Paleostress Analysis of Joints in Part of Basement Complex Area of Southwestern Nigeria

This study was carried out to understand structural features of joints of Owo area with the intention of unravelling the paleostress history of the area. The study area is a detachment of the Igarra schist belt, southwestern Nigeria. In this study, field mapping techniques and structural interpretations of joints using acceptable international methods were employed. The study was carried out in Owo, Ondo State, Nigeria from February, 2015 to July, 2016. Field mapping techniques involved the identification of joints and the measurement of strike and dip values using compass clinometer. A total of 623 joints were measured from nine mapping stations and their eigenvalues of with their trends and plunge values were plotted and input into the Win_Tensor Version: 5.8.4 software to determine the tensor direction. Three sets of joints that are gently to moderately dipping were observed in the area. They generally belong to radial and pure extensive regime. These joints were possibly formed under a stress condition of about 30-33 MPa. It further revealed that they were reactivated possibly during the pan-African orogeny. The radial and pure extensional tensor is similar to fracture trend related to major episodes of pan-African orogeny across Nigeria which generally NE-SW.