TECTONIC EVOLUTION OF PROTEROZOIC AUSTRALIA

Proterozoic Australia has long been interpreted as a single intact con tinent in which all tectonic and magmatic activity was intracratonic. This paper proposes an alternative hypothesis in which numerous fragme nts of continental crust were assembled by plate tectonic processes. T he assembly was completed between 1300 and 1100 Ma when the crustal fr agments were combined as an early component of the Rodinian superconti nent. Rifting and fragmentation of Archaean continents began in the la te Archaean and continued into the Proterozoic. Passive margin deposit s, such as those of the Hamersley Basin, accumulated on isolated fragm ents of Archaean crust. These numerous fragments were subsequently ass embled into three cratons by similar to 1830 Ma. A West Australian Cra ton was established by collision of the Archaean Pilbara and Yilgarn c ratons, which were joined along the Capricorn Orogen. Similarly, a Sou th Australian Craton developed by amalgamation of the proto-Gawler and proto-Curnamona cratons along the Kimban Orogen. A North Australian C raton appears to have formed by accretion of numerous crustal fragment s, including the Kimberley, Pine Creek, Lucas, and Altjawarra cratons, with sutures marked by the King Leepold, Halls Creek, Tennant Creek a nd proto-Isan orogens. The southern margin of the North Australian Cra ton was the site of repeated terrane accretion and orogenic activity b etween similar to 1880 Ma and 1400 Ma This included an orogenic event at similar to 1880 - 1850 Ma; the Strangways (1780 - 1730 Ma), Argilke (1680 - 1650 Ma), and Chewings (1620 - 1580 Ma) orogenies; and the in tracratonic Anmatjira uplift (1500 - 1400 Ma). Intracratonic rifting a t similar to 1750 to 1710 Ma and similar to 1640 to 1600 Ma produced t he McArthur Basin and related minor basins, parts of which were deform ed by the Isan Orogeny at similar to 1600 and similar to 1530 Ma. Rift ing along the line of the Capricorn Orogen led to deposition in the ov erlying intracratonic Bangemall Basin between 1630 and 1300 Ma. Along the eastern margin of the South Australian Craton, the 1670 to 1600 Ma Olarian Orogeny marks interaction with now obscured continental crust to the east. Tectonic activity between 1300 and 1100 Ma led to the as sembly of Proterozoic Australia as an early component of the supercont inent of Rodinia This first involved the amalgamation of the West Aust ralian and North Australian cratons, followed by collision with the So uth Australian Craton. The Centralian Superbasin developed over the ju nction of the North, South, and West Australian cratons between simila r to 830 and 750 Ma. Rifling to the east formed the ''Adelaide Geosync line'' at similar to 830 Ma. This was followed by the breakup of Rodin ia, with the rifting apart of Laurentia and Gondwanaland along the eas tern margin of Proterozoic Australia at similar to 750 Ma, and the sub sequent formation of the Palaeo-Pacific Ocean. After the breakup of Ro dinia, a series of northeast-southwest compressional events followed b y periods of relaxation, reflect the assembly of a new supercontinent. Old lines of weakness were reactivated, culminating in the intracrato nic King Leopold, Paterson, Petermann Ranges, and Pinjarra orogenies b etween 620 and 540 Ma. Subsequent reactivation continued into the Phan erozoic, with the widespread eruption of continental flood basalts and the formation of intracratonic basins (540 - 530 Ma).