Crust-mantle interaction processes in an Australian Proterozoic intracontinental boundary revealed by Gravity Inversion and Seismic Studies

Abstract:

The composition and lithospheric architecture of the continental crust between the West Australian Craton (WAC) and the North Australian Craton (NAC) is poorly understood. The nominally Proterozoic terranes are buried beneath thick and extensive Phanerozoic cover and are of unknown age, composition, and origin. Furthermore, the internal structure of the lithosphere derived from seismic models suffers from both poor data coverage and nonuniqueness. Here, we infer crust and uppermost mantle compositions and identify structures within continental crust between the WAC and NAC. We achieve this by performing 3D seismically-constrained gravity inversions in which we retrieve crustal and mantle densities and Moho depths. The numerous models are interpreted in conjunction with active and passive source seismic models, wells data, and geologic mapping that assist with inferring geological processes at the crust-mantle boundary. We use different P wave speed models to derive seismic Moho depths that we compare with our gravity results. Comparison between gravity and seismic models resulting from different assumptions aided us in restricting outcomes. We employ a hypothesis-based approach in which the mass-balance of the net gravity is explained by different tectonic scenarios that fit both gravity and seismic data. Our results indicate that the Paterson Orogen consists of a high-grade lower crust with an inferred felsic to intermediate bulk crustal composition and a complementary metasomatized mantle resulting from convergent tectonics. In contrast, the eastern Kidson sub-basin has an inferred intermediate to mafic high-density bulk crustal composition interpreted to reflect mantle-derived magmatic additions to the lower crust and crustal anatexis associated with the occurrence of Proterozoic to Cambrian LIPs. In the coastal Canning Basin, a mafic high-density lower crust is suggested to be associated with Phanerozoic magmatism.