Mineralogy and geochemistry of pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain monogenetic volcanoes in the central part of the Cameroon Volcanic Line

Abstract

Pozzolans from the Tombel Plain, Bamileke Plateau, and Noun Plain, 3 monogenetic volcanic fields in the central part of the Cameroon Volcanic Line (the Tombel Plain, Bamileke Plateau, and Noun Plain), were explored in order to constrain their petrology and make some predictions on their pozzolanicity. The rocks in this study include alkaline and subalkaline basalts, trachy-basalts, and basanites. Most of these rocks present an overall composition that overlaps with primitive mantle, suggesting rapid ascent of magmas, limited crustal contamination and crystal fractionation of olivine, clinopyroxene, and feldspar. The pozzolans present enrichment of LREE relative to HREE and high chondrite normalized ratios of La/Yb and Tb/Yb, ranging between 7 and 20 and > 1.9 respectively, similar to those of Ocean Island Basalts. Like other nearby volcanoes, partial melting in a dominantly garnet-bearing mantle zone can be assumed. Quantitative mineralogy by X-ray diffraction revealed various mineral phases with dominantly plagioclase, augite, olivine, and Fe–Ti oxides. The samples contains important amorphous phase up to 23, 51, and 69 wt% in the Tombel Plain, Noun Plain, and Bamileke Plateau, respectively. This elevated amount of amorphous phases together with the sum of SiO2, Al2O3, and total Fe2O3 (SAI = 68.50–83.50 > 70 wt%) according to ASTM C 618 standard and the sum of CaO, FeO, and MgO (CIM = 14.5–30.52 wt% and 23.58–31.08 wt%) suggest interesting pozzolanicity character for the studied pozzolans.