Development of the Continent-Ocean Transform Boundary of the Southern Exmouth Plateau

A two-stage model is proposed to explain the principal tectonic and magmatic features observed in multichannel seismic reflection and refraction data across the southern transform margin of the Exmouth Plateau (northwestern Australia): (1) The rifting stage, in which detachment surfaces developed under conditions of extension at a high angle to the future transform and were later sheared by right-lateral strike-slip faulting. Final transform rupture was attended by large fault-block rotation and mafic intrusions in conditions of pure shear. (2) In the drifting stage, as the oceanic ridge abutted the continent, the continental rim was underplated (at this location, resulting in a 10-km-thick, 7.3 km/s, 3 g/cm3 layer), resulting in a permanent isostatic uplift of the crust and tilting of synrift sedimentary deposits. This wedge extends laterally, forming a thickened oceanic layer 3. Transient heating of the continental lithosphere induced thermal uplift and erosion of up to 3.5 km of sedimentary units over a 50-km distance from the continent-ocean contact.