TITLE:
Petrological Characterization of Pyroclastics from the Manengouba Maars Volcanoes, Coastal/Southwest Region, Cameroon
AUTHORS:
Bibiche Scheila Zemfack Dongmo, Jules Tamen, Théophile Njanko, Paterne Mulimbi Kagarabi
KEYWORDS:
Manengouba Maars, Hydrothermal Alteration, Magmatic Fractionation, Phreatomagmatic Explosions, Diatreme Growth model
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.13 No.9,
September
26,
2025
ABSTRACT: This study explores the magmatic and eruptive processes of the Manengouba maars, located along the Cameroon Volcanic Line (CVL). Petrographic analyses of the samples reveal a diverse mineralogical composition with clinopyroxenes (20% - 35%), plagioclases (19% - 35%), olivines (5% - 15%), and sanidines (up to 15%). Positive Europium (Eu) anomalies observed suggest crystallization under reducing conditions. X-ray diffraction analyses show a significant presence of smectite (25.99% to 76.05%), kaolinite, and other clay minerals, indicating extensive hydrothermal alteration. Geochemical diagrams reveal clear trends of magmatic fractionation, with an increase in Zr (up to 200 ppm) with increasing SiO2 (45% to 60%) and a decrease in MgO (from 10% to less than 5%) accompanied by an increase in Nb (from 10 to 50 ppm). These trends suggest magmatic differentiation prior to the eruption. Explosive interactions between ascending magma and groundwater led to phreatomagmatic explosions, forming complex diatremic structures. The presence of mantle xenoliths and host rock fragments indicates significant assimilation of the host rocks during magma ascent, modifying its chemical composition. The results allow proposing a diatreme growth model, highlighting the importance of phreatomagmatic interactions and magmatic fractionation processes. Compared to other volcanic regions, the geology of Manengouba shows significant similarities with other volcanoes along the CVL and with maars and diatremes studied elsewhere in the world. In conclusion, this study enriches our understanding of volcanic and magmatic processes in the Manengouba region, providing crucial insights into eruptive dynamics and associated geochemical and mineralogical conditions.