Palaeomagnetic Tests of Tectonic Models of the Tasman Fold Belt during the Neoproterozoic and Palaeozoic

Abstract

Current palaeomagnetic data support a late Mesoproterozoic (1050 Ma) to mid-Neoproterozoic (725 Ma) reconstruction in which Laurentia (North America) was juxtaposed against the eastern margin of Australia and Antarctica. Neoproterozoic apparent polar wander paths (APWPs) for Laurentia and East Gondwanaland suggest that by the late Vendian (late Neoproterozoic III) the two continents were separated latitudinally by up to 50°, and by an unknown amount longitudinally. The breakup of Rodinia, arguably around 700 Ma, formed the Pacific Ocean, and implies that any ocean crust flooring the Tasman Fold Belt should date from that time. Tasmania, the only exposed Precambrian continental fragment in the Tasman Fold Belt, could have developed as part of a continental ribbon stranded in the Pacific Ocean. Most of the palaeomagnetic data from the Tasman Fold Belt comes from the Late Devonian to ?Early Carboniferous Lambian overlap assemblage, a circumstance which has helped calibrate the Australian APWP but left open questions about whether any of the older rocks are allochthonous with respect to the Gondwanan continental margin. Preliminary palaeomagnetic data from Tasmania suggest that northwestern Tasmania was in its current position with respect to the craton by the end of the Cambrian, and palaeomagnetic data from the Snowy River Volcanics in the eastern Lachlan Fold Belt are permissive of that part being adjacent to the Gondwanan continental margin by the earliest Devonian. More work is required on the Late Ordovician to Early Devonian and the mid-Carboniferous parts of the APWP of Australia and Gondwanaland, as well as in the Tasman Fold Belt, before questions about whether parts are exotic, or have rotated, can be addressed.