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ABSTRACT: Western Tasmania: Geophysics and Mapping of a "Passive" Wrench Margin

MOORE, AIDAN, Bureau of Mineral Resources, Canberra Australian Capital Territory, Australia, P. W. BAILLIE, Department of Resources and Energy, Rosny Park, Tasmania, J. B. WILLCOX, Bureau of Mineral Resources, Canberra Australian Capital Territory, Australia, and J. PEMBERTON, Department of Resources and Energy, Rosny Park, Tasmania

The top of the acoustic basement has been mapped for some 600 km along the western margin of Tasmania, on the shelf and upper

slope. The area comprises the southern sector of the Otway basin and the entire Sorell basin. Within the Sorell basin on the continental shelf, four rhomboidal depocenters of significant (3 km or greater) sediment accumulation are termed the King Island, Sandy Cape, Strahan, and Port Davey subbasins: the main basin depocenter lies on the continental slope. The margin is at the eastern extremity of a series of predominantly extensional basins of Late Mesozoic and Cainozoic age which formed in response to rifting and separation of the Australian and Antarctic Plates. Basin development probably began about 160 million years ago. A slow sea-floor spreading episode is generally considered to have commenced at about 95 Ma, with faster sea-floor spreading commencing at 43.5 Ma. Unlike the ba ins to the west, which some have regarded as "classic" continental margin extensional basins, those on the Tasmanian margin formed within a highly-oblique, extensional ("transtensional") tectonic regime, related to left-lateral movements between the major plates. Major Cainozoic structures occurring onshore in western Tasmania may be interpreted as belonging to the same wrench assemblage and are also consistent with left-lateral movements.

 

AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)