Geoelectric structure of Tasmania from multi-scale magnetotelluric data

The current understanding of Tasmania’s enigmatic tectonic history has been informed by geological information observed or sampled at the Earth’s surface coupled with geophysical data sets sensitive to magnetic, density and seismic properties of the rocks forming the crust and mantle beneath. With the completion of the Tasmanian portion of the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP), new 3D and 2D geophysical models describing the electrical properties of the Tasmanian lithosphere at different spatial scales have been derived to compliment these data.

At the whole-of-state scale, 3D inverse models of the long period magnetotelluric (MT) data have illuminated the electrical structure of the mid-crustal to lithospheric mantle depths. This model images the full extent of the Tamar Conductivity Anomaly, a crustal-scale conductor extending from northern to southern Tasmania along the boundary between eastern and western Tasmanian geologic terrains.

In the west of the state, a 2D inverse model transecting the Cambrian Mount Reid Volcanics brings the electrical structure of the upper- to mid-crustal depth range in this economically important part of the state into sharper focus. The model images west-dipping conductive structures spatially coincident with major faults and associated copper mineralisation near Queenstown.

Finally, in the central east of Tasmania, a joint inversion incorporating legacy broadband MT data with newer AusLAMP MT data using the whole-of-state scale model as a priori geoelectric structure was conducted. Inversion results demonstrate a potential use case for regional scale AusLAMP models to improve higher resolution geoelectric structure modelling, with the joint inverse model imaging the Lemont geothermal field at higher resolution while simultaneously mapping geologically feasible 3D resistivity structures.