METAMORPHIC ROCKS FROM THE SOUTHERN MARGIN OF TASMANIA AND THEIR TECTONIC SIGNIFICANCE

Off the southern margin of Tasmania is a large area of thin continenta l crust (South Tasman Rise and East Tasman Plateau) derived from Mesoz oic Gondwana. Dredging during two scientific cruises in this area reco vered metamorphic rocks at 28 localities. Upper amphibolite facies par agneiss, from the western section of the South Tasman Rise records a C ambrian metamorphic event which is correlated with the Wilson terrane in Antarctica. The age and metamorphic history of rocks from this area are consistent with recent Cretaceous reconstructions of eastern Gond wana which suggest that the western South Tasman Rise is derived from west and north of Tasmania. Metasedimentary rocks from the eastern Sou th Tasman Rise are more like Tasmanian basement rocks and have less af finity with Antarctica. Granitic gneiss is the most common metamorphic rock dredged from the East Tasman Plateau, the northeastern margin of the South Tasman Rise and the southeast margin of Tasmania. These roc ks are correlated with the Koettlitz Group in Southern Victoria Land a nd their metamorphic age correlates with the Wickham Orogeny on King I sland. One possible interpretation is that the eastern South Tasman Ri se and the East Tasman Plateau are rifted fragments from the Ross Sea region, unrelated to Tasmania. Alternatively, the correlations fit mod els of the 'Beardmore microcontinent' colliding with Gondwana in the N eoproterozoic.