Mount Cameroon: an active volcano of the Cameroon Line

Abstract

Mt Cameroon is a large volcanic horst which belongs to the Cameroon Line. The morphology of the massif depends on tectonic control. Mt Cameroon is built upon a Precambrian metamorphic basement covered with Cretaceous to Recent sediments of the Douala and Rio del Rey basins. The oldest lavas could be of Upper Miocene age. Mt Cameroon has erupted six times in the 20th Century. The 1982 eruption took place inside the crater of an ancient cone. Volcanic risks are actual for the human constructions, mostly along the axis of the horst. The lavas are picrites (with forsteritic olivine phenocrysts), alkali basalts (with salitic augite phenocrysts), hawaiites (with labrador-bytownite plagioclase phenocrysts) and mugearites (with scarce kaersutite phenocrysts and microlitic phlogopite or nosean). FeTi oxides phenocrysts are ubiquitous. All the lavas are Ne-normative. The distribution of major and trace elements in the lava series is well explained by fractionations of the minerals found as phenocrysts, but plagioclase does not fractionate (Sr and Eu contents in the lavas increase with the differentiation). Thus, olivine, augite and FeTi oxide fractionations are respectively correlated with MgNi, CaCrSc and TiV distributions. Primitive magmatic liquids contain about 1 ppm uranium. Ta-Th-Hf correlation and REE distribution clearly indicate that the Cameroon lava series is typically alkaline with no tholeiitic or transitional trend. This fact asserts that the Cameroon Line is not a rift system but the result of tension gashes due to the Adamaoua sinistral strike-slip faulting zone.