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 archi- tecture of the West Australian Craton. The survey has imaged three principal suture zones, as well as sev- eral 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 architec- ture of the Mesoproterozoic Edmund and Collier basins. These features were formed during the punctu- ated 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 19:18 682 S. P. Johnson et al. 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 bound- aries 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 Architecture of the Capricorn Orogen 683 Downloaded by [Australian National University] at 15:07 07 November 2013 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 19:18 684 S. P. Johnson et al. 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 over- lie 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