Dominant symmetry of a conjugate southern Australian and East Antarctic magma-poor rifted margin segment

Abstract

Synthesis and modeling of published deep seismic and potential field data from the conjugate, magma-poor, rifted margins of the Great Australian Bight, southern Australia, and central Wilkes Land, East Antarctica, show that there is pronounced symmetry of structures in a 300 km wide zone straddling the axis of final breakup. This symmetry is observed consistently for a distance of some hundreds of kilometers along strike. From inboard to outboard, both margins comprise a narrow zone of attenuation of the crystalline continental crust; an approximately 4 km high basement ridge, interpreted as unroofed peridotites, at the location of maximum thinning of the continental crust; and a 60–70 km wide continent-ocean transition zone that contains a sedimentary basin that may be underlain by altered mantle and fragments of crystalline continental crust. The marked breakup symmetry described here is in contrast to the asymmetry of the Iberia-Newfoundland margin and is consistent with the operation of a symmetrical extensional detachment system deforming the whole crust in the center of the rift, as envisaged by some numerical models for the continental rifting process.