PALEOGEOGRAPHIC RECONSTRUCTIONS OF THE PAN-AFRICAN BRASILIANO OROGEN - CLOSURE OF AN OCEANIC DOMAIN OR INTRACONTINENTAL CONVERGENCE BETWEENMAJOR BLOCKS

A reconstruction of the Pan-African/Brasiliano orogen has become possi ble thanks to new data from the southern Pan-African belt and by using published data. Geological mapping, which included structural, thermo barometric, and geochemical studies in Togo and neighbouring countries have enabled to define the existence of a pre-orogenic continental ri ft, whose closure followed soon after its opening. Continental crust c onvergence induced an oblique collision that caused nappe stacking. Th is involved external nappes thrust over the West African craton, inter mediate nappes including metabasic rocks with eclogitic assemblages, a nd internal nappes composed of high-grade anatectic gneiss, and intrus ive granite and charnockite. Comparison with data from other regions ( Hoggar, Adrar des Iforas, northeastern Brazil, Nigeria, Central Africa ) has led to the recognition of a pre-orogenic continental rift that b ordered the West Africa/Sao Francisco/Congo cratons in the southern pa rt of the chain. Farther north, in the Hoggar and Adrar des Iforas, th is continental rift opened on a wider oceanic domain, which involved a passive margin along the West African craton and an active margin to the east. After these rifting and subduction stages, continental colli sion followed that was dominated by strike-slip movement oblique to th e plate boundaries. The general organization of the Pan-African/Brasil iano belt can be considered as the result of a confrontation between t hree major continental domains. These were the West African and Sao Fr ancisco/Congo cratons, and a reworked shield composed, in its inner pa rt, of polycyclic basement rocks, and bounded by a fringe of monocycli c metasedimentary thrust belts that faced the cratons.