Mean magnetic contrasts between oceans and continents

The magnetic contrast between continents and oceans is an important constraint for understanding the regional distribution of magnetic sources in the crust and upper mantle. This magnetic difference was investigated using satellite 〈2°C〉 scalar magnetic anomalies collected by NASA's MAGSAT mission over the Atlantic and eastern Pacific Oceans, North and South America, Europe, and Africa. Reducing the magnetic anomalies differentially to vertical polarization yields mean anomaly values which correlate with the tectonic ages of the various continental and oceanic regions. The range of magnetic anomaly values of tectonically older lithosphere is greater than that of younger lithosphere. Statistically at the 99.9% confidence level the mean radially polarized magnetic anomaly of the continents is greater than that of the oceans. A careful inversion was performed for regional effective susceptibility contrasts which accurately fit the MAGSAT data assuming a model in which the Moho represents a boundary between crustal magnetic and predominantly non-magnetic mantle rocks. The root mean square of the magnetic properties of oceans compares favorably with magnetic properties predicted from models constrained by magnetic studies of the oceanic rocks and which incorporate viscoremanent components from rocks near the base of the crust. The mean magnetic anomaly and property contrasts of the oceans are negative and show large variability, indicating widespread deviations from the "standard" oceanic crust. The effective susceptibility contrasts obtained facilitate quantitative testing of inferences concerning large-scale petrologic variations, crustal thickness and thermal perturbations, and other geologic processes which control the regional distribution of magnetic properties within the lithosphere.