Geochemical Features of Alkaline Lavas from Nkondjock (Littoral-Cameroon): Geodynamic Implication

This study presents a comprehensive geochemical analysis of alkaline lavas from the Nkondjock area along the Cameroon Volcanic Line (CVL). Employing thin-section microscopy, ICP-AES (major elements), and ICP-MS (trace/REE elements), we characterize basanites (plagioclase, olivine, augite, opaque minerals and accessory spinel), hawaiites (plagioclase, olivine, augite and opaque minerals), mugearites (plagioclase, augite, aegirine, hornblende, opaque minerals and olivine), and benmoreites (plagioclase, augite, nepheline, sanidine, opaque minerals and accessory olivine). These lavas exhibit microlitic to porphyritic textures, indicating multi-stage crystallization: initial megacryst formation in magma chambers, phenocryst development in conduits, and rapid surface cooling. Geochemically, they are MgO-depleted (2.13 - 9.01 wt%) and Al2O3-enriched, with primitive mantle-normalized patterns showing LILE/LREE enrichment and OIB-like signatures. Crustal contamination is negligible, except in evolved samples (mugearite, benmoreite). Trace element ratios (e.g., La/Ta = 14.91 - 21.5; ΔNb > 0) confirm an asthenospheric garnet-lherzolite source, with low-degree partial melting (0.5% - 2%) at 70 - 80 km depth. Zr/Y (9.28 - 16.53) and Ti/Y (260 - 827) ratios classify them as intraplate basalts, consistent with reactivated Pan-African fault magmatism.