Abstract
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 (∼1115±26, ∼ 1070±25, ∼1040±24, ∼1000±23, and ∼905±21 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.
Highlights
Direct dating of brittle faulting is crucial for determining the absolute timing of the inscrutable time–space distribution of tectonothermal events in concealed Precambrian terranes
A major objective of this study was to provide insight into the enigmatic time– space distribution of middle to late Mesoproterozoic tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant potential for energy and mineral resources (Korsch et al, 2011, 2012)
The undifferentiated Millungera sequence intersected in Julia Creek 1 and Dobbyn 2 comprises medium- to coarse-grained, pink to dark red quartzose sandstone with minor interbeds of micaceous clay siltstone and claystone
Summary
Direct dating of brittle faulting is crucial for determining the absolute timing of the inscrutable time–space distribution of tectonothermal events in concealed Precambrian terranes. The dating of illitic clay from near-surface fault gouges has increasingly become a routine approach to defining the timing of brittle deformations (van der Pluijm et al, 2001; Uysal et al, 2006; Mutlu et al, 2010; Zwingmann and Mancktelow, 2004, Zwingmann et al, 2010; Duvall et al, 2011; Hetzel et al, 2013; Torgersen et al, 2014; Mancktelow et al, 2016; Viola et al, 2016; Algea et al, 2019; Babaahmadi et al, 2019). The current study investigates fault rocks and the host sandstone intersected in drill cores from the newly discovered Millungera Basin in northern Queensland, north-central Australia (Fig. 1) It demonstrates how illite geochronology in combination with microstructural and mineralogical studies can be used to reveal a concealed, previously unrecorded Proterozoic tectonic event. A major objective of this study was to provide insight into the enigmatic time– space distribution of middle to late Mesoproterozoic tectonic zones in central Australia, which are responsible for the formation of a number of sedimentary basins with significant potential for energy and mineral resources (Korsch et al, 2011, 2012)
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