The ‘Cameroon Hot Line’ (CHL): A unique example of active alkaline intraplate structure in both oceanic and continental lithospheres

The Cameroon Hot Line (CHL) is an active N30°E tectono-magmatic alignment, extending from Pagalu Island to Lake Chad. Its oceanic sector is comprised of six major volcanoes, and the continental sector of seven major volcanoes, numerous monogenic cones and more than sixty plutonic anorogenic ring complexes. The lavas and plutonic rocks have the typical mineralogy of the alkaline series. Nephelinites and alkaline lamprophyres are also present. The basalts from the oceanic and continental sectors have similar trace elements and Sr and Nd isotope compositions, attesting that the source is sublithospheric and that the continental crust plays no significant role in the magma genesis. Uncommon intermediate lavas originate through mixing between basaltic and felsic magmas. The evolution from basaltic to phonolitic magmas is explained through crystal fractionation. Compositions of most continental trachytes and of rhyolites require a crustal component. Metasomatism of carbonatitic affinity affected the lithospheric mantle during the magma ascent. DM and FOZO mantle components were involved in the genesis of the CHL parental magmas.