Controls on the locus of intraplate deformation in central Australia

Abstract

The locus of intraplate deformation in central Australia changed from the presently preserved southern margin of the Amadeus Basin during the late Neoproterozoic to early Phanerozoic Petermann Orogeny to the northern margin in the late Phanerozoic Alice Springs Orogeny. Immediately prior to each event the thickness of the Amadeus basin sediments varied from as little as 1.5 km in the central parts of the basin to as much as 7 km in the vicinity of the presently preserved margins of the basin with the locus of deformation mimicking the locus of maximum sedimentary thicknesses at the onset of each orogenic event. As such these orogenies represent extreme examples of basin inversion; a process observed in many intracratonic basins worldwide. We show that differential burial of the central Australian Proterozoic basement complexes beneath the Amadeus basin is capable of producing variations in Moho temperature of up to 30°C prior to the Petermann Orogeny and up to 110°C prior to the Alice Springs Orogeny. For a 'Brace-Goetze' model of lithospheric rheology, the variations in Moho temperature equate to variations in effective lithospheric strain rate of 1-4 orders of magnitude, implying that variations in thickness of the sedimentary blanket may have played a primary role in localising Phanerozoic intraplate deformation in central Australia. An appealing aspect of this model lies in its corollary: that the removal of the sedimentary blanket during denudation of the orogen will be accompanied by dramatic cooling and strengthening of the lithosphere. This may provide a plausible explanation for the long-term persistence of the extraordinary gravity anomalies (~150 mGal) developed during these central Australian intraplate orogenies.