Datensatz

Zusammenfassung

Reliable global crustal field anomaly maps produced from magnetic measurements of the CHAMP satellite mission now allow for quantitative geological studies of crustal structure and composition. We have developed a GIS based forward modeling technique to model these anomaly maps. On the basis of the geologic and tectonic maps of the world, laboratory susceptibility values of the occurring rock types, and the seismic thickness of the crust, a vertically integrated susceptibility grid is generated in the GIS system. In addition, a remanent magnetization grid is computed for the oceanic crust using a digital isochron map of the ocean floor and rotation models of the paleoplates. Combining the global VIS and remanent magnetization grids, the vertical magnetic field anomaly is computed at satellite altitude and compared with the corresponding CHAMP magnetic anomaly map. Over the oceans, induced and remanent magnetization explains well the prominent observed anomalies over the Cretaceous quiet zones. We also find a good agreement between predicted and observed anomalies over the continents. Remaining discrepancies between the predicted and observed anomalies can be used to adjust poorly known boundaries and the composition of the buried Precambrian provinces, until the recomputed anomalies fit the observed anomalies. The feasibility of this approach is demonstrated on Greenland, the West African Craton, Bangui in central Africa, and the Kolyma-Omolon Block in Siberia. We conclude that quantitative information on the lateral extent, the composition and the thickness of the lower crust within a Precambrian province can thus be inferred from the new satellite magnetic anomaly maps.