Abstract

Two deep seismic reflection profiles across the zone of convergence between Australia and the Banda arc east of Timor reveal the structures formed during lithosphere deformation in response to continental collision. Australian continental crust is bent down to the north to form the lower lithospheric plate. The immediately overlying upper plate is made up of a former outlier of the Australian continental shelf, now squeezed between the Australian continent to the south and the Banda arc to the north. The ages of metamorphism and of a regional unconformity in Timor indicate that the outlier began to accrete to the upper plate in the late Miocene. Near the Timor trough, at the junction between the two plates, seismic reflection data show the upper plate to be cut by north-dipping structures interpreted as thrusts in an accretionary prism formed since the arrival of the Australian continental shelf at the collision zone at about 2.5 Ma. The northern part of the collision zone is dominated by structures dipping southwards, antithetic to subduction, which penetrate the lithosphere to depths of at least 50 km. Earthquake data indicate that these are active thrust faults which divide the upper plate into imbricate slices. The seismic reflection sections, supported by gravity data and seismicity patterns, have been used to develop a model of plate convergence and continental collision which now consists of a 200 km wide zone in which both oceanic and continental material is being shortened, thickened and uplifted.