The conductivity structure of the Georgina-Arunta region from magnetotelluric data

Abstract

We present an updated resistivity model from inversion of the 09GA-GA1 deep magnetotelluric survey, also known as the Georgina-Arunta survey. The data were originally collected in 2009 under Geoscience Australia’s Onshore Energy Security Program, together with deep seismic reflection data along the same line. The magnetotelluric data comprise broadband and long-period data. The broadband data were originally processed to a bandwidth of 0.04 s to 100 s, but have been reprocessed yielding an extended bandwidth of 0.04 s to 1000 s, which improves the resolution of deeper (>20 km depth) structures. Inversions have been carried out using the ModEM 3D inversion code given that the data indicate the presence of 3D geoelectric structure. The updated resistivity model reveals that the Casey Inlier and Irindina Province are associated with high resistivities (>2000 Ωm). In contrast, the Aileron Province, which underlies and surrounds the Irindina Province, is predominantly conductive (resistivities <50 Ωm). The Georgina Basin is associated with low resistivities, as would be expected for a sedimentary basin, while the Amadeus Basin is associated with low resistivities in the southern part of the line (where it overlies the Casey Inlier), and higher resistivities further north.