Etude structurale par la méthode audiomagnétotellurique des complexes du Protérozoïque inférieur au Sénégal oriental

Audiomagnetotelluric (AMT) soundings have been made at 14 sites along a 7 km profile in the Tonkouto-Léoba area across Early Proterozoic formations of the Kedougou Inlier in Eastern Senegal. The purpose of the study was to gain information about the electrical properties of the Mako Supergroup. The results, shown in the form of apparent resistivity pseudosections, indicate marked anisotropies for orthogonal components recorded at all sites. Consequently, two-dimensional (2-D) modelling is required to establish the electrical characteristics of the major geological units. The modelling results indicate resistivities in the range 20 000– 100 000 Ωm for the Early Proterozoic units which extend to depths of 18 km. A major discontinuity characterized by a resistivity of 1000 Ωm may arise from a structural change associated with the southeastern boundary of the Kakadian batholith. Beneath the highly resistive formations, a sharp fall of resistivity has been detected, which may be due in part to the presence of trapped fluids.