Deep seismic reflection data from the Curnamona Province, South Australia: crustal architecture and tectonic implications

Abstract

In 2003 and 2004, PIRSA, pmd*CRC and Geoscience Australia, in conjunction with ANSIR, acquired ~200 line km of deep seismic reflection data along an east-west transect across the Curnamona Province in South Australia. At the eastern end of the seismic transect, the crust is divided into several horizontal ``bands' of differing reflectivity. In the middle part of the seismic transect, there is a distinctive bland zone within the middle to lower crust. Its significance is unknown but in terms of its origin, it could result from reduced acoustic impedance contrasts due to partial melting, metasomatism, or be a zone of high fluid flow that has homogeneously altered a large part of the crust. It is interesting to note that similar bland zones have been noted on seismic sections in the Olympic Dam and Kalgoorlie regions. In the western part of the seismic section, a westward-thickening wedge of Neoproterozoic-Cambrian sediments up to 9 km thick overlies basement, and passes west into the even thicker, and more highly deformed, cover of the same age in the Flinders Ranges. This deformation is inferred to be Delamerian in age. Much of the crust beneath this succession is highly reflective, but it is not as obviously partitioned into subhorizontal layers as the eastern end of the line. A shallowly east-dipping surface is potentially the boundary between two different types of crust, one underlying Willyama Supergroup, and the other at depth beneath the Flinders Ranges.