Nature 305, 42 - 43 (01 September 1983); doi:10.1038/305042a0

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

J. P. Liegeois^*, H. Bertrand^†, R. Black^‡, R. Caby^§ & J. Fabre

^*Musée Royal de L'Afrique Centrale, Tervuren, Belgium
^†Laboratoire de Pétrologie, Université Claude Bernard, Lyon, France
^‡Laboratoire de Pétrologie et ERA 1011, Université Paris VI, France
^§Centre géologique et géophysique, Montpellier, France
Institut Dolomieu, Grenoble, France

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.

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