Section 5 Continental rifting and continental margins: implications from structural and sedimentological studies Coincident with the fragmentation of Gondwanaland there was continued exploitation of lineaments leading to continental separation and the development of continental margins from the Cretaceous onwards. As well as the development of marginal basins ancient lineaments are exploited leading to continental rifting. Such features are an important facet of African geology which is still evolving to the present day. This section therefore covers all aspects pertinent to the study of lineaments, sedimentary basins, magmatism, and the evolution of continental margins on the African plate.
During the evolution of the Alpine fold belt in North Africa, deformation occurred within the African plate, and Precambrian/Palaeozoic fracture systems were reactivated as major lineaments. One set of lineaments follow east-west trends in North Africa, and from Guinea to the Nubian Province in west, central and north-eastern Africa. The other set constitute major megashears orientated approximately north-south. This study which is presented as the first paper in Section 5 is a welcome review by Guiraud and his cci-workers on post-Hercynian tectonics, particularly in North Africa and West Africa. The authors suggest that magmatic activity with alkaline affinities, and folding, are considered to be related to major fault systems especially in northern Cameroon and the Mamfe basins. In the Benue trough an intracontinental chain with abundant igneous intrusions can be correlated with the opening of the Atlantic near the Gulf of Guinea. The authors suggest that the whole of the African continental domain from the Alpine chain to Cameroon and southern Chad, was subjected to post-Hercynian deformation. If the Alpine continental margin has structures which demonstrate compression, then in contrast the Atlantic margin off the western coast of Africa can be modelled as a contrasting extensional regime, linked to shearing along transform fault systems. Intraplate deformation can be correlated with six tectonic episodes in various regions of the North African continental domain identified as occurring 0 1987 by John Wiley & Sons, Ltd.