Pan-African rifting and orogenesis in southern to equatorial Africa and eastern Brazil

Abstract

The Upper Proterozoic Pan-African belts of Africa and Brasiliano belts of South America are assumed to have evolved from an elaborate system of continental rifts which formed on the West Gondwana continent 1100-1000 Ma ago. Reviews of the Damara belt, Kaoko belt, Gariep belt, Saldania belt, West Congolian belt, Lufilian Arc and Zambezi belt of southern and equatorial Africa and the Ribeira-Mantiqueira belt of Brazil show the applicability of the continental rifting model to all these belts. Strict application of the rifting model describing the formation and further evolution of rift structures in the continental crust leads to the conclusion that the West Congolian belt, as traditionally described, is incomplete and has to be supplemented by the Mayumbian belt and a rift structure situated farther to the west. The Lufilian Arc is assumed to have evolved from two rift structures separated from each other by the later ‘Domes region’. The ‘Golfe du Katanga”, which branches off northeastwards from the Lufilian Arc is interpreted as an aulacogen (‘Shaba aulacogen’). The Pan-African-Brasiliano rift system is comparable to the Mesozoic Arctic-North Atlantic rift system with regard to size and distribution of rifts. Ocean floor spreading and opening of a proto-South Atlantic Ocean most probably occurred along a main line of rifting situated between the west coast of Africa and eastern Brazil. The wedge-like ocean may have terminated at the ‘São Francisco-Congo cratonic bridge’ between northeastern Brazil and Gabon-Cameroon. There is no evidence of ocean-floor spreading in the Zambezi belt, the Lufilian Arc and the traditional West Congolian belt, which are arranged along another major line of rifting. Closure of the Pan-African-Brasiliano rift system took place during two successive orogenic episodes. The Zambezi belt, Lufilian Arc and West Congolian belt underwent their main orogenic deformation with prevailing ENE- and WSW-oriented tectonic transportation directions during the Katangan episode, at ∼900−750 Ma. The transcontinental sinistral Mwembeshi Shear Zone adjusted opposite movement directions in the Zambezi belt and Lufilian Arc and, at its western prolongation, concurrently supported opening of the Khomas Trough in the southern Damara belt. The proto-South Atlantic Ocean, still opening during the Katangan episode, was gradually closed during the Damaran episode, at ∼750−500 Ma. Closure proceeded from north to south and was accompanied by northwest-directed subduction underneath the Brazilian plate and southeast-directed tectonic transportation in the Kaoko, Damara and Gariep belts. In the previously formed West Congolian belt, Lufilian Arc and Zambezi belt a second deformation phase characterized by strike-slip faulting and local emplacement of nappes occurred during this episode.