The resistivity structure of the crust and upper mantle in the central Eromanga Basin, Queensland, using magnetotelluric techniques

Abstract

Abstract Magnetotelluric data from the central Eromanga Basin indicate that one‐dimensional resistivity models are appropriate for the region. The uppermost Jurassic‐Cretaceous Eromanga Basin sequence contains flowing aquifers and has an average section resistivity in the range 1 to 7 ohm m with a mean of 4 ohm m. This overlies the older sedimentary sequences of the Cooper (Permo‐Triassic) and Adavale (Devonian) Basins with resistivities in the range 10 to 400 ohm m, which present good resistivity contrasts for determining sub‐surface morphology at the base of the Eromanga sequence. The depth extent of the older sequences is not well resolved because of the overlying highly conductive layers, but it appears to be greater than that determined from seismic reflection data in the Coonavalla Syncline and Warrabin Trough. Basement rocks of the Thomson Fold Belt have resistivities in the range 750 to 3800 ohm m with an average of 1300 ohm m. This resistivity is evident to depths of 40–60 km, and consequently represents the conductivity of the Earth's crust in the region. No highly conductive layers were detected within this crustal sequence. In the depth range 60 to 150 km, resistivities decrease to less than 5 ohm m. Such resistivities at 150 km depth are in broad agreement with data obtained from magnetometer array studies in southeastern Australia, which are explained by other authors in terms of a 5% partial basalt melt. Key words: Magnetotelluric datacrustupper mantleEromanga BasinQueenslandresistivityconductivityaquifers