GEODYNAMIC EVOLUTION OF THE 600 MA PAN AFRICAN-BRASILIANO BELT IN CAMEROON

In Cameroon the 600 Ma Pan-African orogenic belt of central Africa has benefited in recent years from many petrographic, structural and geochronologic studies which have improved our understanding of belt. However those studies have also produced various and often divergent evolutionary models for the belt, some of which do not even involve well defined cratons. After review of available data, we propose a model of continent-continent collision which involved the Archean Congo craton and its north-facing active margin in north-central Cameroon as the southern component. This belt shows complex crustal evolution including Archean isotopic inheritance and Paleoproterozoic granulitic assemblages reworked during Pan-African orogenesis. This model is based on: (a) the prominent role of the Congo craton as shown by regional extension of external nappes on its northern edge and exhumation of 620 Ma high-P granulites representing the root of the collision zone; (b) granitic plutonism which includes pre- to syn-collisional calc-alkaline rocks, post-tectonic alkaline high level massifs, and crustal melting with S-type granites; and (c) late development of strike slip faulting in central Cameroon as the result of horizontal movement following multistage collision. In the Pan-African belt and its westward continuation in NE Brazil, the Brasiliano belt, a comparison of the kinematics and ages of deformation north of the Congo craton with those to the east of the West African craton suggests that the overall tectonic evolution of the mobile domain between both cratons was controlled by their relative motions during convergence.