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

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, inline-formula⁴⁰Ar–inline-formula³⁹Ar, 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, inline-formula⁴⁰Ar–inline-formula³⁹Ar total gas, and K–Ar ages are largely consistent in indicating late Mesoproterozoic and early Proterozoic episodes (inline-formula $M7inlinescrollmathml\sim \mathrm{normal\; 1115}\pm \mathrm{normal\; 26}$ 60pt10ptsvg-formulamathimg04d37468330a30c275423a8edb988c26 se-11-1653-2020-ie00001.svg60pt10ptse-11-1653-2020-ie00001.png , inline-formula∼ inline-formula1070±25, inline-formula $M10inlinescrollmathml\sim \mathrm{normal\; 1040}\pm \mathrm{normal\; 24}$ 60pt10ptsvg-formulamathimg2a0e73721cf95e11e7498599a5555662 se-11-1653-2020-ie00002.svg60pt10ptse-11-1653-2020-ie00002.png , inline-formula $M11inlinescrollmathml\sim \mathrm{normal\; 1000}\pm \mathrm{normal\; 23}$ 60pt10ptsvg-formulamathimge7ced1b371947f8c809028c925bc651e se-11-1653-2020-ie00003.svg60pt10ptse-11-1653-2020-ie00003.png , and inline-formula $M12inlinescrollmathml\sim \mathrm{normal\; 905}\pm \mathrm{normal\; 21}$ 54pt10ptsvg-formulamathimgf8f1b64383323cbec6a4c90f6de7e7f3 se-11-1653-2020-ie00004.svg54pt10ptse-11-1653-2020-ie00004.png  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.