New Insight on Petrogenesis and Geochronology of the Alkaline Volcanism of Ngaoundéré Area of Adamawa Plateau, Cameroon, Central Africa

Abstract

Understanding the physical and mechanical properties of local rock formations is crucial for ensuring the quality and durability of infrastructure, particularly in rapidly developing regions. New insight on petrogenesis and geochronology of the alkaline volcanism of Ngaoundéré in Adamawa plateau have allowed us to distinguish basaltic (basalts, hawaiites and mugearites) and felsic (benmoreites, phonolites, trachyte, peralkaline phonolites and trachytes) lavas of microlitic porphyritic textures. All lavas are of Mio-Pliocene age, between 7.8 ± 1.4 and 10.9 ± 0.4 Ma. Equilibrium crystallization temperatures of minerals classically decrease from basalts to felsic lavas. Decrease in major elements concentrations (MgO, Fe2O3, TiO2, CaO) with increasing SiO2 contents results from the fractionation of olivine, clinopyroxene and Fe-Ti-oxides in the parental basaltic magma. Similarly, for felsic magmas, a decrease in Al2O3, Na2O and K2O contents depends upon feldspar fractionation and decrease in P2O5 from apatite fractionation, thus underlining a typical feature of alkaline basaltic lavas of Ngaoundéré volcanism. Mass-balance crystal fractionation and closed-system Assimilation and Fractional Crystallization (AFC) modeling were performed for the Ngaoundéré volcanism and demonstrate differentiation dominated by fractional crystallization processes. Parental magmas of Ngaoundéré volcanism have undergone a low degree of partial melting at a rate of 2 wt. % of the mantle source composed of 0.18 DM + 0.81 MORB + 0.01 sediment (wt. %). Sr and Nd isotopic data of Ngaoundéré lavas preclude any contamination. Magma mixing, selective crustal contamination or fluids metasomatism may have affected the petrogenesis of Ngaoundéré alkaline lavas.