Petrology and Structural Geology of Lankpeshi Area of Igarra Schist Belt, Southwestern Nigeria

Abstract

Field study of the area shows that the major rock groups are migmatites, gneisses, schists, quartzites and calc-silicate rocks which have been intruded by a series of granites and pegmatites. The gneisses are sandwiched by the migmatites while the schists are highly weathered. Petrographic analysis reveals the presence of quartz, biotite, plagioclase, K-feldspar and accessory minerals in many of the rock samples. Migmatites in the study area range in textural characteristics from medium to coarse-grained with mafic bands defined by biotite and hornblende while feldspar with quartz forms the granular lighter coloured layers. Structural evidence shows that the area is a typical metamorphic terrain with rocks of diverse nature, complexly deformed with development of foliations and lineations and the presence of both planar and linear structures. Structural evidence also shows that most structures in the area include joints, strike-slip faults, quartz veins, asymmetric folds, drag folds. The fracture trends show that the dominant trend is in the N-S and NNW-SSE direction. The plot of foliation trend of the area shows NW-SE and NE-SW, indicating imprint of Pan-African and relict of pre-Pan African structural pattern. The nature of the minerals contain in the rocks, together with their geometry reveal that the rocks have undergone more than one deformational, metamorphic and magmatism event.