Major Elements Geochemistry of Basaltic Rocks from the Kerang Volcanoes, Jos Plateau, Central Nigeria

Abstract

This study focuses on classifying, tracing the origins of, and describing the main constituents that make up the basaltic rocks of the Kerang volcanoes. The Kerang volcanoes are a pair of particularly massive composite volcanoes that are prominent landmarks in the Jos Plateau Volcanic Province of central Nigeria. They have wellpreserved volcanic cones-built product of eruptive lapilli, scoria, breccias, basalts, and pyroclastic materials (ash, granitic, lava flow, etc.). The volcanic edifices extruded the Precambrian Basement migmatite–gneiss complex, the Pan-African biotite granites (Older Granites) and are aligned in an NNW–SSE direction that is controlled by a major deep-seated structure within the host Precambrian Basement Complex. Thirty carefully chosen basaltic rocks from lava flows and volcanoes were sampled for major oxide studies using XRF. The basalts from the Kerang volcanoes show a steady decline in main oxide concentrations (Al₂O₃, Fe₂O₃, MgO, CaO, P₂O₅, and K₂O) compared to SiO₂. The progressive decline with rising Mg# was also shown in the plot of Mg# vs these oxides. Such significant elements association follows the typical patterns of fractional mineral crystallization and/or accumulation in a mafic melt of olivine and olivine + clinopyroxenes. The Kerang volcanoes' rocks are categorized as alkaline basalts according to their total alkaline silica classification diagram. These geochemical findings imply that these rocks evolved at vast depths through partial melting that produced rocks with low silica saturation. Additionally, there was no discernible difference in their geochemical signatures between the basaltic rocks formerly thought to be older and newer. In essence, they are more recent basalts.