Geochemistry of tertiary-quaternary lavas of Mt. Oku Northwest Cameroon

Abstract

The Oku massif occupies the central position amongst the continental sector volcanoes of the Cameroon Volcanic Line (CVL). Field observations, petrographic major, trace and REE geochemistry show that lavas are basanite/alkali basalt-trachyte/rhyolite suited with a distinct compositional gap within the benmoreite field. This gap, which cannot be explained by sampling bias, may therefore reflect density filtration within the magmatic plumbing system. However, accumulation and fractionation of major mineral phases: pyroxenes, olivines and plagioclases appear to have controlled magma evolution. Fractional crystallization has been shown to be the major differentiation process that gave rise to the spectrum of magmas of this stratovolcano though crustal contamination in high level magma chambers cannot be precluded in this intraplate continental setting. K-Ar age determinations show that the volcanic activity in Mt. Oku occurred in three distinctive episodes 25-22 Ma, 18-14 Ma and < 1 Ma. There is no evidence for volcanic activity between 14 and 1Ma. Less than 1 Ma BP, activity resumed creating abundant cones and craters.