Mantle sources beneath the Cameroon Volcanic Line: geochemistry and geochronology of the Bamoun plateau mafic rocks

Abstract

The age and origin of the volcanism along the Cameroon Volcanic Line (CVL) are still a matter of debate. We present major and trace element compositions as well as Sr–Nd–Pb–Hf isotopic results for mafic rocks from the Bamoun area, in the central part of the Cameroon Volcanic Line, as well as for two samples from recent eruptions of Mt. Cameroon. Lava flows are mostly basalts and hawaiites with transitional affinity. Some samples are among the oldest rocks of the CVL, with ages older than 51 My while some rocks are very young, around 0.05 My. All the samples are enriched in incompatible elements, indicating that melts were formed in a garnet-bearing mantle source. Different mantle sources participated to the formation of the Bamoun lavas. One source is isotopically similar to the main volcanic rocks of the CVL and probably represents an important part of the subcontinental lithospheric mantle. The second source is enriched in incompatible elements and shows a marked positive Eu anomaly, probably related to the participation of pyroxenites in the partial melting processes. The third mantle source is similar to the source of the Mt. Cameroon. This mantle source was known previously only in the Mt. Cameroon lavas, and we report its occurrence for the first time in old lavas and in other location along the CVL.