Structure of the crust and upper mantle beneath Bass Strait, southeast Australia, from teleseismic body wave tomography

We present new constraints on the lithospheric velocity structure of Bass Strait and the adjoining landmasses of mainland Australia and Tasmania in order to better constrain their geological and tectonic relationship. This is achieved by performing teleseismic tomography using data from fifteen deployments of WOMBAT and BASS transportable arrays, which span southeastern Australia. The starting model for the teleseismic tomography includes crustal velocity structure constrained by surface waves extracted from ambient seismic noise data and a Moho surface and broad-scale variations in 3-D upper mantle velocity structure from the Australian seismological reference Earth model (AuSREM). As a consequence, we produce a model with a high level of detail in both the crust and upper mantle. Our new results strengthen the argument for a low velocity upper mantle anomaly that extends down to ~150 km depth directly beneath the Newer Volcanics Province in Victoria, which is likely related to recent intra-plate volcanism. Beneath Bass Strait, which is thought to host the entrained VanDieland microcontinent, upper mantle velocities are low relative to those typically found beneath Precambrian continental crust; it is possible that failed rifting in Bass Strait during the Cretaceous, opening of the Tasman Sea, extension of VanDieland during Rodinian break-up and recent plume activity in the past 5 Ma may have altered the seismic character of this region. The data nevertheless suggest: (1) the velocity structure of the VanDieland microcontinent lacks continuity within its lithosphere; (2) the Moyston Fault defines an area of strong velocity transition at the boundary between the Cambrian Delamerian Orogen and the Cambrian-Carboniferous Lachlan Orogen; and (3) there is a rapid decrease in mantle velocity inboard of the east coast of Australia, which is consistent with substantial thinning of the lithosphere towards the passive margin.