Depth of the lithospheric mantle discontinuities beneath the northwest flank of Oku Volcanic Complex, Cameroon Volcanic Line: constraints from mantle xenolith and teleseismic data

In Northwestern Cameroon, the northwest flank of Oku Volcanic Complex forms part of the continental sector of the Cameroon Volcanic Line (CVL). Detailed study of petrology and mineral chemistry of nine mantle xenoliths from the NW flank of Oku Volcanic Complex with derived teleseismic data have been conducted to determine the nature and depth of the lithospheric mantle beneath the flank and CVL as a whole. Petrographically, mantle xenoliths are olivine websterite and plagioclase-spinel lherzolite consisting of a five-phase mineral assemblage (olivine, orthopyroxene, clinopyroxene, spinel and plagioclase) with varied textural changes (protogranular, porphyroclastic and porphyroblastic) characterizing the equilibrium conditions of the upper mantle. Mineralogically, magnesian olivine (forsterite and chrysolite), clinopyroxene (diopside), and orthopyroxene (clinoenstatite) with plagioclases (labradorite with rare bytownite) dominate. We propose hereditary representations to explain the occurrence of plagioclase in the mantle peridotites. (1) Subsolidus transformation of spinel to plagioclase, (2) crystallisation of melt pockets from partial melting of the upper mantle and (3) accumulations from melts that impregnated the lithospheric mantle. Velocity and synthetic models obtained from the inversion of the receiver functions indicate that the Moho depth or crustal discontinuity is 33.2 km for CM20 and 40.8 km for CM23 with a mean thickness of 37 km. The lithospheric mantle thickness is 28.1 km and 20.5 km for CM20 and CM23 respectively with a mean thickness of 24.3 km. The low velocity zone is located at intervals of 61.3 to 113 km, exhibiting a thickness of 51.7 km and 42.5 km for CM20 and CM23 respectively, resulting in a mean thickness of 47.05 km. The discontinuities are located at 37 km for the Mohorovicic discontinuity and between 61.3 km and 61.5 km for the Lithospheric-Asthenospheric Boundary. The occurrence of plagioclase in the mantle peridotite, coupled with results from the receiver function techniques, provides evidence of mantle upwelling beneath this region, particularly within the continental sector of the CVL.