An interpretation of magnetic signatures of subduction zones detected by MAGSAT

Abstract The magnetic anomalies detected by MAGSAT over subduction zones are related to the thermal state and the location with respect to the geomagnetic poles of the subducting oceanic lithosphere. It is shown that an old (about 100 m.y.) subducting lithosphere produces about twice as strong a magnetic anomaly as that associated with a young (about 40 m.y.) one. Also, a given subducting oceanic lithosphere produces a stronger magnetic anomaly at high geomagnetic latitudes than near the geomagnetic equator. Based on the thermal evolution models of the oceanic lithosphere, and assuming a mean magnetic susceptibility of 13 × 10 −3 SI, the Pacific plate subducting along the Kuril trench produces a magnetic anomaly similar to the observed one. The Nazca plate subducting along the Peru-Chile trench produces a magnetic anomaly of less than 0.5 nT. No distinct anomaly observed by MAGSAT over this region.