Magnetotelluric soundings over a Precambrian contact in Australia

Summary. The Willyama Complex near Broken Hill represents a major exposure of the Precambrian terrain in Australia. However, the eastern limits are obscured by recent cover in the Murray/Darling basin. The nature and extent of the contact with the younger basement to the east is unknown.
Magnetotelluric data have now been obtained as an aid to regional mapping. Profiles are based on observations at 14 sites in a traverse east of Broken Hill. Apparent resistivities presented as pseudosections reflect the major structural units identified from surface geology. Continuity between sites is indicated from similarity in apparent resistivities and lateral changes east of the Block are generally gradational.
Characteristic divergences in orthogonal resistivity components are consistent with 2-D structure. The foliated Precambrian complex appears to form a semi-vertical contact at the margin of the Murray/Darling basin, thus generating the required anisotropy at depths from 15–35 km. Seismic evidence indicates an equivalent structural contact possibly extending into the mantle.