Tectonic framework for the Cenozoic cratonic basins of Australia

Abstract

Variations in the extent of Cenozoic marine inundation of Australia, as revealed by the distribution of marine and nearshore deposits, points to a tectonic regime involving three distinct modes of deformation. At the longest wavelengths (order 103 km), the continent has experienced southwest-up, northeast-down tilting with an amplitude of ∼300 m since the Late Eocene. We attribute this tilting to the dynamic topographic response to the northward motion of Australia towards the subduction realm of Indonesia and the western Pacific, as well as its passage across a complexly structured mantle. At short wavelengths (order 101 km), variations in elevation are associated with cumulative fault movements up to the order of 100 m. Fault-slip vectors are generally compatible with the prevailing in situ stress field and therefore can be allied to distant plate-boundary forcing. At intermediate wavelengths (order 102 km), undulations with amplitudes of the order of ∼100 m reflect, at least in part, lithospheric buckling due to relatively high levels of intraplate stress arising from plate-boundary forcing. Understanding the patterns of surface deformation associated with each of these deformation modes provides a tectonic framework against which the broader significance of the Australian Cenozoic record for such things as eustasy must be evaluated.