Aeromagnetic characterization of parts of Ondo and Ekiti States, Southwestern Nigeria

Abstract

Aeromagnetic data of Ikole Sheet 245 covering Ikole, Akoko and Kabba areas was studied with the aim of delineating subsurface geological structures towards detailed information on exploration, engineering construction and environmental assessment of the study area. The colour shaded Total Magnetic Intensity (TMI) was interpreted for anomalous zone, structural trends, lithological differentiation and closures. Reductions were made on Residual Field data produced. TMI map revealed high intensity amplitudes within 65 – 180 nT representing crystalline and undeformed basement rocks, -150 to -65 nT for very low magnetic amplitudes representing infilled weathered and non-magnetic materials. Regional lineament trends diagonally from NE-SW dividing the map into equal halves, normal faults trending N–S and a NW–SE trending ridge (intrusive granitic rock) between two large depressions in Akoko axis were seen on TMI map. The reduction to the equator (RTE) map showed that below lineament (Akoko to Kabba) and above lineament (Ikole) have high and low magnetic anomalies respectively. Upward continuation maps revealed rocks trend generally in NW–SE and identified structures as deep-seated. Tilt-angle Derivative (TDR) map showed extent of structures, NE–SW lineaments (R-R’) and phases of N–S trending normal fault (F-F’) to be over a wide area. The spectral depth analysis plot showed that shallow and deeper magnetic sources have an estimated depth of 140 m and 1.60 km respectively. This method has proved valuable in mapping basement structures and targeting suitable areas for groundwater exploration, metalliferous mineral deposits and delineates zones of faulting in bedrock of the study area.