Magnetic anomalies at satellite altitude over continent-ocean boundaries

Abstract

A pronounced difference in vertically integrated magnetization produces strong magnetic anomalies at satellite altitude over continent-ocean boundaries. However, these anomalies are seldom seen in satellite anomaly maps. Our simulation of the technique normally used to extract anomaly fields from satellite observations of the geomagnetic field suggests that power leaks from short-wavelength crustal anomalies into the longer wavelengths. This phenomenon distorts the anomaly field and adds power to the lower degrees in the anomaly field power spectrum. We will also show that some of the few magnetic anomalies observed in satellite anomaly maps over continent-ocean boundaries in the Atlantic ocean could be caused by thermal destruction of magnetic minerals rather than by a pronounced difference in vertically integrated magnetization. The very low permeability of sediments deposited along continental margins basically precludes convective heat transfer in the sediments. The low thermal conductivity of these sediments results in the underlying lithosphere having a high temperature due to the temperature gradient within the sediment blanket. Our calculations predict that thermal destruction should occur along continental margins where several kilometres of sediments have accumulated. In order to produce magnetic anomalies similar to MAGSAT anomalies, we assume that the upper mantle is magnetized.