Comparison through fission-track analysis of portions of Australia and Antarctica adjacent prior to continental drift

Abstract

Australia and Antarctica have been reconstructed by the matching of three terranes in western Victoria (Glenelg River, Grampians-Stavely, Stawell) with three terranes in northern Victoria Land (Wilson, Bowers, Robertson Bay). Apparent fission-track ages from granitic rocks of these matched regions are compared. In western Victoria, Australia, data reflect a history of slow cooling following intrusion in early to middle Paleozoic time. In northern Victoria Land, Antarctica, a complex history of cooling and uplift is indicated, with uplift of the present-day mountains commencing approximately 50 Ma. Fission tracks in apatites from most samples from northern Victoria Land were completely re-set to zero by the thermal effects of Jurassic tholeiitic magmatism. Apatite in three samples from the western margin of the Wilson Terrane, however, predate the Jurassic and were only partially re-set by this event. Apparent sphene fission-track ages indicate that the three terranes in northern Victoria Land have shared a common thermal history since the Devonian. With the exception of one small area adjacent to the Cretaceous-Tertiary Otway Basin in western Victoria, neither western Victoria nor northern Victoria Land data show a clear influence of rifting and breakup in the late Cretaceous. Overall, the data indicate that once the breakup of Australia and Antarctica had occurred, their thermal and tectonic histories evolved independently along differing paths. It is suggested that during extension northern Victoria Land, Antarctica, was flanked by two upper plate margins, whereas southeastern Australia was flanked by an upper plate and a lower plate margin, thus accounting for the present-day geomorphic differences between the two regions.