General Geology and Geochemistry Studies of Basement Rock Types of Zagun Area, North Central Nigeria

Abstract

The mapped area is part of the Basement Complex of Jos Plateau, Central Nigeria and is made up of rock types that include migmatite gneiss, porphyritic biotite granites, microgranite, basalt and dolerite. Field relations revealed the occurrence of structures such as foliations, joints, quartz veins, aplitic dykes, pegmatite dyke, basic dykes, enclaves, shear zones and mylonites, trending dominantly in a NE-SW, N-S, NNE-SSW and NW-SE, respectively. These suggested that the rocks were affected dominantly by the PanAfrican Orogeny (600±150). Microscopic studies revealed that the rocks contain varying percentages of quartz, K-feldspar, plagioclase, biotite, hornblende, pyroxene and augite as the major minerals. Geochemical studies showed that the rocks have limited variation in their major element compositions and give a decrease in CaO wt. %, and increasing Ba/Sr, Zr/Y ratios, K₂O wt. % with increasing silica. The rocks are distinctly calc-alkaline as they plot in the sub-alkaline and cal-alkaline, syn-collision-postcollision fields on various discrimination diagrams. The above characteristics suggest that the Basement rocks of the study area were formed from the fractional crystallization of a calc-alkaline magma in a synpost collision tectonic terrain.