A crustal conductor on Eyre Peninsula, South Australia

Abstract

Short period variations in the geomagnetic field components were recorded in a closely spaced network of sites on southern Eyre Peninsula, South Australia. They reveal the existence of a linear zone of very good electrical conductivity within the late Archaean–early Proterozoic Gawler Craton. There is strong enhancement of the horizontal component variations transverse to the zone and an abrupt phase change in the vertical component, particularly for periods near 2×103s. These features are consistent with a line or narrow thin sheet of current flowing in a conductor at a depth ⩽10 km; this almost certainly requires a major fracture or shear zone within the crystalline basement, for which there is supporting geophysical evidence. Superficial Cenozoic deposits blanket much of the area and consequently the basement geology is not known in detail, although there are structures parallel to the conductor 20 km to the east. Identification of a major linear crustal feature in such an area demonstrates the usefulness of geomagnetic variation studies for understanding deep geology.