The Mesoproterozoic thermal evolution of the Musgrave Province in central Australia - Plume vs. the geological record

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 ~1.5millionkm<sup>2</sup> 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

Piggy-back supervolcanoes-long-lived, voluminous, juvenile rhyolite volcanism in mesoproterozoic central Australia

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°C. Comagmatic basalt is of mantle origin with minor Proterozoic basement contamination. The rhyolites cover the same range of Nd isotope compositions (εNd(1070) +1·24 to –0·96) and La/Nb ratios (1·2–2·1) as the basalts (εNd(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 εNd(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 230 000 km3 of parental basalt is required to form the >22 000 km3 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 >30 Myr 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 1090–1040 Ma 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 >200 Myr legacy of enhanced crustal geotherms that followed the final cratonic amalgamation of central Australia

The burning heart - The Proterozoic geology and geological evolution of the west Musgrave Region, central Australia

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. 1600-1550. Ma orthogneiss and in the west Musgrave Province as isolated outcrops of granulite-facies metagranites of the c. 1575. Ma Warlawurru Supersuite. Zircon Hf-isotopic data suggest an earlier major juvenile crust-forming event at c. 1950-1900. Ma. There is, however, no evidence that the province evolved over Archean crust. The c. 1600-1550. Ma period probably involved evolution within a primitive arc setting, perhaps developed on c. 1950-1900. Ma oceanic or oceanic-arc crust. Voluminous calc-alkaline plutonism was accompanied by clastic and volcaniclastic basin formation during the 1345-1293. Ma 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. 1400. Ma 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. 1220-1150. Ma Musgrave Orogeny as this central part of the new combined craton entered an extraordinary period of high heat flow characterised by c. 100. m.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. 1090-1040. Ma 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 50. m.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 1150. Ma 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