Precambrian faulting episodes and insights into the tectonothermal history of north Australia: Microstructural evidence and K-Ar, 40Ar-39Ar, and Rb-Sr dating of syntectonic illite from the intracratonic Millungera Basin

Abstract

Australian terranes concealed beneath Mesozoic cover record complex Precambrian tectonic histories involving a successive development of several Proterozoic to Palaeozoic orogenic systems. This study presents an integrated approach combining K Ar, 40Ar 39Ar, and Rb Sr geochronologies of Precambrian authigenic illites from the recently discovered Millungera Basin in north-central Australia. Brittle deformation and repeated fault activity are evident from the sampled cores and their microstructures, probably associated with the large-scale faults inferred from interpretations of seismic surveys. Rb Sr isochron, 40Ar 39Ar total gas, and K Ar ages are largely consistent in indicating late Mesoproterozoic and early Proterozoic episodes (111526, 107025, 104024, 100023, and 90521 Ma) of active tectonics in north-central Australia. K Ar results show that illites from fault gouges and authigenic matrix illites in undeformed adjacent sandstones precipitated contemporaneously, indicating that advection of tectonically mobilized fluids extended into the undeformed wall rocks above or below the fracture and shear (fault gouge) zones. Isotopic age data clearly indicate a Mesoproterozoic minimum age for the Millungera Basin and thus previously unrecorded late Mesoproterozoic early Neoproterozoic tectonic events in north-central Australia. This study provides insight into the enigmatic time space distribution of Precambrian tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant energy and mineral resources.