The Geology of Eshiawa in Igarra Area, Southwestern Nigeria.

Abstract

The Nigerian Basement complex has undergone polyphase metamorphism and polycyclic deformation during the Late Proterozoic and Early Phanerozoic Periods. The structures of the Pan- African belt in the southwestern Nigeria (Eshiawa area of Igarra) are the result of a succession of several events. Igarra environ provided detailed information on the structures and the following deformations were identified: (1) the original bedding surface (S0) undergoes the first episode of deformation (Di) and produced folds (Fi). This indicates an early Pan-African stage (Di) of tangential movement. (2) Mineralogical banding (Si) produced in first episode of deformation (Di) undergoes second episode of deformation (D2) to produce disharmonic folds (F2). (3) The axial plane cleavage (S2) formed as a result of second episode of deformation undergoes third episode of deformation (D3) to produce asymmetric folds (F3). D2 phase is heterogeneous simple shear in dextral transpressive context and D3 tectonic phase, also marked by dextral transpressional movements, is the phase of superposed folding with a NNW-SSE, kinematics direction. D2 and D3 are associated with medium-grade amphibolites facies metamorphic. (4) The Fourth episode of deformation (D4) is responsible for the emplacement of granitic veins, faults and joints. The first three episodes of deformations were related to ductile deformation while the latter was related to brittle deformation. The similarities of these last phases with the central Cameroon shearzone suggest that the D3 and D4 stages are controlled by transcurrents tectonics. Transpressive tectonic seem to be the main deformation style in major shear zones of Igarra