Glenburgh Terrane Research Articles

Seismic Reflection and Potential Field Constraints on Imbrication and Exhumation of the Paleoarchean Narryer Terrane, Yilgarn Craton

AbstractThe Narryer Terrane, which is located on the northwest margin of the Yilgarn Craton, is one of the oldest preserved blocks of continental crust on Earth with rocks as old as 3.73 Ga and detrital zircons up to 4.4 Ga. In 2010‐11, three deep seismic reflection profiles were acquired over the terrane, and interpreted to show that during the Neoarchean the Narryer Terrane was thrust over the northwest edge of the Youanmi Terrane, which represents the core of the Yilgarn Craton, and in turn underthrust from the north by the Glenburgh Terrane during the Paleoproterozoic. We have reprocessed the seismic data to improve the imaging, extract 3D reflector orientations, and determine near‐surface velocity models. We locate the shear zone along which the Narryer Terrane was exhumed and correlate upper crustal faults interpreted in the seismic data with near‐surface faults and shear zones identified in a regional map of the first vertical derivative of the total magnetic field. One >150 km and two ∼50 km long shear zones divide the exposed Narryer Terrane into distinct structural domains that were probably juxtaposed relatively late in the thrusting of the Narryer Terrane over the Youanmi Terrane in the Paleoproterozoic. While most supracrustal rocks occur in the Northern and Southern domains, the Western Domain where magmatic ages are <3.0 Ga, high mass density, consistent with exhumation from the middle‐lower crust, and is made up of four blocks that exhibit differing patterns of seismic reflectivity, indicating they were likely combined prior to their exhumation.

Zircon U–Pb Geochronology and Hf–O Isotope Characteristics of Granitoids from the Capricorn Orogen, Western Australia

AbstractThe Capricorn Orogen, Western Australia, is a complex orogenic zone that records the convergence and collision of the Archaean Yilgarn and Pilbara cratons in forming the West Australian Craton (WAC), then over one billion years of subsequent intracontinental reworking. Granites associated with these tectonothermal events (the Dalgaringa, Bertibubba, Moorarie, Durlacher and Thirty Three supersuites) are exposed in the western part of the Capricorn Orogen. This study integrates radiogenic (U–Pb and Hf) and stable isotope (O) analysis of zircon grains from granitic rocks in the Capricorn Orogen to determine their ages and magmatic sources, including the relative contributions of mantle versus crustal material. Granites from the margin of the Yilgarn Craton record periods of crustal growth and reworking during the Archaean that influenced later Proterozoic magmatic events. Components of the Capricorn Orogen, collectively termed the Glenburgh Terrane, have previously been considered to be exotic to the adjacent Pilbara and Yilgarn cratons. However, new U–Pb zircon geochronology and Lu–Hf isotope compositions of basement rocks in the Glenburgh Terrane (the Halfway Gneiss) have similarities to some terranes of the Yilgarn Craton, and are interpreted to represent a reworked portion of the craton that was re-accreted during the Glenburgh Orogeny. Arc magmatism during the Ma Glenburgh Orogeny resulted in a period of crustal growth, with magmas representing a mixture of 50–90 % mantle-derived magmas and 50–10 % magmas derived from an evolved crustal component with an isotopic composition equivalent to that of the Halfway Gneiss. Following assembly of the WAC, granite magmatism in the Capricorn Orogen records a significant change from one dominated by mantle-derived magmatism to one dominated by crustal melting and an increased contribution from metasedimentary material. This transition reflects a geodynamic evolution from subduction–accretion to collision and intracratonic reworking. The isotopic characteristics of granites from the Moorarie Supersuite indicate three distinct sources: (1) a metasedimentary component; (2) an evolved crustal component, comparable with the Glenburgh Terrane; (3) a mafic juvenile component. Following this, the Hf–O compositions of the Durlacher Supersuite indicate that they were derived from reworking of the Moorarie Supersuite granites, and require no juvenile contribution or any additional sedimentary source. The isotopic compositions of the Thirty Three Supersuite pegmatites indicate that they were largely derived from reworking of the Moorarie and Durlacher supersuites.

Lu-Hf systematics of 4.0 – 2.3 Ga old zircons from the Turee Creek Group (Pilbara Craton, W. Australia): Implications on the rise of atmospheric oxygen and global glaciation during the Paleoproterozoic

We investigated the Hf isotopic systematics of detrital zircons in a succession of siliciclastic sediments and glacial diamictites from the early Paleoproterozoic sequence of the Boolgeeda Iron Formation (Hamersley Group) and overlying Turee Creek Group of the Pilbara Craton, Western Australia. About 400 detrital zircons yielding >95% concordant U-Pb ages were analyzed for Hf isotopes to constrain their magmatic sources. 70% of the analyzed zircons display super-chondritic initial Hf isotopic compositions, demonstrating crystallization in mantle-derived magmas. Most of the data are comprised between model age lines at ~2.5 and 3.2 Ga, which suggests a sub-continuous crust generation by extraction from the depleted mantle during this time period. A single grain yields a 4.0 Ga age, which represents the first Hadean age for a zircon from the Pilbara Craton. Our results are significantly different from zircon Hf isotope data of the Glenburgh Terrane, in the southern border of the Turee Creek Group, or older successions of the Pilbara, Kaapvaal and Superior cratons, but show overlap with some of the Yilgarn Craton. This together with the occurrence of a Hadean zircon crystal preserved in the Boolgeeda glacial diamictite with similar Hf isotopic signature than the Jack Hills zircons makes the Yilgarn Craton a possible source material for the Boolgeeda glacial horizon. Alternatively, the majority of the zircons analyzed show ages which are consistent with those of the underlying 2.45–2.78 Ga Hamersley and Fortescue groups, formed by sedimentary successions interleaved with thick subaerial volcanic sequences associated with the emplacement of Large Igneous Provinces. Such subaerial volcanic rocks could account for the relatively juvenile character of the zircon analyzed. A local provenance of the siliciclastic material delivered to the Turee Creek Basin would support the role of large subaerial magmatic provinces as triggers of the rise of atmospheric oxygen and the onset of glaciations at the beginning of the Proterozoic.

Improved Interpretation of Deep Seismic Reflection Data in Areas of Complex Geology Through Integration With Passive Seismic Data Sets

AbstractThe Capricorn Orogen records the Paleoproterozoic amalgamation of the West Australian Craton. 2‐D deep‐seismic reflection data across the Orogen are difficult to interpret due to the complex geology, and fundamental questions remain about the nature of the basement in the northern part of the Orogen. Passive seismic data have been collected along a 250‐km‐long transect across the central part of the Capricorn Orogen. The passive seismic recordings utilized teleseismic arrivals to construct a velocity section using the receiver function common conversion point method and to estimate crustal thickness and Vp/Vs using the H‐k method. A shear velocity cross section was created using ambient noise‐based methods. An integrated interpretation of all the seismic data sets shows that basement in the central Capricorn Orogen comprises a series of distinct terranes. These are recognized based on changes in crustal reflectivity, velocity and Vp/Vs. We interpret these terranes as originating from an island arc caught in the collision between the Glenburgh Terrane and the Pilbara Craton as part of the 2215–2145 Ma Ophthalmia Orogeny. Although passive seismic data do not have the resolution of reflection data, the information gained from the passive data places important constraints on the reflection interpretation and provides complementary information about changes in crustal composition. We propose that passive seismic data represent a cost‐effective complementary geophysical data set that can greatly assist with the interpretation of deep reflection sections in areas of complex geology.

A Probabilistic Shear Wave Velocity Model of the Crust in the Central West Australian Craton Constrained by Transdimensional Inversion of Ambient Noise Dispersion

AbstractThe Capricorn Orogen in central Western Australia played important roles in initializing and finalizing the West Australian craton. Surface geological mapping and isotopic studies show that the crust has recorded over a billion years of tectonic history spanning from its crustal formation in the Archean to episodes of tectonothermal events during the Proterozoic cratonization processes. The region therefore provides us with an ideal laboratory to characterize the seismic signature associated with tectonic processes. We constructed a crustal shear wave velocity model of the core region of the orogen, the Glenburgh Terrane and its north boundary, by inverting the array group velocity dispersion data measured from a high‐density temporary array. A modified Bayesian transdimensional tomography technique, which incorporates a smooth‐varying regional reference velocity model and Moho topography, was used to invert for the crustal velocity variations. The inverted velocity model adds great detail to the intracrustal structure and provides complementary seismic velocity information to refine the regional tectonic processes. Distinct patterns in the velocity structure support that the Glenburgh Terrane is an Archean microcontinent and favor the role of Paleoproterozoic subductions/accretions during the assembly of the West Australian Craton.

Genesis of the Archean–Paleoproterozoic Tabletop Domain, Rudall Province, and its endemic relationship to the West Australian Craton

ABSTRACTThe Tabletop Domain of the Rudall Province has been long thought an exotic entity to the West Australian Craton. Recent re-evaluation of this interpretation suggests otherwise, but is founded on limited data. This study presents the first comprehensive, integrated U–Pb geochronology and Hf-isotope analysis of igneous and metasedimentary rocks from the Tabletop Domain of the eastern Rudall Province. Field observations, geochronology and isotope results confirm an endemic relationship between the Tabletop Domain and the West Australian Craton (WAC), and show that the Tabletop Domain underwent a similar Archean–Paleoproterozoic history to the western Rudall Province. The central Tabletop Domain comprises Archean–Paleoproterozoic gneissic rocks with three main age components. Paleo–Neoarchean (ca 3400–2800 Ma) detritus is observed in metasedimentary rocks and was likely sourced from the East Pilbara Craton. Protoliths to mafic gneiss and metasedimentary rocks are interpreted to have been emplaced and deposited during the early Paleoproterozoic (ca 2400–2300 Ma), and exhibit age and isotopic affinities to the Capricorn Orogen basement (Glenburgh Terrane). Mid–late Paleoproterozoic mafic and felsic magmatism (ca 1880–1750 Ma) is assigned to the Kalkan Supersuite, which is exposed in the western Rudall Province. The Kalkan Supersuite provided the main source of detritus for mid–late Paleoproterozoic metasedimentary rocks in the Tabletop Domain. Similarities in the age and Hf-isotope compositions of detrital zircon from these metasedimentary rocks and Capricorn Orogeny basin sediments suggests that a regionally extensive, linked basin system may have spanned the northern WAC at this time. The Tabletop Domain records evidence for two metamorphic events. Mid–late Paleoproterozoic deformation (ca 1770–1750 Ma) was high-grade, regional and involved the development of gneissic fabrics. In contrast, early Mesoproterozoic (ca 1580 Ma) high-grade deformation was localised and associated with more widespread, late-stage, greenschist facies alteration. These new findings highlight that the Tabletop Domain experienced a much higher grade of deformation than previously assumed, with a Paleoproterozoic metamorphic history similar to that of the western Rudall Province.

A tale of two basins? Stratigraphy and detrital zircon provenance of the Palaeoproterozoic Turee Creek and Horseshoe basins of Western Australia

The 2445–2010Ma tectonic evolution of the southwestern Pilbara Craton is recorded by two depositional basins, but considering the time span involved it is pertinent to question whether only two are preserved and others have vanished. The first, the Turee Creek Basin, developed conformably on an ∼2450Ma back-arc volcanic province, and was closed long before ∼2208Ma. It was a retroarc basin sited in front of a magmatic fold-thrust belt on the southwestern margin of the craton. Its folded strata were intruded by ∼2208Ma dolerite sills that are the preserved rock record of a large igneous province. The basin and dolerites were deformed by the N-verging ∼2195–2145Ma Ophthalmia Fold-Thrust Belt. The second, the Horseshoe Basin, formed at ≤2050Ma, unconformably truncating folded strata of the Turee Creek Basin and the ∼2208Ma dolerites, and was closed prior to intrusion of ∼2008Ma dolerite dykes. It was an intracontinental rift basin sited on the inverted fold-thrust belt. Detrital zircon age-spectra for the basins have poor fit to the zircon age-spectrum of the Pilbara, and differ significantly in their youngest modes. The youngest mode for the Turee Creek Basin is ∼2442Ma, whereas the youngest mode for the Horseshoe Basin decreases upwards from ∼2276Ma to ∼2206Ma. Although differing in youngest detrital zircon age-modes, zircon age-spectra of the basins are otherwise similar, and broadly match the Glenburgh Terrane on the southwestern margin of the craton. While Turee Creek sediments were derived from the southwest, Horseshoe sediments were derived from the north and northeast. This conundrum is resolved by the Ophthalmia Fold-Thrust Belt, which tectonically loaded the craton to the north and northeast to form a now-vanished Ophthalmia foreland basin that derived sediment from the south and southwest, thereby emplacing zircon with an exotic age-spectrum on the North Pilbara. Inversion of tectonic elements occurred during formation of the Horseshoe Basin, with the fold-thrust belt subsiding beneath the rift while the foreland basin was uplifted. Recycling of the foreland basin inverted its detrital zircon age-spectrum, explaining why the youngest detrital zircon age-mode of the Horseshoe Basin decreases in age upwards.

The evolution of a Precambrian arc-related granulite facies gold deposit: Evidence from the Glenburgh deposit, Western Australia

Gold deposits are rare in upper-amphibolite to granulite facies environments. Known examples commonly attract debate about whether they formed under these conditions or instead represent metamorphosed, metasomatic, or superimposed (retrograde) mineralization. The Glenburgh gold deposit is located in the Paleoproterozoic upper-amphibolite to granulite facies Glenburgh Terrane in the southern Gascoyne Province of Western Australia. Gold at the Glenburgh deposit is free and disseminated within quartz–biotite–garnet gneiss, amphibolite, and (post-gold) quartz–chlorite veins. No clear association with a specific host lithology has been identified and mineralization does not have a visually distinct proximal alteration assemblage.The rocks hosting the deposit represent a distinct sedimentary package that was deposited, mineralized, buried, and metamorphosed, all during arc magmatism. Features within the internal structure of gold grains, such as high-purity gold veinlets, incoherent twinning, and low silver content, suggest the gold has been through post-depositional processes such as metamorphism and deformation. Abundant sulfide minerals are interpreted to have formed by sulfidation of the host rock contemporaneously with gold mineralization, and the presence of rounded sulfide inclusions within garnet porphyroblasts illustrates the presence of a sulfide phase prior to peak metamorphism. Geochronology of zircon and monazite constrains the timing of mineralization to be younger than c.2035Ma—the maximum depositional age of the metasedimentary host rocks—but older than c.1991Ma—the peak of M1 metamorphism during the Glenburgh Orogeny; these events were synchronous with arc magmatism. Rocks at the Glenburgh deposit were likely deposited in a fore-arc or accretionary wedge, a favourable setting for porphyry Cu–Mo–Au, epithermal Au, polymetallic (Sn, W) skarn, and orogenic Au mineralization. Phase equilibria modelling of a pelitic migmatite constrains peak P–T conditions to be 865–885°C, 6.8–7.6kbar, consistent with elevated thermal gradients within the arc, followed by conductive cooling of arc magmas. Partial melting during peak M1 metamorphism possible caused gold remobilization. The lack of an alteration assemblage further suggests that the alteration assemblage and mineralization were recrystallized during deformation and metamorphism. However, increases in Ca and K abundance and magnetic susceptibility decreases toward mineralization, suggesting that they may constitute ore vectors.

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

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

Two collisions, two sutures: Punctuated pre-1950 Ma assembly of the West Australian Craton during the Ophthalmian and Glenburgh Orogenies

The Gascoyne Province lies at the western end of the Capricorn Orogen, and includes a range of Neoarchean to Paleoproterozoic gneisses and metasedimentary basins (the Glenburgh Terrane) that record the amalgamation of the Archean Pilbara and Yilgarn Cratons to form the West Australian Craton. New Lu–Hf zircon data, integrated with the existing framework of U–Pb zircon and monazite data, provide direct evidence for the punctuated assembly of the West Australian Craton as a result of two discrete pre-1950 Ma collision/accretion events. First, 2555–2430 Ma granitic gneisses of the Glenburgh Terrane, interpreted as being exotic to both the Pilbara and Yilgarn Cratons, collided with (or were accreted to) the southern margin of the Pilbara Craton during the 2215–2145 Ma Ophthalmian Orogeny. The predominantly psammitic protoliths to the Moogie Metamorphics were deposited in a pro-foreland basin across the Glenburgh Terrane in response to this collision, with detrital zircon Lu–Hf signatures indicating significant Pilbara-type crust in the source region. The Lu–Hf isotopic signatures of magmatic zircons from granitic gneisses and granites of the 2005–1970 Ma Dalgaringa Supersuite, and of detrital zircon from 2000 to 1955 Ma-aged fore-arc deposits (Quartpot Pelite of the Camel Hills Metamorphics), indicate that the magmatic rocks formed in a continental margin arc, by the mixing of juvenile, mantle-derived material with older continental crust. The isotopic signature of this older crustal material is similar to that of the Glenburgh Terrane, suggesting that oceanic plate subduction occurred toward the north, under the southern, leading edge, of the Glenburgh Terrane. Although the arc was initiated at c. 2080 Ma, the older parts (pre-2005 Ma) are no longer exposed. Ocean basin closure and collision between a combined Pilbara Craton–Glenburgh Terrane and the Yilgarn Craton occurred during the latter part of the Glenburgh Orogeny between c. 1965 and c. 1950 Ma.

Seismic structure of the crust and uppermost mantle of the Capricorn and Paterson Orogens and adjacent cratons, Western Australia, from passive seismic transects

The seismic structure of the Proterozoic Capricorn and Paterson Orogens and adjacent Archaean Yilgarn and Pilbara Cratons, Western Australia, is determined using a passive seismic approach. We use recordings of distant earthquakes made along two transects of 3-component broadband stations. The stations were deployed for approximately 1year (mid 2006–2007) during which time 70 earthquakes were recorded at each station with a suitable signal to noise ratio for receiver function analysis and hence the S wavespeed profiles of the crust and uppermost mantle beneath each recording station are determined. We investigate the deep crustal constraints on terrane boundary locations, the patterns of seismic discontinuities in the crust, and the variations in the depth and character of the Moho. This broad-scale information regarding the present day crustal architecture, and hence the crustal evolution, of Western Australia, complements previous surface geological and other geophysical studies. Western Australia is an exceptionally large, well preserved region of ancient crust and hence this work also adds to the body of knowledge regarding Proterozoic orogenic processes in general. The new passive seismic work shows a region of double crust or upper mantle discontinuities beneath the Glenburgh Terrane, adjacent to the northwest Yilgarn Craton. The upper crust of the orogens is always layered whereas the cratons have a simple upper crust. Both the Capricorn and Paterson Orogens are characterised by deeper Moho discontinuities with a lesser wavespeed contrast than the very sharp discontinuity observed beneath the adjacent Pilbara and Yilgarn Cratons. This is consistent with the weaker orogenic crust of the Capricorn and Paterson Orogens accommodating most of the horizontal deformation during assembly and reworking of the West Australian Craton while the Pilbara and Yilgarn Cratons acted as rigid crustal blocks.

Identifying the lithospheric structure of a Precambrian orogen using magnetotellurics: The Capricorn Orogen, Western Australia

A 300-km long magnetotelluric (MT) survey was carried out across the Capricorn Orogen in Western Australia. The Capricorn Orogen includes reworked crust of the Archaean Yilgarn and Pilbara Cratons, and the allochthonous latest Archaean to Palaeoproterozoic Glenburgh Terrane in the southern Gascoyne Complex and the Palaeoproterozoic northern Gascoyne Complex. The survey aimed to increase our understanding of the juxtaposition of these crustal elements by obtaining information about their electrical structure with depth. Phase tensor analysis of the data showed that 2D MT inversion could only be carried out for stations in the centre of the profile, crossing the Gascoyne Complex. The resulting model showed that there is no electrical distinction between the Glenburgh Terrane and the northern Gascoyne Complex, suggesting that the Glenburgh Terrane may form basement to the whole of the Gascoyne Complex. 3D forward modelling was carried out for the entire survey line, incorporating the basement blocks as well as the surrounding ocean and sedimentary basins. Station data are most closely reproduced by a model in which the margin between the Glenburgh Terrane and the Yilgarn Craton (the Errabiddy Shear Zone) dips south, with crust of the Glenburgh Terrane wedged beneath the northern Yilgarn Craton. Forward modelling results also suggest that the main boundary between the Gascoyne Complex and the Pilbara Craton to the north is a steeply dipping structure beneath the Edmund and Collier Basins that may correlate with the Talga Fault.

Reconnaissance dating of events recorded in the southern part of the Capricorn Orogen

Abstract Zircon geochronology confirms the Errabiddy Shear Zone as a major structural boundary separating two distinct geological terranes within the southern part of the Palaeoproterozoic Capricorn Orogen of Western Australia. Rocks on the south side of the Errabiddy Shear Zone represent parts of the Archaean Yilgarn Craton that were variably reworked during the c. 2.0 Ga Glenburgh and c. 1.8 Ga Capricorn orogenies. Rocks on the north side represent an exotic terrane (the ‘Glenburgh Terrane’) comprising c. 2500 Ma (and possibly older) gneisses which evidently record tectonothermal activity c. 2390 Ma, and which, together with quartzitic metasedimentary units deposited after c. 2270 Ma, collided with the Yilgarn Craton during the Glenburgh orogeny. Regional deformation, high-grade metamorphism and voluminous felsic plutonism occurred throughout the complex in association with both the Glenburgh and Capricorn orogenies.

Palaeoproterozoic crustal accretion and collision in the southern Capricorn Orogen: the Glenburgh Orogeny

The Capricorn Orogen in central Western Australia records the Palaeoproterozoic collision of the Archaean Pilbara and Yilgarn Cratons. Until recently only one orogenic event was thought to be the cause of this collision, the 1830–1780 Ma Capricorn Orogeny. However, recent work has uncovered an older event, the Glenburgh Orogeny that occurred between 2000 and 1960 Ma. The Glenburgh Orogeny reflects the collision of a late Archaean to Palaeoproterozoic microcontinent (the Glenburgh Terrane) with the Archaean Yilgarn Craton and is therefore tectonically distinct as well as significantly older than the widespread 1900–1800 Ma tectonothermal events recorded in northern Australia. The Glenburgh Terrane preserves a different history from either the Yilgarn or Pilbara Cratons. Granitic gneiss protoliths dated at ca. 2550 Ma were intruded by widespread granite magmatism dated at 2005–1970 Ma, accompanied by high-grade metamorphism and deformation throughout the terrane. At ca. 1960 Ma silicic granite of the Bertibubba Supersuite intruded the northern margin of the Yilgarn Craton along the Errabiddy Shear Zone, a crustal-scale shear zone that today marks the contact of the Glenburgh Terrane and Yilgarn Craton. At ca. 1950 Ma silicic dykes intruded the southernmost part of the Glenburgh Terrane, marking the end of the Glenburgh Orogeny. East of the Glenburgh Terrane the Glenburgh Orogeny resulted in the cessation of mafic volcanism in the Bryah Basin, and the basin’s eventual closure. Siliciclastic, carbonate and chemical sedimentary rocks were deposited in the Padbury Basin that formed a retro-arc foreland basin on top of the Bryah Basin, and probably records the later stages of the Glenburgh Orogeny collision.

A 2005–1970 Ma Andean-type batholith in the southern Gascoyne Complex, Western Australia

Palaeoproterozoic granitic rocks of the Dalgaringa Supersuite dominate the Glenburgh Terrane, which forms the southern part of the Gascoyne Complex in the Capricorn Orogen, Western Australia. The Capricorn Orogen is a complex Proterozoic tectonic zone that is thought to reflect oblique collision of the Archaean Yilgarn and Pilbara Cratons at ca. 1800 Ma. Rocks of the Dalgaringa Supersuite do not intrude the adjacent Yilgarn Craton, and basement to the supersuite consists of ca. 2550 Ma granitic gneiss that has no equivalent in the Archaean Yilgarn and Pilbara Cratons on either side of the Capricorn Orogen. The supersuite comprises sheets, dykes and veins of 2005–1985 Ma foliated and gneissic I-type tonalite, granodiorite, quartz diorite and monzogranite, intruded by a large pluton of ca. 1975 Ma mesocratic and leucocratic I-type tonalite (Nardoo Granite). Initial ε Nd values of −1.3 to −6.0 for the supersuite are consistent with partial melting of ca. 2550 Ma granitic gneiss and variable proportions of basaltic rock, but petrogenesis of the granites probably involved a range of processes. At 1965–1945 Ma, silicic I-type granites of the Bertibubba Supersuite intruded the northwestern edge of the Yilgarn Craton and the southern margin of the Glenburgh Terrane, and are the first element common to both terranes. The Dalgaringa Supersuite represents an Andean-type batholith formed along the edge of the Glenburgh Terrane before collision with the passive margin of the Yilgarn Craton. In contrast to Phanerozoic batholiths in similar settings, generation of the Dalgaringa Supersuite involved a large degree of crustal recycling.

Deformation in a complex crustal-scale shear zone: Errabiddy Shear Zone, Western Australia

Abstract Detailed mapping of four areas representing different geological units with varying formation histories within the crustal-scale Errabiddy Shear Zone shows an apparently simple temporal progression from foliation and mineral lineation development to folding and then to brittle deformation across the shear zone. However, in detail the structural evolution of the shear zone shows considerable complexity. The dominant foliation throughout the shear zone was formed in the upper greenschist to amphibolite facies during the 2000–1960 Ma Glenburgh Orogeny, which involved the accretion of the Archaean to Palaeoproterozoic Glenburgh Terrane onto the Archaean Yilgarn Craton and the subsequent formation of the Errabiddy Shear Zone. Orthorhombic kinematic indicators formed during the Glenburgh Orogeny as did the widespread mineral lineation. These fabrics were overprinted by a greenschist facies deformation and metamorphic event during the 1830–1780 Ma Capricorn Orogeny. During the Capricorn Orogeny mineral lineation development was rare, and mostly took place in high-Capricorn strain zones in areas where a pre-existing Glenburgh-aged mineral lineation was present. Such mineral lineations trend parallel to Capricorn-aged fold hinges. Regardless of the presence or absence of Capricornaged mineral lineations, dextral strike-slip kinematics and simple shear indicated by delta and sigma porphyroclasts, and displacement along detachment faults, are prevalent close to discrete shear zone boundaries, within the Errabiddy Shear Zone. However, between shear zone boundaries flattening and coaxial strain dominated during the Capricorn Orogeny. This difference in Capricorn Orogeny kinematics throughout the shear zone is caused by strain partitioning — although progressive deformation throughout the shear zone with dextral strike-slip faults overprinting older structures formed by pure shear also took place. These results suggest that analyses of small parts of shear zones may not give the complete history of an evolving transpressional shear zone because of the presence of strain partitioning and strain localization over time.

Assembling and reactivating the Proterozoic Capricorn Orogen: lithotectonic elements, orogenies, and significance

Abstract The Capricorn Orogen was initiated during Palaeoproterozoic suturing events that brought together the Archaean Yilgarn and Pilbara cratons to form the West Australian Craton. The orogen comprises Palaeoproterozoic plutonic and medium- to high-grade metamorphic rocks of the Gascoyne Complex, a series of Palaeoproterozoic volcano-sedimentary and sedimentary basins, including the Ashburton, Blair, Yerrida, Bryah, Padbury and Earaheedy basins, and the deformed margins of the Pilbara and Yilgarn cratons. Major pulses of deformation and metamorphism took place during the ca. 2200 Ma Ophthalmian Orogeny, the 2000–1960 Ma Glenburgh Orogeny, the 1830–1780 Ma Capricorn Orogeny, and a more localized unnamed event at the end of the Palaeoproterozoic (∼1670–1620 Ma). The orogen has been the site of repeated intracratonic reactivation with renewed basin formation, magmatism and orogeny during the Mesoproterozoic and the Neoproterozoic. The exhumed Palaeoproterozoic components of the orogen are unconformably overlain by the intracratonic Mesoproterozoic Edmund and Collier Basins (Bangemall Supergroup), which have been deformed during the Neoproterozoic Edmundian Orogeny. The Ophthalmian and Glenburgh orogenies affected the northern and southern margins of the orogen, respectively. The former resulted in the development of a foreland basin along the Pilbara Craton margin, whereas the latter is associated with accretion of an allochthonous element, the Glenburgh Terrane of the Gascoyne Complex, to the northwestern margin of the Yilgarn Craton. Effects of the Capricorn Orogeny extended across the entire orogen and provide a younger limit for amalgamation of the Yilgarn and Pilbara cratons. A number of basins developed along both the northern and southern margin of the orogen during this event, and were filled with sediment eroded from the Yilgarn Craton, the Gascoyne Complex, and a presently unexposed early Palaeoproterozoic terrane. The Capricorn Orogeny corresponds with a major phase of continental collision both in Australia and world wide, which appears to mark a major phase of supercontinent assembly. Mineralization within the orogen includes a wide variety of deposit types that can be related to collisional settings, including the world-class iron orebodies of the Hamersley Basin.

Geology and tectonic evolution of Palaeoproterozoic basins of the eastern Capricorn Orogen, Western Australia

Abstract The Palaeoproterozoic Yerrida, Bryah, Padbury, and Earaheedy Basins extend for about 700 km along the northern margin of the Yilgarn Craton and are part of the Capricorn Orogen. The basins developed between ca. 2.2 and 1.8 Ga, recording periods of sedimentation, volcanism, rifting, accretion and passive-margin tectonism. The oldest is the 2.17 Ga Yerrida Basin, which began as an intracontinental sag within which siliciclastics and evaporites accumulated. At about 2.0 Ga convergence of the Yilgarn Craton and the Glenburgh terrane closed an oceanic arm, resulting in the accretion of oceanic crust and plateaux onto the Yilgarn margin and the western side of the Yerrida sag basin. This accretion produced the Narracoota Formation, which together with the clastic and chemical (banded iron-formation) sedimentation that followed, forms the Bryah Basin. Continuing collision resulted in the establishment, around 1.96 Ga, of the Padbury foreland basin, developed on top of the Bryah Basin rocks. The ca. 1.83 Ga convergence and collision of the Pilbara and Yilgarn Cratons (Capricorn Orogeny), resulted in deformation of the Bryah–Padbury Basins and orogenic uplift with coarse clastic sedimentation accompanied by the eruption of flood basalts into the Yerrida Basin. To the east of the collision zone, and possibly postdating collision, a passive margin was present. Sedimentation along it consisted of clastic and chemical sediments (granular iron-formation), which form the Earaheedy Basin. During the ca. 1.79 Ga Yapungku Orogeny, due to the convergence of the North Australian and Western Australian cratons, the northern margin of the Earaheedy Basin was deformed (Stanley Fold Belt). This last deformation event concludes the Palaeoproterozoic history of the eastern Capricorn Orogen basins.

Provenance of the Earaheedy Basin: implications for assembly of the Western Australian Craton

Abstract The Palaeoproterozoic Earaheedy Basin in Western Australia lies at the southern end of the Capricorn Orogen. The Earaheedy Group, the sole lithostratigraphic unit comprising the basin fill, is a 5 km thick succession of shallow-marine siliciclastic and carbonate sedimentary rocks. It consists from oldest to youngest of the Yelma, Frere, Windidda, Chiall, Wongawol, Kulele and Mulgarra formations. U–Pb age data for 312 detrital zircon grains from seven siliciclastic samples from the Yelma Formation, the Wandiwarra and Princess Ranges members of the Chiall Formation and the Mulgarra Sandstone reveal the presence of both Archaean (3.4–2.5 Ga) and Palaeoproterozoic (2.4–1.8 Ga) detritus. Zircon grains of Archaean age are dominantly in the range 2.7–2.6 Ga, similar to those of the Yilgarn Craton, which unconformably underlies the southern margin of the Earaheedy Basin. Age peaks in the range 2.3–2.2, 2.0 and 1.8 Ga, characterise the Palaeoproterozoic detritus. The two younger ages overlap with those of the adjoining Gascoyne Complex of the Capricorn Orogen to the west of the basin. Source components with ages in the range 2.3–2.2 Ga are extremely rare in Western Australia. Undeformed granite in the Mullingarra Complex within the Pinjarra Orogen to the west of the Darling Fault yielded an age of around 2.2 Ga. In addition, rare rims on detrital zircon grains from gneisses within basement of the Glenburgh Terrane of the Gascoyne Complex as well as a few detrital grains in metamorphosed quartz arenites of the terrane have yielded ages of around 2.4–2.2 Ga, suggesting early Palaeoproterozoic activity in this region. Detrital grains as young as 1800 Ma, combined with deposition of the unconformably underlying strata in the Yerrida Basin at c. 1840 Ma and deformation of the Earaheedy Group at around 1750 Ma, provide a relatively tight constraint on the depositional age of the Earaheedy Group.