Constraining the VanDieland microcontinent at the edge of East Gondwana, Australia

Abstract

Using airborne magnetic and marine gravity data, the geological subdivisions of western Tasmania have been interpreted north across Bass Strait into Victoria. The three westernmost Tasmanian zones, the King Island, Rocky Cape and Burnie zones, are inferred to form the largely concealed Selwyn Block in Victoria. The Eastern Tasmania Zone correlates with the Victorian Tabberabbera Zone. Thus the Tasmanian Tamar Fracture Zone corresponds with the Victorian Governor Fault. The Victorian Ceres Gabbro is correlated with magnetic rocks west of King Island that are tentatively considered to be Neoproterozoic. Most of the Cambrian felsic volcanic rocks of the Tasmanian Mount Read Volcanics lie above the Burnie Zone, as do the similar rocks exposed in the Jamieson, Licola and Glen Creek windows in central Victoria. Reinterpretation of a Victorian deep seismic reflection line indicates Burnie Zone equivalent rocks were thrust south-west over Rocky Cape Zone equivalents.A link between western Tasmania and central Victoria is evident from Upper Devonian granites intruded into the Selwyn Block region. The eastern end of the Upper Devonian Cobaw Complex and the Warburton Granodiorite contain calcsilicate enclaves interpreted to be derived from a northern equivalent to the Smithton Basin. The Mount Disappointment Granodiorite has high Ni and Cr contents and pseudomorphs after orthopyroxenes, consistent with having been partly sourced from the underlying basaltic rocks like those on the eastern margin of the King Island Zone. The magnetic responses under the Strathbogie Complex, the Cerberean Caldera and the Lysterfield Granodiorite are attributed to metamorphism of part of an extension of the Smithton Basin, probably equivalents to the 580Ma Spinks Creek Volcanics. Quartzite cobbles in a Devonian conglomerate in the south-eastern Melbourne Zone may be derived from Rocky Cape Group equivalents. When integrated with the geological interpretation of Tasmania, we provide a stratotectonic map of the VanDieland micro-continent.