The tectonic development of the Amadeus Basin, central Australia

The Amadeus Basin is a Late Proterozoic to early Phanerozoic basin in central Australia, in which at least nine tectono-stratigraphic intervals (megasequences) are recognized, separated by regional unconformities. A major change in basin shape characterizes each interval. Although plausible basin-forming mechanisms can be suggested for each interval, the dominant mechanism is not always clear in each case. Tectono-thermal processes, not necessarily related to rifting, may be applicable to the initiation of subsidence within the basin during interval 1 (Heavitree Quartzite-Bitter Springs Formation). A modification of the contractional tilted-fault block model may be an appropriate explanation for the basin shape in the early stages of intervals 2 and 3 (Areyonga Formation to Julie Formation). However, increased subsidence in the later stages of intervals 2 and 3 may relate to a drop in the regional stress. Extensional tectonism may explain depositional patterns established during interval 4 (Arumbera Sandstone and Todd River Dolomite). Accommodation zones dividing depositional compartments in the north of the basin are interpreted as transfer faults. The extrusion of plateau basalts at province boundaries surrounding the central Australian region may correspond to the culmination of deep-seated lithospheric extension. The widespread subsidence which started gradually with the onset of interval 5 (Chandler Formation to lower Goyder Formation) is interpreted to correspond to the beginning of a thermal relaxation phase following the end of the lithospheric thinning and continental break-up. A two-layer extension model is invoked to explain subsidence during intervals 4 and 5. It is proposed that extension was initially minimal and heterogeneously distributed. As the extension increased, it became progressively concentrated in the lower crust and lithospheric mantle due to an increasing ductility with depth. A mid-crustal detachment zone formed between a less extended upper crust and a more extended lower crust and mantle. This model can explain the lack of normal faulting during interval 4 and the widespread subsidence during interval 5. Inherited characteristics are considered to be particularly important to basin development during intervals 6, 7, and 8.