| Abstract: | Using the Bullard predrift reconstruction for the southern Atlantic, analysis of the major gravimetric trends of the West African craton (2000 Ma) and the surrounding mobile belts allows us to delineate the upper Proterozoic shield boundary and to put forward an evolutionary model for late Precambrian time.Over the cratonic area gravimetric anomalies are related to a basement framework or to sedimentary basins whose geometry is linked to reactivation of ancient faults. Gravity anomalies and LANDSAT imagery show a NE-SW lineament in West Africa which can be correlated with a variety of geologic features, the largest being the late Precambrian Gourma aulacogen.At the margins of the craton the deformation patterns and gravity signatures associated with the 600 Ma orogeny were largely controlled by the geometry of the stable craton itself. On the eastern edge (Pan-African belt and Brazilian belt east of the São Luis and Amazonian cratons), the distribution of the anomalies and deduced structures can be explained by a continental collision process. On the western and southern edge (Brazilian belt between the São Luis and Amazonian cratons, Rokelide belt, Mauritanide belt) the gravity signature is different, suggesting a large amount of intensely tectonized basic rocks. A limited spreading process followed by an intense compressional episode is suggested. |
