Seafloor magnetic patterns: seafloor spreading and magnetization in the Southern Ocean

Abstract

An extensive network of magnetic survey lines now extends over the Southern Ocean (Fig. 1). Measurements of total field have been made by ship, aircraft, and at high altitude from satellites. However, because of the vastness of the region, coverage is mostly at reconnaissance level, with some areas such as the Antarctic continental margin very sparsely mapped. Exploration by oceanographic institute research vessels equipped with towed magnetometers began in the early 1960s. The first surveys providing systematic coverage were made between 1968 and 1972 by the Eltanin, generally along north?south oriented lines spaced at 5°C of longitude. From these data, Weissel and Hayes (1972) were able to map the overall magnetic anomaly lineation pattern of the Southern Ocean seafloor, develop a tectonic framework for the region, and outline the development of the Australia?Antarctica separation. They placed the onset of seafloor spreading at Magnetic Anomaly (MA) 22. Cande and Mutter (1982) have since produced a revised interpretation, putting the initiation of spreading at about MA 34 (85 Ma) with much slower spreading rates prior to MA 18 time. Veevers (1986), in an analysis of all available data, concurs with Cande and Mutter's interpretation of an early phase of slow spreading, but has refined the time of initiation to 96 Ma.