The North–South Paleozoic to Quaternary trend of alkaline magmatism from Niger–Nigeria to Cameroon: Complex interaction between hotspots and Precambrian faults

The alkaline magmatism from Niger–Nigeria to Cameroon forms large scale magmatic provinces across the African plate. It displays a N–S trend from Aïr in Niger to Jos Plateau in Nigeria changing southeastwards towards Cameroon. We have compiled recent petrological, geochemical and structural data on these magmatic provinces. The data show that although there is a general age decrease from one province to another (407 ± 8 Ma in Aïr to ⩽66 Ma in Cameroon), there is no age migration in any given province, except in the Nigeria province (Younger Granites) where a rough NE–SW age decrease is observed. The relationship between these different magmatic provinces that share similar geochemical data, added to the SW–NE parallel trends of Nigeria, Benue Trough and Cameroon Line, is difficult to explain in terms of a simple northward motion of the African plate over a single hotspot. In the light of recent tectonic models, we suggest complex interaction between, on the one hand, at least two mantle plumes acting in succession (including the St. Helena mantle plume) and, on the other hand, lithospheric fractures that induce oblique alignments of new magmatic complexes.