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概要

Crystallization Paths of Basaltic Rocks in Afikpo Basin Southern Benue Trough, Nigeria

Onwualu-John JN and Nwozor KK

The crystallization paths of basaltic magma have been studied using the basaltic rocks (e.g. gabbro, dolerites and basalts) that occur in Ameta, Mgbom and Ozaraukwu areas in southeast Nigeria. Regional mapping and petrography show that the basaltic magma in Ameta crystallizes to form gabbro. The mineral paragenesis in the gabbro is plagioclase + olivine + pyroxene + hornblende + biotite ± quartz. However, in Mgbom, the magma crystallizes as dolerites. In thin sections, the dolerites consist of plagioclase, olivine, pyroxene, and biotite. Paths of tectonism extended up to Ozaraukwu where the magma crystallized as dolerites and basalts that occur as a dyke in the sedimentary sequence of the area. The basalt consists of plagioclase, olivine, pyroxene, biotite, while quartz occur as accessory mineral. The variable concentrations of the minerals and their pattern of emplacement depict that magmatic differentiation, assimilation and contamination played major roles in the evolutionary history of magmatic rocks in the study area.