Permian alkaline undersaturated and carbonatite province, and rifting along the West African craton

Abstract

Recent work^1,2 carried out in north-east Mali, which showed the Pan-African orogeny (600 Myr) to be the result of a collision between the passive margin of the West African craton and the active margin of a continental mass situated to the east, has also outlined an entire province of alkaline undersaturated ring complexes and carbonatites, the first to be discovered in West Africa excluding Morocco^3,4 (Fig. 1). This province is quite distinct petrologically and structurally from the Iforas alkaline younger granite province situated in the Pan-African domain east of the suture which has yielded Rb/Sr whole-rock ages of between 560 and 520 Myr (ref. 5). The undersaturated province is located along a well-defined rift on the edge of the West African craton which is totally devoid of Pan-African magmatism. We report here that the Permian radiometric age obtained for one of these intrusions shows the existence of a hitherto unsuspected important tectono-magmatic event in this part of Africa, which may have far-reaching structural implications as well as economic interest.