3-D structure of the Australian lithosphere from evolving seismic datasets

Abstract

During the last 20 years, seismic tomography has frequently been used to provide information on the structure of the lithosphere beneath the Australian continent. New tomographic models are presented using two complementary seismological techniques in order to illustrate the current state-of-knowledge. Surface wave tomography is the ideal method to obtain information of velocity variations across the whole continent. The latest models use data from over 13 000 source-receiver paths, allowing a higher resolution than in previous studies using the same technique. In Western Australia the results at 100 km depth clearly reveal the contrast in structure between the Pilbara and Yilgarn Cratons and the Capricorn Orogen. At greater depths, the Kimberley Block has a distinct fast velocity anomaly in comparison with the surrounding mobile belts. In the east of the continent, strong horizontal gradients in velocity indicate transitions in lithospheric structure, although the new high resolution models reveal a complexity in the transitions through central Victoria and New South Wales. Complementing the surface wave tomography, we also present the results from the inversion of over 25 000 relative arrival times from body wave phases recorded in southeast Australia and Tasmania. The body wave tomography uses the surface wave model to provide information on long-wavelength structure and absolute velocities that would otherwise be lost. The new results indicate a distinct boundary between the Delamerian and Lachlan orogens within the upper mantle, the location of which is consistent with an east-dipping Moyston Fault, as observed by deep seismic reflection profiling. The new models also confirm a distinct region of fast velocities beneath the central sub province of the Lachlan Orogen. A significant new observation is that the inferred eastern edge of this central sub-province has a strong correlation with the location of copper/gold deposits; a similar relationship is observed at a larger scale in Western Australia where mineral deposits appear to flank the regions of fastest velocity within the West Australian Craton.