Metamorphic rocks from the southern margin of Tasmania and their tectonic significance∗

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Abstract
Off the southern margin of Tasmania is a large area of thin continental crust (South Tasman Rise and East Tasman Plateau) derived from Mesozoic Gondwana. Dredging during two scientific cruises in this area recovered metamorphic rocks at 28 localities. Upper amphibolite facies paragneiss, from the western section of the South Tasman Rise records a Cambrian 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 Gondwana which suggest that the western South Tasman Rise is derived from west and north of Tasmania. Metasedimentary rocks from the eastern South Tasman Rise are more like Tasmanian basement rocks and have less affinity 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 rocks are correlated with the Koettlitz Group in Southern Victoria Land and their metamorphic age correlates with the Wickham Orogeny on King Island. One possible interpretation is that the eastern South Tasman Rise and the East Tasman Plateau are rifted fragments from the Ross Sea region, unrelated to Tasmania. Alternatively, the correlations fit models of the ‘Beardmore microcontinent’ colliding with Gondwana in the Neoproterozoic.