Structural-event framework for the eastern Yilgarn Craton, Western Australia, and its implications for orogenic gold

Precambrian Research 183 (2010) 203–229

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Structural-event framework for the eastern Yilgarn Craton, Western Australia, and its implications for orogenic gold R.S. Blewett ∗ , K. Czarnota, P.A. Henson pmd*CRC, Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia

a r t i c l e

i n f o

Article history: Received 6 October 2009 Received in revised form 26 March 2010 Accepted 1 April 2010

Keywords: Structural geology Deformation Eastern Yilgarn Craton Archaean tectonics Gold mineralisation

a b s t r a c t The NNW-trending tectonic grain of the eastern Yilgarn Craton (EYC) was established as a result of predominantly ENE–WSW directed extension (D1 and D3) and E(ENE)–W(WSW) (D2, D4) to NE–SW directed (D5) contraction. The result has been a succession of NNW-striking temporally discrete fabric elements, which can be difficult to interpret reliably at any single location. Despite this, many past workers interpreted the NNW-striking fabric as the result of only one regional contractional event, and used it as a marker for correlating structural events across the region. In order to unravel the complexity, this paper presents a new sixfold (D1–D6) deformation nomenclature based on >10,000 new mesoscale structural observations, including their kinematic analysis and cross-cutting relationships. These mesoscale data were referenced with regional 3D map patterns, stratigraphic-magmatic-metallogenic considerations, and deep seismic reflection images. This integrated geodynamic-architectural approach is applicable to solving structural-event histories in other polydeformed terrains. Gold mineralisation occurred during the first five events, but was particularly concentrated from D3 onwards. The D3 event marked the most profound change in the tectonic evolution of the EYC, with changes in greenstones, granites and tectonic mode (lithospheric extension and core complexes), with the first significant gold deposited within extensional shear zones that dissect the crust. Later contraction (D4) was imposed at a high angle to the previously established anisotropic architecture. The outcome was the creation of a new dynamic permeability framework, which resulted in gold mineralisation during NNW-striking sinistral strike-slip faulting and associated thrusting. A further stress switch (D5) further modified the architecture resulting in N- to NNE-striking dextral strike-slip faulting, and the final period of gold mineralisation, before late-stage extension (D6). Crown Copyright © 2010 Published by Elsevier B.V. All rights reserved.

1. Introduction The gold deposits of the eastern Yilgarn Craton (EYC) are structurally controlled. The structural geology of the region has been extensively studied to both understand the controls, and to use this understanding to predict the location of undiscovered structurally-controlled gold deposits. Much of the regional structural understanding was developed initially in the southwest part of the EYC (greater Kalgoorlie region), and was extrapolated outwards to the rest of the region (Fig. 1). The work by Swager (1997) represented a seminal synthesis of over 10 years of prior research and extensive mapping, and it was this work that became the benchmark structural-event framework to which other workers matched their studies.

∗ Corresponding author. Fax: +61 26 249 9983. E-mail address: [email protected] (R.S. Blewett).

Building on the work of Swager (1997, and references therein), we present a new, integrated structural-event framework for the EYC which incorporates a further decade of research from various projects conducted by Geoscience Australia, Geological Survey of Western Australia, AMIRA, and the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC). This new proposed framework allows integration of the greenstone stratigraphy, granite evolution, structure, tectonic mode, and mineralisation into a coherent understanding in time and three-dimensional space. Underpinning this revised structural-event framework are new structural observations (>10,000) from across the entire EYC. In addition to selected mapping and regional outcrop studies, attention was given to the well-exposed granite pavements (most with U–Pb SHRIMP geochronological age dates) and to the mines. These are places where exposures permit reconciliation of the key overprinting relationships, and thus provide critical temporal constraints on the framework. The geographic scope of the new study was from Wiluna in the north, to Kambalda in the south, from the Ida Fault in the west, to the Yamarna Fault in the east (Figs. 1 and 2). The new observations were made in all granite types (Champion

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Fig. 1. Map of the terranes and domains of the eastern Yilgarn Craton (Eastern Goldfields Superterrane) with superimposed major faults (after Cassidy et al., 2006; Pawley et al., 2009). Major towns and localities are shown. The boxed area is the outline of Fig. 2.

and Sheraton, 1997) and all the greenstone1 stratigraphic units (Barley et al., 2002). The studied locations were chosen carefully to cross all structural positions, in terms of strain and possible structural level. These new data are available in Blewett and Czarnota (2007a), and are summarised in Appendix A. To highlight our new advances in understanding, a review of the prior structural paradigm is outlined before the new structuralevent framework is presented and discussed. This contribution is a companion paper to Czarnota et al. (2010), which is a review and synthesis of the greenstone stratigraphy, granite magmatism

1 Greenstones are a collective local term applied to the supracrustal rocks, and include: komatiite, basalt, andesite, volcaniclastic and sedimentary rocks. The youngest greenstones are locally known as late-basin successions, and by definition contain no volcanic detritus.

and metamorphism with this new structural-event framework, and how these elements interrelate to the broader geodynamic system.

2. Regional setting and previous work 2.1. Regional geology, stratigraphy and metamorphism The EYC, also known as the Eastern Goldfields Superterrane (Cassidy, 2006; Cassidy et al., 2006), consists of three elongate NNW-trending terranes. These are, from west to east: the Kalgoorlie, Kurnalpi, and Burtville Terranes (Fig. 1). The terranes and domains are bounded by interconnected systems of NNW-trending faults (Swager et al., 1992; Swager, 1997; Liu et al., 2000), with the main crustal-scale structures being the Ida, Ockerburry and

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Fig. 2. Simplified geological map of the EYC, with major faults named. Map shades are pale grey (granites), medium grey (greenstones) and dark grey (late-basin successions). Black dots are data sites used in this study to constrain the revised structural-event framework. The named dots are geographical sites specifically mentioned in the text, and the E–W transect of sites denoted by a star are shown in more detail in Fig. 6. Note that the structural sites are located across all terranes and domains, and in both granites and greenstones at a range of structural levels. Boxes show location of maps in Figs. 8A, 9, 11C and F.

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Hootanui Fault Systems (Fig. 1). Deep seismic reflection data reveal these fault systems as E-dipping crustal structures that intersect the Moho (Goleby et al., 2002, 2003; Blewett et al., 2010a). The terrane subdivision was originally based on the assumption that the Yilgarn Craton represents the accretion of allochthonous, exotic crustal fragments (Myers, 1995; Krapeˇz and Barley, 2008). While this tectonic assumption is not necessarily valid (Swager, 1997); the terminology is used here as a geographical subdivision of groups of rocks with common geological features, and is used here without presuming an allochthonous origin. Czarnota et al. (2010) have recently proposed a largely autochthonous rift setting, driven by subduction roll back, for the formation of the EYC. Each terrane contains a record of at least two distinct periods of volcanism, including a fragmented record between 2960 Ma and 2750 Ma, and a more consistent record starting around 2720 Ma (Czarnota et al., 2010). Tholeiitic mafic, komatiitic ultramafic and calcalkaline felsic volcanic and clastic sedimentary rocks, which developed dominantly between ∼2720 Ma and 2655 Ma, form the bulk of the greenstone successions in the EYC. There is an overall younging towards the west, such that the greenstone successions in the Kalgoorlie Terrane contain the youngest volcaniclastic units (Barley et al., 2002, 2003). The greenstones are preserved in synformal basins up to 7 km deep (Henson and Blewett, 2006), and the stratigraphy generally dips and faces away from the granite domes. The oldest exposed parts of the stratigraphy (>2750 Ma) are often exposed adjacent to, or within, sheared margins of some of the granite domes, and represent autochthonous basement to the younger greenstone units. These old rocks record significantly higher pressures and low thermal gradients in comparison to the bulk of the younger greenstone stratigraphy (Goscombe et al., 2009). The <2710 Ma greenstone successions in the Kalgoorlie Terrane are divided into the 2710–2690 Ma tholeiitic and komatiitic mafic-ultramafic (Kambalda Sequence) and 2690–2660 Ma felsic volcaniclastic (Kalgoorlie Sequence) sequences (Barley et al., 2002, 2003). The Kalgoorlie Sequence (incorporating the Black Flag Group) is a TTG volcaniclastic association restricted to the Kalgoorlie Terrane and was deposited as a series of unconformity-bounded tectonic sequences in an interpreted extensional, deep-marine, intra-arc basin, between 2690 Ma and 2660 Ma (Barley et al., 2003). The Kurnalpi Terrane includes 2715–2705 Ma mafic volcanic rocks, intermediate calc-alkaline complexes, feldspathic sedimentary rocks, mafic intrusive rocks and 2695–2675 Ma bimodal HFSE-enriched rhyolite-basalt and intermediate-felsic calc-alkaline complexes that extend along a linear belt (principally in the Gindalbie Domain) at the eastern edge of the Kalgoorlie Terrane (Cassidy, 2006). In the older Laverton Domain, <2808 Ma mafic and ultramafic volcanic rocks, BIF, fine-grained tuffaceous sediments, and possibly <2870 Ma mafic and ultramafic volcanic rocks and BIF of the Dingo Range greenstone belt, occur (Cassidy, 2003). The Burtville Terrane has an older western domain and a younger eastern domain, separated by the NNW-trending Yamarna Fault (Fig. 1). The western domains include ∼2960 Ma, ∼2805 Ma and 2770 Ma successions of intermediate and felsic volcanic rocks and associated mafic (±ultramafic) rocks, which have lithological and temporal affinities with the Youanmi Terrane in the western Yilgarn Craton (Pawley et al., 2009). The eastern Yamarna Domain greenstones range in age from 2720 Ma to 2680 Ma, sharing lithological and temporal affinities with the Kurnalpi and Kalgoorlie Terranes to the west (Pawley et al., 2009). The late basins are younger fining-up successions of siliciclastic rocks that unconformably overlie, or are in fault contact with, the volcano-sedimentary successions. Based on detrital zircon populations, they are interpreted to have been deposited after 2665 Ma (Krapeˇz et al., 2000; Barley et al., 2003). These successions are similar to the Timiskaming assemblages of the Abitibi Subprovince of

the Superior Craton in Canada (Poulsen, 2008). These successions are common to the Kalgoorlie and Kurnalpi Terranes, but appear absent to the east (Krapez and Barley, 2008). Approximately 65% of the map area consists of granite (Fig. 2), of which around 60% is High-Ca tonalite–trondhjemite–granodiorite (TTG) (Champion and Sheraton, 1997). Most of the large granite batholiths form structural domes, and contain the youngest phases (Low-Ca type) in the dome centres. The history of granite magmatism, with the exception of the High-HFSE granites, is broadly similar across the EYC (Champion and Sheraton, 1997; Cassidy et al., 2002; Champion and Cassidy, 2002). High-Ca, Mafic and High-HFSE granites correspond to specific volcanic associations in the greenstone belts, in terms of timing as well as chemistry, demonstrating the largely autochthonous nature of the greenstones. Low-Ca and Syenitic granites have no extrusive equivalents preserved in the EYC (Czarnota et al., 2010). Granites have been locally called ‘internal’ when they intrude the main greenstone basins, and ‘external’ elsewhere. Goscombe et al. (2009) has recently revised the metamorphic evolution of the EYC, and shown that the temporal and spatial patterns contrast with previous tectonic models, especially the concept of an invariant crustal depth with a single prograde metamorphic event (Binns et al., 1976). There are large variations in peak metamorphic crustal depths (12–31 km), and five different metamorphic periods are now recognised: • Ma: Very localised, low-P granulite of high temperature/depth ratio (>50 ◦ C/km). • M1: High-P (8.7 kb), low temperature/depth ratio (20 ◦ C/km) assemblages localised to major shear zones with clockwise isothermal decompression P–T paths. • M2: Regional matrix parageneses with T ranging 300–550 ◦ C across greenstone belts and elevated temperature/depth ratio of 30–40 ◦ C/km throughout. Tight clockwise paths with peak metamorphic pressures of 3.5–5.0 kb. • M3a: An extension-related thermal pulse localised on the Ockerburry Fault and late basins successions. Anticlockwise paths to peak conditions of 500–580 ◦ C and 4.0 kb, define moderately high temperature/depth ratio of 40–50 ◦ C/km. • M3b: Multiple localised hydrothermal alteration events (associated with gold mineralisation) during a period of uplift and exhumation from 4 kb to 1 kb. 2.2. Previous structural frameworks Modern structural analysis was not systematically applied to the EYC until the studies of Platt et al. (1978), Archibald et al. (1978) and Swager (1989). These workers were the first to publish regional deformational event histories which were adopted as a framework by subsequent workers. Swager (1997) summarised many of the interpretations of the regional deformation history, and it is this framework that is further refined. Henson et al. (2004) produced a structural event history that honoured the 2D and 3D geological map patterns, and was built on the work of Swager (1997) and Blewett et al. (2004a). The map pattern analysis of Henson et al. (2004) defined the geometry of the essential structural elements and their relative timing; these are integrated in this study. Previously, a nomenclature of ‘D1’ to ‘D4+’2 (Table 1) was used to describe the various contractional deformational events of the EYC (Swager, 1989, 1997). Broadly, the contractional history was

2 Note that in this paper deformational events that are presented in quotations (e.g., ‘D1’) refer to designations from previous studies, while designations in the current study, which may differ from the earlier work, are not placed in quotations (e.g., D1).

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Table 1 Comparative deformation chronology of various workers in the EYC. Summary of dominant structures and inferred vector of shortening or extension also shown for each event. Note the predominance of ENE–WSW shortening or extension. The D4b event is an exception, with shortening oriented WNW–ESE. This study

Mueller et al. (1988)

Swager (1997)

Nguyen (1997)

Blewett et al. (2004a,b)

Miller (2006)

Minor extension

D6

Dextral strike-slip

D5

D3

D4

D4

D3

D4

NW–SE local comp.

D4b

D2

D3

D3

D3

D3

Late Basin upright folding

D4a

D1

D2

D2

D2b

D2

D3

DE

DE3

D2e

Upright folding and reverse faulting

D2

D2

Extension with intermittent compression

D1

DE

Collapse

Late De

Sinistral transpression

Extensional doming Late Basins

thought to have involved the following sequence: early ‘D1’ recumbent folding and thrusting during N–S shortening; E–W shortening with large-scale upright ‘D2’ folding and thrusting; a period of strike-slip ‘D3’ faulting with associated folding, and; continued regional ‘D4’ transpressive, oblique and reverse, faulting. Within this contractional history were a series of early, intermediate, and late periods of extension, which were enumerated as ‘De’ events (Table 1).

3. Defining a new structural-event framework 3.1. Outline of the science problem The EYC has heterogeneous partitioning of strain, with large areas of relatively intact greenstone stratigraphy (with weak fabric development), which envelop and dip gently and young away from broad, elongate, gently NNW–SSE-plunging, granite-cored domes. These areas contrast with intervening localised zones of shear-dominated high-strains up to 5 km in width with intense foliation, steep dips (with steeply plunging folds), and dismembered stratigraphy (Goscombe et al., 2009). These high-strain zones are commonly areas of significant reworking and were subject to intense extensional, thrust and strike-slip (both sinistral and dextral) contractional events, resulting in a pronounced NNW-trending structural grain (Figs. 3A and 4A). Despite being separate events, the finite strain results in fabric elements that are superficially similar, but separated in time by up to 25 Ma (Figs. 4B and 5). These factors, together with the poor exposure, make it difficult to correlate structures between sites and thus define a robust structural-event framework for the region as a whole. Therefore, past studies based on the assumption that the main penetrative foliation was ‘S2’ should be re-examined (Cassidy et al., 2002). Since the distribution of orogenic gold deposits is largely structurally controlled, a regional understanding of the type, orientation and interaction between structures is critical.

D2a

DE1–2

D1

De

3.2. Method In order to address the problem of correlation of deformation events across the EYC, a modified P–T dihedra method of strain analysis has been developed and applied (Blewett and Czarnota, 2007a). This analysis was aided by the 3D geological map patterns of the macroscale structural elements and their relative timing by Henson et al. (2004). These 3D maps were constructed in gOcad® at several scales, from individual mines and camps to the entire craton, and the geometrical and temporal insights from these maps have been integrated in this study. See the companion paper by Blewett et al. (2010a) for further details. A mesoscale structural analysis was conducted on over eighty individual sites that were selected to sample a representative range of structural levels, lithologies and positions with respect to strain intensity within the EYC (Fig. 2). The approach, using the modified P–T dihedra method of strain analysis, has four distinct interpretative stages which have progressively more regional implications. Stage one involved gathering raw data at a number of sub-sites within a larger site such as an open pit, underground mine or granite pavement (Fig. 2). The number and dimensions of the sub-sites varied according the size of the larger site, but was in the range of five to fifteen sub-sites, generally around 5 m wide. The raw data acquired included type and style of structure, its intensity, its orientation, its kinematics, mineralogy and, critically, its temporal relationship to other structural features and lithologies. Typically 10–20 observations and measurements were taken for each structure, and each structure was digitally photographed. The stage one result for each sub-site was the determination of a sequence of structural events assigned to a local D1, D2, etc., nomenclature. These raw data, along with a scan of the field notebooks, are available in the appendices of Blewett and Czarnota (2007c). Stage two involved strain analysis for each local event at each sub-site, by applying a P–T dihedra method modified from Angelier (1984). While Angelier applied the method exclusively to brittle faults with slickensides, in the modified method utilised here, both brittle and ductile structures are analysed. Ductile structures with preserved kinematic indicators, from which a movement vector can

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Fig. 3. (A) Regional aeromagnetic image (total magnetic intensity reduced to pole) with major trends superimposed. The NNW-trending Ida Fault (I) and Hootanui Fault (H) are the master D1 border faults (terrane boundaries) for the main greenstone depocentre. The NW-trending internal strike is coincident with the late-basin successions (Fig. 2), which were developed in the hangingwall of D3 faults, with an extension direction oriented NE–SW. Note the intact granite batholiths with high-strain shear zones enveloping them and transecting the EYC. (B) Sandbox modelling (modified after McClay et al., 2002) of extension with a basement anisotropy showing the complex interplay of the border faults (solid lines) and the internal extension faults (pecked lines). In this model, a NE–SW directed extension is superimposed upon a N–S striking basement anisotropy. The early extension developed the border faults (akin to Ida and Hootanui Faults), which ultimately influenced the geometry of the later extension (cf. a in this figure). Note the similarity in the gross trends in the magnetics and geology of the EYC. (C) View to the SE of a mesoscale D1 extensional fault (growth?) from the North Pit near Wiluna (Fig. 2). Note the variable offset of sedimentary layering on the fault plane (highlighted by arrows). The D1 fault is now rotated along with the stratigraphy, but on inception would have been a steeply dipping D1 normal fault with extension to the ENE. (D) Nd depleted-mantle model age map of the granites of the Yilgarn Craton. Image produced by gridding Nd depleted-mantle model ages calculated from Sm–Nd point data from Champion and Cassidy (2007). Note the pronounced NNW trends in the distribution of crustal ages—this trend marks the earlier grain established during D1 extension, and sets up the border faults that define the Kalgoorlie and Kurnalpi Terranes. Boxed area shows study area of Fig. 2.

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Fig. 4. (A) Extract of ‘S2’ foliation data for the entire EYC, extracted from Geoscience Australia’s OZROX database. Stereographic projection of poles to ‘S2’ foliation planes, contoured at 1%, 2%, 4%, 8% and 16% intervals, with strikes shown in the rose diagram below. Note the pronounced NNW-oriented ‘S2’ trend. (B) Stereographic projection of poles to dominant foliation planes at four selected sites, contoured at 1%, 2%, 4%, 8% and 16% intervals, with strikes shown in the rose diagram below (see Fig. 5). Note the same NNW trend as (A). These four sites developed their dominant foliation during four discrete events (D2, D3, D4, and D5), and by different tectonic modes. The similarity in trends between the summed trends from the four different events and the regional summed trends, shows the potential for miscorrelation when simply using a penetrative foliation of similar orientation as a marker of correlating structures between different areas (Czarnota and Blewett, 2007).

be determined, are particularly conducive. The use of the method on ductile structures is justified because the same palaeostress was resolved from both brittle (instantaneous strain ellipsoid) and ductile structures (finite strain ellipsoid) developed during the same event at a particular sub-site (Blewett and Czarnota, 2007a). Individual P–T dihedra were stereographically constructed for each structural feature, which typically resulted in a reduction of possible orientations of 1 to two quarters of a stereonet. The possible areas of 3 were also resolved in this way. These individual results for each measurement were then overlaid in order to more tightly define the regions of possible 1 (and 3) for each local sub-site event. In the case of structures for which P–T dihedra could not be constructed (e.g., folds and pervasive foliations), and structures formed due to flattening rather than shear, the pole to the axial plane or foliation was used as a proxy for 1 (Fig. 6). In the case of folds, 2 and 3 can also be determined. Stage three involved correlating events from one sub-site to another throughout the site. The correlation of events was based on the style of structures and the resolved palaeostress associated with that event. Once the correlation was completed, P–T dihedra constructed for each event at each sub-site were combined to constrain the palaeostress field that was active at the scale of the site during any one event. In some instances, this combination reduced possible orientations of 1 and 3 to only a few degrees on the stereonet (e.g., Sunrise Birthday D3 in Fig. 6). The determination of palaeostress through this method assumes that deformation at the scale of the site is coaxial and there has been no significant rotation of early structures by later events. The consistency of the results suggests that the assumptions are valid at this site scale although in other terrains large-scale folds may need to be taken into account.

Stage four, the final stage, involved correlating structural events between sites (Fig. 2, Appendix A), and thereby correlating the interpreted deformation sequence across the EYC. Map pattern considerations, together with the available geochronology to provide maximum and minimum constraints (Table 2, Fig. 7), were used to correlate between sites (e.g., Fig. 6, Appendix A). During Stage four of the correlation, the pattern of resolved palaeostress orientation changes was more important than the actual palaeostress orientation changes determined for each site. By pattern of palaeostress orientation changes we mean a sequence of characteristic changes, rather than the precise orientations of these events. For example, the palaeostress orientation changes from ∼E–W shortening, to ∼NW–SE shortening, and finally to ∼NE–SW shortening, for the D4a, D4b, and D5 sequence of events respectively, is a predictable and correlatable pattern (Fig. 6). Examples of the results of the process are illustrated in Fig. 6 for fifteen of the eighty representative sites which were studied, documenting the relative (superposition) and where determined, absolute (dating) constraints of each event identified at these sites. The site distribution, in a transect across the EYC, is shown in Fig. 2. For a full discussion of the modified P–T dihedra methodology see Blewett and Czarnota (2007a), and for the complete correlation see Appendix A. An important outcome of the analysis revealed by Fig. 6 is the repeated patterns of change in the orientation of inferred palaeostress, both in vector and mode (contraction or extension). It also shows that the direction of 1 throughout much of the contractional part of the sequence was oriented ENE–WSW (D2, D4a) to NE–SW (D5). The result of the approximately coaxial nature of this shortening direction has been the development of successive, but temporally and kinematically different, NNW-trending folia-

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reason (e.g., Mt Dennis in Figs. 6 and 7). There are also many instances where contraction and extension are mutually exclusive (in terms of intensity), and so the critical overprinting relationships are not available (e.g., Yunndaga/Mertondale cf. Lancefield/Sunrise Birthday in Fig. 6). The reasons for this mutual exclusivity are not well understood, but the role of the large granite batholiths in partitioning strain or in controlling a vertical component to the tectonic mode maybe a factor (Goscombe et al., 2009). In some localities (e.g., Riverina, Waroonga, Peperill, Mt Redcliffe, King of Creation; Fig. 2), it is not possible, due to the lack of overprinting relationships, to determine whether a specific dominant fabric is D5, D4a, or D2. All of these events are contractional and approximately coplanar, so direct dating of the foliations is likely to be the only method available to discriminate. 3.3. Granite structural studies Most previous structural studies in the EYC were focused on the greenstone successions. Granites make up ∼65% of the area and many are well-exposed pavements providing unique lateral continuity to map structures. The granites expose a range of crustal levels and occur in high- and low-strain zones (Fig. 3A). The granites also have a longer preserved geochronological record, and they continue some 30 myr after the last greenstone succession was deposited. This good exposure, coupled with high-resolution U–Pb zircon SHRIMP geochronology (Nelson, 1997; Fletcher et al., 2001; Cassidy et al., 2002; Dunphy et al., 2003; Black et al., GA unpublished data), allowed Blewett et al. (2004c) to erect a new structural-event history for the granites, which was constrained in time, and these results are integrated in the new framework outlined below. 4. A new structural-event framework for the eastern Yilgarn Craton The following section describes the characteristic macro- and mesoscale elements of a new structural-event framework from D1 to D6. Fig. 7 illustrates some examples of critical absolute and relative timing relationships used to constrain the framework. All of the timing relationships are based on a single isotopic system (SHRIMP U–Pb) and cross-cutting relationships, and are therefore directly comparable with one another (see also Table 2). 4.1. pre-D1 deformation Fig. 5. Example stereographic projections for each of the individual deformational events D2, D3, D4, and D5, which collectively comprise the integrated foliations data shown in Fig. 4B. (A) S2 (flattening ∼2665 Ma at Westralia); (B) S3 (extension ∼2660 Ma at Harbour Lights near Sons of Gwalia); (C) S4 (flattening and sinistral strike-slip ∼2655 Ma at Yunndaga), and; (D) S5 (dextral strike-slip ∼2640 Ma at King of Creation). Each individual deformational event shows a similar NNW-oriented strike, and yet each event is fundamentally unique in genesis, kinematics and age. The parallelism of penetrative fabrics of different ages and kinematics invalidates the arbitrary use of a NNW-oriented penetrative foliation (frequently called ‘S2’) as a structural marker for correlation purposes in the EYC (Czarnota and Blewett, 2007).

tions (Fig. 5). As a consequence, it can be very difficult to reliably interpret a foliation at any single location. Thus, there is a need for caution in using foliations alone as a regional correlation marker (Czarnota and Blewett, 2007). Where the D3 extensional event separates contractional D2 from contractional D4 structures, reconciliation of these contractional structures is relatively easy (cf. Westralia and Mertondale in Fig. 6). Another constraint is provided by the late-basin successions and/or Low-Ca granites. The late-basin successions, by definition, cannot host a D2 structure as they overprint them (e.g., Genesis–New Holland in Fig. 6). The widespread Low-Ca granites, which are all <2655 Ma in age (Cassidy et al., 2002), cannot host D1 through to D4 structures for the same

Slivers of stratigraphy older than 2720 Ma are preserved mostly on the margins of some of the larger granite domes in the Kalgoorlie and Kurnalpi Terranes (Cassidy, 2006), and in greenstone belts in the western Burtville Terrane (Cassidy, 2006; Cassidy et al., 2006; Pawley et al., 2009). Granite gneisses, with ages >2750 Ma, have also been described from a number of localities in these regions (Cassidy, 2006). These poorly understood rocks record a history that is fragmentary and weakly constrained, and they likely contain a structural history that developed prior to the main crustal growth stage in the EYC (i.e., after 2720 Ma). 4.2. D1 ∼ENE–WSW extension Most workers agree that major extension occurred in the EYC, with major crustal growth between 2720 Ma and 2670 Ma (Groves and Batt, 1984; Hallberg, 1985; Williams et al., 1989; Swager and Griffin, 1990; Swager et al., 1992; Hammond and Nisbet, 1992; Swager, 1997; Brown et al., 1999; Squire et al., 2007; Pawley et al., 2009). However, the unequivocal attribution of meso- and macroscale structures to this extensional event is difficult. The difficulty is mostly due to significant reactivation of these early structures. In this study, we enumerate the early formed structures

Table 2 Summary of the timing constraints of the new structural-event framework based on overprinting relationships. The ‘>’ means the event is older than the age, ‘<’ means the event is younger than the age, and syn is synchronous with the age. Event

Timing summary

Stratigraphy

Dominant granite type

Minor extension N-S dextral strike-slip transtension

D6 D5

<2630 Ma variable? 2635–2650 Ma

Eroded Eroded

Low Ca rare Low Ca (commencing younger to west)

NNW sinistral transpression and thrusting

D4b

2650–2655 Ma

Eroded

Waning High Y TTG some syenite

NNW upright folding and reverse faulting Extensional doming and NE-directed extension

D4a

2655 Ma

Eroded

High Y TTG some syenite

D3

2655–2665 Ma

Late Basins—includes significant granite detritus (so deep exhumation)

Mafic/Syenite

NNW upright folding and reverse faulting

D2

2665 Ma (W) 2670 Ma (E)

Termination of volcanism

Low Y TTG

ENE extension

D1

2670–2720 Ma

Bimodal volcanic sequences on Youanmi basement

HHFSE passing into Low Y TTG

Age constraints linked to structures, based on U–Pb SHRIMP dates of granites, or maximum depositional ages in basins

References

>2638 ± 2 Ma (Ironstone Point) Syn 2647 ± 3 Ma (Mars Bore) <2652 ± 5 Ma (Pink Well), <2650 ± 8 Ma (Mount Denis); <2645 ± 6 Ma (Surprise Rocks) > All the Low-Ca granite ages reported above <2555 ± 6 Ma (Kanowna Belle) <2663 ± 7 Ma (Isolated Hill) > All the late basin ages reported below >2657 ± 15 Ma (Wallaby syenite); >2640 ± 8 Ma (Clarke Well) Syn gold 2658 ± 4 (Sunrise Dam); 2664 ± 2 Ma (Hanns Camp); 2660 ± 5 Ma (Bulla Rocks) <2666 ± 5 Ma (Mt Belches); <2673 ± 5 Ma (Wallaby); <2668 ± 9 Ma (Golden Valley); <2667 ± 10 Ma (Grave Dam); <2656 Ma (Ballarat); <2665 ± 5 Ma (Jones Creek); <2662 ± 5 Ma (Scotty Creek); <2664 ± 6 Ma (Merougil); <2664 ± 4 Ma (Pig Well-Yilgangi); <2657 ± 4 Ma (Kurrawang); <2663 ± 5 Ma (Granny Smith) >2664 ± 2 (Hanns Camp); >2667 ± 5 Ma (Porphyry), >2657 ± 8 Ma (Porphyry); >2660 ± 5 Ma (Bulla Rocks); >2665 ± 4 Ma (Granny Smith) <2668 ± 4 Ma (Ironstone Point); <2667 ± 4 Ma (Pindinnis); S1 Gneissic fabric: 2672 ± 2 Ma (Two Lids Soak); 2675 ± 2 Ma (Barrett Well); <2670 ± 10 Ma (Ivor Rocks); 2681 ± 4 Ma (Isolated Hill); 2674 ± 3 Ma (Wilbah)

Cassidy et al. (2002), Dunphy et al. (2003), Blewett et al. (2004c), Cassidy (2006) Dunphy et al. (2003), Ross et al. (2004)

Nelson (1997), Krapeˇz et al. (2000), Fletcher et al. (2001), Barley et al. (2002), Cassidy et al. (2002), Dunphy et al. (2003), Miller (2006), Tripp et al. (2007), Standing (2008)

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Style

Cassidy et al. (2002), Blewett et al. (2004c)

Nelson (1997), Cassidy et al. (2002)

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Fig. 6. A selection of fifteen sites, out of more than eighty, to form a representative structural transect across the EYC. The full database of sites was used to constrain the structural-event framework (Appendix A). The best constraints occur at sites that have dated granite(s) or late basin successions. Stereonets are lower hemisphere projections of P–T (compression–tension) dihedra and their associated structures. See Angelier (1984) and Blewett and Czarnota (2007a) for a description of the method. The white sectors in the stereonets show the 3D region of possible 1 and the black sectors show the 3D region of possible 3. The small numerals next to the stereonets indicate number of data points measured for that structural element at that site (2280 measurements were made in these fifteen sites). The greater the relative number indicates the predominance of that structural element at that site. These dihedra are analogous to fault-plane solutions used in seismology. Timing uncertainty is shown by pecked lines with arrow terminations. Note the heterogenous palaeostress distribution associated with the D4b event as a consequence of shortening at a high angle to the pre-existing D3 anisotropic domal architecture. Note also that gold was deposited during all events except the first and last. The temporal positions of the separate events in Fig. 5A–D are labelled in their spatial and temporal context. The locations of these representative fifteen sites are shown as stars in Fig. 2. Figure number of photographs illustrating some of the structures are also shown.

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Fig. 6. (Continued ).

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Fig. 7. Photographs of some of the dated granite sites (ages reported in Fletcher et al., 2001; Cassidy et al., 2002; Dunphy et al., 2003) and relationship to structures (see Blewett et al., 2004c for a comprehensive study of the structural geology of the granites). All photographs are looking downwards onto pavements, except (C). (A) Ivor Rocks (Fig. 2) is a host High-Ca granite with a U–Pb age of 2670 ± 10 Ma with a younger gneissic fabric (S1) which is isoclinally folded (D1). D1 structures are folded about younger upright N-plunging F2 folds. (B) Mylonitic shear fabric (S2) developed in host High-Ca granite with a U–Pb age of 2674 ± 3 Ma at Wilbah Gneiss (Fig. 2). The S2 foliation is cut by a Low-Ca granite with a U–Pb age of 2647 ± 3 Ma. (C) Gently dipping S3 mylonitic extensional fabric with top down to the SSE shear sense developed at Hanns Camp Syenite (Fig. 6). The syenite has a U–Pb age of 2664 ± 2 Ma. Inset diagram shows the S3 foliation being dragged into a N–S trending subvertical S5 dextral shear. (D) Well developed sinistral strike-slip mylonites, interpreted to be S4b developed in host High-Ca granite with a U–Pb age of 2663 ± 7 Ma at Isolated Hill (Fig. 2). Inset shows asymmetrical tails around a 5 cm feldspar phenocryst. (E) Dextral strike-slip shear zone (D5) developed in a High-Ca granite with a U–Pb age of 2652 ± 8 Ma at Pink Well (Fig. 2). An earlier foliation (S4?) is being dragged into the shear zone. (F) Low-Ca granite dyke at Moon Rocks (Fig. 2), with a U–Pb age of 2637 ± 7 Ma, intruded into a N–S dextral shear zone (D5) that overprints a foliated (S1) High-Ca granite with a U–Pb age of 2732 ± 16 Ma.

as D1, in preference to previous nomenclature which named this event as ‘DE’ (Tables 1 and 2). The prominent NNW-trending grain is reflected in the macroscale distribution of the greenstone terranes and domains and the temporal variations of their constituent stratigraphy (Swager et al., 1992; Swager, 1997; Brown et al., 1999;

Barley et al., 2002), the spatial changes in granite types (Champion and Sheraton, 1997), the map patterns of the Sm–Nd granite isotopes (Cassidy and Champion, 2004; Fig. 3D), and the geochemical signatures of the magmatic and volcanic stratigraphy (Barley et al., 2002; Said and Kerrich, 2009).

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The D1 event commenced with rifting of the eastern margin of the Youanmi Terrane, and the start of the main greenstone rock record (2720 Ma). Extension continued through to the onset of the first significant contraction at around 2670 Ma (Fig. 7A). Relicts of the older basement (with Youanmi Terrane affinities) are preserved as small slivers of >2810 Ma granites and greenstones especially in the Burtville Terrane (Pawley et al., 2009). They are also preserved as exhumed slices of higher pressure M1 rocks in the footwall of D3 core complexes. These older and deeper rocks likely represent the D1 rifted remnants of the basement (Cassidy et al., 2002). The elongate map patterns and changes across linear NNWtrending structures are interpreted to be a result of extensional tectonics during basin development (Brown et al., 1999). This interpretation is supported at a mesoscale, where synvolcanic extensional faults have been observed. Many of these structures occur as growth faults within the major gold deposits of the region, such as the Carey Shear at Sunrise Dam (Henson et al., 2010), the Golden Mile Fault at Kalgoorlie (Gautier et al., 2007), and the Playa Shear at St Ives (Connors et al., 2003; Miller et al., 2010) or small gold deposits like North Pit at Wiluna (Fig. 3C), and in the Kambalda nickel deposits (Brown et al., 1999). Some of the older granites, especially the gneisses, contain foliations that are interpreted to be related to D1 extension (Table 2; Figs. 6, 7A and F). Many of these foliations are developed in granitic orthogenesis with a concentration of ages at around 2675 Ma (Cassidy et al., 2002; Dunphy et al., 2003). These structures include the common gneissic fabric elements developed across the entire EYC, irrespective of the terrane or the domain. The fabric elements developed at this time, including melanosome–leucosome differentiated layering, are commonly isoclinally folded and transposed (e.g., Poison Creek and Mt Dennis in Figs. 6, 7A and B). When unfolded for the effects of upright F2 folding, Blewett et al. (2004c) interpreted these early isoclinal folds as recumbent lower-plate folds developed during vertical flattening and extension (e.g., Harris et al., 2002). 4.3. D2: ∼ENE–WSW contraction Extension ended with the onset of D2 contraction, which was a low-strain event that developed mostly without pervasive regional foliation. Evidence for D2 shortening is found in the regional map patterns, and Blewett et al. (2004b) described two examples of regional macroscale F2 folds; one at Ora Banda, and another at Welcome Well (Fig. 8A). At both these localities, late-basin successions unconformably overlie and truncate F2 folds, providing a minimum age of 2660 Ma for the development of these underlying folds. Another macroscale example, in the Kurnalpi Terrane, occurs where the map patterns of the Mt Margaret Anticline around Laverton show that the pre-late-basin succession greenstones are folded more tightly than the outline of the batholith, and the more openly folded geometry of the 2665 ± 5 Ma Wallaby basin (Standing, 2008). This map pattern relationship indicates that ENE-oriented shortening had commenced before the deposition of the late-basin successions (Table 2). In the southern EYC, the ENE-directed Foster Thrust at Kambalda is interpreted as a D2 structure (Blewett et al., 2010b; Miller et al., 2010). Clear examples of mesoscale D2 contraction are uncommon in the greenstones (Fig. 6). This is partly due to reactivation by later events as discussed above. Westralia, which is close to the Celia Fault System, has a flattening fabric and associated folds (Figs. 5A and 8B), whereas Tarmoola shows a D2 flattening fabric cross-cut by gold-bearing quartz-carbonate ± fuchsite veins. These veins were formed along NE–SW trending dextral strike-slip faults (Fig. 6). Flattening fabrics are also present in the Bannockburn mine (Fig. 2) northwest of Leonora (Fig. 1).

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At the mesoscale, across many of the granite sites, D2 is represented by upright asymmetrical (Z-shaped) folds, and N–S to NE–SW trending dextral shear zone transposition of D1 extensional fabric elements (Figs. 7A and 8C). There can be difficulty separating D2 structures from D4 structures at some granite sites (e.g., Poison Creek in Fig. 6). There appears to be a general change through time from folding to dextral shearing in the external granites (see Appendix A). Age constraints suggest a diachroneity of D2 contraction from east to west (Table 2), commencing around 2670 Ma in the east and around 2665 Ma in the west (Blewett et al., 2004b; Standing, 2008; Czarnota et al., 2010). 4.4. D3: extension—core complex formation The structures specifically developed by the D3 event are evident at a range of scales. Particularly instructive is the relationship between the geometry of the late-basin successions and the granite-cored domes, as these provide important macroscale timing and kinematic constraints on the D3 event. The mesoscale fabric element observations confirm the macroscale findings. Both scales record granite-up and greenstone-down kinematics across extensional shear zones. 4.4.1. Regional map patterns The EYC is a typical granite-greenstone terrane, with a general map pattern of granites, most of which were emplaced below the base of the greenstones, being juxtaposed against upper-crustal greenstones. The contact between these two crustal levels is commonly faulted and sheared (e.g., Williams and Whitaker, 1993), with granites projecting underneath greenstones (i.e., dome outwards). The map pattern relationship indicates an extensional tectonic mode, with granite-up and greenstone-down movements across the shear zones/faults. The upper-crustal greenstone successions young outwards away from the granite margins which is consistent with the extensional tectonic mode. These contacts are mapped by gravity data, which readily distinguishes dense greenstones from less dense granites (Blewett et al., 2010a). Crosssections through these map patterns by several deep seismic reflection profiles show that most major faults dip east, that the greatest thickness and youngest late-basin successions are preserved on the hangingwall (eastern) side, and deeper mid-crustal rocks (granites) are in the footwall (Czarnota et al., 2007). The basic geometry of the large-scale architecture is therefore also extensional (down to the east or northeast). The timing of this extension and map pattern formation is 2665 Ma and younger. The age constraint is provided by the late-basin successions and the Mafic-type granites and syenites (Table 2). For example, the Hanns Camp Syenite is dated at 2664 ± 2 Ma (Dunphy et al., 2003), and is overprinted by a subhorizontal shear fabric of likely extensional origins (Fig. 7C). 4.4.2. Macroscale map patterns of the late-basin successions Late-basin successions occur in two typical map pattern forms. The first type is arcuate and located in the hangingwall of extensional shear zones, at the noses of some granite domes (e.g., Wallaby and Kanowna Belle). The second type is more common, and is characterised by NW-trending elongate grabens in the hangingwall of NW-trending (Fig. 2). These examples include: the Kurrawang, Merougil, Belches and Pig Well–Yilgangi basins in the central parts of the EYC (Fig. 2). These basins are interpreted to have developed during NE-directed asymmetrical extension. Late-basin successions preserved adjacent to the Hootanui and Ida Faults vary from the main NW-trending map patterns. The Scotty Creek basin strikes NNE, while the Granny Smith basin strikes NNW. Both basins strike parallel to their adjacent major fault (Fig. 2), suggesting a likely pre-existing basement control on basin architecture, rather

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Fig. 8. Mesoscale examples and macroscale map pattern relationships illustrating D2 contractional structures: (A) Example of NW-trending Pig Well basin which is folded into the D4a Butcher Well syncline unconformably overlying N- to NNW-trending regional F2 folds such as the Corkscrew Anticline and Kilkenny Syncline (from Blewett et al., 2004b). (B) View north in Westralia (Fig. 2) of F2 folds intruded by D2 porphyry and refolded by ongoing F2 folding. Note also E-over-W D4 reverse faulting. Field of view 3 m wide. (c) Flattening with the development of shallow plunging upright isoclinal F2 folds at Moon Rooks (Fig. 2). The foliation being folded is the D1 gneissic fabric which is developed in a 2732 ± 16 Ma aged High-Ca granite. Material in the top left is an undeformed Low-Ca granite that is transecting the F2 folded S1 fabric – this granite is dated at 2637 ± 7 Ma (ages after Dunphy et al., 2003).

than a different regional extension direction compared to the NWtrending basins. The late-basin successions are the first record of the deposition of granite detritus in the EYC (Krapeˇz et al., 2000). Accommodation space for the sediment accumulation in the late-basin successions was created in the hangingwall of D3 extensional shear zones. The source region for the detritus was the exhumed the granites in the footwall of the same D3 extensional shear zones. 4.4.3. Macroscale patterns of the granite-cored domes Granite-cored domes are a common map feature of the EYC (Fig. 2). These domes are N- or S-trending, mostly gently-plunging, structures. Higher up the fold profile (outer arc), and on the limbs of the domes, lie outward facing and younging greenstone successions with either intrusive and/or variably sheared con-

tacts. Two examples are described here—Mt Margaret and Lawlers (Fig. 2). The Lawlers Dome is located in the west of the Kalgoorlie Terrane (Figs. 2 and 9). It is a gently north-plunging, upright, granite-cored dome with outward facing and younging mafic–ultramafic rocks of the Kambalda Sequence. The Lawlers Tonalite (a Mafic-type granite) in the centre of the dome has an age of 2666 ± 3 Ma (Fletcher et al., 2001). Phases of this granite cut up into the core of the fold and transect previously folded greenstones (Fig. 9). In contrast to Mt Margaret, there is no known late-basin succession wrapping around the profile of the fold (Fig. 9). However, along the western margin of the anticline, lies the Scotty Creek basin, which has a maximum depositional age of <2662 ± 5 Ma (Dunphy et al., 2003). At Lawlers, a penetrative solid-state foliation in both granites and greenstones is parallel to the margins of the

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dome (Fig. 9; after Beardsmore, 2002). A weak axial planar crenulation cleavage of this main foliation occurs locally in the hinge region of the fold, and was generated by later contraction (D4a). The associated stretching lineations plunge gently to the north in the north, progressively steeper in the northeast and plunge steeply to the east along the eastern limb of the fold (Fig. 9). In contrast, along the western limb the lineations plunge gently north. The Mt Margaret Dome (Fig. 2) is a south-plunging structure in the east of the Kurnalpi Terrane. In the core lies a granite batholith with an open upright fold (at the surface), passing structurally upwards (southwards) into greenstones with a tight south-plunging fold. Overlying these greenstones is the Wallaby basin (<2665 Ma), whose lower contact is a south-dipping zone of shear and flattening that is gently folded parallel to the profile shape of the granite core. These relationships demonstrate that the development of the regional anticline and associated intrusion of the granites in the dome core occurred after an earlier phase of E–W shortening (i.e., D2). The Granny Smith basin is farther from the influence of the domes and its development was controlled by regional extension and the proximity to the pre-existing D1 Hootanui Faults (Figs. 2 and 3B). 4.4.4. Macroscale metamorphic patterns Low-angle extension is an effective mechanism for juxtaposing higher metamorphic grade rocks in the lower plate (M1 assemblages) against lower metamorphic grade rocks in the upper plate (M2 and M3a assemblages). Williams et al. (1989) and Williams and Whitaker (1993), related the juxtaposition of high-grade greenstones (immediately adjacent to the Raeside and Mt Margaret Batholiths) against low-grade greenstones across batholith-away dipping shear zones, as a function of extension. Williams and Currie (1993) noted there was at least 5 km of excision from this extensional event across the Gwalia Shear Zone. Similarly, Swager and Nelson (1997) dated significant extensional exhumation of high metamorphic grade gneisses from beneath low metamorphic grade greenstones near Two Lids Soak and Barrett Well along the SE margin of the Kurnalpi Terrane, at 2660 Ma (Fig. 2). Goscombe et al. (2007, 2009) showed that the general metamorphic gradients record not only steadily increasing temperature towards the granites from the greenstone synforms (Binns et al., 1976), but also significantly increasing pressure, confirming the extensional excision of deep stratigraphy (Williams and Currie, 1993). Pressures of up to 8.7 kb have been documented from these M1 lower plate rocks (Goscombe et al., 2009). The metamorphic conditions in the upper-plate late-basin successions are unique within the metamorphic evolution of the EYC. The conditions are characterised by tight anticlockwise PTt paths in contrast to the clockwise paths from M2 (Goscombe et al., 2009). These anticlockwise PTt paths are characteristic of extension (Sandiford and Powell, 1986; Wickham and Oxburgh, 1987). 4.4.5. D3 extensional structures Mesoscale structures related to D3 extension, doming and core complex formation are best developed adjacent to the margins of large granite domes. In general, the most intense mesoscale structures are developed where the oldest stratigraphy (pre-Kambalda Sequence) is adjacent to a dome. This intensity of strain is reflected in the large amounts of displacement across these extensional faults, and accounts for metamorphic excision and exhumation of

Fig. 9. Map and stereonet of the main foliation (solid-state mylonites) and associated lineation in the Lawlers region (data after Beardsmore, 2002). The foliation and lineation data are consistent with granite doming and extensional uplift. SRB = location of Sunrise Birthday (see Fig. 10E and F). (A) The foliation is parallel to the dome margin (and stratigraphy) and dips outwards and away from the

N-plunging dome (see also stereonet insert). (B) The lineation trajectories are parallel to the hinge in the axial region and western limb, and fan outwards away from the hinge on the eastern limb. The stereonet of lineations show gentler hinge parallel plunges and steep plunges to the east. Note the absence of W- and SW-plunging lineations.

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the higher pressure M1 assemblages to the surface (see Goscombe et al., 2007, 2009; Czarnota et al., 2010). Around the granite domes the S3 foliations dip gently outward, and have extensional kinematics, expressed as welldeveloped S–C–C fabrics (Figs. 5B, 7C, and 10A–F), with mostly down-dip stretching lineations commonly defined by amphibole (Figs. 9B and 10C). The zone of shearing defined by the S3 foliation at Sons of Gwalia is imaged in a deep seismic reflection profile as a band of high amplitude reflectivity up to 5 km wide (to the east), extending at depth onto a convex detachment between 3 km and 5 km deep (Blewett and Czarnota, 2007c, Fig. 22d). To the north of the Sons of Gwalia mine the main Raeside Batholith has a series of west-stepping embayments (Fig. 2). Victor Well and Tarmoola (Figs. 2 and 6) are two localities in this vicinity that illustrate the influence the granite-cored domes have on controlling D3 extensional strain. The main foliation at both these localities strikes ∼E–W, parallel to the granite dome margin, and both record toP–To-the-north extensional kinematics. At Tarmoola, the D3 structures include gently to moderately N-dipping S–C mylonites, horizontal crenulation cleavages and brittle-ductile normal faults. These structures overprint the earlier D2 gold mineralisation (Czarnota et al., 2008). In the Laverton area, the Mt Margaret Dome strongly influenced D3 extension. Mylonitic foliations occur in the granite and overlying greenstone, and parallel the dome margins, with lineations plunging outward from the dome (see also Williams and Whitaker, 1993). Where measured for kinematics (e.g., Lancefield—Figs. 6 and 10D), these structures show SE-down extensional strains. Elsewhere, the D3 structures include a gently dipping mylonite with SSE-plunging stretching lineations developed in the 2664 ± 2 Ma Hanns Camp Syenite (Figs. 6 and 7C). At Westralia (Fig. 2), normal faults with ENE-directed extension, cut earlier contractional structures (D2) and are cut by later contractional structures (D4) (Fig. 6). These normal faults are interpreted as D3 extensional structures developed as a result of extension on the nearby NNW-trending Celia Fault (Fig. 2). 4.5. D4: contraction and sinistral strike-slip D4 was a mostly low-strain contractional event across broad areas of the EYC, with intense high-strain corridors localised to the steep margins of granite batholiths (Fig. 11A), and within the latebasin successions. Sites of D3 extension, especially those marked by late-basin successions, were mechanically and thermally weakened by the extension, and therefore became the focus of D4 contractional deformation. Despite earlier gold deposition during D2 and D3, the D4 event marks the onset of the most endowed period of gold mineralisation in the EYC (e.g., at Lawlers, Laverton, Kalgoorlie and Kambalda). Two distinct stages of deformation, D4a and D4b, define the D4 event (Table 1). 4.5.1. D4a: ENE–WSW contraction The first stage (D4a) involved horizontal contraction, with 1 oriented ENE–WSW resulting in the tightening of earlier F2 and F3 folds, and thrusting to the WSW along many of the major NNWtrending faults. The geometrical consequence was the steepening of stratigraphy (including late-basin successions) along the margins of east-facing granite domes (e.g., Bardoc Tectonic Zone north of Kalgoorlie, the Scotty Creek basin at Lawlers, and the Mt Varden area north of Laverton). This D4a event is equivalent to ‘D2’ of Swager (1997) and ‘D2b’ of Blewett et al. (2004b), as it overprints (inverts) the D3 late-basin successions (Tables 1 and 2). At the macroscale, regional F4a folds developed in the latebasin successions strike NNW, and most are preserved as synclines (e.g., Butchers Well, Merougil, Kurrawang, Pig–Well). In contrast, the Wallaby basin is folded into a S-plunging F4a antiform. This

regional fold is along strike, but unconformably on top of, the earlier F2 formed Mt Margaret Anticline (Blewett and Czarnota, 2007a; Standing, 2008). At the mesoscale, D4a structures include flattening cleavage/schistosity and S–C shear foliations, isoclinal folds and thrusts, all indicate that shortening was oriented ENE–WSW, consistent with their macroscale counterparts. The localities with particularly well-developed or intense mesoscale D4a deformation described here include Yunndaga, Mertondale and New Holland (Figs. 2 and 6). Gold was deposited during D4a at Jupiter and New Holland, and these structures are described later. At Yunndaga (Figs. 2 and 6) an intense S4a schistosity dips steeply NE, and is axial planar to gently NW-plunging F4a isoclinal folds. Locally, cm-scale quartz-rich veins strike ENE, at a high angle to the dominant fabric in the deposit. These veins were interpreted as extension veins developed during the waning stages of ENE–WSW oriented contraction (Blewett and Czarnota, 2007c; Morey, 2007). Both these veins and dominant foliation are overprinted by gold-bearing sinistral strike-slip shear zones, interpreted as D4b. The dominant foliation at Mertondale (Fig. 2) is an intense schistosity that strikes N–S and dips steeply to the east (Fig. 6). The foliation is axial planar to upright isoclinal folds, which tend to be transposed with a reverse shear sense. A rare down-dip stretching lineation is also recorded (Blewett and Czarnota, 2007c—see Fig. 37a and b). The resolved shortening direction at this locality is approximately E–W, so without other constraints, these structures could be correlated with either the regional D2 or D4a deformation (Fig. 6). The preferred interpretation is for these structures to be D4a in age because: (1) the high strains recorded are atypical of D2 deformation, (2) the strain is a product of contraction so cannot be D3, and (3) in the absence of other older structures, the next deformation event at this locality was a series of NNW–striking sinistral shear zones, which are characteristic of the D4b deformational event. 4.5.2. D4b: NNW–SSE sinistral strike-slip shearing and linked thrusting The D4b event was a particularly pervasive phase of deformation, with its impact recorded in most localities (Fig. 6; Appendix A). The D4b deformational event involved a characteristic regional clockwise rotation of the stress field (Fig. 6), with regional shortening oriented approximately WNW–ESE (see also Mueller et al., 1988; Chen et al., 2001; Weinberg et al., 2003; Miller, 2006; Morey, 2007; Henson et al., 2010; Miller et al., 2010). In detail, the resolved stress field for the D4b event varies locally from E–W to NW–SE to N–S (Fig. 6; Appendix A). Despite this local complexity, the D4b event can usually be distinguished because it is generally preceded, and almost always succeeded, by structures developed under a contractional field in the ∼NE–SW quadrant (Blewett and Czarnota, 2007c). The variation in resolved stress field was caused by the obliquity between the regional far-field shortening direction and the complex anisotropy/geometry following earlier deformation events. Sinistral strike-slip shearing was most intense where regions have steeply dipping stratigraphy which strikes NNW (close to the WNW–ESE shortening direction). In these regions, thrusting and flattening ceased to be effective in dissipating the stress. Localities with intense D4b sinistral shear include Matilda, Yunndaga (Fig. 5C), Isolated Hill (Fig. 7D), Barrett Well, Two Lids Soak, Jasper Hill, Poison Creek, Ivor Rocks (Fig. 11C), and Turkey Well (Fig. 2; Blewett and Czarnota, 2007a). Major sinistral strike-slip shearing occurred as reactivation along earlier developed NNW-trending regional faults such as the Zuleika, Ockerburry, Emu, Celia, Hootanui and Yamarna Faults (Figs. 2, 5C, 7D, 11A). The major D4b thrusts trend ENE and record

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Fig. 10. Photographs illustrating D3 extensional structures. (A) View NE onto a wall exposing gently-dipping S3 foliation. The foliation has a pronounced S–C fabric recording top-to-the-left (NW) extensional shearing at Keringal gold mine, which is located on the NW margin of the Kirgella Dome (Fig. 2). Inset enlargement in bottom left of S–C fabrics from the centre of the view. This site is a mirror image of the Lancefield deposit (D). (B) View N onto a wall exposing S–C–C extensional fabrics at Sons of Gwalia gold mine near Leonora (Fig. 1). Shear sense is normal down-to-the-east (see also Williams et al., 1989). The foliation is equivalent to that shown along strike at Harbour Lights (see Fig. 5B). (C) Down-dip stretching lineations (parallel to the arrow) on the C-plane (B) of the main foliation at Sons of Gwalia gold mine. The extensional (normal) nature of these fabric elements is also shown by the down-dip boudinage (within the shear plane) of the amphibole lineation (within encircled area). (D) S–C foliations showing top-to-the-right (SE) extensional D3 strains in the Lancefield gold mine (Fig. 2). The Mt Margaret Dome is to the NW and the Granny Smith Late Basin is to the SE. This site is a mirror image of the Keringal deposit (A), both have granite-cored domes in the footwall and late basin successions in the hangingwall. Gold was deposited into these D3 extensional shear zones. (E) View west into the Sunrise Birthday pit (Figs. 2 and 9) showing the ‘rolling’ of the foliation. The majority of this host gabbro is unfoliated, with the penetrative fabric confined to high-strain gold-rich shear zones. Note that the Sunrise Birthday pit is close to the hinge of the Lawlers Anticline (Fig. 9) and the foliation is not axial planar to a contraction fold, but is at a high angle to the hinge. (F) Sunrise Birthday as a neo-formed S3 S–C fabric that was developed during down-to-the-north-northeast extension. Photograph taken from the ore envelope, demonstrating gold is syn-D3 extension and likely related to exhumation of the Lawlers Tonalite to the south (see Fig. 9).

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Fig. 11. Photographs and selected map pattern relationships illustrating D4 contractional structures. (A) Regional aeromagnetic image of the northern Leonora and southern Sir Samuel 1:250,000 sheet areas. The prominent folds and magnetic highs in the west are from Kalgoorlie Sequence ultramafic rocks enveloping the northern end of the Lawlers Dome. Note the prominent sinistral drag of the magnetic fabric (shear arrows), especially along the granite margins. The interpreted regional shortening direction is shown by the white ESE–WNW oriented arrows. (B) View of the SE wall of the Jupiter gold mine. The dark host rocks are pillow basalts, formed during D1 extension, which dip moderately south due to F2 folding around the S-plunging regional Mt Margaret Anticline (Fig. 2). This F2 folded sequence was intruded by syenites (pink dykes), which were emplaced during D3 extension and formation of the Wallaby basin (now eroded at this site). These D3 dykes are overprinted by mineralised D4a thrusts (shown by arrows), with a top-to-the-SW sense of transport consistent with ENE–WSW shortening (Fig. 6). (C) View east onto a granite pavement at Ivor Rocks (Fig. 2) east of Laverton, with a ductile NNW-trending subvertical D4b sinistral strike-slip fault, which is cut by a Low-Ca granite of around 2640 Ma age. The inferred shortening direction was oriented ESE–WNW for this sense of shear on a fault of this trend. (D) View to the northeast of a wall containing mineralised contractional vein arrays in the Victory–Defiance gold mine. These veins developed during ESE–WNW shortening (thrusting) across the Kambalda Anticline, and accommodated sinistral strike-slip faulting on the edges of the anticline (see also Miller et al., 2010). (E) Simplified geological map of the structural elements of the St Ives area (modified from Nguyen, 1997). D4b NE–SW trending thrusts (Tramways and Republican) cutting NNW-trending F2 folds. These thrusts are top to the NNW-directed and accommodate the sinistral strike-slip motion on the eastern and western margins of the elongate Kambalda Dome, and are analogous to the Mongolian example (F). The D4b thrust faults were previously interpreted as ‘D1’ structures (Swager and Griffin, 1990). (F) Thrust faults developing at a high angle (and acting as transfers) to sinistral strike-slip shear zones from the Altai region of Mongolia (after Bayasgalan et al., 1999). These transfer or accommodation thrusts are analogous to structures adjacent and across many of the domes in the EYC. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of the article.)

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transport to the NW and SE (Fig. 11D and E), and were previously interpreted as ‘D1’ (Swager, 1997). The thrusts are only recorded in the hinge regions of SE- or NE-plunging domes and anticlines. Some of these thrusts initiated during D3 extension along the noses of rising granite domes, such as Thets Fault at Wallaby and Sunrise shear zone at Sunrise Dam (Henson et al., 2010), and the Fitzroy shear zone at Kanowna Belle (Davis et al., 2010), as they all contain young late-basin successions in their hangingwalls. These thrusts are all highly mineralised (Henson et al., 2010). In the Lawlers area, Beardsmore (2002) described sinistral strike-slip faults associated with WNW-ESE-oriented 1 to overprint an earlier E–W oriented shortening event. These events equate to D4a and D4b respectively in this framework. Based on superposition of structures, the style, and the inferred shortening direction, the following mesoscale structures are interpreted to be D4b in age. At Sunrise Birthday, Poison Creek, Yunndaga (Fig. 5C), Mertondale, Hanns Camp and Mt Dennis are a series of NNW-trending brittle-ductile sinistral strike-slip faults, S-asymmetrical folds, together with some mutually cross-cutting E–W dextral faults. The fault offsets are typically less than 1 m, and locally associated with the intrusion of granite-pegmatite dykes along the shear planes (Fig. 6). At Westralia, Phoenix, and Sons of Gwalia (Fig. 2), the D4b mesoscale structures are represented as thrusts, with most recording hangingwall transport to the NW (Fig. 6). At Lancefield, D4b is manifest as ENE-trending crenulation cleavage of the earlier S3 extension fabric (Fig. 6). In some localities the first significant deformational event is D4b. This is particularly the case for the internal granites, especially those located in a corridor between Bernie Bore and Yarrie (Fig. 2). For example, the 2714 ± 21 Ma Yarrie Monzogranite is an otherwise undeformed rock, with narrow (1–3 m wide) shear zones which strike NNW. The shear sense is sinistral strike-slip, based on S–C fabrics and the shallow N-plunging stretching lineation. The shear zones are sites of minor gold mineralisation (Blewett et al., 2004c), and this deformation is interpreted as D4b in age, with shortening oriented ESE–WNW. The Puzzle deposit is another example (Fig. 2). Here, the late-basin succession rocks host a penetrative foliation that dips steeply to NW, and is interpreted as a flattening fabric developed during NW–SE oriented shortening. This S4b foliation is crosscut by the Kookynie granite, dated with large error bars at <2643 ± 14 Ma (age unpublished GA data, reported in Blewett and Czarnota, 2007a), and providing a minimum age for D4b deformation in this locality. Low-Ca granites were almost always intruded after the D4b deformational event (e.g., Fig. 11C). These intrusive rocks provide robust minimum age constraints for the D4b deformational event (Table 2). 4.6. D5: NE-SW contraction and dextral strike-slip The D5 event is largely characterised by dextral strike-slip faulting late in the deformational history (Campbell and Hill, 1988), and was developed across the entire EYC (Blewett and Czarnota, 2007c). The D5 event equates to ‘D4’ in the Swager (1997) nomenclature, and many workers have suggested that it was a progressive event from earlier ENE–WSW to NE–SW oriented shortening (e.g., Weinberg et al., 2003; and references therein). The interpretation of separate stages of sinistral (D4b), followed by later dextral (D5) shearing, as opposed to ongoing progressive deformation, was first suggested by Mueller et al. (1988). This is because for the reversal from sinistral to dextral shear across the same NNW-oriented structure demands a significant rotation of the stress field, rather than ongoing progressive deformation. The main feature of the D5 deformational event was the establishment of a regionally consistent NE–SW oriented shortening vector (Table 1). Despite this, there are marked local differences

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in the style of D5. These differences are due to the influence of the preexisting strike of faults and the geometry of adjacent granite batholiths and shear zones, with respect to the regional direction of 1 (Fig. 12A–E). Evidence for this consistent regional shortening vector is provided by the relationship between different fault strikes and resultant D5 kinematics. Where the regional strike is NW or NNW, perpendicular to the shortening direction, the faults behaved as NE- or SW-directed thrusts. An example of this style of D5 deformation occurs at Mulgarrie (Davis et al., 2010), located on the NE margin of the Scotia–Kanowna Dome (Fig. 2). Yunndaga (Figs. 2 and 6) records another example of SW-directed D5 thrusting. The total magnitude of D5 thrust movement is unknown. However, many of the mesoscale thrusts appear to be relatively small displacement structures, which is inconsistent with major crustal thickening. Where the regional strike is N or NNE, at a low angle to the shortening direction, the faults behaved as dextral strike-slip (e.g., Westralia: Fig. 6), to dextral-normal faults (e.g., Mertondale: Fig. 6). An example of this occurs at King of Creation (Fig. 2), which has a history of progressive dextral strike-slip shearing (Fig. 6). Ductile D5 structures at King of Creation include boudinage of veins, transposition of folds, S–C foliations (Fig. 12D), crenulation cleavage and box folds (Blewett and Czarnota, 2007a,c). Where the regional strike is NE-trending, parallel to the shortening direction, the faults reactivated with mostly normal displacement. Examples include the highly mineralised NE-trending Sunrise shear zone (Henson et al., 2010), and the Fitzroy shear zone (Davis et al., 2010). In the Kalgoorlie area, the D5 deformational event was manifest as NNE-trending brittle faults with dextral strike-slip kinematics. Major structures such as the 12 km long Alpha Island Fault at St Ives (Blewett et al., 2010b) and the 25 km long Black Flag Fault at Kundana, are characteristic examples. Both these faults have dextral offsets of <1 km. Small dextral strike-slip faults are common throughout the EYC, and in addition to those localities mentioned above, are recorded at Sunrise Birthday, New Holland, Sons of Gwalia, Victor Well, Jupiter (Fig. 12A), Hanns Camp and Mt Dennis (Fig. 6). Many of these faults have well-developed slickenlines on their fault planes, with Fig. 12A from Jupiter being a characteristic example. Analysis of the P–T dihedra for the D5 deformational event indicate that 3 was subhorizontal (Fig. 6), consistent with an overall strike-slip tectonic mode (Blewett and Czarnota, 2007a). The original (D1) border faults (Ida and Hootanui Faults: Fig. 3A) record the greatest degree of D5 strain, indicating that this event reactivated long-lived zones of crustal weakness. Along the eastern margin of the Kurnalpi Terrane (e.g., King of Creation—Fig. 12D), dextral shear predominates, especially on the Hootanui Fault (Blewett and Czarnota, 2007a,b). The D5 event is least evident along the Ockerburry Fault Zone, the boundary between the Kalgoorlie and Kurnalpi Terranes (Fig. 1), although D5 dextral strike-slip shearing is recorded at Trevor’s Bore and Victor Well (Fig. 2), and along strike on the Desdemona granite (Fig. 12B). The youngest Archaean rocks of the EYC are the Low-Ca granites, and these are cut by, or cut, D5 structures. Some Low-Ca dykes intrude into active D5 structures. For example, a 2637 ± 7 Ma LowCa granite dyke at Moon Rocks (Dunphy et al., 2003), intrudes into a N–S trending dextral shear zone (Fig. 7F). Another timing constraint is provided at Pink Well in the western part of the Kalgoorlie Terrane (Fig. 2), where N–S trending dextral shear zones cut a granite dated at 2652 ± 8 Ma (Fig. 7E). 4.7. D6: Low-strain vertical shortening The last Archaean event of significance was a phase of lowstrain vertical shortening and horizontal extension (Passchier, 1994; Swager, 1997; Davis and Maidens, 2003; Weinberg et al., 2003; Weinberg and Van Der Borg, 2008). The D6 event

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Fig. 12. Photographs illustrating D5 structures (both brittle and ductile). (A) D5 dextral slickenlines in brittle–ductile faults that overprint D4b thrusts in the Jupiter gold mine (Figs. 2 and 6). Note the gentle plunge of the lineation – best observed just above the hammer. (B) Aeromagnetic image showing that the concealed Desdemona granite pluton is a magnetic body intruding the older Raeside Batholith southwest of Leonora (Fig. 1). The SE and NW ends of the pluton have tails consistent with dextral strike-slip shearing. These shear zones are along strike from the gold-bearing D5 dextral shear zones at Victor Well (Figs. 6 and 12e) and Trevor’s Bore (Fig. 2). The pluton is 3 km across from east to west. (C) View to the ESE of the deformed granite clasts in a pavement of the Scotty Creek basin along the Waroonga shear zone along the western margin of the Kalgoorlie Terrane (Fig. 1). The clasts were exhumed and deposited during D3 extension, and the entire package was subjected to intense D5 dextral strike-slip shearing and foliation development. (D) View to the west of the dextral S–C fabrics developed in a pavement within the King of Creation gold mine (Fig. 2) along the eastern margin of the Kurnalpi Terrane. This is an example of gold deposited during D5 dextral shearing (Fig. 6). (E) Dextral S–C mylonite in a pavement within Victor Well, a small gold deposit north of Leonora (Fig. 2), and along strike of the Desdemona granite (B).

occurred across the EYC, and is represented by the development of crenulations with subhorizontal axial planes at a range of amplitudes from millimetres to metres, and brittle to locally brittle–ductile normal faulting. The accompanying fold hinges

have a highly irregular plunge direction. Some of the extensional faults are associated with quartz veins (e.g., at Lancefield) suggesting that hydrothermal fluids were still circulating at this time.

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The D6 event was most intensely developed on the western margin of the Kalgoorlie Terrane (Ida Fault) and the eastern margin of the Kurnalpi Terrane (Hootanui Fault). There is a spatial coincidence in the intensity of D5 shortening and dextral strike-slip shearing and the amount of subsequent D6 extension (Blewett and Czarnota, 2007a). No specific vector of D6 extension has been defined, and the driver for this extension may have been readjustment of localised topographic highs from earlier events, rather than a regional farfield control. For example, at Phoenix and Mertondale the extension direction is to the NE, whereas it is to the west at King of Creation, E at Lancefield, SE at Westralia, and vertical flattening at Yunndaga and Genesis–New Holland (Fig. 6). The coincidence of strain intensity of D5 and D6 may reflect readjustment of the crust to the previously partitioned D5 event, or reactivation associated with the fundamental D1 border faults. Goscombe et al. (2007) noted extreme thermal gradients (up to 50 ◦ C per km) associated with post-2650 Ma mineralisation (i.e., where the mines are). The occurrence of D6 structures in these mines may link D6 to a thermal contraction/relaxation rather a regional gravity-driven collapse. This interpretation is based on the limited observation of D6 structures in the regions outside of the mines, although this observation may be skewed by lack of suitable exposure. Goleby et al. (1993) and Swager (1997) suggested that extension during D6 (Table 1) was responsible for the juxtaposition of the high-grade Youanmi Terrane against the Kalgoorlie Terrane across the Ida Fault System. However, a metamorphic juxtaposition of this magnitude is inconsistent with the characteristically low strain structures associated with D6 extension, and the main juxtaposition is here interpreted as earlier (e.g., D3 extension). Furthermore, the 2640 ± 8 Ma Clark Well Monzogranite (age from Nelson, 1997) stitches the high-strain extensional fabrics across the Ida Fault (Table 2), and provides a temporal constraint on extension along this structure. 4.8. Post-Archaean and other minor events At a regional scale, there are numerous E–W trending lowdisplacement (<1 km) sinistral strike-slip brittle faults that offset the main NNW-trending structures (D5 and older). These faults are particularly common in aeromagnetic images, especially in the granite batholiths (Fig. 3A). These are all probably Proterozoic in age and may reflect events at the craton margin (e.g., Albany–Fraser and Capricorn Orogens). Proterozoic dolerite dykes with E–W strikes are both normal and reverse magnetised, and represent different times of ∼N–S extension (Keats, 1987). In the Victory–Defiance area, gypsum-bearing NE-directed thrusts cut an otherwise undeformed dolerite dyke. These faults are probably Proterozoic in age, as the similarly oriented Majestic Dyke is around 2400 Ma in age (Turek, 1966). Numerous small displacement faults are mapped in the granite pavements of the external granites (Swager, 1997; Blewett et al., 2004a). These brittle faults have centimetre-scale displacements and are variably oriented. 5. Discussion 5.1. Tectonic evolution of the eastern Yilgarn Craton (EYC) The D1 event, between 2720 Ma and 2670 Ma, extended the basement of the EYC across a series of extensional faults, creating sufficient geographical separation for the evolution of each terrane’s characteristic stratigraphy. The separation was not of sufficient magnitude to see major differences in the granitic history, which is broadly shared across the terranes. Similarly, the time equivalents of the older stratigraphic fragments in the EYC with the

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Youanmi Terrane in the west, suggest a common, and not exotic, heritage (Cassidy, 2006). The Nd isotope map is characterised by NNW-trending domains of contrasting model ages (Fig. 3D). This large-scale map pattern is interpreted to have developed during D1 extension with a dominantly ENE-directed polarity, and was likely to be the result of roll back of a subduction zone(s) to the ENE (Czarnota et al., 2010). The NNW-trending domains reflect the ENE-directed extensional rift system, with the most juvenile domains (Gindalbi domain) recording the greatest thinning. The main border fault with the old Youanmi Terrane hinterland is represented by the Ida Fault, which forms the western boundary of the Kalgoorlie Terrane (Fig. 3A). Although predominantly extensional in tectonic mode, the 50 myr time period ascribed to D1 is likely to have involved intermittent stages of contraction. The geological record is too fragmentary to elucidate these complexities. The first significant contraction (D2) commenced diachronously at around 2670 Ma and 2665 Ma in the Kurnalpi and Kalgoorlie Terranes respectively, terminating greenstone volcanism, also diachronously (Czarnota et al., 2010). The D2 structures indicate that shortening was oriented ENE–WSW (Fig. 6), perpendicular to the grain of the D1 margin. Czarnota et al. (2010) interpreted the driver for D2 contraction as the accretion of an external body (such as a plateau) into the receding subduction zone. The operation of D2 shortening can also be inferred from the fact that disparate volcanic associations (Kalgoorlie and Kurnalpi) were brought together (as determined from their chemistry and age distribution: Barley et al., 2002). Metamorphic conditions give typical burial depths of around 4 kb, and the M2 PTt paths are open and clockwise in their trajectories (Goscombe et al., 2007). These metamorphic conditions suggest that major crustal thickening did not occur during this contraction. A major change in tectonics occurred across the EYC with the onset of D3 extension between 2665 Ma and 2655 Ma (Table 2). The D3 event was characterised by the deposition of late-basin successions (Krapeˇz et al., 2000), the development of extensional core-complexes and domes (Williams and Whitaker, 1993; McIntyre and Martyn, 2005), and the intrusion of Mafic and Syenitic type granites from a metasomatised mantle source (Champion and Cassidy, 2002). The cause of this lithospheric extension may have been lower-crustal to lithospheric delamination (Czarnota et al., 2010), or renewed roll back of a subduction zone (Goscombe et al., 2009). The metamorphic conditions were unique at this time; with the widespread development of anticlockwise M3a PTt paths in upper plate rocks, reaching burial depths of up to 4 kb (Goscombe et al., 2009). In the lower plate, older higher pressure M1 and M2 assemblages were exhumed during this D3 extension. The major NNW-trending terrane-bounding faults (e.g., Hootanui and Ida Faults) were likely initiated during ENE-directed D1 extension. The late-basin successions were developed in the hangingwall of NW-trending D3 faults during NE-directed extension. These two extension directions are mirrored in the magnetic patterns of the EYC, with NNW-trending faults on the margins and NW-trending faults between (Fig. 3A). Basement control on younger extension has been investigated in analogue sandbox models (e.g., McClay et al., 2002). In Fig. 3B a model with a preexisting NNW-trending structural grain is subjected to a younger NE-directed extension. Despite the pre-existing faults not being optimally oriented to the new extension direction, they strongly influenced the geometry of the neoformed extensional faults. These analogue patterns of older fault control of younger basins are mapped in the EYC (cf Fig. 3A and B). Most of the late-basin successions were deposited in NW-trending basins, in a strike perpendicular to the D3 extension direction. These basins include the Kurrawang, Merougil and Pig Well basins (Figs. 2 and 8). The late-basin successions that developed close to the main D1 border faults tend to mirror the strike of the adjacent border fault. This is

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evident in the NNW to N trends of the Granny Smith basin near the Hootanui Fault, and the N and NNE trends in the Scotty Creek basin adjacent to the Ida Fault. By ∼2655 Ma, the EYC was again in contraction, with the onset of the D4a stage of shortening which was oriented ENE–WSW (Table 2). All the events up to, and including, this period of time (D1–D4a) had involved block movements up and down to the NE or to the SW within a NNW- to NW-oriented architectural framework (Fig. 6). An exception to this was around the noses of the granite-cored domes, and this difference may be part of the reason for the gold endowment in these regions. The ∼2650 Ma D4b event, however, marked a significant deviation in the regional stress field (Fig. 6), with regional shortening oriented WNW–ESE (Blewett and Czarnota, 2007a). This change in the regional stress field created a significant obliquity with the preexisting architecture. The result was a highly variable and complex local stress field. During the WNW–ESE-oriented regional contraction, sinistral strike-slip shearing occurred along the NNW-trending dome margins and previously steepened greenstone panels. Across the dome hinges, the sinistral strike-slip faults linked into ENE-trending thrusts with NW-directed transport (e.g., Scotia–Kanowna Dome and Mt Margaret Dome) and SE-directed transport (e.g., Kirgella Dome, Lawlers Dome). D4 was coincident with the waning stages of the High-Ca type magmatism (around 2655 Ma), especially in the Kalgoorlie Terrane with melts displaying a crustal signature (high-Y subgroup of Champion and Sheraton, 1997). Syenite magmatism of lower crustal affinity (generally absent from the Kalgoorlie Terrane) peaked at this time in the Kurnalpi Terrane. The present erosion level means that there are no preserved greenstone rocks of this age. If they developed, it is possible they could have formed in a foreland basin to the west of the generally W-directed D4 thrusts, or small strike-slip basins, like the Panglo basin adjacent to the Kanowna Belle deposit (Tripp et al., 2007; Davis et al., 2010). A further change was imposed on the EYC after 2650 Ma, involving a return to NE–SW oriented shortening during the D5 event (Table 2). The dominant NNW-trending architecture underwent dominantly dextral strike-slip shearing. The metamorphic conditions at this time were characterised by high geothermal gradients, with up to 70 ◦ C/km under low pressure conditions of around 1 kb (Goscombe et al., 2009). Prior to these metamorphic conditions, the pressures recorded at 2665–2655 Ma were around 4 kb (i.e., M3b and older metamorphic events). Therefore the crust underwent widespread uplift and erosion over a 10–15 myr period, which is consistent with the crustal response expected from delamination during D3 (e.g., England and Houseman, 1989). The commencement of the intrusion of the widespread Low-Ca granites marked a fundamental change in the thermal régime of the crust (Champion and Sheraton, 1997; Cassidy and Champion, 2004). These granites are high-temperature crustal melts of the earlier High-Ca granites, and they were emplaced between <2655 and 2630 Ma, together with D5 dextral shears. Because the Low-Ca granites are widespread and easily dated, they provide temporal markers and minimum age constraints for many of the earlier events (Fig. 7E and F). 5.2. Timing of N–S shortening and relationship to sinistral strike-slip faulting A major difference between this work, and that of Swager (1997), is the relative timing of the main period of ∼N–S shortening. Swager (1997) interpreted this shortening event to be early, and enumerated it as ‘D1’. The so-called ‘D1’ thrusts – Foster, Tramways Republican, and Fitzroy Thrusts – are commonly cited these as the main examples (e.g., Swager and Griffin, 1990; Swager, 1997; Davis, 2002; Weinberg et al., 2003; Krapeˇz and Barley, 2008). A number of lines of evidence are discussed here to demonstrate

that the main period of ∼N–S shortening was relatively late in the structural-event history. The evidence presented includes: (1) map pattern geometry and relative timing of cross-cutting relationships; (2) misidentification of intrusive sills as volcanic flows; (3) absolute age relationships with thrusts and apparently younger late basin successions; and (4) the relationships between regional domes/anticlines, NNW-trending sinistral strike-slip faults and N–S directed thrusting. 1. Henson et al. (2004) used the geometry and macroscale maps patterns in the Kambalda area (Fig. 2) to demonstrate that the N–S-directed thrusts could not be the earliest contractional structures, as they crosscut pre-existing NNW-trending folds (Fig. 11E). Furthermore, if N–S regional thrusting occurred before NNW-trending regional folding, then the early thrust planes and duplicated stratigraphy would occur across both the later anticlines and synclines. Map patterns show this not to be the case, as regional thrusts only occur across the anticlines and domes and are absent in the associated synclines. There are also numerous mesoscale examples of structures developed with a shortening direction oriented WNW–ESE to NW–SE, overprinting previously deformed rocks. Examples of relatively young N- and NW-directed thrusts, folds and crenulation cleavages have been mapped at Sunrise Birthday, Poison Creek, Yunndaga, Tarmoola, Mertondale, Westralia, Lancefield, Phoenix, Hanns Camp, and Mt Dennis (Figs. 2 and 6). In all these sites, these structures consistently overprint older contractional structures. Based on overprinting relationships these macroscale and mesoscale structures are assigned D4b not ‘D1’ in age (Figs. 2 and 6). 2. The so-called ‘D1’ thrusts (Tramways, Republican and Fitzroy Thrusts) duplicate stratigraphy, especially the Kambalda Komatiite. Mapping in the 1980s and 1990s identified komatiites at several levels in the stratigraphy throughout the Kalgoorlie Terrane, and these were often assumed to be thrust repeated (e.g., Martyn, 1987) rather than different parts of an intact stratigraphy. Geochronology and igneous petrology have shown that there are different ages of komatiites (Barley et al., 2002), and that some are intrusive (Trofimovs et al., 2004). Therefore, komatiites stacked in the stratigraphy are not necessarily repeated by thrusting. 3. In the Swager (1997) model, the late-basin successions were interpreted to have been deposited unconformably on a prefolded basement deformed by ‘D1’ thrusting. On this basis, all ‘D1’ thrusts should be older than the oldest late basin, i.e., older than 2665 Ma. However, the NW-directed Fitzroy Thrust in the Kanowna Belle region (Fig. 2) cuts the 2655 ± 6 Ma Kanowna Porphyry (age after Ross et al., 2004), making the thrusting up to 10 myr younger than the late-basin successions. These thrusts are here assigned to the D4b deformational event. 4. In the Swager (1997) model, the main sinistral strike-slip shearing on NNW-trending structures was interpreted as ‘D3’ (Table 1). As described above, the NNW-trending sinistral strikeslip faults link into the NNW-directed thrusts, and these are all assigned to the D4b deformational event. The linkage and correlation is justified on structural overprinting relationships recorded at many sites, for example at Bannockburn, Lawlers, Mertondale, Phoenix and Tarmoola (Figs. 2 and 6) and by Miller et al. (2010) at St Ives. At the macroscale, the main map pattern in the St Ives district (Fig. 2) is dominated by the gently plunging regional D2 Kambalda Anticline and NNW-trending faults on the limbs (Fig. 11E). In the south of the area, across the axis of the regional fold, are the ENE-trending Tramways and Republican Thrusts (previously interpreted as ‘D1’ – see above). During D4b contraction, the main NNW-trending faults, such as the Lefroy, Speedway and Playa, operated as sinistral strike-slip structures,

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whereas across the hinge of the regional anticline, toP–To-theNW thrusting was accommodated (Table 1). As an analogue for strike-slip faulting and linked thrusting at a high angle, the Eastern Gobi–Alty region of Mongolia (Fig. 11F) can be considered (Bayasgalan et al., 1999). Thrusts in this example develop at the terminations of major strike-slip faults and function as accommodation structures to rotational strain. Thrusts also develop at restraining stepovers, accommodating displacement between parallel strands of the strike-slip fault system. 5.3. Relationship of structure to gold mineralisation Gold mineralisation is structurally controlled, and was deposited during most of the deformational events in the EYC. Strain was heterogeneously distributed in time and space throughout the EYC, with some areas being a locus for repeated deformation. The best gold deposits in terms of tonnage and/or grade are those that have been deformed and mineralised repeatedly. Examples include Kalgoorlie, St Ives, Sunrise Dam and Kanowna Belle, making these different to the smaller deposits. The reason for this size difference is likely to be associated with site-specific architecture, which repeatedly facilitated creation of deformation-induced permeability, resulting in focused flow of fluid, magma, heat/energy and metal throughout the deformational history. All of these favoured sites have D1 (growth) faults at their centre, probably indicating that the early history was a vital ingredient (Miller, 2006; Gauthier et al., 2007; Blewett et al., 2010b; Davis et al., 2010). Only minor mineralisation has been reported in gold-bearing veins hosted within sedimentary clasts of the Black Flag Group at Kanowna Belle (Ross et al., 2004). This early gold could be described as D1 (Table 2). The fault and stratigraphic architecture developed during D1 extension, however was a significant contributor to endowment in subsequent events. The first known lode gold is associated with D2 contraction at Tarmoola (Blewett and Czarnota, 2007a; Fig. 6). This gold deposit is somewhat unusual as there is little other known gold of this age (see Appendix A), despite the widespread influence of D2 deformation (Blewett and Czarnota, 2007a) and associated M2 metamorphism (Goscombe et al., 2009). The D3 extensional event was the first major gold event recorded in the EYC. The largest gold deposits formed during D3 extension include the Sons of Gwalia, Harbour Lights, Tower Hill deposits adjacent to the Raeside Dome (Fig. 2), and the Lancefield deposit adjacent to the Mt Margaret Dome (Fig. 2). Mineralisation is hosted within the extensional shear zone, in regions where D3 strain was greatest (Fig. 6). At the 3 M oz Sons of Gwalia gold deposit in Leonora, the dominant foliation is associated with a series of extensional S-C and C foliations (Fig. 10B). Regionally, this penetrative foliation mantles the Raeside Batholith and occurs in a zone of high strain up to 5 km wide (Williams et al., 1989). The kinematics of the D3 fabrics are consistently east-block-down extension (Williams et al., 1989; Passchier, 1994; Blewett et al., 2007b). The orebody pinches and swells down plunge to the southeast, parallel to the main L3 stretching lineation (Fig. 10C). The strain is high, as boudins and fold axes which initiated at a high angle, are rotated towards the stretching lineation – suggesting the partial development of sheath folds. A lower strain example of D3 extension occurs at the Lawlers Dome (Figs. 2 and 9). The presence of the Kambalda Sequence around the dome indicates that the amount of exhumation was less than that observed around the Mt Margaret or Raeside (Leonora), which have exhumed deeper and older successions. As a consequence, the localities with lower degrees of exhumation tend to have smaller extensional gold deposits (Sunrise Birthday: 30K oz cf. Sons of Gwalia ∼3 M oz). These small deposits are instructive to study, as

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their simplicity means that the fabrics can be unambiguously interpreted (Fig. 6). The foliations in the gold deposits associated with extension in the Lawlers Dome vary in intensity (Fig. 10E), but in the ore zones they are expressed as S–C–C fabrics which dip gently to moderately to the NNE (Fig. 10E), and have extensional kinematics (Fig. 10F). The fabrics host an amphibole lineation plunging to the N and NNE. These fabric elements have recorded the exhumation of the Lawlers Tonalite footwall and the downthrow northwards of the greenstones (Fig. 9). In low strain regions of the Sunrise Birthday deposit, especially where there is a competent gabbro, the extensional strain is recorded as steeply dipping conjugate veins and brittle normal faults (Blewett and Czarnota, 2007a). These brittle faults have well-developed slickenlines that together resolve a subvertical 1 and a subhorizontal 3 (plunging NNE-SSW) in P–T dihedra space, identical to that resolved for the ductile fabrics in the high-strain zones. The link between D3 extension and formation of the late-basin successions provides insight into the empirical observation that large gold deposits occur in proximity (within 1 km of the unconformity) to these basins (Hall, 2007). This observation also applies to other granite–greenstone terranes, such as the Timiskaming assemblages of the Canadian Abitibi (Poulsen, 2008). In terms of process understanding, late-basin successions are merely a proxy for a series of factors important for gold mineralisation during the D3 extensional event. These factors include: • The late-basin successions lie in the hangingwall above an extensional detachment that tapped at least into the mid crust. This is known because the granite batholiths of the mid crust were exhumed to the surface in the footwall to supply granite detritus into the extending basins. These detachments have been imaged seismically, and in fact they link into shear zones that penetrate the entire crust (Goleby et al., 2003; Czarnota et al., 2007). • These deep-penetrating shear zones are necessary to tap deep fluids and metals, especially from the mantle (Kerrich and Wyman, 1990). The emplacement of Mafic and Syenite type granites along restricted NNW-trending corridors and in this restricted D3 time period maps the active pathways deep in the crust to the upper mantle (Czarnota et al., 2010). • The D3 extensional event was primarily responsible for setting up the dome and basin architecture. Domes at a range of scales and structural levels have been mapped under many of the major gold deposits of the EYC, suggesting an empirical link (Henson et al., 2007). In terms of process understanding, these domes were a critical architectural factor for fluid/magma/energy focus, especially into the apical regions, during subsequent gold mineralising events. The domes also created an anisotropy which localised strain heterogeneities on their margins during later inversion events. • Anticlockwise PTt paths are characteristic of extension (Sandiford and Powell, 1986). Goscombe et al. (2009) has recently defined tight M3a anticlockwise PTt loops that were associated with formation of the late-basin successions and metamorphism. The geothermal gradient associated with this event was also anomalously high, adding to the energy budget of the system. • Extension is also an efficient mechanism for the downward flow of fluids along shear zone pathways (Sheldon et al., 2008). This downward flow would facilitate the process of mixing a reduced basinal fluid with an oxidised magmatic fluid, leading to geochemical gradients and gold deposition (Walshe et al., 2008). Extensional shear zones occur in other parts of the EYC (Williams et al., 1989), so there is significant potential for finding Sons of Gwalia-like ore deposits (SRK Consulting, 2000). A feature of these gold deposits is that they are thin, tabular-shaped orebodies located within the extensional shear zone, with a plunge parallel

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to the stretching lineation and a footwall perturbation. An easy targeting approach is to map the shape of the granite dome paying careful attention to any protuberances. Gravity data are particularly helpful for this sort of exercise. The strategy is to identify the plane containing the stretching lineation and the perturbation, and to drill at an angle back towards the granite within this perturbation–lineation plane. The biggest deposits developed by this style occur where the greenstone stratigraphy is the oldest and the metamorphic grade is the highest (see Goscombe et al., 2007). These localities reflect the greatest amount of excision and hence strain, leading to the sites of greatest dynamic permeability creation. Although the D3 deformational event was important for preparing the EYC for its world-class gold endowment, it was during D4b that most of the region’s gold was deposited. Between these two events however, are two noteworthy deposits with mineralisation interpreted as D4a in origin. These deposits are Jupiter and possibly New Holland (Figs. 2 and 6), which are described below. The Jupiter gold deposit (Fig. 2) is hosted by a syenite, whose intrusion cross-cuts prefolded pillow basalts in the hinge of the S-plunging F2 Mt Margaret Anticline (Czarnota et al., 2008). The syenites, intruded during D3 extension, are crosscut by a series of mineralised SW-directed thrusts (Fig. 11B). Offsets of 2–3 m are common, and the thrusts are associated with quartz-carbonate veins and gold mineralisation, with grades of over 3.0 g/t (Czarnota et al., 2008). Strain was strongly partitioned towards the thrust planes; with well-developed ductile S–C foliations recording a shear sense consistent with ENE–WSW directed shortening (Fig. 6). These thrusts and gold mineralisation are interpreted to be examples of the regional D4a deformational event. A Pb isotope model age of ∼2660 Ma has been acquired on galena from a gold-bearing vein in a D4a thrust at Jupiter, providing a direct model age constraint on D4a mineralisation. The model age is calculated with the evolved Uchi-Wabigoon model ( value of 9.10) of Thorpe et al. (1992). The sample returned initial ratios of 206 Pb/204 Pb 13.788, 207 Pb/204 Pb 14.877, and 208 Pb/204 Pb 33.541. The New Holland gold deposit is hosted in the Scotty Creek Conglomerate, a late-basin succession on the western margin of the Lawlers Anticline (Fig. 2). The basin is steeply W-dipping, with spectacular quartz vein arrays developed within a competent sandstone horizon. The tilting and flattening of the stratigraphy, and the development of a steep N–S trending cleavage, is interpreted to have occurred during D4a contraction. Ackroyd et al. (2001) reported that gold was deposited in horizontal extension veins (>50 g/t), in gently to moderately E- and W-dipping shear veins (<10 g/t), and in moderate to steep S-dipping extension veins (<1 g/t). These vein arrays are overprinted by N–S trending brittle faults with dextral kinematics, which Blewett and Czarnota (2007c) interpreted as regional D5. The D4b event saw a rotation in the shortening direction, which created a new network of stress heterogeneity with both dilation and contractional jogs being developed (Witt and Vanderhor, 1998; Chen et al., 2001; Weinberg et al., 2004; Cox and Ruming, 2004; Davis et al., 2010; Henson et al., 2010; Miller et al., 2010). The consequence was the development of numerous sites favourable to enhanced fluid flow and, ultimately, gold deposition, with good examples of D4b sinistral strike-slip shear zones hosting gold at Kalgoorlie, Wallaby, Sunrise Dam, St Ives, Kanowna Belle, and Lawlers (Mueller et al., 1988; Ackroyd et al., 2001; Miller, 2006; Ruming, 2006; Blewett et al., 2010b; Davis et al., 2010; Henson et al., 2010). The direct dating of many gold deposits at around 2650 Ma (Vielreicher et al., 2007 and references therein) is a measure of the endowment impact of this late-stage event (Groves, 1993). The final gold event was associated with N- to NNE-trending D5 dextral shearing, which was mostly associated with brittle struc-

tures (Fig. 12A). Deposits include Sunrise Dam (Miller, 2006), St Ives (Miller et al., 2010), Transvaal (Blewett and Czarnota, 2007a), Wiluna camp (Hagemann et al., 1992), Golden Mile–Charlotte (Keats, 1987), St Ives camp (Nguyen, 1997; Blewett et al., 2010b), and Kundana (Mueller et al., 1988). Low-Ca granites make up 20% of the exposed area of granites and, almost without exception, were intruded after 2655 Ma into the cores of the domes (the lower plate). The significance of their presence within the dome cores beneath the major gold deposits (Henson et al., 2005) can therefore only be speculated on, but if present, these high-temperature rocks would have driven off any last vestiges of fluid/metal into the upper crust above (Sheldon et al., 2008), or provided an additional magmatic fluid for the latest gold. In contrast to the earlier gold-only events (D2–D4), the mineralogy associated with D5 included significant base metals and tellurides (e.g., Clout, 1989), which may reflect the influence of the Low-Ca granites (Cleverley et al., 2007), which are temporally linked to this event (Blewett and Czarnota, 2007b). 6. Conclusions Based on an improvement in geological knowledge over the past decade, a revised sixfold deformational-event framework, D1–D6, has now been established, which builds on the previous paradigm of Swager (1997). Most of the deformational events formed approximately NNW-trending penetrative foliations, which are unreliable markers for correlating the events across the region. Kinematics, rock relationships, and geochronology, together with 3D map patterns are all needed to construct a reliable and consistent structural-event framework. The tectonic régime of the EYC was such that a change in a structural event, such as a tectonic mode or stress switch, was matched by an equally significant change in magmatism, basin development, metamorphism and mineralisation. A number of changes to the Swager (1997) paradigm, and subsequent related interpretations, is proposed here. The main areas of revision including the following interpretations: 1. Extension, transtension and transpression were the dominant tectonic modes, and they are expressed in the regional 3D map patterns, stratigraphic relationships, and deep seismic reflection imaging. When contraction occurred, the direction of shortening ranged in orientation between NE–SW and ESE–WNW. Contraction did not cause major crustal overthickening, and it was the emplacement of voluminous High-Ca granites (magmatic thickening) beneath greenstone basins that likely destabilised the crust. 2. The margin to the EYC was located to the ENE, and was likely oriented NNW in present day coordinates. The main NNWtrending tectonic grain of the EYC was inherited during D1 extension of the eastern margin of the Younami Terrane. Major extension commenced around 2720 Ma, resulting in the development of basins, represented as the Kalgoorlie, Kurnalpi and eastern Burtville Terranes, on top of variably attenuated older Younami Terrane crust. All subsequent events re-used and modified this fundamental architecture. 3. Basin closure and ‘terrane amalgamation’ occurred with ENE–WSW oriented D2 contraction. This contraction terminated volcanism, and developed regional-scale NNW-trending folds, but without significant foliation. 4. Late-basin successions were developed in a complex extensional tectonic mode (D3) following D2 contraction. Granite doming, core complex development, late-basin sedimentation, intrusion of mantle melts and D3 extension are all linked by a common process. Deep penetrating extensional shear zones

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5.

6.

7.

8.

9.

10.

cut through the entire crust during this event, as imaged by the deep seismic reflection profiles. A highly anisotropic upper crustal architecture consisting of competent granite-cored domes and associated basins with linked deep-penetrating faults was created by the end of the D3 extensional event. It was this architectural complexity that was a key ingredient in the spectacular later gold mineralisation – the so-called late-orogenic gold. Return to ENE–WSW oriented shortening during D4a resulted in the tightening of preexisting folds, folding of the late-basin successions, and thrusting and foliation development. A clockwise rotation of the stress field to ESE–WNW occurred, coupled with the now steeply dipping stratigraphy, made the orogen unfavourable to dip-slip movements; sinistral strikeslip shearing (D4b) became the dominant tectonic mode. This change resulted in the development of accommodation stepovers, where local- to district-scale N–S to NW–SE oriented contraction produced thrusts and folds across specific structures and geometries (e.g., strike-slip stepovers). The timing of the first N–S contraction (Swager, 1997 ‘D1’) is younger than the late-basin successions and is now considered part of the regional D4b event (point 7 above). Low-Ca granites were associated with D5 dextral strike-slip tectonics, which was long-lived, and was a result of a switch to NE–SW oriented contraction. Late extension or vertical shortening (D6) may not have occurred at the same time everywhere in the EYC, and its intensity is variable.

Gold was deposited during each structural event, in particular from D3 time onwards. At <2665 Ma, the D3 event occurred late in the history of the EYC, and was associated with lithospheric extension, core-complex development, and orogenic gold in extensional shear zones and detachments. The unified mesothermal or orogenic gold model invokes contraction or strike-slip/oblique-slip as the only tectonic mode for this class of mineralisation. However, these extensional gold deposits show that contraction is not a prerequisite for significant gold mobilisation and formation of large gold deposits. These findings have significance for the assumed boundary conditions in fluid-flow and stress modelling/prediction. Tectonic mode switches from contraction to extension or switches in shortening direction from NE–SW to ESE–WNW were triggers for subsequent major gold mineralisation during the D4 and D5 events. These latter deformational events were associated with the most extensive pulse of gold deposition in the EYC.

Acknowledgements The sponsors of the Y1-P763 and pmd*CRC (Y2 and Y4 projects) are acknowledged for their financial support. The Geological Survey of Western Australia provided extensive field support. David Champion, Kevin Cassidy and Alan Whitaker contributed to mapping in the granites. John Beeson contributed to mapping gold mines around Laverton, and Lloyd White to mapping at Wiluna and Jundee. Terry Brennan assisted with some graphics. David Huston calculated the Pb model age of Jupiter. Discussions with Ben Goscombe, Cees Swager, Brett Davis, Gerard Tripp, Bryan Krapeˇz, Martin van Kranendonk and John Miller help to shape and clarify the ideas presented here. Reviews of early drafts by Songfa Liu and George Gibson improved the manuscript. Journal reviews by David Rhys, Stephen Wyche and Russell Korsch are gratefully acknowledged. This paper is an output from the Y4 project, and is published with permission of the CEO of Geoscience Australia. Geocat number 68826.

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Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.precamres.2010.04.004.

References Ackroyd, B.J., Hagemann, S.G., Neumayr, P., Ingle, L.J., Inwood, N.A., Smolonogov, S., 2001. Hydrothermal alteration and gold mineralization at the sandstone-hosted New Holland gold deposit, Agnew-Lawlers gold camp, Western Australia. In: Hagemann, S.G., Neumayr, P., Witt, W.K. (Eds.), Fourth International Archaean symposium. Perth, West. Aust., Australia, Geological Survey of Western Australia Record 2001/17, pp. 99–125. Angelier, J., 1984. Tectonic analysis of fault slip data sets. Journal of Geophysical Research 89, 5835–5848. Archibald, N.J., Bettenay, L.F., Binns, R.A., Groves, D.I., Gunthorpe, R.J., 1978. The evolution of Archaean greenstone terrains, Eastern Goldfields Province, Western Australia. Precambrian Research 6, 103–131. Barley, M.E., Brown, S.J.A., Krapeˇz, B., Cas, R.A.F., 2002. Tectonostratigraphic Analysis of the Eastern Yilgarn Craton: an improved geological framework for exploration in Archaean Terranes. AMIRA Project P437A, Final Report. Barley M.E., Brown, S.J.A., Cas, R.A.F., Cassidy, K.F., Champion, D.C., Gardoll, S.J., Krapeˇz, B., 2003. An integrated geological and metallogenic framework for the eastern Yilgarn Craton: Developing geodynamic models of highly mineralised Archaean granite-greenstone terranes. AMIRA Project P624, Final Report. Bayasgalan, A., Jackson, J., Ritz, J.F., Carretier, S., 1999. Field examples of strikeslip fault terminations in Mongolia and their tectonic significance. Tectonics 18, 394–411. Beardsmore, T.J., 2002. The geology, tectonic evolution and gold mineralisation of the Lawlers region: a synopsis of present knowledge. Barrick Gold of Australia, Technical Report 1026, 279 p. Binns, R.A., Gunthorpe, R.J., Groves, D.I., 1976. Metamorphic Patterns and Development of Greenstone Belts in Eastern Yilgarn Block, Western Australia. John Wiley & Sons, New York, USA, pp. 303–313. Blewett, R.S., Cassidy, K.F., Champion, D.C., Henson, P.A., Goleby, B.R., Kalinowski, A.A., 2004a. An orogenic surge model for the eastern Yilgarn Craton: implications for gold mineralising systems. In: Muhling, J., et al. (Eds.), SEG 2004, Predictive Mineral Discovery Under Cover, vol. 33. Centre for Global Metallogeny. The University of Western Australia, Publication, pp. 321–324. Blewett, R.S., Cassidy, K.F., Champion, D.C., Henson, P.A., Goleby, B.R., Jones, L., Groenewald, P.B., 2004b. The Wangkathaa Orogeny: an example of episodic regional ‘D2’ in the late Archaean Eastern Goldfields Province, Western Australia. Precambrian Research 130, 139–159. Blewett, R.S., Cassidy, K.F., Champion, D.C., Whitaker, A.J., 2004c. The characterisation of granite deformation events in time across the Eastern Goldfields Province, Western Australia. Geoscience Australia Record 2004/10. 25 p. https://www.ga.gov.au/products/servlet/controller?event=GEOCAT DETAILS &catno=47616. Blewett, R.S. Czarnota, K., 2007a. The Y1-P763 project final report November 2005. Module 3—Terrane Structure: Tectonostratigraphic architecture and uplift history of the Eastern Yilgarn Craton, Geoscience Australia Record 2007/15, 113 p. http://www.ga.gov.au/image cache/GA10678.pdf. Blewett, R.S. Czarnota, K., 2007b. A new integrated tectonic framework of the Eastern Goldfields Superterrane. In: Bierlein, F.P., Knox-Robinson, C.M., (Eds.), Proceedings of Geoconferences (WA) Inc. Kalgoorlie ’07 Conference. Geoscience Australia Record 2007/14, 27–32. Blewett, R.S., Czarnota, K., 2007c. Diversity of structurally controlled gold through time and space of the central Goldfields Superterrane—a field guide. Geological Survey of Western Australia Record 2007/19, 65p. Blewett, R.S., Henson, P.A., Roy, I.G., Champion, D.C., Cassidy, K.F., 2010a. Scaleintegrated architecture of the world-class gold mineral systems of the Archaean Eastern Yilgarn Craton. Precambrian Research 183, 230–250. Blewett, R.S., Squire, R., Henson, R.S., Miller, J.M., Champion, D.C., 2010b. Architecture and geodynamic evolution of the St Ives region, south central Kalgoorlie Terrane, Western Australia. Precambrian Research 183, 275–291. Brown, M.A.N., Jolly, R.J.H., Stone, W., Coward, M.P., 1999. Nickel ore troughs in Archaean volcanic rocks, Kambalda, Western Australia: indicators of early extension. In: McCaffrey, K.W.J., Lonergan, L., Wilkinson, J. (Eds.), Fractures, Fluid Flow and Mineralization, vol. 155. Geological Society Special Publications, pp. 197–211. Campbell, I.H., Hill, R.I., 1988. A two-stage model for the formation of the granitegreenstone terrains of the Kalgoorlie-Norseman area, Western Australia. Earth and Planetary Science Letters 90, 11–25. Cassidy, K.F., 2006. Geological Evolution of the Eastern Yilgarn Craton (EYC), and terrane, domain and fault nomenclature. In: Blewett, R.S., Hitchman, A.P., (Eds.), 3D Geological Models of the Eastern Yilgarn Craton—Y2 Final Report pmd*CRC. Geoscience Australia Record 2006/04, 1–19. http://www.ga.gov.au/image cache/GA13801.pdf. Cassidy, K.F., Champion, D.C., 2004. Crustal evolution of the Yilgarn Craton from Nd isotopes and granite geochronology: implications for metallogeny. In: Muhling, J., et al. (Eds.), SEG 2004, Predictive Mineral Discovery Under Cover, vol. 33. Centre for Global Metallogeny, The University of Western Australia, Publication, 317–320.

228

R.S. Blewett et al. / Precambrian Research 183 (2010) 203–229

Cassidy, K.F., Champion, D.C., Fletcher, I.R., Dunphy, J.M., Black, L.P., Claoue-Long, J.C., 2002. Geochronological constraints on the Leonora-Laverton transect area, north-eastern Yilgarn Craton. Geoscience Australia Record 2002/18, 37–58 pp. http://www.ga.gov.au/image cache/GA9340.pdf. Cassidy, K.F., Champion, D.C., Krapeˇz, B., Barley, M.E., Brown, S.J.A., Blewett, R.S., Groenewald, P.B., Tyler, I.M., 2006. A revised geological framework for the Yilgarn Craton, Western Australia: Western Australia Geological Survey, Record 2006/8, 8p. Champion, D.C., Cassidy, K.F., 2002. Granites in the Leonora-Laverton transect area, north eastern Yilgarn Craton. In: Cassidy, K.F., (Ed.), Geology, geochronology and geophysics of the north eastern Yilgarn Craton, with an emphasis on the Leonora-Laverton transect area. Geoscience Australia, Record 2002/18, 13–35. http://www.ga.gov.au/image cache/GA9340.pdf. Champion, D.C., Sheraton, J.W., 1997. Geochemistry and Nd isotope systematics of Archaean granites of the Eastern Goldfields, Yilgarn Craton, Australia; implications for crustal growth processes. Precambrian Research 83, 109–132. Chen, S.F., Witt, W., Liu, S.F., 2001. Transpressional and restraining jogs in the northeastern Yilgarn Craton, Western Australia. Precambrian Research 106, 309–328. Cleverley, J.S., Walshe, J.L., Nugus, M., 2007. Tracing deep fluid sources in gold deposits of the Eastern Goldfields. In: Bierlein, F.P., Knox-Robinson, C.M., (Eds.), Proceedings of Geoconferences (WA) Inc. Kalgoorlie ’07 Conference. Geoscience Australia Record 2007/14, 133–137. Clout, J.M.F., 1989. Structural and isotopic studies of the Golden Mile gold-telluride deposit, Kalgoorlie, Western Australia: Unpub. Ph.D. thesis, Monash University, 352 p. Connors, K., Donaldson, J., Morrison, B., Davy, C., Neumayr, P., 2003. The Stratigraphy of the Kambalda-St Ives District: workshop notes Goldfields Pty Ltd St Ives operation, unpublished Technical note No: TN SIG0329, 99 p. Cox, S.F., Ruming, K., 2004. The St Ives mesothermal gold system, Western Australia—a case of golden aftershocks? Journal of Structural Geology 26, 1109–1125. Czarnota, K. Blewett, R.S., 2007. Don’t hang it on a foliation to unravel a structural event sequence: an example from the Eastern Goldfields Superterrane. Specialist Group: Tectonics and Structural Geology, Geological Society of Australia Abstracts, Deformation I the Desert, Alice Springs, 9–13 July 2007, 75. Czarnota, K., Blewett, R., Champion, D.C., Henson, P.A., Cassidy, K.F., 2007. Significance of extensional tectonics in orogenic gold systems: an example from the Eastern Goldfields Superterrane, Yilgarn Craton, Australia. In: Andrew, C.L., et al. (Eds.), Digging Deeper. Proceedings of the Ninth Biennial Meeting of the Society for Geology Applied to Mineral Deposits Dublin. Ireland 20–23 August 2007, pp. 1431–1434. Czarnota, K., Blewett, R.S., Goscombe, B., 2008. Structural and metamorphic controls on gold through time and space in the central Eastern Goldfields Superterrane—a field guide. Geological Survey of Western Australia Record 2008/9, 66p. Czarnota, K., Champion,.D.C., Cassidy, K.F., Goscombe, B., Blewett, R.S., Henson, P.A., Groenewald, P.B., 2010. The geodynamics of the Eastern Goldfields Superterrane. Precambrian Research 183, 175–202. Davis, B.K., 2002. The Scotia–Kanowna Dome, Kalgoorlie Terrane: Deformation history, structural architecture and controls on mineralisation. Australian Institute of Geoscientists Bulletin Field Guide, 61p. Davis, B.K., Maidens, E., 2003. Archaean orogen-parallel extension; evidence from the northern Eastern Goldfields Province, Yilgarn Craton. Precambrian Research 127, 229–248. Davis, B.K., Blewett, R.S., Squire, R., Champion, D.C., Henson, P.A., 2010. Granitecored domes and gold mineralisation: Architectural and geodynamic controls around the Archaean Scotia-Kanowna Dome, Kalgoorlie Terrane, Western Australia. Precambrian Research 183, 316–337. Dunphy, J.M., Fletcher, I.R., Cassidy, K.F., Champion, D.C., 2003. Compilation of SHRIMP U–Pb geochronological data, Yilgarn Craton, Western Australia, 2001–2002. Geoscience Australia Record 2003/15, 139p. http://www.ga.gov.au/image cache/GA6422.pdf. England, P., Houseman, G., 1989. Extension during continental convergence, with application to the Tibet Plateau. Journal of Geophysical Research 94, 17561–17579. Fletcher, I.R., Dunphy, J.M., Cassidy, K.F., Champion, D.C., 2001. Compilation of SHRIMP U–Pb geochronological data, Yilgarn Craton, Western Australia, 2000–2001. Geoscience Australia, Record 2001/47, 111p. Gauthier, L., Hagemann S., Robert, F., 2007. The geological setting of the Golden Mile gold deposit, Kalgoorlie, WA. In: Bierlien, F., Knox-Johnson, C. (Eds.), Kalgoorlie: Geoscience Australia Record 2007/14, 181–185. Goleby, B.R., Rattenbury, M.S., Swager, C.P., Drummond, B.J., Williams, P.R., Sheraton, J.E., Heinrich, C.A., 1993. Archaean crustal structure from seismic reflection profiling, Eastern Goldfields, Western Australia, AGSO Record, 1993/15, 54 pp. Goleby, B., Blewett, R.S., Champion, D.C., Korsch, R.J., Bell, B., Groenewald, P.B., Jones, L.E.A., Whitaker, A.J., Cassidy, K.F., Carlsen, G.M., 2002. Deep seismic profiling in the NE Yilgarn: insights into its crustal architecture. Australian Institute of Geoscientists Bulletin 36, 63–66. Goleby, B.R., Blewett, R.S., Groenewald, P.B., Cassidy, K.F., Champion, D.C., Korsch, R.J., Whitaker, A., Jones, L.E.A., Bell, B., Carlson, G., 2003. Seismic interpretation of the northeastern Yilgarn Craton seismic data. In: Goleby, B.R., Blewett, R.S., Groenewald, P.B., Cassidy, K.F., Champion, D.C., Jones, L.E.A., Korsch, R.J., Shevchenko, S., Apak, S.N., (Eds.), The 2001 Northeastern Yilgarn Deep Seismic Reflection Survey. Geoscience Australia Record 2003/28, 143p. Goscombe, B., Blewett, R.S, Czarnota, K., Maas, R., Groenewald, B.A., 2007. Broad thermo-barometric evolution of the Eastern Goldfields Superterrane. In: Bierlein, F.P., Knox-Robinson, C.M., (Eds.), 2007. Proceedings of Geoconferences

(WA) Inc. Kalgoorlie ’07 Conference. Geoscience Australia Record 2007/14, p33–38. Goscombe, B., Blewett, R.S., Czarnota, K., Groenewald, B., Maas, R., 2009. Metamorphic evolution and integrated terrane analysis of the Eastern Yilgarn Craton: Rationale, methods, outcomes and interpretation. Geoscience Australia Record 2009/23, 270p. Groves, D.I., 1993. The crustal continuum model for late-Archaean lode-gold deposits of the Yilgarn Block, Western Australia. Mineralium Deposita 28, 366–374. Groves, D.I., Batt, W.D., 1984. Spatial and temporal variations of Archaean metallogenic associations in terms of evolution of granitoid-greenstone terrains with particular emphasis on the Western Australian Shield. In: Kroner, A., Hanson, G.N., Goodwin, A.M. (Eds.), Archaean Geochemistry: The Origin and Evolution of the Archaean Continental Crust. Springer-Verlag, pp. 73–98. Hagemann, S.G., Groves, D.I., Ridley, J.R., Verncombe, J.R., 1992. The Archean lode-gold deposits at Wiluna, Western Australia: high level brittle-style mineralisation in a strike-slip regime. Economic Geology 87, 1022–1053. Hall, G., 2007, Exploration success in the Yilgarn Craton insights from the Placer Dome experience the need for integrated research. In: Bierlein, F., et al., (Eds.), Kalgoorlie 2007, Geoscience Australia Record 2007/14. Hallberg, J.A., 1985. Geology and Mineral Deposits of the Leonora–Laverton Area, Northeastern Yilgarn Block, Western Australia. Hesperian Press, Perth, Western Australia, 140p. Hammond, R.L., Nisbet, B.W., 1992. Towards a structural and tectonic framework for the Norseman-Wiluna Greenstone Belt, Western Australia. In: Glover, J.E., Ho, S.E. (Eds.), The Archaean—Terrains, Processes and Metallogeny, vol. 22. Geology Department and University Extension, The University of Western Australia, Publication, pp. 39–50. Harris, L.B., Koyi, H.A., Fossen, H., 2002. Mechanisms for folding of high-grade rocks in extensional tectonic settings. Earth-Science Reviews 59, 163–210. Henson, P.A., Blewett, R.S., Champion, D.C., Goleby, B.R., Cassidy, K.F., 2004. Using 3D ‘map patterns’ to elucidate the tectonic history of the Eastern Yilgarn. In: Barnicoat, A.C., Korsch, R.J., (Eds.), Predictive Mineral Discovery Cooperative Research Centre: Extended Abstracts from the June 2004 Conference. Geoscience Australia, Record 2004/9, 87–90. http://www.ga.gov.au/image cache/GA6761.pdf. Henson, P.A., Blewett, R.S., Champion, D.C., Goleby, B.R., Cassidy, K.F., Drummond, B.J., Korsch, R.J., Brennan, T., Nicoll, M., 2005. Domes: the characteristic 3D architecture of the world-class lode-Au deposits of the Eastern Yilgarn: Economic Geology. Research Unit Contribution 64, p60. Henson, P.A., Blewett, R.S. 2006. 3D interpretation of the Eastern Yilgarn: new architectural insights from construction of the 3D map. In: Blewett, R.S., Hitchman, A.P., (Eds.), 3D Geological Models of the Eastern Yilgarn Craton—Y2 Final Report pmd*CRC. Geoscience Australia Record 2006/04, 207–216. http://www.ga.gov.au/image cache/GA13801.pdf. Henson, P.A., Blewett, R.S., Champion, D.C., Goleby, B.R., Czarnota, K., 2007. How does the 3D architecture of the Yilgarn Control Hydrothermal Fluid Focussing? In: Bierlein, F.P., Knox-Robinson, C.M., (Eds.), Proceedings of Geoconferences (WA) Inc. Kalgoorlie ’07 Conference. Geoscience Australia Record 2007/14, 56–61. Henson, P.A., Blewett, R.S., Roy, I.G., Miller, J.McL., Czarnota, K., 2010. The 4D architectural framework of the Laverton camp, Eastern Yilgarn Craton. Precambrian Research 183, 338–355. Keats, W., 1987. Regional geology of the Kalgoorlie-Boulder gold-mining district. Western Australia Geological Survey, Record 1987/21, 44p. Kerrich, R., Wyman, D.A., 1990. Geodynamic setting of mesothermal gold deposits: an association with accretionary tectonic régimes. Geology 18, 882–885. Krapeˇz, B., Brown, S.J.A., Hand, J., Barley, M.E., Cas, R.A.F., 2000. Age constraints on recycled crustal and supracrustal sources of Archaean metasedimentary sequences, Eastern Goldfields Province, Western Australia: evidence from SHRIMP zircon dating. Tectonophysics 322, 89–133. Krapeˇz, B., Barley, M.E., 2008. Late Archaean synorogenic basins of the Eastern Goldfields Superterrane, Yilgarn Craton, Western Australia. Part III. Signatures of tectonic escape in an arc-continent collision zone. Precambrian Research 161, 183–199. Liu, S.F., Stewart, A.J., Farrell, T., Whitaker, A.J., Chen, S.F., 2000. Solid Geology of the north Eastern Goldfields, Western Australia. Geoscience Australia 1:500,000 scale print on demand map (Catalogue No 53233). Martyn, J.E., 1987. Evidence for structural repetition in the greenstones of the Kalgoorlie district, Western Australia. Precambrian Research 37, 1–18. McClay, K.R., Dooley, T., Whitehouse, P., Mills, M., 2002. 4-D evolution of rift systems: insights from scaled physical models. AAPG Bulletin 86, 935–959. McIntyre, J.R., Martyn, J.E., 2005. Early extension in the Late Archaean northeastern Eastern Goldfields Province, Yilgarn Craton, Western Australia. Australian Journal of Earth Sciences 52, 975–992. Miller, J.M., 2006. Linking structure and mineralisation in Laverton, with specific reference to Sunrise Dam and Wallaby. In: Barnicoat, A.C., Korsch, R.J., (Eds.). Predictive Mineral Discovery CRC-Extended Abstracts for the April 2006 Conference. Geoscience Australia Record 2006/7, 62–67. Miller, J.M., Blewett, R.S., Tunjic, J., Connors, K., 2010. Structural evolution of the Victory to Kambalda region of the St Ives gold camp: the role of early formed structures on the development of a major gold system. Precambrian Research 183, 292–315. Morey, A., 2007. Controls on gold endowment within the Bardoc Tectonic Zone, Eastern Goldfields Province, Western Australia, PhD thesis Monash University (unpub). Mueller, A.G., Harris, L.B., Lungan, A., 1988. Structural control on of greenstonehosted gold mineralisation by transcurrent shearing: A new interpretation

R.S. Blewett et al. / Precambrian Research 183 (2010) 203–229 of the Kalgoorlie mining district, Western Australia. Ore Geology Reviews 3, 359–387. Myers, J.S., 1995. The generation and assembly of an Archaean supercontinent. Evidence from the Yilgarn craton, Western Australia. In: Coward, M.P., Ries, A.C. (Eds.), Early Precambrian Processses, vol. 95. Geological Society Special Publication, pp. 143–154. Nelson, D.R., 1997. Compilation of SHRIMP U–Pb zircon geochronology data, 1996. Geological Survey of Western Australia Record 1997/2, 189 pp. Nguyen, T.P., 1997. Structural controls on gold mineralisation at the Revenge Mine and its tectonic setting in the Lake Lefroy area, Kambalda, Western Australia, PhD thesis (unpublished), 205p. Passchier, C.W., 1994. Structural geology across a proposed Archaean terrane boundary in the eastern Yilgarn craton, Western Australia. Precambrian Research 68, 43–64. Pawley, M.J., Romano, S.S., Hall, C.E., Wyche, S., Wingate, M.T.D., 2009. The Yamarna Shear Zone: a new terrane boundary in the northeastern Yilgarn Craton? Geological Survey of Western Australia, Annual Review 2007–08, 27–32. Platt, J.P., Allchurch, P.D., Rutland, R.W.R., 1978. Archaean tectonics in the Agnew supracrustal belt, Western Australia. Precambrian Research 7, 3–30. Poulsen, K.H., 2008. Polymictic conglomerate as a guide to gold in Archean greenstone belts. In: International Field Workshop on Gold Metallogeny in India, PrE–Workshop Volume, pp. 10–14. Ross, A.A., Barley, M.E., Brown, S.J.A., McNaughton, N.J., Ridley, J.R., Fletcher, I.R., 2004. Young porphyries, old zircons; new constraints on the timing of deformation and gold mineralisation in the Eastern Goldfields from SHRIMP U–Pb zircon dating at the Kanowna Belle gold mine, Western Australia. Precambrian Research 128, 105–142. Ruming, K.J., 2006. Controls on Lode Gold Mineralisation in the Victory Thrust Complex, St Ives Goldfield, Western Australia. Unpublished Ph.D thesis, The University of Newcastle. Said, N., Kerrich, R., 2009. Geochemistry of Coexisting Depleted and Enriched Paringa Basalts, in the 2.7 Ga Kalgoorlie Terrane, Yilgarn Craton, Western Australia: Evidence for a Heterogeneous Mantle Plume Event. Precambrian Research 174, 287–309. Sandiford, M., Powell, R., 1986. Deep crustal metamorphism during continental extension; modern and ancient examples. Earth and Planetary Science Letters 79, 151–158. Sheldon, H.A., Zhang, Y., Ord, A., 2008. Gold mineralisation in the Eastern Yilgarn Craton: Insights from computer simulations. In: Blewett R.S., (Ed.), Concepts to Targets: a scale-integrated mineral systems study of the Eastern Yilgarn Craton, pmd*CRC Y4 project Final Report, Part III, 177–190. http://www.pmdcrc.com.au/final reports projectY4.html. Squire, R.J., Cas, R.A.F., Champion, D.C., 2007, The Black Flag Group: a vector to ore at St Ives. In: Bierlien F., Knox-Johnson, C., (Eds.), Kalgoorlie 2007: Geoscience Australia, Record 2007/14, 39–43. SRK Consulting, 2000, Global Archaean Synthesis – Yilgarn module. Unpublished consultants report, 88 p. Standing, J.G., 2008. Terrane amalgamation in the Eastern Goldfields Superterrane, Yilgarn Craton: evidence from tectonostratigraphic studies of the Laverton Greenstone Belt. Precambrian Research 161, 114–134. Swager, C.P., 1989. Structure of the Kalgoorlie greenstones regional deformation history and implications for the structural setting of gold deposits within the Golden Mile. Western Australia Geological Survey Report 25, 59–84. Swager, C.P., 1997. Tectono-stratigraphy of late Archaean greenstone terranes in the southern Eastern Goldfields, Western Australia. Precambrian Research 83, 11–42. Swager, C.P., Griffin, T.J., 1990. An early thrust duplex in the Kalgoorlie-Kambalda greenstone belt, Eastern Goldfields Province, Western Australia. Precambrian Research 48, 63–73.

229

Swager, C.P., Nelson, D.R., 1997. Extensional emplacement of a high-grade granite gneiss complex into low-grade granite greenstones, Eastern Goldfields, Western Australia. Precambrian Research 83, 203–209. Swager, C.P., Witt, W.K., Griffin, T.J., Ahmat, A.L., Hunter, W.M., McGoldrick, P.J., Wyche, S., 1992. Late Archaean granite-greenstones of the Kalgoorlie Terrane, Yilgarn Craton, Western Australia. In: Glover, J.E., Ho, S.E. (Eds.), The Archaean—Terrains, Processes and Metallogeny, vol. 22. Geology Department and Extension Service, University of Western Australia Publication, pp. 107–122. Tripp, G.I., Cassidy, K.F., Rogers, J., Sircombe, K., Wilson, M., 2007. Stratigraphy and structural geology of the Kalgoorlie greenstones: Key Criteria for gold exploration. In: Bierlien, F., Knox-Robinson, C.M., (Eds.), 2007, Proceedings of Geoconferences (WA) Inc. Kalgoorlie ’07, Conference. Geoscience Australia Record 2007/14, 203–208. Trofimovs, J., Davis, B.K., Cas, R.A.F., 2004. Contemporaneous ultramafic and felsic intrusive and extrusive magmatism in the Archaean Boorara Domain, Eastern Goldfields Superterrane, Western Australia, and its implications. Precambrian Research 131, 283–304. Thorpe, R.I., Hickman, A.H., Davis, D.W., Mortensen, J.K., Trendall, A.F., 1992. Constraints to Models for Archaean Lead Evolution from Precise Zircon U–Pb Geochronology for the Marble Bar Region, Pilbara Craton, vol. 22. Geology Department (Key Centre) & University Extension, The University of Western Australia, Publication, Western Australia, pp. 395–407. Turek, A., 1966. Rubidium-strontium isotopic studies in the Kalgoorlie—Norseman area, Western Australia, Unpublished PhD thesis, Australian National University, Canberra, A.C.T., 202p. Vielreicher, N.M., Groves, D.I., McNaughton, N.J., Snee, L.W., 2007. Timing of Gold Mineralisation at Kalgoorlie, Western Australia. In: Andrews, C.J., et al. (Eds.), Digging Deeper Volume 1, Proceedings of the Ninth Biennial SGA Meeting. Dublin, pp. 341–344. Walshe, J.L., Neumayr, P., Petersen, K., Roache, A., Young, C., 2008. Depositional processes in Eastern Yilgarn gold systems. Concepts to Targets: a scaleintegrated mineral systems study of the Eastern Yilgarn Craton. In: Blewett R.S., (Ed.), Concepts to Targets: A Scale-integrated Mineral Systems Study of the Eastern Yilgarn Craton, pmd*CRC Y4 project Final Report, Part III, 154–168. http://www.pmdcrc.com.au/final reports projectY4.html. Weinberg, R.F., Moresi, L., van der Borgh, P., 2003. Timing of deformation in the Norseman-Wiluna Belt, Yilgarn Craton, Western Australia. Precambrian Research 120, 219–239. Weinberg, R.F., Hodkiewicz, P.F., Groves, D.I., 2004. What controls gold distribution in Archean terranes? Geology 32, 545–548. Weinberg, R.F., van der Borgh, P., 2008. Extension and gold mineralization in the Archaean Kalgoorlie Terrane, Yilgarn Craton. Precambrian Research 161, 77–88. Wickham, R.M., Oxburgh, E.R., 1987. Low-pressure regional metamorphism in the Pyrenees and its implication for the thermal evolution of rifted continental crust. Royal Society of London, Philosophical Transactions 321, 219–242. Williams, P.R., Currie, K.L., 1993. Character and regional implications of the sheared Archaean granite—greenstone contact near Leonora, Western Australia. Precambrian Research 62, 343–365. Williams, P.R., Nisbet, B.W., Etheridge, M.A., 1989. Shear zones, gold mineralization and structural history in the Leonora district, Eastern Goldfields Province, Western Australia. Australian Journal of Earth Sciences 36, 383–403. Williams, P.R., Whitaker, A.J., 1993. Gneiss domes and extensional deformation in the highly mineralised Archaean Eastern Goldfields Province, Western Australia. Ore Geology Reviews 8, 141–162. Witt, W.K., Vanderhor, F., 1998. Diversity within a unified model for Archaean gold mineralization in the Yilgarn Craton of Western Australia: an overview of the late-orogenic, structurally-controlled gold deposits. Ore Geology Reviews, 29–64.