| Popis: |
A reconstruction of the Pan-African/Brasiliano orogen has become possible thanks to new data from the southern Pan-African belt and by using published data. Geological mapping, which included structural, thermobarometric, and geochemical studies in Togo and neighbouring countries have enabled to define the existence of a preorogenic continental rift, whose closure followed soon after its opening. Continental crust convergence induced an oblique collision that caused nappe stacking. This involved external nappes thrust over the West African craton, intermediate nappes including metabasic rocks with eclogitic assemblages, and internal nappes composed of highgrade anatectic gneiss, and intrusive 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 bordered the West Africa/Sao Francisco/Congo cratons in the southern part of the chain. Farther north, in the Hoggar and Adrar des Iforas, this 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 collision followed that was dominated by strike-slip movement oblique to the plate boundaries. The general organization of the Pan-African/Brasiliano belt can be considered as the result of a confrontation between three major continental domains. These were the West African and Sao Francisco/Congo cratons, and a reworked shield composed, in its inner part, of polycyclic basement rocks, and bounded by a fringe of monocyclic metasedimentary thrust belts that faced the cratons. |
