SOUTH AUSTRALIAN RECORD OF A RODINIAN EPICONTINENTAL BASIN AND ITS MID-NEOPROTEROZOIC BREAKUP (SIMILAR-TO-700 MA) TO FORM THE PALAEO-PACIFIC OCEAN

The Neoproterozoic Adelaidean System and overlying Cambrian rocks are a thick succession of terrestrial and shallow-marine sediments that we re deposited on older continental crust near the eastern edge of the e xposed Precambrian rocks in Australia. The Adelaidean System records f our major tectonic regimes: (1) early Neoproterozoic formation of an e picontinental, partly rifted basin; (2) mid-Neoproterozoic (approximat ely 700 Ma) continental breakup and accumulation of a passive margin w edge; (3) latest Neoproterozoic/Early Cambrian renewed rifting, and (4 ) Middle to Late Cambrian conversion of the passive margin to a conver gence zone during the development of the Delamerian Orogen. Deposition of the Adelaidean System commenced by approximately 830 Ma, when Aust ralia was contiguous with Laurentia in the Rodinia supercontinent. San dstone and evaporitic carbonate of an initial epicontinental basin are preserved as the lowest succession of the Adelaide Geosyncline and th e Amadeus, Georgina, Ngalia, Officer and Savory-Yeneena basins. Mafic volcanics were extruded under NE-SW continental extension during the W illouran, which was overprinted by a more widespread E-W Torrensian ex tension. Continental breakup occurred around 700 Ma, during accumulati on of the Sturtian glaciogenic deposits in rift valleys. The succeedin g siltstone, sandstone and carbonate were deposited on a passive conti nental margin that faced the newly formed Palaeo-Pacific Ocean as Laur entia rotated clockwise away from Australia. A wide Palaeo-Pacific Oce an existed at the time of the younger Ice Brook (Laurentian) and Marin oan (Australian) glaciations. Dextral shear between northern and south ern Australia along the Paterson-Petermann Ranges Orogen in the 600-55 0-Ma interval, broke up the continuity of the central Australian basin s through uplift of the Musgrave Block, and led to renewed rifting, re flecting the latest Neoproterozoic continental breakup that formed the eastern margin of Laurentia. The South Australian passive margin pers isted until the Middle Cambrian when convergence along the Pacific Oce an margin led to development of the Delamerian Orogen. Deposition of t he marine siliciclastic Kanmantoo Group commenced in the late Early Ca mbrian in a rapidly subsiding trough, for which both extensional (rift -basin) and compressional (foredeep) origins have been proposed. Rever sal of the eastward-dipping Early Cambrian palaeoslope in the Middle C ambrian shed siliciclastic sediments back onto the continent from an i nitial uplift in advance of Delamerian deformation.