The structure and evolution of the Bass Basin as delineated by aeromagnetic data

Abstract

The Bass Basin, a failed Mesozoic rift, located offshore between Tasmania and Victoria, was formed by extension associated with the separation of the Australian and Antarctic continents. Integration of the first available complete aeromagnetic coverage of the area, newly available gravity data, existing seismic data, drillhole information and outcrop geology mapping, indicates that northeast?southwest tension ruptured and separated fragments of the upper crust to create a depocentre up to 60 km wide. Fracturing along pre-existing basement lithological contacts and structures allowed transfer fault movements to accommodate this extension. Three main compartments developed in the basin, each of which underwent different degrees of extension. These compartments overlie accumulations of dense magnetic mafic material, evident on 14 s seismic reflection data, which were apparently produced by a mantle decompression process associated with crustal thinning. The largest of these mafic bodies displays the characteristics of a preserved, embryonic, oceanic spreading centre.