Contribution de la géophysique a l’investigation structurale et tectonique superficielle et profonde du Cameroun : Afrique centrale

Abstract

This work concerns at geophysical investigation of the Cameroon lithosphere from gravity and magnetic data. The aim is to determine the geometric parameters of the Cameroon Volcanic Line (CVL) from geophysical models in order to better Understand its origin, its tectonic implication on the Pan-African Chain and its geodynamic interaction with the Congo Craton (CC). The simple methodical approach, based on the exploitation of numerical filters for qualitative and quantitative analyses of Bouguer anomalies and total magnetic field, allowed to study the behavior of geological structures on the CVL, CC and to reveal that these two megastructures are not only of mantle origin but also have a mantle interconnection. The multiscale analysis of these anomalies allowed us to propose a precise geophysical lineament map in order to obtain a synoptic view for identity of a complex and multifractured tectonic context of the Cameroon lithosphere. The 2D1/2 modeling of gravity anomalies along five selected profiles allowed us to hypothesize the existence of several hot spots in the lithosphere,probably at different depths, triggered by convective flows from the lower mantle to explain the origin of the CVL and to highlight the geometry of the geological structures in the region. Our models show that thrusting and uplift of the deep crust at the northern boundary of CC would have forced the South Pan-African domain block fragments associated with granulite metamorphism to tilt towards the Neoproterozoic juvenile crustal granitoids of the North Pan-African domain and the Cenozoic volcanic-plutonic structures of the West Pan-African domain of the CVL. Thus, if our interpretation is correct, it may explain the geodynamic interaction between the CVL and CC as a mechanical compressional constraint of the volcanic and volcano-plutonic structures of the CVL by the lithospheric structures of the cold mantle of CC, the dense structures of the Adamawa Plateau and the Benue Trough.