Petrology and geochemistry of monogenetic volcanoes of the Barombi Koto volcanic field (Kumba graben, Cameroon volcanic line): Implications for mantle source characteristics

The Barombi Koto volcanic field (BKVF) is located northeast of Mount Cameroon and constitutes a portion of the Kumba graben, one of the monogenetic volcanic fields of the Cameroon volcanic line (CVL). Tortonian fissural eruptions yielded picritic flows reworked by subsequent explosive eruptions, which generated two maars and ten cinder cones. The lavas comprise picrobasalts, basanites, alkali basalts, and hawaiites. Some clinopyroxene crystals exhibit a Cr-reverse zoning (0.15 to 0.58 wt%) that we attribute to a subsequent magma Cr-enrichment. Lavas are alkaline and range from primitive to moderately evolved. They are similar to volcanics of the other monogenetic volcanic fields of the CVL (e.g., Tombel, Nyos), but contain less incompatible elements than polygenetic volcanics. The absence of correlations on bivariate plots of most of the incompatible elements, the wide variability of Zr/Nb and Ba/La ratios (4.41–6.04 and 6.87–11.14, respectively) and the values of Dy/Yb, La/Yb, Nb/Y and Zr/Y ratios suggest that the different volcanic centres correspond to independent plumbing systems, resulting from low degrees of melting (2.12–6.85 wt%) of a heterogeneous asthenospheric mantle source characterized by a HIMU prevailing component.