Lateral variations of apparent magnetic susceptibility of lithosphere deduced from Magsat data

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Abstract
A method for determining the lateral variations of the apparent magnetic susceptibility of lithosphere from a global scalar magnetic anomaly map is presented in this paper. The method is then applied to a magnetic anomaly map of the earth deduced from Magsat data, and a global magnetic susceptibility anomaly map of the earth's lithosphere is derived. The main features of the susceptibility anomalies are as follows: (1) Oceanic regions younger than about 80 Ma, except the South Indian Ocean, have almost no significant susceptibility variations; the anomalies are seen mainly in the older regions. (2) The Circum‐Pacific subduction zones have positive susceptibility anomalies. These phenomena can arise from different thermal states beneath the regions. High temperatures beneath the younger oceanic regions cause demagnetization, while low temperatures beneath the subduction zones enhance the effective magnetization of the lithosphere. (3) Continents tend to have relatively stronger magnetic susceptibility anomalies than oceans, indicating that the oceanic lithosphere is magnetically more uniform than the continental lithosphere. (4) Small‐scale Archean nuclei of shields have positive susceptibility anomalies, while there is no obvious correlation between anomalies and major shields. (5) Most of the aulacogens associated with the rupture of the Atlantic Ocean have negative susceptibility anomalies. These phenomena can be explained by models of the magnetized major shields, which are locally demagnetized and fragmented into several small segments by the hot asthenospheric intrusions into the recent aulacogens and by the underlying hot spots. (6) Some of the sedimentary basins associated with the old rifts have positive susceptibility anomalies, while some of the mountain ranges and modern uplifts have negative anomalies.