Interpretation of CHAMP Crustal Field Anomaly Maps Using Geographical Information System (GIS) Technique

Crustal field models from CHAMP magnetic measurements are increasingly stable and reliable. In particular, they now allow for quantitative geological studies of crustal structure and composition. Here, we use a forward modeling technique to infer deep crustal structure of continental regions overlain by younger sediments. For this, a Geographical Information System (GIS) based technique has been developed to model the various geological units of the continental crust. Starting from geologic and tectonic maps of the world and considering the known rock types of each region, an average magnetic susceptibility value is assigned to every geological unit. Next, a vertically integrated susceptibility (VIS) is computed for each unit, taking into account the seismic crustal thickness, as given by models 3SMAC and CRUST2.1. From this preliminary VIS model, an initial vertical field anomaly map is computed at a satellite altitude of 400 km and compared with the corresponding CHAMP vertical field anomaly map. We demonstrate that significant geological inferences can be made from the agreement and the discrepancies between the predicted and observed anomaly maps. In particular, the lateral extent of Precambrian provinces under Phanerozoic cover is revealed.