure 4). tons of the 1680–1620 Ma Durlacher Supersuite. Following peak metamorphism in the Mangaroon Zone, magmatism stepped across into the other parts of the Gascoyne Prov- THE 1820–1770 MA CAPRICORN OROGENY ince, especially the Mutherbukin Zone (Figures 3, 4), Although the Capricorn Orogeny had been widely inter- where large volumes of megacrystic K-feldspar-phyric preted to be the result of oblique collision between the monzogranite (the Davey Well batholith; Figures 2, 4) Yilgarn and Pilbara Cratons (Myers 1990; Tyler & were emplaced between ca 1670 and ca 1650 Ma. Thorne 1990; Krapez 1999; Evans et al. 2003), most of Although the driver of orogenesis is currently those models were based largely on interpretations of unknown, the high-temperature–low-pressure metamor- poorly dated metasedimentary successions in the north- phic conditions, and short duration of metamorphism, ern part of the orogen, or else did not take into account magmatism and sedimentation imply extension- the ages, spatial distribution and composition of granitic dominated orogeny (Sheppard et al. 2005). magmatism in the Gascoyne Province. The recognition of pre-1950 Ma tectonometamorphic events associated MESOPROTEROZOIC SEDIMENTATION IN THE EDMUND with the assembly of the West Australian Craton also AND COLLIER BASINS negates a Capricorn Orogeny-aged collision. Structures and metamorphic mineral assemblages Following the Mangaroon Orogeny, mostly fine-grained related to the Capricorn Orogeny, and granites of the siliciclastic and carbonate sediments were deposited in TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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the Edmund and Colliers basins (Figures 2, 4). The Mutherbukin Zone in the central part of the Gascoyne Edmund and Collier groups consist of 4–10 km of silici- Province (Johnson et al. 2011d), although hydrothermal clastic and carbonate metasedimentary rocks that were alteration and transpressional strike-slip faulting also deposited under fluviatile to deep marine conditions. affected rocks of the Edmund Basin. This event does not The groups have been divided into six depositional pack- appear to have been associated with any significant peri- ages, each being separated by an unconformity or basal ods of magmatism or sedimentation. marine-flooding surface (Martin & Thorne 2004). In the Gascoyne Province, the event is characterised The Edmund Basin extends from the Pingandy Shelf by amphibolite facies metamorphism and deformation, in the north, and continues south across the Talga Fault which is restricted to a narrow 50 km wide corridor, as an extensional basin over 180 km in width (NE–SW) bounded by the Ti Tree and Chalba shear zones and 400 km in length (NE–SE) (Figures 1, 2). The sedi- (Figures 2–4). Dating of metamorphic monazite, mainly mentary rocks unconformably overly granites of the from garnet–staurolite schists, from widely spaced local- 1680–1620 Ma Durlacher Supersuite of the Gascoyne ities provides a range of ages between ca 1280 and ca 1200 Province (Sheppard et al. 2010b), and in the uppermost Ma, interpreted as the age of deformation and metamor- part of the basin, locally includes volcaniclastic rocks phism (Johnson et al. 2011d). In the overlying Edmund dated at 1463 8Ma(Figure 4; Wingate et al. 2010). These Group, evidence for Mutherbukin-age deformation is constraints indicate deposition sometime between ca more cryptic, owing to its very low metamorphic grade 1620 and ca 1465 Ma. Deposition within the Edmund and restriction to narrow shear zones and faults, which Basin was controlled mainly by extensional movements have subsequently been reactivated. Nevertheless, on the Talga Fault (Martin & Thorne 2004), with the Mutherbukin-aged hydrothermal monazite and xeno- basin fill dramatically thickening to the southwest from time within these sedimentary rocks indicates that they the Pingandy Shelf. U–Pb SHRIMP dating of detrital zir- were subject to low-grade metamorphism and hydrother- cons from the Edmund Group, and associated paleocur- mal alteration at this time (Rasmussen et al. 2010; rent directions indicate that detritus was sourced Johnson et al. 2011d). predominantly from the northern part of the orogen, Although the driver of tectonism is not precisely including the Fortescue and Hamersley groups of the known, it is noted that the timing and duration of defor- southern Pilbara region (Martin et al. 2008). Subsequent mation and hydrothermal fluid flow were synchronous basin inversion took place during the 1385–1200 Ma with Stages I (1345–1260 Ma) and II (1225–1140 Ma) of the Mutherbukin Tectonic Event and the 1030–955 Ma Albany-Fraser Orogeny (Spaggiari et al. 2011), as well as Edmundian Orogeny, with minor fault reactivation tak- the Mount West (1345–1293 Ma) and Musgrave Orogeny ing place during the ca 570 Ma Mulka Tectonic Event. (1220–1150 Ma) in the west Musgrave Province (Howard Sedimentary rocks within the Collier Basin were et al. 2011). The synchronicity of tectonism across the deposited across both basement of the Gascoyne Prov- West Australian Craton, implies a period of continent- ince and locally deformed sedimentary rocks of the wide activity, possibly associated with a major period of Edmund Basin. In the western part of the Capricorn continent-scale plate reorganisation, i.e.during progres- Orogen, in the region of the seismic traverse, the basin sive break-up of the Nuna Supercontinent (e.g. Evans & is relatively restricted; although it widens significantly Mitchell 2011; Johnson 2013). to the east, to a maximum of 200 km (Figures 1, 2). The depositional age of the Collier Group is poorly con- THE 1030–955 MA EDMUNDIAN OROGENY strained. Faulting associated with the 1385–1200 Ma Mutherbukin Tectonic Event (Johnson et al. 2011d) does The latest Mesoproterozoic to earliest Neoproterozoic not appear to affect rocks of the Collier Group, thus pro- Edmundian Orogeny is best known for widespread fold- viding an upper age constraint for deposition. The lower ing and low-grade metamorphism in the Edmund and age constraint is provided by voluminous dolerite sills of Collier basins (Martin & Thorne 2004), although the the ca 1070 Ma Kulkatharra Dolerite (Figure 4)—which orogeny was also responsible for reworking a south- Downloaded by [Australian National University] at 15:07 07 November 2013 form part of the Warakurna Large Igneous Province east-striking corridor between the Chalba and Ti Tree (Wingate et al. 2002)—and intrude rocks of both the shearzonesintheGascoyneProvince(Figures 2–4; Edmund and Collier basins, thus deposition took place Sheppard et al. 2007). Within this corridor, deformation sometime between ca 1200 and ca 1070 Ma. Deposition and metamorphism were accompanied, and post-dated, also appears to have been less influenced by significant by the intrusion of leucocratic granite stocks and fault movements, which characterised the deposition sheets, and rare earth element-bearing pegmatites, of within the Edmund Basin (Martin & Thorne 2004). U–Pb the 1030–925 Ma Thirty Three Supersuite. SHRIMP dating of detrital zircons from the Collier In the Edmund and Collier basins, the Edmundian Group, and associated paleocurrent directions imply Orogeny was responsible for low- to very-low-grade that detritus was sourced predominantly by the erosion metamorphism, thrust faulting and transpressional- of the underlying Edmund Basin (Martin et al. 2008). related upright and open folding (Martin & Thorne 2004; Subsequent basin inversion took place during the 1030– Martin et al. 2005). The fold and fault structures strike 955 Ma Edmundian Orogeny. west–east to northwest–southeast, and are concordant with both the general basin architecture and the regional-scale structures in the underlying Gascoyne THE 1385–1200 MA MUTHERBUKIN TECTONIC EVENT Province basement (Figure 2). The Mutherbukin Tectonic Event is a poorly defined tec- The interval between ca 1050 and ca 1000 Ma is com- tonothermal event, known primarily from the monly thought to mark the assembly of the Rodinia TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

Architecture of the Capricorn Orogen 691

Figure 6 Migrated seismic section for line 10GA–CP1 across the northern Capricorn Orogen, showing both uninterpreted and interpreted versions. Display shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s. Com- mon Depth Point (CDP) locations are shown in Figures 2 and 3 (100 CDP ¼ 2 km).

supercontinent (e.g. Li et al. 2008 and references although cumulative offsets across the Chalba Shear therein), of which the Australian continent may have Zone are up to 35 km (Sheppard et al. 2010b). The Mulka been an integral part. Collision between the eastern Tectonic Event is coeval with the Petermann, Paterson margin of Australia and a partly assembled Rodinia is and King Leopold Orogenies, and reflects an episode of estimated at ca 1000 Ma (Li et al. 2008), the timing of intracontinental reactivation during the assembly of the which coincides with the growth of peak metamorphic Gondwana Supercontinent (Johnson 2013). phases during the Edmundian Orogeny. In all recon- structions of Rodinia (e.g. Pisarevsky et al. 2003;Liet al. 2008), however, the western margin of the West Austra- GEOLOGICAL INTERPRETATION OF THE SEISMIC

Downloaded by [Australian National University] at 15:07 07 November 2013 lian Craton is shown to face an open ocean. If so, then DATA the deformation and metamorphism associated with the The seismic reflection profiling provided very clear Edmundian Orogeny may have been a response to plate images, identifying many structures that extend right reorganisation and collisions elsewhere in Rodinia, through the crust (Figures 6–9). The depth to the base of since no other impinging crustal block was inferred to the crust varies significantly, changing from a shallow be present to the west. but variable Mohorovici c( ‘Moho’) character visible beneath the Pilbara Craton (Figures 6, 9), to a deep, indistinct crust–mantle boundary beneath the southern THE CA 570 MA MULKA TECTONIC EVENT part of the Capricorn Orogen (Figures 7–9), and passing The Mulka Tectonic Event is responsible for a series of into a shallower Moho once the northern edge of the Yil- anastomosing shear zones or faults that cut rocks of the garn Craton is reached at the southern end of line Gascoyne Province and Edmund and Collier groups 10GA–CP3 (Figures 8, 9). The upper crust can be subdi- across the southwestern part of the Capricorn Orogen vided into several provinces, basins and zones, based (Figure 4). This tectonic event is characterised by fault principally on surface geological mapping and potential- reactivation, rather than reworking. Mulka-aged faults field data (Johnson et al. 2011b). By comparison, are generally concentrated within discrete corridors the lower crust appears to consist of at least three dis- such as the Chalba and Ti Tree shear zones (Figures 2–4) crete seismic provinces. Following Korsch et al. (2010), and show small dextral offsets in the order of 10–100 m, we use the term ‘seismic province’ to refer to a discrete TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

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Figure 7 Migrated seismic section for line 10GA–CP2 across the Gascoyne Province, showing both uninterpreted and interpreted versions. Display is to 60 km depth, and shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s. Common Depth Point (CDP) locations are shown in Figures 2 and 3 (100 CDP ¼ 2 km).

volume of middle to lower crust, which cannot be traced TWT (25–27.5 km). The crust to the south of the Baring to the surface, and whose crustal reflectivity is different Downs Fault is interpreted as a separate seismic entity, to that of laterally or vertically adjoining provinces. the Bandee Seismic Province, which also is not exposed at the surface. In addition to the Baring Downs Fault, other major The Pilbara Craton (seismic line 10GA–CP1) crustal structures—the Nanjilgardy, Soda, Moona, Beas- The Moho is weakly defined and has a gently undulating ley and Blair faults—are imaged in the seismic data (Fig- character, at a depth of 11.5–12.3 s two-way travel time ures 6, 9). Both the Soda and Nanjilgardy faults are (TWT) (about 34–37 km using an average crustal velocity interpreted to extend through the crust to the Moho. The of 6000 ms1)(Figures 6, 9). The Baring Downs Fault is a Nanjilgardy Fault is a single, steep, north- to northeast- Downloaded by [Australian National University] at 15:07 07 November 2013 moderate to steeply north-dipping fault that extends dipping structure in middle- to lower-crustal levels, but through the crust to the Moho. The seismic character of splays upwards into a complex, transpressive flower the mid and lower crust on either side of this fault is structure defined by steep to flat-lying, northeast- or markedly different. To the north of the Baring Downs southwest-dipping, minor faults (Figure 6, 9). Both the Fault, beneath the Archean to Paleoproterozoic supra- Moona and Soda faults are steep to subvertical close to crustal rocks, the crust shows a broad twofold subdivi- the surface, but flatten out to form irregular, northeast- sion into a generally weakly reflective upper crust, erly dipping listric structures in the middle to lower corresponding to the exposed granite–greenstones of the crust. The Blair and Beasley faults are moderately to Pilbara Craton, and a moderately reflective lower crust steeply southward-dipping in the upper parts of the pro- referred to as the Carlathunda Seismic Province, as its file, although become flatter at depth. Although all the composition is not known, since it has not been tracked major faults across the orogen are subparallel (Figure 2), to the surface. The boundary between these crustal divi- the Baring Downs Fault marks a major axis across sions is undulating and offset by the major faults, but which the dip direction of the major faults change, with generally occurs at a depth of 4–7 s TWT (12–21 km). To those to the north, all dipping moderate to steeply north- the south of the Baring Downs Fault, the mid- to lower- eastward, and those to the south, dipping moderately crustal levels can be subdivided into a generally strongly south-westward (Figure 6). reflective middle crust, and a weakly reflective lower At the northeastern end of 10GA–CP1 (Figure 6), crust, the boundary undulating at depths of 8.3–9.5 s granite–greenstones of the Pilbara Craton imaged in the TAJE_A_826735.3d (TAJE) 09-10-2013 19:19

Architecture of the Capricorn Orogen 693

Figure 8 Migrated seismic section for line 10GA–CP3, showing both uninterpreted and interpreted versions. Display is to

Downloaded by [Australian National University] at 15:07 07 November 2013 60 km depth, and shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s. Common Depth Point (CDP) locations are shown in Figures 2 and 3 (100 CDP ¼ 2 km).

Rocklea Dome are generally weakly reflective, although equates to the mostly basaltic rocks of the Boongal, Pyra- a number of prominent southwest-dipping to flat-lying die and lower Bunjinah formations; and an upper layer reflections are recorded at depth. These reflections are of weak reflections 0.5 s TWT (1.4 km) thick, which interpreted as discontinuous greenstone sheets within includes the upper Bunjinah Formation and Jeerinah the granitic crust. Formation. Although the seismic reflections lose some The Fortescue Group is most prominent in the north- of their definition beneath the Turner Syncline, they eastern part of the section (Figures 6, 9) where it dips suggest a southwesterly thickening of the Fortescue gently to the southwest, and is imaged as a series of Group from about 1.5 s TWT (4.5 km) to about 2 s TWT weak to strong, layered reflections. Based on their seis- (6 km) approaching the Moona Fault. The seismic data mic reflectivity, three units can be recognised within the also suggest that a section of the Hamersley Group about Fortescue Group: a lower layer of weak reflections 0.25 s 1 s TWT (3 km) thick is preserved in the Turner TWT (0.8 km) thick that possibly corresponds to sedi- Syncline. mentary rocks of the Hardey Formation; a middle layer A thick, almost complete, succession of the Fortescue of strong reflections 0.7 s TWT (2.2 km) thick that Group crops out on the southwestern limb of the Rocklea TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

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Figure 9 Cross-section of the transect across the Capricorn Orogen, combining seismic lines 10GA–CP1, 10GA–CP2, and 10GA– CP3, and showing key faults, terranes, zones, basins and seismic provinces.

Dome, and is cut by the Karra Well and Soda faults (Fig- of rocks of the upper Wyloo Group, consisting of the ures 6, 9). Farther west, between the Soda and Nanjil- Mount McGrath Formation, Duck Creek Dolomite, and gardy faults, a succession of weakly to strongly reflective Ashburton Formation, although this structural complex- lower and middle Fortescue Group rocks 1.7 s TWT ity is not imaged in the subsurface, probably because of a (5 km) thick is interpreted to overlie the weakly reflec- lack of continuous reflective markers within the stratig- tive granite–greenstone rocks. raphy.In the surface geology,the presence of both Fortes- The stratigraphic succession between the Nanjil- cue and Hamersley group rocks to the south of the gardy Fault and southwestern end of 10GA–CP1 (Fig- Nanjilgardy Fault along strike of the seismic traverse, ures 6, 9) has been difficult to interpret from the seismic implies that both successions should be present beneath reflection data alone. The surface geology consists of the Ashburton Basin. The 2.5D forward modelling of polyphase-deformed fold- and fault-repeated succession gravity and aeromagnetic data (Johnson et al. 2011b) TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

Architecture of the Capricorn Orogen 695

suggest that banded iron formation of the Hamersley Terrane on seismic line 10GA–YU1 at around 15–16 s Group must be present to the south of the Baring Downs TWT (45–48 km). Fault and so these units, although somewhat thinned, have been extend southward onto the northern part of line 10GA–CP2 (Figures 7, 9). Although these layers do CRUSTAL TERRANES, SEISMIC PROVINCES AND SUTURE ZONES not have the same reflective signature as the exposed On the basis of seismic character and surface geology, Hamersley and Fortescue groups observed at the north- two terranes—the Glenburgh and Narryer Terranes— ern end of 10GA–CP1 (Figure 6), this may be due to an and three seismic crustal provinces—the Yarraquin, increased structural complexity and, in particular, the MacAdam and Bandee Seismic Provinces—have been presence of numerous low-angle faults, beneath the Ash- identified within lines 10GA–CP2 and 10GA–CP3 (Fig- burton Basin. On the northern part of 10GA–CP2 (Fig- ures 7–9). Most of these are separated by major crustal ures 7, 9), these layers are dissected by a series of north- structures, which coincide with mapped surface faults verging thrust faults which terminate within the lower or shear zones (Figures 2, 3). Wyloo Group. Within line 10GA–CP2, the Glenburgh Terrane and MacAdam Seismic Province are separated from the Ban- dee Seismic Province by the moderately south-dipping The Gascoyne Province and Yilgarn Craton Lyons River Fault (Figures 7, 9),whichinthemiddleand (seismic lines 10GA–CP2 and 10GA–CP3) upper crust splays into the Ti Tree Shear Zone. Since The location and character of the Moho varies consider- rocks of the Bandee Seismic Province are not exposed at ably across 10GA–CP2 and 10GA–CP3 (Figures 7–9). the surface, it is not possible to determine if this province Under the Gascoyne Province, in 10GA–CP2 (Figure 7), is similar to the Glenburgh Terrane in terms of its age, the Moho is deep and undulating, varying between 12 lithological makeup and composition. However, the con- and 15.3 s TWT (36–46 km), and continues this trend into tact between the two, along the Lyons River Fault, is the northern part of 10GA–CP3 (Figure 8), where the marked by a zone of strong seismic reflections that paral- Moho is at 15 s TWT (45 km) depth. In the central part lel the fault (areas A and B in Figure 10); there is a signifi- of 10GA–CP3, the Moho is interpreted to be at about 16 s cant step in the Moho where the Lyons River Fault TWT (48 km) depth, but at the southernmost end of the intersects the upper mantle (area C in Figure 10); and seismic line, the Moho is difficult to interpret. Line although the seismic characters of the middle crust of 10GA–CP3 ties to another, more recently acquired, line both the Glenburgh Terrane and Bandee Seismic Prov- across the southern Carnarvon Basin, 11GA–SC1 ince are relatively similar, the Glenburgh Terrane is char- (Korsch et al. 2013), and ends 40 km to the west of the acterised by a non-reflective lower crust—the MacAdam start of the Youanmi seismic line, 10GA–YU1 (Zibra et al. Seismic Province—that is not evident in the Bandee Seis- 2013). Based on these three seismic lines, the Moho at the mic Province immediately north of the Lyons River Fault southern end of 10GA–CP3 is interpreted to have been (Figures 7, 10). These observations suggest that the Lyons faulted and duplicated by crustal-scale thrusting (Fig- River Fault represents a major suture zone that separates ure 8) marking the subsurface boundary between the Yil- two, distinct pieces of continental crust. garn Craton and the Glenburgh Terrane. Therefore, the Based on the interpretation of deep seismic reflection Glenburgh Terrane may be present below the Narryer data in 11GA–SC1 (Korsch et al. 2013), which crosses the Downloaded by [Australian National University] at 15:07 07 November 2013

Figure 10 Interpreted migrated seismic section of part of line 10GA–CP2, showing the location of the suture zone between the Glenburgh Terrane and Bandee Seismic Province at the Lyons River Fault. Display shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s. TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

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southern part of 10GA–CP3, and 10GA–YU1 (Zibra et al. THE TALGA AND GODFREY FAULTS 2013) to the east, the Yilgarn Craton at the southern end Although the Talga and Godfrey faults do not appear to of 10GA–CP3 has been subdivided into the Narryer Ter- separate crust of differing seismic character, they are rane and the Yarraquin Seismic Province, the two sepa- important structures because they transect the entire rated by the Yalgar Fault. The Yarraquin Seismic crustal profile, joining together before intersecting Province (Korsch et al. 2013) forms a highly reflective the Moho (Figures 7, 9, 11). Both faults are listric in the lower crustal package that underlies the entire Youanmi upper 10 s TWT ( 30 km) of crust offsetting rocks as Terrane (Zibra et al. 2013). The position of the Yalgar young as the 1620–1465 Ma Edmund Group, indicating Fault in 10GA–CP3 has been tied from 11GA–SC1 they are Paleoproterozoic to Mesoproterozoic exten- (Korsch et al. 2013) where the fault is imaged as an east- sional structures which accommodated the deposition of verging, west-dipping thrust. The flat geometry of the sediments into the Edmund Basin. However, from 3 to Yalgar Fault in this section is due to the thrust fault 7 s TWT (9–21 km), the Talga Fault is parallel to an being imaged normal to its movement direction, with imbricate set of faults (area A in Figure 11) that are the Narryer Terrane moving out of the plane of section. defined by series of parallel reflectors (area B in Fig- Movement on this fault and the juxtaposition of the ure 11) indicating that it is a zone of intense deforma- Narryer Terrane with the Yarraquin Seismic Province tion. The faults offset units of both the Fortescue and is interpreted to predate the final collision of the Yilgarn Hamersley groups (area C in Figure 11) and terminate Craton and the Glenburgh Terrane since the Yalgar within the lower Wyloo Group, suggesting the faulting Fault is cut by Glenburgh Orogeny-aged (ca 1950 Ma) may be related to thrusting during the Ophthalmian structures (Korsch et al. 2013). Orogeny. The northward-directed thrust sense of move- The Narryer Terrane and Yarraquin Seismic Prov- ment is parallel to the transport direction of exposed ince are separated from the Glenburgh Terrane by a northward-verging thrusts in the Ophthalmia Fold and series of anastomosing, north-dipping faults known as Thrust Belt (Tyler 1991). Therefore, the Talga Fault the Errabiddy Shear Zone, and a single, moderately appears to be a major crustal shear zone that forms part south-dipping fault named the Cardilya Fault, which is of a north-verging fold and thrust system that was subse- interpreted to be the main suture (Figures 8, 9). These quently reactivated as an extensional fault, accommodat- two fault systems also segment the Glenburgh Terrane ing the deposition of the Edmund Group. into two crustal elements:

The Dalgaringa Supersuite, including the Nardoo Gran- ite, which at the surface, represents the exhumed mid- BATHOLITHS AND GRANITE INTRUSIONS crustal portions of a continental-margin arc known as Within the Glenburgh Terrane and upper part of the the Dalgaringa Arc (Sheppard et al. 2004; Johnson et al. Bandee Seismic Province, the upper 5 s TWT (15 km) 2010, 2011a), and which occurs structurally above (the of the crust is defined by numerous, irregular and seis- hangingwall) both the Errabiddy Shear Zone and the Car- dilya Fault. mically non-reflective bodies (Figures 7, 9, 10), which are indicated by the mapped surface geology (Figure 2)tobe – The remainder of the Glenburgh Terrane, including the granite plutons of the 1820 1775 Ma Moorarie Supersuite basement gneisses into which the continental-margin arc and 1680–1620 Ma Durlacher Supersuite. magmas were intruded, occur in the footwall of the Cardi- In the Mutherbukin Zone (Figures 2, 3, 9, 10), a single, lya Fault, lying structurally below the Narryer Terrane. large intrusion—the Davey Well batholith—belonging to the 1680–1620 Ma Durlacher Supersuite is imaged The Cardilya Fault, which separates the Yilgarn Cra- between the Chalba and Ti Tree shear zones (CDPs ton (the Narryer Terrane–Yarraquin Seismic Province) 11075–13325). The intrusion has a concave basal contact from the Glenburgh Terrane and MacAdam Seismic with the underlying Glenburgh Terrane (Figure 10) and Province, transects the entire crustal profile and can be ranges in thickness from 0.6 s TWT (1.8 km) in the cen- Downloaded by [Australian National University] at 15:07 07 November 2013 imaged down to 15.5 s TWT (46.5 km). It is interpreted tre of the Mutherbukin Zone, to 3.8 s TWT (11.5 km) at to offset and duplicate the Moho, which under the its northerly contact where it is truncated by the Ti Tree Narryer Terrane, is much shallower at 12.5 s TWT Shear Zone. The pluton thins rapidly to about 2 s TWT (37.5 km) depth (Figures 8, 9). These results are compa- (6 km) on the southern side of the Chalba Shear Zone, rable to those obtained by passive-seismic methods where it has been downthrown across this fault to the (Reading et al. 2012) and gravity modelling (Hackney south. Weak seismic reflections within and beneath the 2004). At the northern end of line 10GA–CP3, the footwall intrusion are parallel to the concave basal contact, sug- of the Cardilya Fault is marked by a thick package, up to gesting that the shape and orientation of the pluton is 3 s TWT (9 km) thick, of strong seismic reflections due to folding during the Mutherbukin Tectonic Event. (area A in Figure 8) that are parallel to the fault. Similar Prior to folding, the pluton would have been a flat-lying packages are also observed adjacent to the boundary or gently dipping, tabular body greater than, or equal to, with the MacAdam Seismic Province (area B in Fig- 11.5 km at its thickest. ure 8), and these areas are interpreted to represent In the Limejuice Zone, the Minnie Creek batholith strongly deformed parts of the Glenburgh Terrane. (Figures 2, 3, 7, 9, 10) is imaged north of the Ti Tree Shear Lithological variations within the Errabiddy Shear Zone at CDP 11075, and is interpreted to continue north- Zone, such as imbricate slices of Narryer Terrane, or ward, underlying rocks of the Edmund Basin in the intrusions of the Bertibubba Supersuite, cannot be dif- Cobra Syncline to CDP 8975 (Figure 10). North of the ferentiated seismically. Edmund Fault at CDP 9450, the batholith is cut by TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

Architecture of the Capricorn Orogen 697

Figure 11 Interpreted migrated seismic section of part of line 10GA–CP2, showing the attitude and orientation of the Talga and Godfrey faults. Display shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s.

numerous listric normal faults, which have produced a Supersuite, in the Limejuice Zone, have sheet-like geom- series of rotated (southwest-side down) half grabens. The etries (Sheppard et al. 2010a, b). Minnie Creek batholith has not been imaged north of Weakly reflective crust is imaged in the Mangaroon these half grabens (between CDP 8975 and the Lyons Zone (Figures 7, 11, 12), which is bounded by the Lyons River Fault at CDP 8725), where the area is dominated by River Fault in the south (CDP 8720), and the Godfrey rocks of high seismic reflectivity (Figures 7, 10). The Fault to the north (CDP 6575). The area north of CDP base of the Minnie Creek batholith is mostly interpreted 8300 is covered by sedimentary rocks of the Edmund as a fault contact, but between CDP 9900 and 10400, the Basin, and there are no surface exposures of basement batholith has a relatively sharp, flat, possibly intrusive rocks in this region (Figure 2). The crust in the Manga- contact with the underlying Glenburgh Terrane. In this roon Zone is interpreted as mostly granitic rocks of the section, the batholith has a thickness of 2.25 s TWT 1680–1620 Ma Durlacher Supersuite, and metasedimen- (6.75 km), but its maximum thickness, immediately tary rocks of the 1760–1680 Ma Pooranoo Metamorphics. north of the Ti Tree Shear Zone, is 4.5 s TWT (13.5 km); In the centre of the zone (CDP 8300–8550), a package of Downloaded by [Australian National University] at 15:07 07 November 2013 nevertheless, as the basal contact in this region is tec- moderately north-dipping, seismically reflective mate- tonic in origin, it is possible that the Minnie Creek bath- rial (Figure 12) is interpreted to be a 6 km long raft of olith has been thickened during folding or faulting. metasedimentary material of the Pooranoo Metamor- At several localities within the batholith (e.g. CDP phics. The reflective package also parallels numerous 10300, 10500, and 11000), regions of highly planar seismi- other weak seismic reflections that occur throughout cally reflective material dip at moderate angle toward the zone, and which are interpreted to reflect relict sedi- the batholith centre (Figure 10). At the surface, these mentary or lithological layering within the Pooranoo bodies have been shown to be kilometre-scale rafts of Metamorphics. The presence of parallel seismic reflec- low-metamorphic grade pelitic and semipelitic schist tions down to 2.0 s TWT indicates that the Pooranoo belonging to the 1840–1810 Ma Leake Spring Metamor- basin was at least 6 km thick in the Mangaroon Zone. phics (Figure 2). These packages, some of which are up Farther north, in the area underlying the Edmund to 8 km in length, most likely represent vestiges of a for- Basin (south of the Godfrey Fault; Figure 11), it is diffi- merly coherent sedimentary succession, into which the cult to determine if the non-reflective packages are gran- granites were intruded. The preservation of these tabu- ites of the Moorarie or Durlacher Supersuites, and for lar metasedimentary packages suggest that the batholith simplicity they are tentatively shown as a continuation may have formed by a series of sheet-like plutons, an of the interlayered granitic and metasedimentary mate- interpretation supported in part by field evidence, which rial of Durlacher Supersuite and Pooranoo indicates that many of the granites in the Moorarie Metamorphics. TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

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ARCHITECTURE OF THE EDMUND AND COLLIER BASINS 2630 Ma Fortescue Group, since these rocks were deposited across the suture. The pre-ca 2775 Ma age for the col- Although the Collier Basin succession in the Wanna Syn- lisional episode suggests that it may be contemporary cline is relatively thin, both Edmund and Collier basins with other suturing events during the 3070–3060 Ma Prin- are well imaged in line GA10–CP2 (Figures 7, 11). The sep Orogeny, which amalgamated the East Pilbara Ter- maximum thickness of the Edmund Basin is 2.25 s TWT rane and the numerous terranes of the West Pilbara (6.75 km) thick on the southern side of the Godfrey Superterrane (Van Kranendonk et al. 2007; Hickman & Fault, and in the core of the Wanna Syncline, the Collier Van Kranendonk 2008; Hickman et al. 2010). Basin is <0.25 s TWT (750 m) thick. A relatively large Deposition of over 20 km of sediments into the Fortes- package, up to 1 s TWT (3 km) thick, of highly seismi- cue, Hamersley, Turee Creek, and Ashburton basins has cally reflective material occurs between the base of Pack- covered the original suture, but the seismic reflection age 2 and the top of Package 4 (Figure 11); these data indicate that reactivation of this structure has reflections are interpreted to be abundant dolerite sills extended the fault to the surface, where it is mapped as of the ca 1465 Ma Narimbunna Dolerite and ca 1070 Ma the present-day Baring Downs Fault. The seismic data Kulkatharra Dolerite, which intrude the upper parts of also show evidence of post-1800 Ma (the minimum age of the Edmund Basin. the upper Wyloo Group within the Ashburton Basin) Three principal southwest-dipping structures, the extensional displacements on this structure with signifi- Talga, Godfrey and Lyons River faults define three half cant downthrow on the northeastern side (Figures 6, 9). grabens (Figures 7, 9, 11), into which sediments of the The exact age or setting for reactivation is not known, Edmund Basin were deposited (Martin & Thorne 2004), nor is it clear whether any fault reactivation accompa- and across which significant variations in sediment nied deposition of the upper Wyloo Group in the Ashbur- thickness are evident. On the Pingandy Shelf, to the ton Basin. north of the Talga Fault (Figure 11), the maximum thick- Although the Nanjilgardy Fault, which lies to the ness of Packages 1 and 2 are 0.5 s TWT (1.5 km), north of the Baring Downs Fault (Figures 6, 9), does not whereas to the south they increase to 1.25 s TWT represent a suture zone, the fault transects the entire (3.75 km). Across the Godfrey Fault, Packages 1 and 2 crustal profile, rooting in the Moho. At the surface, the increase from 2.0 s TWT (6 km) to >2.75 s TWT fault forms the major lithological boundary between (8.25 km) thick. Packages 1 and 2 are consistently the 1840–1800 Ma upper Wyloo Group in the Ashburton thicker in the hangingwall of the basin-bounding exten- Basin and older >ca 2200 Ma metasedimentary and meta- sional faults, suggesting that extensional downthrow on volcanic rocks of the lower Wyloo, Turee Creek, Hamers- these major faults was toward the southwest. Packages 1 ley and Fortescue groups. The age of initiation, or and 2 are not present south of CDP 8300, presumably hav- significance of the Nanjilgardy Fault, is not known, but ing been incised and eroded away prior to the deposition the present-day architecture as a positive flower struc- of Packages 3 and 4 (Martin et al. 2008). In this region, ture must have been imparted during or after the 1820– Package 3 is at least 1 s TWT (3 km) thick. 1770 Ma Capricorn Orogeny as rocks of the upper Wyloo Between the Godfrey Fault (CDP 6575) and the Group have been displaced. Edmund Fault (CDP 9465), the Edmund Basin (Package 3) is intensely folded, with numerous imbricate thrust faults truncating the limbs of the tight, upright folds THE BANDEE SEISMIC PROVINCE–GLENBURGH TERRANE (Figure 11). SUTURE The Glenburgh Terrane–MacAdam Seismic Province DISCUSSION and Pilbara Craton–Bandee Seismic Province are sutured along the moderately south-dipping Lyons Crustal architecture, assembly and reactivation River Fault (Figures 2, 7, 9). From a variety of surface geological information, the collision is interpreted to

Downloaded by [Australian National University] at 15:07 07 November 2013 of the West Australian Craton have occurred during the 2215–2145 Ma Ophthalmian The new deep seismic reflection imaging, extending Orogeny (Occhipinti et al. 2004; Johnson et al. 2010, from the southern Pilbara Craton to the northern Yil- 2011a, c;Martin&Morris2010). However, intense garn Craton, provides, for the first time, a holistic view crustal reworking of the entire northern Gascoyne of the crustal architecture of the Capricorn Orogen Province and the intrusion of voluminous plutonic gra- (Figure 9). These data are important because they not nitic rocks during episodic reworking (including the only provide critical information on the timing, assem- 1820–1770 Ma Capricorn and 1680–1620 Ma Mangaroon bly and reworking history of the West Australian Craton, orogenies) has obscured any evidence of this collision but also provide a rare insight into the anatomy of conti- (Sheppard et al. 2005, 2010a, b). The suture zone is now nental collision zones in general. represented at the surface by faults that have propa- gated through the younger magmatic and metamorphic rocks. To the north of the Lyons River Fault, metasedi- THE PILBARA CRATON–BANDEE SEISMIC PROVINCE SUTURE mentary and metavolcanic rocks of the Fortescue and The Pilbara Craton granite–greenstones and underlying Hamersley groups are interpreted to underlie much of Carlathunda Seismic Province are separated from the the Ashburton Basin, occurring as far south as the Bandee Seismic Province by the steeply north-dipping Talga Fault in the Gascoyne Province (Figures 6, 7, 9). Baring Downs Fault. The timing of amalgamation is Both groups appear to be faulted and dissected by a uncertain, but must pre-date the deposition of the 2775– series of north-directed thrusts that terminate within, TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

Architecture of the Capricorn Orogen 699

Figure 12 Interpreted migrated seismic section of part of line 10GA–CP2, showing the architecture of the Mangaroon Zone, including the raft of metasedimentary material that is parallel to other weak seismic reflections (shown as dashed form lines) within the granitic body. Display shows vertical scale equal to the horizontal scale, assuming a crustal velocity of 6000 m/s. Abbreviations: D, Durlacher Supersuite; E, Edmund Group.

and are progressively truncated by, the lower parts of lived and punctuated reverse movements. Regional-scale the 2450–2210 Ma lower Wyloo Group, suggesting that post-depositional basin inversion is evident as a series of thrusting was related to collision during the Ophthal- thrusts and hangingwall anticlines on fault splays mian Orogeny. Uplift and erosion of the Fortescue and between the Lyons River and Godfrey faults (Figure 11). Hamersley groups along this axis during thrusting, This corridor of intense deformation has been mapped may have provided much of the detritus for the fore- in the surface geology (Figures 2, 3), and does not appear land basin deposits of the lower Wyloo Group (Martin to have significantly affected rocks of the Collier Basin, &Morris2010) and the Moogie Metamorphics in the suggesting either that the deformation is related to the Gascoyne Province (Johnson et al. 2011a). 1385–1200 Ma Mutherbukin Tectonic Event, or that the During intracontinental reactivation, the Lyons Godfrey Fault acted as a backstop to the northward- River and Geegin faults (Figure 12) were reactivated propagating thrust system during the 1030–955 Ma as extensional structures allowing the deposition of up Edmundian Orogeny. to 6 km of turbiditic sedimentary rocks (the 1740–1680 Ma the Pooranoo Metamorphics) into the Mangaroon THE GLENBURGH TERRANE–YILGARN CRATON SUTURE Zone, immediately prior to the 1680–1620 Ma Manga- Downloaded by [Australian National University] at 15:07 07 November 2013 roon Orogeny. Outside the Mangaroon Zone, the Poora- The final assembly of the West Australian Craton noo Metamorphics consist of less than 700 m of occurred when the northern margin of the Yilgarn Cra- medium- to coarse-grained fluvial to shallow-marine ton was sutured to the composite Pilbara–Bandee–Glen- sedimentary rocks. burgh craton at about ca 1965 Ma, during the Glenburgh Following the Mangaroon Orogeny, the Lyons River, Orogeny, along the Cardilya Fault. Owing to the intru- Talga and Godfrey faults, appear to have controlled sion of voluminous post-collisional granitic rocks of the much of the depositional history of the 1620–1465 Ma 1820–1775 Ma Moorarie Supersuite across the Cardilya Edmund Basin (Johnson et al. 2011a). These three Oph- Fault during the Capricorn Orogeny (Sheppard et al. thalmian-aged structures were reactivated in an exten- 2010a), the significance of this structure as the main sional setting to form a series of half grabens (Figures 7, suture zone was not recognised until the interpretation 9, 11) into which sediments of the Edmund Group were of the seismic data. Prior to the seismic investigation, deposited. Package thickness variations across the the moderately well-exposed north-dipping Errabiddy major faults, especially from the Pingandy Shelf south- Shear Zone, which contains an imbricate assemblage of ward across the Talga Fault (Figure 11), imply intermit- lithologies from both the Glenburgh and Narryer Ter- tent and variable amounts of extensional movements on ranes, was thought to be the main suture zone (e.g. all three faults. The progressive truncation of older pack- Sheppard et al. 2010b). ages by units higher in the succession indicates syn- Although there is little evidence of post-collisional depositional uplift and erosion during periods of short- reactivation on the Cardilya Fault and Errabiddy Shear TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

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Zone in the seismic data, the Cardilya Fault truncates obduction, backthrusting and crustal delamination. and displaces plutonic magmatic rocks, specifically the This implies that the crustal architecture was preserved Landor batholith, of the 1820–1775 Ma Moorarie Super- relatively late in the orogenic cycle and that pre- suite, indicating reactivation during, or after, the 1820– collisional features may not be inherently preserved in 1770 Ma Capricorn Orogeny.Uplift and reworking across the orogenic architecture. Additional information, such the Errabiddy Shear Zone are also recorded by several as whole-rock geochemical and isotopic data (e.g. 40Ar/39Ar mica dates between ca 960 and ca 820 Ma Sheppard et al. 2004), or where the subduction-related (Occhipinti 2007), indicating a long-lived post-collisional magmatic rocks are not accessible, in situ Lu–Hf isotopic history for this fault system. composition of appropriately aged inherited zircon grains, are thus required to constrain pre-collisional relationships. However, such information is not avail- IMPLICATIONS FOR CONTINENTAL COLLISION AND able to constrain the subduction polarity leading up to SUBSEQUENT CRUSTAL REWORKING the pre-ca 2775 Ma collision between the Pilbara Craton The West Australian Craton was built progressively and Bandee Seismic Province or the 2215–2145 Ma Oph- over one billion years from the punctuated collision of thalmian-aged collision between the Bandee Seismic continental blocks (the Bandee Seismic Province, the Province and the Glenburgh Terrane. Glenburgh Terrane and the Yilgarn Craton) to the Following the final assembly of the West Australian southern Pilbara Craton margin. Owing to significant Craton, the orogen was subject to over one billion years post-collisional tectonomagmatic reworking and verti- of punctuated intracontinental reactivation and rework- cal extension of the major fault structures into youn- ing (e.g. Sheppard et al. 2010b), including present-day ger rock packages, the principal crustal sutures only seismic movements (Revets et al. 2009; Keep et al. 2012). have a weak expression at the surface, and ophiolites, The three principal sutures associated with the assem- high-pressure rocks or melanges, which are usually bly of the West Australian Craton, as well as most of the considered key components of continental suture other crustal structures, show evidence for multiple zones, are either not preserved or not exposed. reactivation (Figure 9), in extensional, compressional However, the suture zones, as well as other major and oblique-slip settings. Reactivation of these major crustal-scale structures related to the assembly of the crustal structures has led to their vertical extension into West Australian Craton, are well preserved and younger sedimentary or plutonic rocks (a process com- imaged to great depth in the seismic reflection data mon to ancient collision zones; e.g. O’Driscoll 1986; (Figures 6–9). The preservation of ancient reworked Hronsky et al. 2012), and so the suture zones, and other sutures and crustal-scale structures within the mid- to associated crustal-scale faults, are commonly only lower-crust appears to be a common feature of many weakly expressed at the surface by much younger faults continental suture zones, where examples have been or fault systems (Figures 2, 3, 9). The accommodation of documented in seismic reflection data from the Trans- regional-scale strain (extensional, compressional and Hudson Orogen (e.g. White et al. 2005), Slave Province oblique-slip) during the numerous reworking events (e.g. Clowes et al. 2005;Cook&Erdmer2005)and appears to have been accommodated mostly by the reac- numerous Australian orogenic belts (e.g. Korsch et al. tivation of the pre-existing faults and shear zones, rather 2010, 2012;Cayleyet al. 2011; Wyche et al. 2013). than by the generation of new crustal-scale structures. The preservation of ancient suture zones in the deep Furthermore, in the Gascoyne Province, the orientation crust is therefore critical for understanding the crustal of most tectonometamorphic fabrics and syn-tectonic architecture and evolution of the collision zone, but does magmatic intrusions such as the Minnie Creek, Landor it reliably preserve pre-collisional geometric relation- and Davey Well batholiths (Figure 2) are also coaxial to ships such as the subduction polarity? Furthermore, in the main crustal-scale structures. The depositional complex collision zones, what stage during the colli- architecture of the 1620–1465 Ma Edmund and 1200–1070 sional/orogenic cycle does the present-day architecture Ma Collier basins, and subsequent style of basin inver- Downloaded by [Australian National University] at 15:07 07 November 2013 reflect? In the Capricorn survey, both the 2215–2145 Ma sion were controlled by extensional and transpressional Ophthalmian and 2005–1950 Ma Glenburgh Orogeny movements on these structures and, more importantly, suture zones (the Lyons River and Cardilya faults, their orientation (Johnson et al. 2011a). Therefore, the respectively) dip moderately southward (Figure 9). The crustal architecture, imparted during the assembly of simplest interpretation implies south-directed subduc- the West Australian Craton ca 2200 to ca 1950 million tion of oceanic crust during both events. However, the years ago, has strongly influenced the partitioning of wealth of whole-rock geochemical, isotopic and in situ deformation, metamorphism and magmatism during zircon Lu–Hf isotopic data (Sheppard et al. 2004; Johnson the numerous intracratonic reworking events. et al. 2011a) demonstrates that during the 2005–1950 Ma Glenburgh Orogeny, the subduction of oceanic crust was Mineral prospectivity north-directed with the formation of the Dalgaringa Arc within the southern margin of the Glenburgh Terrane, The Capricorn seismic survey has identified a series of opposite to the present-day dip of the suture zone. The major crustal structures, many of which cut through the current crustal architecture implies significant syn- to crust to the mantle and show evidence for multiple reac- post-collisional modification of the crustal profile either tivation (Figure 9). Numerous mineral deposit types by a style of ‘crocodile tectonics’ (e.g. Meissner 1989; have been recognised throughout the orogen (Figure 3) Sadowial et al. 1991;Xuet al. 2002) or by the interplay of and include the world-class hematite iron-ore deposits of complex syn- to post-collisional events such as crustal the Hamersley Basin; volcanic-hosted massive sulfide TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

Architecture of the Capricorn Orogen 701

Figure 13 Summary cross-section through the Capricorn Orogen, showing the spatial relationship between known mineral deposits and the location of suture zones and other major lithospheric-scale faults.

(VHMS) copper–gold deposits in the Bryah Basin on the Nanjilgardy Fault hosts significant gold deposits in both Yilgarn Craton margin; orogenic lode-gold mineralisa- the Fortescue Group of the Wyloo Dome at Paulsens and tion, such as that at Peak Hill in the southern Capricorn Proterozoic rocks of the Ashburton Basin such as at Orogen margin, Glenburgh and the Star of Mangaroon Mount Olympus. The Baring Downs Fault hosts several in the Gascoyne Province, and Paulsens and Mount gold and base metal deposits in the Ashburton Basin Olympus along the northern Capricorn Orogen margin; such as Star of the West, Glen Florrie and Soldiers various intrusion- and shear zone-related base metal, Secret. In the Gascoyne Province, the composite Lyons tungsten, rare earth element, uranium and rare-metal River–Minnie Creek–Minga Bar Fault system hosts rare deposits in the Gascoyne Province; and lead–copper– earth elements at Gifford Creek, and gold at the Star of zinc sediment-hosted mineralisation at Abra within the Mangaroon. An along-strike extension of the Lyons Edmund Basin (Figure 3). However, the tectonic setting River Fault, the Quartzite Well Fault, hosts the polyme- of these deposits or their relation to the crustal architec- tallic Abra base metal deposit. The Ti Tree and Chalba ture has yet to be adequately assessed. shear zones host numerous tungsten, molybdenum and Central to the orogen’s prospectivity is the growing copper–gold base metal deposits, and the Cardilya–Dead- understanding that the formation of ore deposits is an man Fault hosts gold at Glenburgh. Apart from the Mt expression of much larger earth-system processes, Olympus gold deposit, which has been dated at ca which operate on a variety of scales to focus mass and 1740 Ma (Sener¸ et al. 2005), the age of the various mineral energy flux. Many factors including the geodynamic set- deposits across the orogen are not precisely known, and ting, architecture, metal source, fluid-flow drivers and so it is difficult to determine whether they represent pri- pathways, and depositional mechanisms (Wyborn et al. mary deposits related directly to tectonic setting (i.e.cra- 1994; Knox-Robinson & Wyborn 1997), influence the type, ton edge or island arc), or whether they are younger, style and location of mineralisation. One of the aims of secondary hydrothermal deposits related to fluid flow the seismic survey was to identify large-scale crustal during intracontinental reactivation. structures, including those that cut through the crust to In the case of the Mt Olympus deposit, which lies the mantle, which may form pathways for fluid flow to along the Nanjilgardy Fault, the gold is interpreted to be mineral systems. A recent mineral prospectivity study of hydrothermal origin (Sener,¸ et al. 2005). The seismic of the Gascoyne Province, using the mineral systems data show the Nanjilgardy Fault to have been (re)acti- approach, has also highlighted the significance of these vated during the 1820–1770 Ma Capricorn Orogeny con- Downloaded by [Australian National University] at 15:07 07 November 2013 major crustal structures to sites of potential mineralisa- sistent with the age dating and demonstrate that tion (Aitken et al. 2013). Although factors such as rock hydrothermal fluid flow within this major-crustal struc- type, rock composition and metal source are important ture is an important mechanism for gold mineralisation. for mineralisation, the faults and, in particular, their The polymetallic Pb–Cu–Zn deposit at Abra in the constant reactivation during subsequent and punctuated lower part of the Edmund Group (which lies on an exten- orogenesis are key to focussing the fluids and energy sion of the Lyons River Fault) shows a complex history flux of the mineral system. Especially important are the of monazite and xenotime growth between ca 1385 and ca structures that transect the entire crustal profile (the 1235 Ma (Rasmussen et al. 2010). The deposit has been Nanjilgardy, Baring Downs, Talga, Lyons River, and Car- interpreted to be SEDEX in origin (Vogt & Stumpf 1987; dilya faults; Figures 2, 3, 9, 13), as they provide a litho- Collins & McDonald 1994), but the polyphase growth of spheric-scale deep plumbing system to allow the phosphate minerals implies significant secondary transport of fluid and energy direct from the mantle into upgrading associated with hydrothermal fluid flow the upper crust. (Pirajno et al. 2009; Rasmussen et al. 2010) during fault In most cases, known sites of mineralisation lie along, reactivation. close to or within fault splays related to the major crustal The Lyons River Fault also hosts significant rare structures (Figures 3, 13). The Soda and Karra faults in earth elements within the Gifford Creek Carbonatite the northern Capricorn Orogen are associated with the Suite (formerly the Gifford Creek Complex; Pearson premium martite–microplaty hematite ores. The 1996; Pearson & Taylor 1996; Pearson et al. 1996) TAJE_A_826735.3d (TAJE) 09-10-2013 19:20

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(Figures 3, 13). The suite consists of a series of ferroan continental blocks to the southern Pilbara Craton mar- carbonatite sills that are distributed within a 30 km long gin. This collisional architecture has fundamentally con- northwest-trending belt that parallels the Lyons River trolled the style and orientation of over one billion years Fault (Pearson 1996; Pearson & Taylor 1996; Pearson of intracontinental reactivation, including deformation, et al. 1996). The sills were emplaced into metasedimen- metamorphism, magmatism and sedimentation. tary and granitic rocks of the Pooranoo Metamorphics The three main crustal suture zones, as well as other and Durlacher Supersuite, respectively and so are youn- major crustal structures, are well preserved in the mid ger than ca 1620 Ma. During subsequent tectonometa- and lower crust, but are only weakly expressed at the morphism, hydrothermal alteration of the carbonatites surface by vertical extensions of these structures led to extensive upgrading of rare earth elements into a through younger (meta)sedimentary and (meta)igneous series of mineralised ironstone veins and dykes. rock packages during intracontinental reactivation. The Although the ages of the carbonatite sills and subse- present-day architecture is the culmination of numerous quent rare earth element-rich ironstones are not pre- collision-related processes that may have been preserved cisely known (

Architecture of the Capricorn Orogen 703

Craton, Australia: constraints on basin evolution, volcanic and HOWARD H. M., WERNER M., SMITHIES R. H., KIRKLAND C. L., KELSEY D. E., sedimentary accumulation, and continental drift rates. HAND M., COLLINS A., PIRAJNO F. , W INGATE M. T. D., MAIER W.D.& Precambrian Research 133,143–173. RAIMONDO T. 2011. The geology of the west Musgrave Province and CASSIDY K. F., CHAMPION D. C., KRAPEZ B., BARLEY M. E., BROWN S. J. A., the Bentley Supergroup — a field guide. Geological Survey of West- BLEWETT R. S., GROENEWALD P. B . & T YLER I. M. 2006. A revised geo- ern Australia, Record 2011/4, pp. 116. logical framework for the Yilgarn Craton, Western Australia. Geo- HRONSKY J. M. A., GROVES D. I., LOUCKS R. R. & BEGG G. C. 2012. A unified logical Survey of Western Australia, Record 2006/8, pp. 8 model for gold mineralisation in accretionary orogens and impli- CAWOOD P. A . & T YLER I. M. 2004. Assembling and reactivating the Pro- cations for regional-scale exploration targeting methods. Minera- terozoic Capricorn Orogen: lithotectonic elements, orogenies, lium Deposita 47, 339–358. and significance. Precambrian Research 128, 201–218. JOHNSON S. P. 2013. The birth of supercontinents and the Proterozoic CAYLEY R. A., KORSCH R. J., MOORE D. H., COSTELLO R. D., NAKAMURA A., assembly of Western Australia, pp. 78 Geological Survey of West- WILLMAN C. E., RAWLING T. J. , M ORAND V. J . , S KLADZIEN P. B . & O ’SHEA ern Australia, Perth, Western Australia. P. J. 2011. Crustal architecture of central Victoria: results from JOHNSON S. P., SHEPPARD S., RASMUSSEN B., WINGATE M. T. D., KIRKLAND the 2006 deep crustal reflection seismic survey. Australian Jour- C. L., MUHLING J. R., FLETCHER I. R. & BELOUSOVA E. 2010. The Glen- nal of Earth Sciences 58, 113–156. burgh Orogeny as a record of Paleoproterozoic continent–continent CHAMPION D. C. & CASSIDY K. F. 2007. An overview of the Yilgarn and its collision. Geological Survey of Western Australia, Record 2010/5, crustal evolution. 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