Mantle Xenoliths from Ibal-Oku (Oku massif, North-west Region, Cameroon): Imprints of Superimposed Carbonatitic and Silicic Metasomatisms

Mantle xenoliths have been discovered in Ibal-Oku basalts from Oku Massif, Cameroon Volcanic Line. These xenoliths analyzed in term of major elements by scanning electron microscope, atomic emission spectrometry, traces and rare earth elements by mass spectrometry are peridotites and pyroxenites. Peridotites comprise Fe-rich lherzolites, harzburgites and wehrlites. Pyroxenites comprise websterites, olivine-websterites, clinopyroxenites and olivine-clinopyroxenites. Mineralogically, olivine Fo% values and NiO content vary from 85 to 91 and 0.26 to 0.43 wt.%, respectively. Orthopyroxene is enstatite, Mg# values and Al content ranging from 0.83 to 0.92 and 0.12 to 0.27 atom per formula unit (apfu), respectively. Clinopyroxene is augite and diopside, Mg# values and Al content ranging from 0.83 to 0.93 and 0.23 to 0.37 apfu, respectively. Spinel is aluminous, Cr# and Mg# values ranging from 0.07 to 0.23 and 0.67 to 0.82, respectively. Micas are biotites (Fe#: 0.52-0.76). Feldspars, which are secondary are sanidine, andesine and labradorite. Geochemically, peridotite Mg# values vary from 82.7 to 89.9 and pyroxenites from 80.1 to 83.6. The major element variations and some compatible elements are described in terms of partial melting (14-15 vol.% in lherzolites and 17-18 vol.% in harzburgites), whereas the heterogeneities in trace elements are related to carbonatitic/silicic metasomatism.