Crustal structure and evolution of the central Australian basins

Abstract

The basins of central Australia formed over a period of 600 Ma or more from late Proterozoic to Carboniferous time. These basins appear to overlie crust of normal thickness whereas the crust of the intervening arches has been uplifted and reduced in thickness. The Moho, in consequence, varies in depth by up to ± 10 km about its mean depth, over horizontal distances of 50 km or less. The stresses associated with this lower crustal structure are of the order of a few kbars and extend throughout the crust. These stresses have existed since at least late Proterozoic time, and because the Moho undulations appear to follow the near surface deformations, this rules out the existence of a mechanically weak lower crust. The region is out of isostatic equilibrium and this state must be maintained by either a mechanically strong lithosphere of more than 150 km thickness or by horizontal compressive stresses, of the order of a few kbars. The former possibility is ruled out by the available mantle flow laws and geotherms proposed for the central Australian shield. In the latter case the horizontal compressive forces have also played the key role in shaping the basins and crustal structure. The horizontal compression must act down to at least the Moho and must characterize the dominant state of stress since late Proterozoic time. Show more