Magnetic anomalies associated with the southeastern continental margin of South Africa

Abstract

A total magnetic intensity, iso-magnetic map is presented and discussed. Between East London and Durban large east-west trending anomalies are known on land and can be traced onto the continental shelf but not beyond the slope. Elsewhere the continental shelf is characterized by a remarkably quiet magnetic field. A feature of the map is the linear anomaly, named the Cape Slope Anomaly, which is parallel to the continental margin and coincides approximately with the 68° small circle about the early pole of opening for the South Atlantic as given by Le Pichon and Hayes (1971). The anomaly is traced between 30°54′S, 30°48′E and 37°45′S, 20°31′E and is interpreted as occurring over the truncated edge of a semi-infinite, sub-horizontal, remanently magnetized plate in oceanic crust beyond the continental margin. Between 37°03′S, 21°49′E and 37°41′S, 21°12′E the Slope Anomaly occurs over a ridge named the Agulhas Ridge. A continuous seismic reflection profile over the ridge shows acoustic basement occurring under a cover of sediments. A two dimensional model study indicates that the basement materials may belong to the body causing the anomaly with the exception of the basement material that forms the landward peak of the ridge, which is non-magnetic.