The >1090 to <1040Ma Giles Event added extraordinary volumes of mantle derived magma to the crust of the Musgrave region of central Australia. This included one of Earth's largest mafic intrusions – ...the Mantamaru intrusion – and the c. 1075Ma formation of the Warakurna large igneous province, which spread dolerite intrusions across ~1.5millionkm2 of western and central Australia. It also included one of the most voluminous additions of juvenile felsic material to Earth's crust, with the development of one of the world's longest-lived rhyolitic centres, including the Talbot supervolcano. Previous suggestions that the event was the result of a deep mantle plume cannot adequately account for the >50m.y. duration of mantle derived magmatism or the fact that isolated localities such as the Talbot Sub-basin preserve the entire magmatic record, with no discernible regional age progressive spatial trend. For at least 100m.y. before the Giles Event, the Musgrave region experienced high- to ultra-high crustal temperatures — possibly as an ultra-hot orogen born from a c. 1300Ma back-arc. Granitic magmatism prior to the Giles Event also involved a significant mantle-derived component and was accompanied by mid-crustal ultra-high temperature (>1000°C) metamorphism reflecting a thin and weak lithosphere. This magmatism also resulted in a mid-crustal (~25km deep) layer greatly enriched in radiogenic heat producing elements that strongly augmented the already extreme crustal geotherms over a prolonged period. The Giles Event may have been triggered when this regional Musgrave thermal anomaly was displaced, and again significantly destabilised, along the Mundrabilla Shear Zone — a continent-scale structure that juxtaposed the Musgrave Province against the easterly extension of the Capricorn Orogen where pre-existing orogen-scale structures were in extension. These orogen-scale structures funnelled the magmas that produced the Warakurna large igneous province and the intersection of the Musgrave thermal anomaly and the Mundrabilla Shear Zone was the site of the Talbot supervolcano. Although previously thought to be a result of a deep mantle plume, the Giles Event was more likely the product of intra-plate tectonic processes involving an anomalous and prolonged thermal pre-history, a magma-focussing lithospheric architecture and large-scale tectonic movements.
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•Voluminous mantle-driven intra-plate magmatism is not necessarily plume-driven.•Plate tectonic processes explain the c. 1070Ma Giles Event in central Australia.•A region's thermal/tectonic history and lithospheric architecture must be considered.
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
Lower crustal flow zones occur in large and hot orogens and rifts, where they occur in association with large areas possessing high gravitational potential energy (GPE) and low lower crust viscosity. ...Lower crustal flow zones are also known from regions where neither the rheological nor GPE conditions are sufficiently well developed for widespread flow to occur. For these examples, the conditions required to form crustal flow zones are less well defined. One such case occurs within the ca. 600–530 Ma Petermann Orogeny in central Australia. This work investigates the conditions under which this flow zone developed, considering differences with the adjacent regions where flow is not observed. A transect of crustal structure in the central Petermann Orogen is developed that takes into account geological and geophysical data, including time-constrained pressure and temperature estimates for the Petermann Orogeny. The deformation of this region is reconstructed, showing that lower crustal flow was driven by high amplitude crustal-scale folding. The folding extruded the lower crust towards the foreland, causing crustal thickening and buoyant uplift of the orogenic core. Channelized lower crustal flow is not known from either the eastern or western parts of the orogen, and a comparison with these regions suggests three main conditions are required: Firstly, the lower crust must be sufficiently hot and volatile-rich to allow melt-weakening. Secondly, crustal rheology must allow ductile deformation of the mid to lower crust without high-strength layers. Finally, a high degree of lateral confinement is required to form pressure-gradients capable of driving flow. These three conditions were met only in the central Petermann Orogen, and not in the east or the west. This example of a lower crustal flow zone illustrates the combined influence of thermal, rheological and kinematic threshold conditions on the initiation and development of channelized lower crustal flow in orogens.
•Boundary conditions are examined for an example of channelized lower crustal flow.•Thermal and rheological conditions are near the threshold for flow to occur.•Crustal-scale folding of a warm crust (Tmoho ≈ 800 °C) is the driver of flow.•Kinematic conditions must also be met for channelized flow to occur.
Eruptions of voluminous 18O-depleted rhyolite provide the best evidence that the extreme conditions required to produce and accumulate huge volumes of felsic magma can occur in the upper 10 km of the ...crust. Mesoproterozoic bimodal volcanic sequences from the Talbot Sub-basin in central Australia contain possibly the world's most voluminous accumulation of 18O-depleted rhyolite. This volcanic system differs from the better known, but geochemically similar, Miocene Snake River Plain – Yellowstone Plateau of North America. Both systems witnessed ‘super’ sized eruptions from shallow crustal chambers, and produced 18O-depleted rhyolite. The Talbot system, however, accumulated over a much longer period (>30 Ma), at a single depositional centre, and from a magma with mantle-like isotopic compositions that contrast strongly with the isotopically evolved basement and country-rock compositions. Nevertheless, although the Talbot rhyolites are exclusively 18O-depleted, the unavoidable inference of an 18O-undepleted precursor requires high-temperature rejuvenation of crust in an upper-crustal chamber, and in this respect the evolution of the Talbot rhyolites and 18O-depleted rhyolites of the Snake River Plain – Yellowstone Plateau is very similar. However, instead of older crustal material, the primary upper-crustal source recycled into Talbot rhyolites was comagmatic (or nearly so) felsic rock itself derived from a contemporaneous juvenile basement hot-zone. Whereas giant low δ18O volcanic systems show that voluminous melting of upper crust can occur, our studies indicate that felsic magmas generated at lower crustal depths can also contribute significantly to the thermal and material budget of these systems. The requirement that very high-temperatures be achieved and sustained in the upper crust means that voluminous low δ18O magmatism is rare, primarily restricted to bimodal tholeiitic, high-K rhyolite (A-type) magmatic associations in highly attenuated lithosphere. In the case of the Talbot system, at least, our data suggest that an unusually hot pre-history might also be required to thermally prime the crust.
•>22000 km3 of 18O-depleted rhyolite in Mesoproterozoic central Australia.•Independent ‘piggyback’ supervolcano sequences over a period of >30 Ma.•Rapidly reprocessed juvenile felsic material – significant crustal growth.•Thermal anomaly related to earlier tectonic history and not a deep mantle plume.•Need voluminous bimodal A-type magmas in the upper crust of attenuated lithosphere.
The Talbot Sub-basin is one of several bimodal volcanic depositional centres of the Mesoproterozoic Bentley Basin in central Australia. It is dominated by rocks of rhyolitic composition and includes ...ignimbrites, some forming large to super-eruption size deposits. Ferroan, incompatible trace element enriched, A-type compositions, anhydrous mineralogy and clear evidence for local rheomorphism indicate high eruption temperatures, with apparent zircon-saturation temperatures suggesting crystallization at >900 degree C. Comagmatic basalt is of mantle origin with minor Proterozoic basement contamination. The rhyolites cover the same range of Nd isotope compositions ( epsilon sub(Nd(1070)) +1.24 to -0.96) and La/Nb ratios (1.2-2.1) as the basalts ( epsilon sub(Nd(1070)) +2.1 to -1.1: La/Nb 1.2-2.3) and are compositionally far removed from all older basement and country-rock components (average epsilon sub(Nd(1070))=-4, La/Nb=10). The rhyolites and basalts are cogenetic through a process probably involving both fractional crystallization of mafic magmas and partial melting of recently crystallized mafic rock in a lower crustal intraplate, extraction of dacitic magmas to a voluminous upper crustal chamber system, and separation of rhyolite by processes involving rejuvenation and cannibalization of earlier chamber material. More than 230000km super(3) of parental basalt is required to form the >22000km super(3) of preserved juvenile rhyolite in the Talbot Sub-basin alone, which represents one of the most voluminous known felsic juvenile additions to intracontinental crust. Zircon U-Pb age components are complex and distinct from those of basement and country rock and contain antecrystic components reflecting dissolution-regrowth processes during periodic rejuvenation of earlier-emplaced chamber material without any significant interaction with country rock. The overall duration of magmatism was >30Myr but can be divided into between two and four separate intervals, each probably of a few hundred thousand years' duration and each probably reflecting one of the distinct lithostratigraphic groups defined in the sub-basin. Neither the composition nor style of felsic and mafic volcanism changes in any significant way from one volcanic event to the next and the range of zircon U-Pb ages indicates that each period utilized and cannibalized the same magma chamber. This volcanism forms a component of the 1090-1040Ma Giles Event in central Australia, associated with magma-dominated extension at the nexus of the cratonic elements of Proterozoic Australia. This event cannot be reasonably reconciled with any putative plume activity but rather reflects the >200Myr legacy of enhanced crustal geotherms that followed the final cratonic amalgamation of central Australia.
The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the ...580–520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results, from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by 40Ar/39Ar muscovite and U–Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by U–Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust, from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende 40Ar/39Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect, 40Ar/39Ar muscovite and zircon (U–Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600–660 °C. Subsequent cooling to 150–220 °C of the core of the orogen occurred between ca. 480 Ma and 400 Ma (zircon U–Th/He data) during reactivation of the Woodroffe Thrust, coincident with the 450–300 Ma Alice Springs Orogeny. Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016 (Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9–7.0 °C/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.
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•Two previously inferred tectonothermal events are dated at ca. 715 Ma and 630 Ma.•The age range for the Petermann Orogeny is redefined to 630–520 Ma.•The Woodroffe Thrust was reactivated at ca. 480 Ma, 400 Ma and 200 Ma and is still seismically active.
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