Crustal velocity and sediment thickness asymmetries along and between the conjugate Australian-Antarctic margins

The Australian-Antarctic conjugate margins are remarkably symmetric in comparison to other magma-poor rifted continental margins, particularly in the central Great Australian Bight section. Here, we use two datasets derived from seismic refraction data to investigate the pre-rift crustal structure of the conjugate Australian- Antarctic margins. We analyse two datasets for the conjugate Australian-Antarctic margins, (i) seismic velocity data derived from a synthesis of seismic refraction and sonobuoy data, and (ii) estimates of total sediment thickness from seismic refraction data calibrated against stacking-derived seismic velocities from seismic reflection profiles along each margin. Using a novel approach involving plate reconstruction and 3D visualistion we utilize these datasets to map the 3D lithospheric structure of the Australian- Antarctic margins. Our approach enables accurate juxtaposition of the Australian-Antarctic conjugate margins at the approximate time of breakup (~83 Ma). We find that the distribution of sediment along and across the conjugate Australian-Antarctic margins is highly asymmetric and that observed asymmetries in crustal structure are predominantly due to the patterns of sediment loading. Our results also indicate that total sediment thicknesses have been significantly underestimated from seismic reflection profile data for large sections of both margins. Underestimations of total sediment thickness appear particularly severe on the Antarctic margin. A significant insight this analysis provides is that the velocity information from seismic refraction data has been grossly under-utilised.