Tectonothermal history and evolving geodynamic setting of the Peake and Denison Block and Northern Gawler Craton, South Australia

2017-02-16T23:40:36Z (GMT) by Ross, George B.
The Peake and Denison Block located in the far north east of South Australia offers a rare geological window into the basement of the dominantly buried northern Gawler Craton Proterozoic basement. The relative position of the Peake and Denison Block is an important location in the context of plate reconstruction models as it represents an interpreted marginal domain. Detrital geochronology of the Peake Metamorphics indicates three distinct depositional sequences were deposited over a 60 Myr period between 1800 and 1740 Ma. The earliest volcano-sedimentary sequence of the Peake Metamorphics was deposited at ~1800 Ma sequence followed shortly after by a second depositional event at ~1780 Ma and a third at ~1740 Ma. The two earliest sequences preserve detrital zircon populations that indicate they may share a common protolith ancestry with similarly aged sequences in Mt Isa's Western Fold Belt. Following a depositional hiatus a third sequence of volcanics and sediments were deposited at ~1740 Ma which may have sourced material from either locally reworked earlier sequences of the Peak Metamorphics or alternately the more distant Arunta Region of Northern Australia. Sediment deposition is interpreted to have been halted by basin inversion associated with the onset of the Kimban Orogeny at ~1710 Ma which produced at least three deformation events. This period of orogenesis was characterised by an early extensional fabric which was later refolded by two orientations of folding, accompanied by Upper Amphibolite facies metamorphism. Regional geophysical analysis indicates Kimban orogenesis extensively affected the Northern Gawler Craton and was proceeded by at least seven additional periods of faulting, shearing or folding. Preliminary geophysical analysis of the region to the south of the traditional margin of the Mt Isa Block appears to indicate the presence of a deeply buried continuation of the North Australia Craton. Multidisciplinary analysis inclusive of structural, chronological and geophysical observations indicate the Peake and Denison Block may represent the translocated southern margin of the North Australian Craton. It is envisaged the Peake and Denison Block was detached, rotated and finally reattached during the latter part of the Proterozoic.