Petrogenesis modeling of the alkaline volcanism of Ngaoundéré (Adamawa plateau, Cameroon, Central Africa)

Abstract

New insights on geochemistry of the alkaline volcanism of Ngaoundéré in Adamawa plateau enable the petrogenesis modelling of Ngaoundéré Miocene lava series. Mass-balance crystal fractionation, closed-system Assimilation, Fractional Crystallization (AFC) and partial melting rate modeling attempted for Ngaoundéré volcanism are re-examined. Inductively Couple Plasma-Mass Spectrometry (ICP-MS) and Inductively Couple Plasma Atomic Emission Spectroscopy (ICP-AES) analyses show that lavas are microlitic porphyritic textures. Decrease of major element (MgO, Fe₂O₃, TiO₂, CaO) with increasing SiO₂ contents results from fractionation of olivine, clinopyroxene and Fe-Ti-oxides in the parental basaltic magma. Similarly, for felsic magma, decrease in Al₂O₃, Na₂O and K₂O contents depends upon feldspar fractionation and decrease in P₂O₅ from apatite fractionation, thus underline a typical feature of alkaline basaltic lavas of Ngaoundéré volcanism. The results evidence the differentiation by fractional crystallization process. Parental magmas of Ngaoundéré volcanism have undergone a low partial melting rate (2 to 3 %) of the heterogeneous mantle source.

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Keywords: Major and trace elements, fractional crystallization, partial melting, modeling, Ngaoundéré volcanism, Adamawa plateau