The origin and evolution of DMM-like lithospheric mantle beneath continents: Mantle xenoliths from the Oku Volcanic Group in the Cameroon Volcanic Line, West Africa

Abstract The lithospheric mantle as sampled by peridotite xenoliths in some continental settings resembles the source of mid-ocean ridge basalts (MORB). Whether this resemblance is a primary feature or result post-formation secondary processes remains controversial. Here, age, origin and thermochemical evolution fertile are constrained based on chemical composition minerals spinel-facies lherzolite websterite from Wum maar Befang cinder cone Oku Volcanic Group (Cameroon Line, West Africa), combined with in-situ Sr isotope compositions clinopyroxene fabric investigation Electron Backscatter Diffraction (EBSD). majority lherzolites (here assigned to I) consist (olivine Fo89, Al-rich pyroxenes, spinel Cr# 0.08-0.10). Clinopyroxene LREE-depleted has depleted 87Sr/86Sr (0.7017-0.7020). Crystal-preferred orientation determined EBSD reveals that clinopyroxene, sporadically both clino- orthopyroxene, post-date olivine framework. Subordinate II also contain which LREE-enriched higher (0.7033). In contrast, scarce III more refractory: they 72-78 vol. % olivine, Al-poor 0.18. (87Sr/86Sr 0.7021) texturally coeval orthopyroxene. Few amphibole 0.7031) post-dates nominally anhydrous minerals. Most websterites (Group A) aluminous (spinel 0.04-0.06) having ratios (0.7017-0.7020) similar I lherzolites. Chemical characteristics coupled crystal-preferred data suggests originated stability field reactive intergranular percolation an incompatible element-depleted MORB-like melt. A likely formed cumulates supposedly occur close lithosphere-asthenosphere boundary record interaction lavas Cameroon whereas shallow part profile represent protolith were formed. Local crystallization concomitant recrystallization host driven supply water event post-dating formation rejuvenated rocks. Migration alkaline melts CVL apparently did not significantly affect mineral mantle, allowed retain very low 87Rb/86Sr (average 0.002) clinopyroxene. This only indicates their Paleoproterozoic (~2.0-2.25 Ga), possibly during Eburnean orogeny at margin Congo craton, but surprisingly little influence regionally-recognized Pan-African event.