Evolving 3D lithospheric resistivity models across southern Australia derived from AusLAMP MT

Abstract

The Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) is an eventual continent-wide deployment of long-period (10-10 000 s) magnetotelluric instruments in a half-degree interval (~55 km) grid across Australia to map the electrical resistivity structure of the continental lithosphere. AusLAMP aims to provide constraints on the tectonic evolution of the continent and the mineral exploration potential as part of the UNCOVER initiative. The coverage of sites in South Australia is nearing completion with about 350 out of 400 sites acquired to date. The survey has already provided new insights into the South Australian subsurface, and will continue to do so as the final stages of data are collected in the APY lands and modelling continues. Areas of economic potential or interest covered by the survey include the Mesoproterozoic Coompana Province, the mineral-rich Archean-Proterozoic Gawler Craton beneath cover of the Neoproterozoic Stuart Shelf, extending across to the east to cover the Neoproterozoic Ikara-Flinders Ranges and Paleo-Mesoproterozoic Curnamona Province. The central Gawler Craton is imaged as a resistive zone with conductive margins surrounding the core of the cratonic block at shallow upper mantle depths. Seismic tomography models across the almost-cratonic Curnamona Province show a fast velocity structure however very low resistivities in the crust indicate an enrichment in carbon and/or hydrogen. The most recent acquisition covers the NE of the state in the Cooper Basin and the Simpson Desert, an area that has minimal coverage by any deep-probing geophysical techniques. Preliminary results indicate the presence of a north-south trending conductor, with final modelling results presented at the AEGC 2018. The results of the inversions of the AusLAMP data highlight the correlative significance with other geochemical data and points towards MT as a geophysical fertility vector for mineral discovery.