DEVELOPMENT OF THE LATE PROTEROZOIC TO MIDPALEOZOIC, INTRACRATONIC AMADEUS BASIN IN CENTRAL AUSTRALIA - A KEY TO UNDERSTANDING TECTONIC FORCES IN PLATE INTERIORS

The intracratonic Amadeus Basin in central Australia is a complex, composite basin covering 17,000 km2, with at least nine distinct episodes of evolution between 900 and 300 Ma. These have been identified in neighboring central Australian basins and are characterized by intervals of renewed subsidence followed by intervals of erosion and changes in basin shape. Several unconformities separating the tectonostratigraphic sequences represent periods of mild regional uplifts and correlate with major episodes of compressive tectonism at the evolving margin of the early Australian plate. In the absence of direct geological evidence for thermal events in the Amadeus Basin after the initial period of subsidence ended, possibly at about 800 Ma, the correlations found between events in the Amadeus Basin, those in the neighboring interconnected basins, and tectonic events at the continental or plate margins emphasize that regional horizontal stress fields contribute significantly to primary basin forming mechanisms. This suggests that stresses generated at continental or plate margins may propagate to the plate interior with the lithosphere acting as a stress guide. Throughout the history of the Amadeus Basin both periods when compressional stresses were dominant and when extensional tectonics controlled subsidence can be identified. There were also transitional periods when neither compression nor extension dominated, so that other processes masked the effects of weak horizontal stresses. The most recent compressional thrust belt concentrated at the northern margin between 300 and 400 Ma and has partly obscured the record of earlier basin shape and size.