Structural Architecture of the Otway and Sorell basins derived from potential field modelling

Abstract

The deepwater Otway and Sorell basins developed during the breakup of Gondwana when Australia rifted from Antarctica. Regional 2D and 3D gravity modelling in conjunction with seismic and geological interpretation has led to an improved understanding of basement architecture in the study area. 2D gravity modelling along selected seismic lines reveals a N-S crustal-scale lineament extending to the Moho. A distinct density contrast of 0.16 t/m3 (i.e., between 3.05 t/m3 and 2.91 t/m3) across the structure points to significant lithological changes at middle to lower crustal depths, interpreted here to reflect a change from dominantly mafic to felsic lower crust. This structure is interpreted to be inherited from a pre-existing basement structure and supports the hypothesis that the evolution of the Sorell Basin was influenced by this basement structure. The 2D models also infer the presence of mafic under-plating in the lower-crust. The computed 3D gravitational response derived from interpreted seismic data correlates moderately well to the observed gravity interpretation and (a) implies consistency between the seismic and gravity response of the interpreted model, and (b) delineates the basement topography and identifies possible depocentres. The independently-derived depth to magnetic basement map supports the 3D forward gravity modelling results.