Tectono-magmatic reactivation of Téfidet Cretaceous trough during Cenozoic (Aïr, Niger)

Abstract

The Tefidet trough (eastern Niger) belongs to the Tenere megasystem set of Cretaceous rifts N130°E to N170°E oriented, corresponding to the direction of the Lake Chad-Hoggar tectonic axis. The study of the relationship between the structure of the trough and alkaline fissural volcanism that developed there from the Oligocene to Plio-Quaternary shows the uniqueness of the Tefidet trough compared to the neighboring contemporary volcanic areas of Hoggar, Cameroon, and southern Air. The tectono-magmatic reactivation of the Cretaceous Tefidet trough developed in two steps: – a period contemporaneous with the Tuareg shield bulging (Air, Hoggar, Iforas); – a subsequent extension period generally N060°E, which has persisted since the opening of the South Atlantic (upper Jurassic to Plio-Quaternary). The fissural volcanism, due to the reactivation of Pan African and Cretaceous faults evolved concomitantly with the N060°E extension (syn-magmatic micro-fractures with basaltic filling), in several steps, from Oligocene to Plio-Quaternary. This study highlights the existence of periods of quietness and recovery of volcanic activity, for which two assumptions can be made: – no enough absolute datings, – apolyphased extension of the rift. The latter hypothesis seems to be supported by three periods of volcanic quietness, 28–24 m.y., 20–14 m.y. and 8–5 m.y., observed in the northern and the southern Air, Greboun and Todgha, respectively.