Thermochronology of ‘The Gap’, Western Australia
Western and South Australia are blanketed by vast areas of sedimentary cover sequences from the Palaeozoic−Mesozoic Canning Basin and the Neoproterozoic−Palaeozoic Officer and Amadeus Basins. Basement rocks are only sporadically exposed in small areas at the edges of the Western, North and South Australian Cratons; however, they preserve key information for reconstructing the thermo-tectonic history of cratonic Australia. Several studies have focussed the early geological history of these crystalline basement rocks within the Rudall, Musgrave, Coompana and Madura Provinces, revealing aspects of their magmatic and metamorphic evolution; however much of the subsequent thermal history is yet to be age constrained. The thermal evolution of these basement regions is characterised by multiple overprinting events that make establishing unique relationships between dates, rates, and P–T events challenging. This study applies a multi-method geochronology approach to reconstruct the thermal history of the Coompana, Madura and Rudall Provinces, and the Petermann Orogen, using a comprehensive set of both established and novel geo- and thermochronometers. The thermal sensitivity of the applied methods spans between ~60 and 800 ºC, and the combined dataset enables unravelling of the timeframe of different geological processes occurring within this wide range of temperatures. The thermal history of the Precambrian Coompana and Madura Provinces is investigated using apatite triple dating: Lu−Hf, U−Pb and fission track (AFT). The apatite Lu−Hf and U−Pb systems record metamorphism during the late Mesoproterozoic tectonomagmatic Maralinga event in both the Coompana and Madura Provinces. Apatite Lu−Hf and U−Pb reset ages of c. 1.20−1.14 Ga were obtained for the eastern Coompana, while for the western Coompana and Madura Provinces, only the apatite U−Pb system records reset Mesoproterozoic ages of c. 1.16−1.12 Ga, and the Lu−Hf system preserves older primary ages. AFT results suggest an early Carboniferous rapid cooling pulse for the Coompana Province, correlated to the Devonian–Carboniferous Alice Springs Orogeny. The Madura Province shows no record of the early Carboniferous cooling episode, instead a protracted monotonic cooling history since the Middle Devonian is recorded. The combination of apatite Lu−Hf, U−Pb and fission track thermochronology allows tracing of differential cooling and exhumation patterns within the Coompana and Madura Provinces, preserving footprints of localised deformation and metamorphism in the eastern part of the Coompana-Madura region, possibly preconditioned by thermal weakening during the late Mesoproterozoic. A combination of multi-method geochronology connected with P–T modelling is used to reconstruct the thermo-tectonic history of the Palaeo‒Mesoproterozoic Rudall Province. This multi-method approach constrains multiple overprinting tectono-metamorphic events over c. 1 billion years of thermal history. Metamorphism associated with high geothermal gradients is identified in the northwestern part of the province at c. 1.78‒1.76 Ga by the garnet Lu‒Hf system. From the combination of the Lu‒Hf and U‒Pb systems and P‒T modelling we suggest a compressional stage during the Middle Mesoproterozoic (1.38−1.36 Ga, Garnet Lu−Hf system) Parnngurr Orogeny, characterised by relative higher-pressure conditions in response to convergence of the Percival Lakes Block to the eastern margin of the Western Australian Craton. This compressional stage was followed by high-T and lower-P metamorphic conditions, interpreted as an extensional-dominated stage during c. 1.34‒1.28 Ga (Garnet Lu-Hf, titanite and rutile U−Pb systems). A late Mesoproterozoic (c. 1.16‒1.15 Ga) thermo-tectonic event is further identified in the Talbot Domain by the muscovite Rb‒Sr system. Biotite Rb−Sr and apatite fission track results reveal a change in cooling rates from 0.1−0.3 to 0.7−1.8 ºC/Myr in the Talbot Domain at c. 650−620 Ma, correlated with the Paterson Orogeny, followed by accelerated cooling ~0.8−1.5 ºC/Myr during the Alice Springs Orogeny in the easternmost part of the orogen, and very slow cooling rates between 0.2 and 0.4 ºC/Myr to present-day surface conditions, in the western part of the Rudall Province. In situ muscovite and biotite Rb−Sr geochronology in combination with Ti-in-quartz thermometry applied to the Ediacaran−Cambrian Petermann Orogen, in central Australia, provides insight into differential cooling across the orogen. Muscovite Rb−Sr dates of c. 598 and 565 Ma in the Petermann Nappe Complex correlate with the timing of deformation during the 600‒520 Ma Petermann Orogeny. Younger mica Rb−Sr cooling ages of c. 556−541 Ma in the east of the Petermann Nappe Complex are correlated with relative higher crustal heat producing areas, suggesting that the geothermal gradient had a significant control on the timing of cooling. Differences in biotite Rb−Sr cooling ages in the orogenic core, are attributed to differential crustal exhumation across the Petermann Orogen. The application of novel and multiple geochronological methods in tandem with P−T modelling, applied in this study to reconstruct the full thermal history of the western Australian basement inliers, allowed to identify the extensive footprint of the Palaeozoic Alice Springs and Paterson-Petermann orogenies, and the repeated compressional-extensional regimes during the Proterozoic that built the western Australian basement.
Thermochronology, Geochronology, LA-ICP-MS/MS, Western Australia, Paterson Orogen, Rudall, Province, Coompana Province, Petermann Orogen
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