GROUND MAGNETIC AND 2-D RESISTIVITY MAPPING OF BASEMENT STRUCTURES AROUND IWARAJA AREA SOUTHWESTERN NIGERIA

A combined geophysical approach of ground magnetic and 2-D resistivity methods were used in mapping basement structures around the Precambrian Basement Complex of Iwaraja area with a view to mapping linear geologic structures such as fractures, geological boundaries of different rock units. In doing this, sixteen traverses were established predominantly in E-W and NE-SW directions. These traverses were marked out at 20 m intervals. Ground magnetic measurements were conducted on the sixteen traverses while electrical resistivity measurements using dipole – dipole array was carried out on three traverses in E-W direction covering the area. The magnetic results revealed the structural complexity of the area as evident in series of fractures delineated. Geological boundaries were also established. The inverted dipole – dipole 2-D resistivity structures complemented the magnetic results by mapping part of a major fault. The major fault (Iwaraja fault), is found between the boundary of quartzite/quartz schist and granite gneiss with lateral and depth extents of 325 m and 100 m respectively. The fault is trending approximately NE-SW.