•Fraser Zone is a 425×50km belt near NW edge of Albany Fraser Orogen, Western Australia.•Belt hosts c. 1300Ma gabbroic and peridotitic sills emplaced in a rift or distal back-arc.•Sills crystallised ...from basalt with 8.8% MgO, 185ppm Ni, 51ppm Cu, and <2ppb PGE.•Fraser basalts are parental to Nova Ni–Cu deposit.•Nova deposit consists of gabbroic–peridotitic sill complex.
The Albany Fraser Orogen is located along the southern and southeastern margins of the Archean Yilgarn Craton. The orogen formed during reworking of the Yilgarn Craton, along with variable additions of juvenile mantle material, from at least 1810Ma to 1140Ma. The Fraser Zone is a 425km long and 50km wide geophysically distinct belt near the northwestern edge of the orogen, hosting abundant sills of predominantly metagabbroic non-cumulate rocks, but including larger cumulate bodies, all emplaced at c. 1300Ma. The gabbroic rocks are interpreted to have crystallised from a basaltic magma that had ∼8.8% MgO, 185ppm Ni, 51ppm Cu, and extremely low contents of platinum-group elements (PGE, <1ppb). Levels of high field-strength elements (HFSE) in the least enriched rocks indicate that the magma was derived from a mantle source more depleted than a MORB source. Isotope and trace element systematics suggest that the magma was contaminated (εNd 0 to −2 throughout, La/Nb around 3) with small (<10%) amounts of crust before and during ascent and emplacement. Larger bodies of cumulate rocks show evidence for additional contamination, at the emplacement level, with country-rock metasedimentary rocks or their anatectic melts. The area has been the focus of considerable exploration for Ni–Cu sulphides following the discovery of the Nova deposit in 2012 in an intrusion consisting of olivine gabbronoritic, noritic and peridotitic cumulates, interlayered with metasedimentary rocks belonging to the Snowys Dam Formation of the Arid Basin. Disseminated sulphides from a drillcore intersecting the structurally upper portion of the intrusion, above the main ore zone, have tenors of ∼3–6.3% Ni, 1.8–6% Cu and mostly <500ppb PGE, suggesting derivation from magma with the same composition as the regional Fraser Zone metagabbroic sills, at R factors of ∼1500. However, the Nova rocks tend to have higher εSr (38–52) and more variable δ34S (−2 to +4) than the regional metagabbros (εSr 17–32, δ34S around 0), consistent with the geochemical evidence for enhanced crustal assimilation of the metasedimentary country-rock in a relatively large magma staging chamber from which pulses of sulphide bearing, crystal-charged magmas were emplaced at slightly different crustal levels. Preliminary investigations suggest that the critical factors determining whether or not Fraser Zone mafic magmas are mineralised probably relate to local geodynamic conditions that allow large magma chambers to endure long enough to sequester country-rock sulphur.
The cratonisation of Western Australia during the Proterozoic overlapped with several key events in the evolution of Earth. These include global oxidation events and glaciations, as well as the ...assembly, accretionary growth, and breakup of the supercontinents Columbia and Rodinia, culminating in the assembly of Gondwana. Globally, Proterozoic mineral systems evolved in response to the coupled evolution of the atmosphere, hydrosphere, biosphere and lithosphere. Consequently, mineral deposits form preferentially in certain times, but they also require a favourable tectonic setting. For Western Australia a distinct plate-margin mineralisation trend is associated with Columbia, whereas an intraplate mineralisation trend is associated with Rodinia and Gondwana, each with associated deposit types. We compare the current Proterozoic record of ore deposits in Western Australia to the estimated likelihood of ore-deposit formation. Overall likelihood is estimated with a simple matrix-based approach that considers two components: The “global secular likelihood” and the “tectonic setting likelihood”. This comparative study shows that at least for the studied ore-deposit types, deposits within Western Australia developed at times, and in tectonic settings compatible with global databases. Nevertheless, several deposit types are either absent or poorly-represented relative to the overall likelihood models. Insufficient exploration may partly explain this, but a genuine lack of deposits is also suggested for some deposit types. This may relate either to systemic inadequacies that inhibited ore-deposit formation, or to poor preservation. The systematic understanding on the record of Western Australia helps to understand mineralisation processes within Western Australia and its past connections in Columbia, Rodinia and Gondwana and aids to identify regions of high exploration potential.
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•Western Australia's geology and mineral deposits are reviewed.•The roles of tectonic setting and secular change are evaluated.•Western Australia's ore deposits indicate major global events.
•We present Nd and Hf data for the Musgrave, Madura and Albany–Fraser.•Musgrave magmatic rocks indicate 1950–1900Ma and 1600–1550Ma crust formation.•Albany–Fraser Orogen (AFO) magmatic rocks indicate ...reworking of Yilgarn crust.•Basement Hf and Nd signature of Musgrave is different to AFO but similar to Madura.•Musgrave is not the strike equivalent of the AFO.
Extensive time constrained isotopic (Sm–Nd, Lu–Hf) datasets on samples with well-studied geological context demonstrates that the Musgrave Province of central Australia and the Albany–Fraser Orogen of south Western Australia evolved through temporally similar Mesoproterozoic orogenies – at 1345–1260 and 1215–1140Ma – but on completely different basement. The West and North Australian Cratons amalgamated before the 1345–1260Ma event, which saw the convergence and final amalgamation of those combined cratons with the South Australian Craton. Well-defined Nd- and Hf-isotopic evolution arrays for the Musgrave Province reflect a juvenile basement with distinct 1950–1900, 1600–1550Ma crust formation events. Rare non-radiogenic material is seen only in detritus and in magmas that assimilated this material. This evolved detritus was derived from non-Yilgarn Archean sources, and reworked Archean sources, which were added to sedimentary basins developed over the Musgrave Province basement during and after c. 1400Ma. To the south of the Musgrave Province, the Madura Province has a similarly radiogenic signature to the Musgrave Province and is likely contiguous with it beneath younger cover sequences. It shows 2.0–1.4Ma mantle extraction ages and is dominated by juvenile rocks reflecting oceanic crust consumed to the north of the South Australian Craton and east of the West Australian Craton. Available data support the suggestion that the Musgrave Province is simply modified Madura Province crust situated along the edge of the North Australian Craton. Together, the Musgrave Province and the Madura Province represent Proterozoic Australia's most juvenile crustal remnant. In stark contrast to this juvenile remnant, the isotopic evolution array for the Albany–Fraser Orogen reveals a much more evolved signature, charting progressive juvenile input into an Archean source with strong isotopic and age similarity to the Yilgarn Craton of the West Australian Craton.
•Provenance analysis of zircon detritus in extensive basin systems in the Albany–Fraser Orogen.•Prolonged Proterozoic modification of an Archean craton margin.•Paleoproterozoic continental rift or ...backarc basin.•Mesoproterozoic ocean basin, oceanic-arc accretion, foreland basin.•Albany–Fraser Orogeny is not simply Mesoproterozoic continental collision.
The Albany–Fraser Orogen is a well-preserved example of Proterozoic modification of an Archean craton margin. The formation of two successive basin systems accompanied by magmatism along the southern and southeastern Yilgarn Craton margin in Western Australia reflect distinct changes in tectonic regimes, resulting in significant transformations of the Archean craton crust. Provenance analysis from detrital zircons indicates that the first basin system – the c. 1815–1600Ma Barren Basin – was dominantly filled with Neoarchean detritus derived from the Yilgarn Craton, and Paleoproterozoic detritus derived from coeval voluminous, mostly felsic magmatism. The abundance of locally derived sediment deposited onto a reworked Archean Yilgarn Craton substrate, coupled with the progressively more juvenile isotopic signature of magmas, indicates a largely extensional tectonic setting, consistent with either a continental rift basin or a long-lived backarc basin system. This extensional regime led to the formation of a passive margin and oceanic basin along the craton edge – the c. 1600–1305Ma Arid Basin – and formation of an ocean-continent transition in the most heavily modified, outboard region of the craton margin (the eastern Nornalup Zone). A change in tectonic regime is denoted by the formation of an oceanic-arc – the c. 1410Ma Loongana Arc, preserved in the adjoining Madura Province. Oceanic subduction led to accretion of the Loongana Arc onto the craton edge, recorded by the presence of exotic detritus derived from this arc deposited into a foreland basin (uppermost Arid Basin). This accretion event triggered crustal thickening and the earliest phase of magmatism of Stage I of the Albany–Fraser Orogeny at c. 1330Ma. A change to west-dipping subduction beneath the accreted portion of the Loongana Arc placed the orogen into a backarc setting, into which the remainder of the Recherche Supersuite mafic and felsic magmas were intruded. Thus, the Albany–Fraser Orogen is regarded as an Archean craton margin that preserves a long history of Proterozoic transformation dominated by extensional processes that resulted in the formation of orogen-wide, basin systems, accompanied by magmatism. The recognition that the Albany–Fraser Orogen has always been part of the West Australia Craton, and the tectonic regimes that have affected it, provide important constraints on reconstructions of the Nuna and Rodinia supercontinents.
The crystalline basement beneath the Cretaceous to Cenozoic Bight and Eucla Basins, in Western Australia has received comparatively little attention even though it lies on the eastern margin of one ...of the most mineral resource endowed regions on the planet. This basement is characterized by a complex geological evolution spanning c. 2billionyears, but paucity of outcrop and younger basin cover present a daunting challenge to understand the basement geology. In this work the composition of the unexposed Proterozoic crystalline basement to the Bight and Eucla Basins is investigated through zircon Hf isotopes and whole rock geochemistry from new drillcore samples. This region includes two geophysically defined basement entities: The Madura Province, containing: 1) c. 1478Ma Sleeper Camp Formation, which has variable isotopic signatures including evolved values interpreted to reflect reworking of rare slivers of hyperextended Archean crust, 2) 1415–1389Ma Haig Cave Supersuite, with mantle-like isotope values interpreted as melting of subduction-modified N-MORB source, and 3) 1181–1125Ma Moodini Supersuite, with juvenile isotopic signatures interpreted to reflect mixed mafic lower-crustal and asthenospheric melts produced at the base of thinned crust. The Coompana Province, to the east of the Madura Province, has three major magmatic components: 1) c. 1610Ma Toolgana Supersuite, with chemical and isotopic characteristics of primitive arc rock, 2) c. 1490Ma Undawidgi Supersuite, with juvenile isotope values consistent with extensional processes involving asthenospheric input and 3) 1192–1140Ma Moodini Supersuite, with strong isotopic similarity to Moodini Supersuite rocks in the Madura Province.
This new isotopic and geochemical data shows that the Madura and Coompana regions together represent a huge tract of predominantly juvenile material. Magma sources recognised, include; 1) depleted mantle, producing MORB-like crust at c. 1950Ma, but also contributing to younger magmatism; 2) recycled c. 1950Ma crust reworked in primitive arcs and in intra-plate settings and; 3) minor evolved material representing fragments of hyperextended continent. The observed isotopic evolution pattern is comparable to that of other central Australian Proterozoic provinces, including the Musgrave Province, the northern margin of the Gawler Craton, and components within the Rudall Province. Linking these isotopic signatures defines the Mirning Ocean, and its subducted and underplated equivalents. In a global context we suggest c. 1950Ma crust production reflects the onset of ordered oceanic spreading centres, which swept juvenile crustal fragments into Nuna.
•Geochemistry, Nd and zircon Hf isotopes from crystalline Eulca basement.•Results indicate huge tract of predominantly juvenile material.•Major magma source is depleted mantle producing MORB-like crust.•Only minor evolved material that represents fragments of hyperextended continent.•Onset of oceanic spreading at 1950Ma swept juvenile crust into Nuna.
The Musgrave Province is one of the most geodynamically significant of Australia's Proterozoic orogenic belts, lying at the intersection of the continent's three cratonic elements — the West, North ...and South Australian Cratons. While remoteness and cultural sensitivity have slowed geological research into this region, recent collaborative programs in Western Australia (the west Musgrave Province) have done much to address this. This Focus Review provides a synthesis of this, and previous, work investigating the Mesoproterozoic to Neoproterozoic geological evolution of the province. The Musgrave Province is a Mesoproterozoic to Neoproterozoic belt dominated by granites formed and deformed during several major events. A cryptic juvenile basement is exposed mainly in the east Musgrave Province as c. 1600–1550Ma orthogneiss and in the west Musgrave Province as isolated outcrops of granulite-facies metagranites of the c. 1575Ma Warlawurru Supersuite. Zircon Hf-isotopic data suggest an earlier major juvenile crust-forming event at c. 1950–1900Ma. There is, however, no evidence that the province evolved over Archean crust. The c. 1600–1550Ma period probably involved evolution within a primitive arc setting, perhaps developed on c. 1950–1900Ma oceanic or oceanic-arc crust. Voluminous calc-alkaline plutonism was accompanied by clastic and volcaniclastic basin formation during the 1345–1293Ma Mount West Orogeny. This stage traced the evolution of a continental arc reflecting the final amalgamation of the combined North and West Australian Craton with the South Australian Craton. The intervening c. 1400Ma primitive crust – the Madura Province – on which the proto-Musgrave Province had evolved, was consumed during amalgamation. The thickened crust resulting from this accretion was drastically thinned at the beginning of the c. 1220–1150Ma Musgrave Orogeny as this central part of the new combined craton entered an extraordinary period of high heat flow characterised by c. 100m.y. of ultrahigh-temperature metamorphism and high-temperature, anhydrous, alkali-calcic magmatism sourced from MASH chambers developed at the base of the thinned crust. The ridged cratonic architecture and a massive accumulation of high radiogenic heat producing granites within the mid crust perpetuated a thin crustal regime. Voluminous magmatism was again triggered during the c. 1090–1040Ma Giles Event with the evolution of the magmatism-dominated, Ngaanyatjarra Rift. This event was likely initiated through renewed movement along translithospheric faults that intersected the thermally perturbed Musgrave Province, pinned at a cratonic junction. Mantle-derived bimodal magmatism extended more or less continuously for 50m.y., producing one of the world's largest layered mafic intrusions and supervolcano-sized additions of juvenile felsic crust, in the form of alkali-calcic to alkali, A-type, rhyolite deposits. Together, the Albany–Fraser Orogen, which developed over the southern margin of the West Australian Craton, and the Musgrave Province mark the preserved edge of the North and West Australian Craton. These two belts show remarkable chronological links between c. 1345 and 1150Ma but contrasting histories before and after that period. Their period of shared evolution reflects collision and accretion of the South Australian Craton, but their tectonic setting and basement geology throughout that event were very different.
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•Review of the Mesoproterozoic Musgrave Province•Role of Musgrave Province in the Proterozoic evolution of central Australia•Comparisons with the evolution of the Albany–Fraser Orogen•Documents the nature of a thermally extreme orogeny
•In situ multiple sulphur isotopes from magmatic sulphides of the Fraser Zone.•Unique δ34S isotopic signatures characterise variably mineralised localities.•δ34S signatures due to variable ...assimilation of sulphur-bearing country rock.•Removal of Archean sulphur by sedimentary processes in assimilated country rock.•Sulphide enrichment processes in addition to sedimentary assimilation required.
Sulphur isotopes have become a widely deployed tool to address the sources of fluids in ore systems, given the widespread interaction of H2S, HS− and S2- with metals. However, the sensitivity of sulphur isotopes to magma source composition relative to other radiogenic isotopes and the nature of processes differentially affecting isotopic systems have not been extensively explored in magmatic mineral systems. In this work we present a case study of sulphide bearing magmas within the Fraser Zone of the Albany-Fraser Orogen in Western Australia that seeks to evaluate the sensitivity of sulphur isotopes to track magma source composition in space and time. New δ34S data from mineralised NRM, Plato and Octagonal localities of the Fraser Zone indicate variable degrees of assimilation of local sediments of the Snowys Dam Formation. Despite an Archean heritage in the Fraser Zone magmas being indicated by radiogenic isotopes, sparse xenocrystic zircon, and whole rock geochemical modelling, Δ33S data from these localities reveal Archean sulphur is absent; implying decoupling of the sulphur component from other geochemical and isotopic systems. This is consistent with a mechanism by which Archean sulphur was removed from detrital material incorporated in the Fraser Zone. We conclude that sulphides were stripped from sediments during uplift, erosion and transport to the Fraser Zone, with these Archean-sulphur depleted sediments then assimilated by the Fraser Zone parental magmas. Our results indicate a coupling between variable assimilation of external sulphur by Fraser Zone magmas and the mineralisation present at the prospects studied. However assimilated sulphur cannot account for all of the sulphur within mineralised samples, indicating the involvement of additional processes such as tenor upgrading.
•Two-year passive seismic deployment in Albany-Fraser Orogen (AFO).•Trough of thickened crust found along AFO.•Change from one-sided a two-sided Moho geometry near the Ida Fault.•Gravity modeling ...shows retrieved Moho geometry can reproduce regional anomalies.•We interpret the retrieved evidence as indicative of Mesoproterozoic crustal wedge indentation.
We use passive seismic and gravity data to characterize the crustal structure and the crust-mantle boundary of the east Albany-Fraser Orogen in Western Australia, a Proterozoic orogen that reworked the southern and southeastern margin of the Archean Yilgarn Craton. The crustal thickness pattern retrieved from receiver functions shows a belt of substantially thickened crust that follows the trend of the orogen, but narrows to the southwest. Common conversion point profiles show a clear transition from a wide, symmetric Moho trough in the northeast to a one-sided, northwestern Moho dip in the southwest, where the Moho appears to underthrust the craton towards its interior. This change appears to coincide with the inferred trace of the Ida Fault, a major terrane boundary within the Yilgarn Craton.
Forward modelling of gravity anomaly data using the retrieved Moho geometry as a geometric constraint shows that a conspicuous, elongated gravity low on the northwestern side of the east Albany-Fraser Orogen is almost certainly caused by thickened Archean crust. To obtain a model that resembles the regional gravity pattern the following assumptions are necessary: high-density rocks occur in the upper crust of the Fraser Zone, at depth inside the Moho trough and in parts of the eastern Nornalup Zone east of the Moho trough. Although our gravity models do not constrain at which crustal level these high-density rocks occur, active deep seismic surveys suggest that large extents of the east Albany-Fraser Orogen’s lower crust include a Mesoproterozoic magmatic underplate known as the Gunnadorrah Seismic Province.
The simplest interpretation of the imaged crustal structure is that the Gunnadorrah Seismic Province is underthrust beneath the Yilgarn Craton, likely as a consequence of crustal shortening during accretion further east. The imaged geometry overall appears to show a wedge of Archean lower crust that was driven between the exhumed Fraser Zone and the Gunnadorrah Seismic Province, effectively splitting the Paleo- to Mesoproterozoic crust of the east Albany-Fraser Orogen. The vertical splitting of Proterozoic crust by a cratonic crustal wedge, comparable to what we image in this study, may be a process that contributed to forming many craton margins around the world.
► We examine the tectonomagmatic evolution of the Albany-Fraser Orogen. ► Isotopic signatures are consistent with the Yilgarn Craton margin being modified by juvenile material during the ...Paleoproterozoic. ► Paleoproterozoic magmas indicate increasing juvenile input through time and chemical data suggest an active margin setting. ► The Paleoproterozoic component (Biranup Zone) of the orogen is not exotic. ► The Biranup Zone was deformed at c. 1680
Ma in the Zanthus Event.
The Albany-Fraser Orogen is considered to be a response to Mesoproterozoic continent–continent collision between the combined North and West Australian Cratons and the combined East Antarctic and South Australian Cratons. However, the tectonic history of the orogen and its components remain enigmatic. Recently, the Kepa Kurl Booya Province has been defined as the crystalline basement of the orogen and divided into the Fraser, Biranup, and Nornalup Zones. New geochronology shows that the Biranup Zone includes 1710–1650
Ma granitic to gabbroic intrusions and is a substantial crustal component extending at least 1200
km along the southern and southeastern margins of the Yilgarn Craton. Previous models interpreted the Biranup Zone as an exotic terrane accreted to the Yilgarn Craton during Mesoproterozoic collision, but new data presented here indicate a strong link to the craton margin during the Paleoproterozoic.
Proterozoic magmatism commenced in the Biranup Zone at 1708
±
15
Ma with metasyenogranite emplacement. This granite has
ɛHf values of −10 to −8 and whole rock
ɛNd of −15, consistent with a reworked Archean Yilgarn source. Volcaniclastic deposition in the Biranup Zone occurred at 1689
±
6
Ma, and was rapidly followed by granitic intrusion at 1686
±
8
Ma. Deformation during the Zanthus Event is constrained by 1676
±
6
Ma folded migmatitic leucosomes and 1679
±
6
Ma cross-cutting axial planar leucosomes. A younger suite of granitic and gabbroic rocks, which exhibit distinct mingling and hybridization textures, is dated at 1665
±
4
Ma. Magmatism in the eastern Biranup Zone displays high-K, calc-alkaline chemistry and a trend towards more juvenile compositions from 1710 to 1650
Ma. Based on the rapidly evolving tectonomagmatic history, modification of the original Yilgarn-like source by juvenile material, and the geochemical evolution of the melts, a feasible tectonic scenario for the Biranup Zone is an arc to back-arc setting on the active Yilgarn Craton margin. Such a model is supported by the 2684
±
11
Ma magmatic crystallization age of an isolated Archean fragment, which has clear Yilgarn affinity, within the Biranup Zone.
The region was subsequently compressed and tectonically dismembered during Stages I (1345–1260
Ma) and II (1215–1140
Ma) of the Albany-Fraser Orogeny. Stage I was dominated by voluminous mafic and granitic magmatism, represented by the Fraser Zone intrusions and the Recherche Supersuite. Two granites from the Fraser Zone, dated at 1298
±
4
Ma, have
ɛHf values overlapping Biranup Zone compositions, indicative of a reworked Biranup source. The Biranup Zone was dominated by granulite facies metamorphism during Stage II. Zircons from the northeastern edge of the Fraser Zone are overgrown by two generations of zircon rims. The earlier rims, at c. 1270
±
11
Ma, are broken and overgrown by a low-uranium fracture-filling phase at 1193
±
26
Ma. This indicates uplift and brittle deformation between Stages I and II.
The Yilgarn Craton has hosted some of the largest earthquakes within the Australian continent in the last 100 years. Earthquakes have mainly been studied in the western part of the craton, and are ...thought to result from the reactivation of Precambrian structures in an E-W compressive regional stress field imposed by plate-scale processes. Here we present moment tensor solutions for three recent moderate-sized earthquakes around the town of Kalgoorlie that are inconsistent with E-W compression, but instead suggest E-W extension in the eastern Yilgarn Craton. Waveforms of earthquakes at Boulder (M
W
= 4.0, 20 April 2010), Kalgoorlie (M
W
= 4.3, 26 February 2014) and Coolgardie (M
W
= 3.9, 31 October 2014) were inverted for moment tensors. All three earthquakes were shallow (centroid depth ≤4 km) normal-faulting events that occurred along roughly N-S-striking planes, either with a steep westward or a relatively shallow eastward dip. The robustness of the retrieved mechanisms has been thoroughly tested, employing different earth models, assuming different locations for the earthquakes and using different period bands for the inversion. The fit of synthetic long-period waveforms to the observations was in all cases substantially improved by assuming a two-layered crust with high S wavespeeds (about 3.9-4 km/s) overlying substantially slower material. Since there is independent evidence from active source profiles for a P velocity increase between the upper and lower crust, a large difference in v
p
/v
s
ratio between upper and lower crust is the only way to explain both lines of evidence. This vertical contrast could represent a dominance of felsic material in the upper crust, and substantially more mafic material in the lower crust. Taken together, our results also appear to imply that the regional stress field is E-W extensive in the Kalgoorlie area, and possibly for the entire Kalgoorlie Terrane. This is contrary to current assumptions from continent-scale stress modelling. That the orientations of rupture planes roughly align with the regional structural grain could indicate that Archean structures are reactivated in response to the current stress field.
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