The Otway Continental Margin Transect: crustal architecture from wide-angle seismic profiling

Abstract

Wide-angle seismic profiling along the Otway Continental Margin Transect defines the velocity structure from the continental crust onshore to the deep Southern Ocean across an area of extended and faulted basement to the Otway Basin. A significant section of Otway Basin sequences (up to 5 km) lies offshore on the continental slope overlying uppermost Palaeozoic basement (P-wave velocity 5.5 km/s to 5.7 km/s). A deeper basement velocity of 6.15 km/s to 6.35 km/s is prominent. The whole basement section thins from 16 km thickness onshore to 3.5 km at 120 km from the coast. The lower crustal velocity of 6.4 km/s to 6.8 km/s extends down to a 1 km to 2 km thick upper mantle transition zone (6.9 km/s to 7.8 km/s) overlying the Moho at 30 km depth onshore, shallowing to 12 km in the deep ocean basin. The upper mantle velocity is 8.05 km/s, increasing to 8.3 km/s at 40 km depth. There is no evidence of a high-velocity lower crust (>7 km/s) that would indicate that this is a 'volcanic' margin as defined on some North Atlantic margins. Analogues for the Otway margin include the 'non-volcanic' Galicia Bank off the Iberian Peninsula and the Nova Scotia margin off eastern Canada.