An interpretation of the western margin of the West African Craton in Senegal and Mauritania from gravity data

The ambient level of gravity field is lower over the West African Craton than over the adjacent younger Mauritanides province in West Africa. The stacks of Bouguer gravity profiles taken across the region over which the ambient gravity field is distinctly different on either side are broadly outlined by minima and maxima anomalies with well-defined steep gravity gradient separating them. The crustal structure on either side of this steep gradient is clearly different. To the east the negative anomalies are over the craton and to the west the positive anomalies are over the younger Mauritanides structure. The gravity maxima with an amplitude of about 50 mgal is considered as the gravity signature of the boundary between the two structural units. The western outline of the craton in Mauritania and Senegal has been delineated on the basis of this gravity signature. The interpretation suggests that there has been overthrusting of the Mauritanides onto the craton of between 50 to 120 km. In Senegal, this interpretation is in close agreement with seismic result which indicates thrusting of about 80 km of the Mauritanides onto the craton. The western limit of the craton in the study area is concealed beneath Mauritanides fold belt making gravity survey more appropriate tool for its delineation than surface mapping as it can delineate structural boundary over hidden basement or where structural units have been overthrust.