Reconstruction of Antarctica and Australia at breakup (95 ± 5 Ma) and before rifting (160 Ma)

Previous reconstructions of Antarctica and Australia were made by fitting the bathymetric outlines of the conjugate margins and aligning pre-existing structures; the precise position of the continent-ocean boundary (COB) and the amount and azimuth of pre-breakup extension were unknown. Seismic and magnetic data collected off Wilkes Land by the S.P. Lee provide: (1) the basis for a unique fit of the COBs by confirming the fit of the oldest magnetic anomalies; and (2) together with information about the deep crustal structure of the Australian margin, an estimate of the azimuth and amount of pre-breakup continental extension. By these means, Antarctica and Australia are reconstructed at the mid-Cretaceous breakup and onset of drift (95 ± 5 Ma) by fitting the conjugate COBs, as determined from seismic and magnetic profiles; and before the mid-Jurassic (160 Ma) onset of rifting by removing the 360 km of continental extension estimated from the crustal structure of the 700 km wide junction zone.