Rachel Ngo Nyouma^{1, 2}, Henri Emile Pougue Eone³, Yvonne Poufone Koffi^{2, 4}, Edouard Olivier Ntomb Biboum^{2, 3,}, Alain Sterve Lepatio Tchieg^{2, 4}, Carole Bapowa Laouna¹, Willy Lemotio^{2, 4}, Patrick Mendi³

A structural study on the Adamawa Massif highlights the major structures (faults) of the shear zone as well as the igneous intrusion near Mayo Baleo. Through this study, a comparison on the use of gravity data from the EGM 2008 and terrestrial models was carried out on the basis of gridded gradient data obtained by applying the MAGMAP filtering algorithm on the Oasis Montaj software system. Using the gradients has an advantage in that they contain much information especially on geological structures. The resulting maxima have strong density contrasts, enabling them to be used as tools in explaining geological contacts. Gravimetric lineaments marked by the geometry of the peaks (elongated shape) and the igneous intrusion corresponding to the circular peak were detected on the horizontal gradient maps. Reconciliation with the geology, the slope map and satellite images justifies the presence of the Djohong-Ngaoundal-Dir-Tibati, Tibati-Banyo and Tignère-Banyo lineaments which indicate the underlying Foumban (extension), Tibati and Tcholliré-Banyo faults respectively, comprising the shear system residing in the massif underlain by a gneiss-migmatite bedrock. The limitation on the use of gravity data from the EGM 2008 model is manifested through the Djohong lineament correlating with the large mylonitized feature trending NE-SW, defined as a steep relief (27° to 60°), separating the Mbere basin from the upper unit with about 358 m in height difference. This terrain is a small area of relief with morphological units adapted as in the case of the mountainous areas of the West to the use of gravity data from the EGM2008. The other lineaments that are part of the shear zone fault system are not elucidated because they correspond to deep mega structures that the EGM 2008 model resolution cannot attain at depth. The use of this model is suitable for studies of superficial structures which are associated with huge formations such as the volcanic dome of Mayo Baleo, an intrusion of young trachytes with steep slopes (27° to 60°) at an altitude of 2419 m.

gravity, horizontal gradient, Bouguer anomaly, lineaments