LATE PROTEROZOIC DEFORMATION IN THE AMADEUS BASIN, CENTRAL AUSTRALIA

Complex structures, including southerly directed fold thrust nappes, found along the northern margin of the Amadeus Basin of central Australia involve only the oldest part of the basin sequence and underlying metamorphic basement. Many of these structures, previously ascribed to the Late Palaeozoic intracratonic Alice Springs Orogeny, probably formed during the older previously unrecognized Late Proterozoic Arltunga Orogeny. This is based on the discovery of a high-angle unconformity well-preserved at the eastern closure of the Gaylad and Mulga Synclines, where the overturned and isoclinally folded Bitter Springs Formation is overlain by shallow dipping Areyonga to Per-tatataka Formations. Observations accord with the suggestion that the main driving mechanism for the Amadeus Basin subsidence was north--south compression, at least from the time of deposition of the Areyonga Formation onwards, the implication being that central Australian intracratonic basins have been localized above relatively 'hard' lithosphere periodically flexed in response to loading from intervening 'soft' Late Proterozoic orogenic belts.