Unearthing the marginal terranes of the South Australian Craton: insights from integrated structural geology, geophysics and isotopic studies

2017-05-15T07:26:40Z (GMT) by Armit, Robin John
The marginal terranes of the South Australian Craton consist of predominantly buried Neoarchean to Early Mesoproterozoic meta-sedimentary and magmatic rocks that cover an area in excess of 150,000 km². The terranes include the buried northern Gawler Craton and the outcropping Mount Painter Province on the north-west margin of the Curnamona Province. The position of these terranes at the margins of the Archaean to Palaeoproterozoic Gawler Craton and the Palaeoproterozoic Curnamona Province makes them the ideal location to test links between these Precambrian terranes and to understand the relationship between the south and north Australian cratons. U-Pb dating of zircon reveals maximum depositional ages for the siliciclastic Radium Creek Group of ca. 1595 Ma. Relatively diverse and evolved Hf isotopic signatures are correlated with zircon signatures from the Olympic and Spencer domains of the Gawler Craton and suggest that the Radium Creek Group is sourced from the Gawler Craton at ca. 1595 Ma. This indicates that the Curnamona Province and the Gawler Craton were co-located at this time. Rapid burial accompanied by ductile deformation followed by exhumation within 6 Myrs of deposition supports tectonic mode switches and suggests that the Mount Painter Province occupied a complex plate tectonic setting in the overriding plate of two convergent margins in the Early Mesoproterozoic and appears to have similar tectonic evolution to the northern Gawler craton and north Australian craton. A validation of the 3D architecture of the Mount Painter Province using a constrained potential-field inversion modelling process argued for the addition of a larger volume of felsic material in the sub-surface and suggests that there was an increased heat budget in the early Palaeozoic and may have be a driver for the pervasive hydrothermal alteration in the region. SHRIMP and LA-ICPMS U-Pb dating from a series of meta-sedimentary horizons intersected in the drill holes into the buried northern Gawler Craton yielded maximum depositional ages of ca. 1736 Ma and minimum depositional ages from cross-cutting leucocratic veins of ca. 1731 Ma. Similar ages, isotopic and REE characteristics are interpreted from meta-sedimentary rocks in the Mabel Creek Ridge, Yoolperlunna and Welbourn Hill regions. Collectively these meta-sedimentary rocks (Manguri Group) are likely derived from the Arunta Province in North Australian Craton. Wider correlations of the ca. 1740 Ma meta-sedimentary rocks suggest that these sequences form part of an extensive and contiguous basin system in the mid-Proterozoic across the Australian continent. Inversion and tectonic mode switches during the ca. 1730-1690 Ma Kimban-Strangways Orogeny and ca. 1590-1560 Ma Kararan-Chewings Orogeny support a far-field back-arc basin setting for the basin system. Systematic similarities in the ages, isotopic and geochemical signatures of Neoarchaean to late Palaeoproterozoic magmatic and meta-sedimentary rocks across crustal-scale faults in the northern Gawler Craton suggest these faults do not represent sutures between allocthonous crustal blocks. In the palaeogeographical reconstruction models the marginal terranes of the South Australian Craton are positioned in the overriding plate of a long-lived north dipping subduction zone along the southern margin of Palaeo-Mesoproterozoic Australia.