CONTROLS ON THE LOCUS OF INTRAPLATE DEFORMATION IN CENTRAL AUSTRALIA

The locus of intraplate deformation in central Australia changed from the presently preserved southern margin of the Amadeus Basin during th e late Neoproterozoic to early Phanerozoic Petermann Orogeny to the no rthern margin in the late Phanerozoic Alice Springs Orogeny. Immediate ly prior to each event the thickness of the Amadeus basin sediments va ried 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 se dimentary thicknesses at the onset of each orogenic event. As such the se orogenies represent extreme examples of basin inversion; a process observed in many intracratonic basins worldwide. We show that differen tial burial of the central Australian Proterozoic basement complexes b eneath the Amadeus basin is capable of producing variations in Moho te mperature of up to 30 degrees C prior to the Petermann Orogeny and up to 110 degrees C prior to the Alice Springs Orogeny. For a 'Brace-Goet ze' model of lithospheric rheology, the variations in Moho temperature equate to variations in effective lithospheric strain rate of 1-4 ord ers of magnitude, implying that variations in thickness of the sedimen tary blanket may have played a primary role in localising Phanerozoic intraplate deformation in central Australia. An appealing aspect of th is model lies in its corollary: that the removal of the sedimentary bl anket during denudation of the orogen will be accompanied by dramatic cooling and strengthening of the lithosphere. This may provide a plaus ible explanation for the long-term persistence of the extraordinary gr avity anomalies (similar to 150 mGal) developed during these central A ustralian intraplate orogenies. (C) 1998 Elsevier Science B.V. All rig hts reserved.