Petrography and geochemistry of mantle xenoliths from Ibal-Oku region (North-West region, Cameroon): Preliminary evidence of mantle heterogeneities

Abstract

Located on the central part of the continental section of Cameroon Volcanic Line, Oku Mountains are one of the largest massifs of this volcano-tectonic structure. These mountains contain ultramafic mantellic xenoliths of peridotites and pyroxenites accidently reared by the Ibal-Oku recent basalts. Petrographically, the peridotites are composed of Fe-rich lherzolites and wehrlites (mg# between 82.7 and 89.9) whereas pyroxenites which constitute the majority of the xenoliths consist of websterites and olivine-websterites (mg# range 80.1–83.6). Some of the pyroxenites Cpx embody apatite and calcite and numerous fluid inclusions. From a geochemical point of view, the study of these xenoliths shows that the upper mantle of the Oku region in general and that of Ibal-Oku in particular has undergone at least two major events: the variations observed among the major elements and some compatible elements can be described in terms of partial melt, whereas the observed heterogeneities in trace elements and rare earths are related to carbonatitic metasomatism. Peridotites are Fe-rich, likely as a result of basaltic melt percolation. Texturally, these xenoliths have secondary protogranular and porphyroclastic textures and bear marks of deformation from the upper mantle. This mantle underwent a lithospheric uplift marked by the presence of clinopyroxenes exsolution lamellae in the orthopyroxenes and screws towards it.