208 AUSTRALIA/Proterozoic AUSTRALIA Contents Proterozoic Phanerozoic Tasman Orogenic Belt Proterozoic I M Tyler, Geological Survey of Western Australia, East Perth, WA, Australia ß 2005, Elsevier Ltd All Rights Reserved Introduction The Proterozoic is the period of geological time extending from the end of the Archaean, 2500 million years ago (Ma), to the start of the Phanerozoic (the base of the Cambrian System), 545 Ma The Proterozoic is divided into the Palaeoproterozoic (2500– 1600 Ma), the Mesoproterozoic (1600–1000 Ma), and the Neoproterozoic (1000–545 Ma) In Australia, Proterozoic rocks are present to the west of the ‘Tasman Line’ that separates ‘Proterozoic Australia’, where geophysical datasets show that Precambrian basement is continuous beneath Phanerozoic sedimentary basins, from the Tasmanides, where predominantly Palaeozoic basement is overlain by Mesozoic and younger sedimentary basins Extensive exposures of Proterozoic rocks are present in western Australia, in northern, central, and north-eastern Australia, and in southern Australia and Tasmania Proterozoic Australia is made up of three distinct cratons, the West Australian Craton, the North Australian Craton, and the South Australian Craton (Figure 1) These probably formed originally as parts of larger cratons or continental blocks (the South Australian Craton together with the previously adjacent part of Antarctica formed the Mawson Craton) and are dominated by Archaean and Palaeoproterozoic to Mesoproterozoic crust The three cratons are separated by two predominantly Mesoproterozoic to Neoproterozoic orogenic belts, the Paterson Orogen and the Albany–Fraser Orogen The Palaeoproterozoic to Neoproterozoic Pinjarra Orogen is present along the western margin of Australia Plate tectonic models can be applied to Proterozoic Australia The increasing availability of high-quality geochronological data has highlighted the presence of distinct tectonostratigraphic terranes with differing geological histories within orogenic belts, and geophysical datasets reveal the heterogeneous nature of the crust throughout Proterozoic Australia However, Proterozoic plate-tectonic processes may differ from modern processes, and the real lack of accretionary complexes and ophiolites, and significant differences in the geochemical and isotopic compositions of igneous rocks, may reflect changes in the nature and composition of the oceanic lithosphere through time Palaeomagnetic evidence is placing greater controls on the movement and relative positions of the constituent crustal components Diverse cratons and continental blocks aggregated during the Palaeoproterozoic and Early Mesoproterozoic to form Proterozoic Australia, which then played an integral part in the formation and breakup of the Meso- to Neoproterozoic supercontinent, Rodinia (Figures 2–7; summarized in Table 1) Proterozoic Australia is host to a wide variety of minerals , including worldclass deposits of iron, uranium, gold, copper–gold, lead–zinc–silver, and diamond orebodies (Figure 8) Neoarchaean to Palaeoproterozoic Assembling Proterozoic Australia: (2770–1600 Ma) West Australian Craton Within the West Australian Craton, large areas of Archaean rocks are exposed in the geologically distinct Pilbara and Yilgarn cratons (Figures and 2) The Hamersley Basin was initiated on the southern part of the Pilbara Craton at the start of the Neoarchaean West- to south-westerly directed rifting within cratonized granite–greenstone basement represents a distinct change to a Proterozoic and Phanerozoic tectonic style The flood basalts (2770–2690 Ma) of the Fortescue Group dominate the rift-related lower part of the basin These were buried beneath a breakup unconformity overlain by a passive margin sequence characterized by cherts and banded iron formations