Investigation of subsurface Geologic Features in Low latitude Crystalline Basement Complex: case study of Oke-Alapata Area, Ogbomoso, South-western Nigeria

Abstract

Ground Magnetic survey has been carried out to investigate subsurface geology of Oke-Alapata area of Ogbomoso, Southwestern Nigeria. Magnetic measurements were recorded using proton precession magnetometer. The objectives of the research include determination of depth to magnetic source, investigation of subsurface reliefs and magnetic anomalies signatures associated with geological features such as joints, fractures and lithologic contacts as well as update the geology of the area.

The ground magnetic survey was preceded by geological mapping of the area. A total of ten profile lines were traversed in an east-west direction with an inter-profile spacing of 100m and station interval of 5m. The magnetic data obtained were processed and plotted on profiles to obtain the magnetic signatures of the subsurface.  The data were subsequently interpreted qualitatively and quantitatively.

The geological mapping revealed the presence of migmatite-gneiss and quartzite at the northern and southeastern part respectively of the study area. The magnetic anomalies ranged from minimum negative peak value of -400nT to maximum peak value of 520nT. The detected geological features include joints and fractures as well as rock-rock contact between Migmatite-gneiss and quartzite. The depth to magnetic source ranged from 6.1m at the southeastern part to 10.8m at the northeastern part of the study area.

The strong correlation between the geological map of Oke Alapata, the identified geologic features and the magnetic anomalies interpretations has exemplified the use of magnetic anomalies signatures in characterizing geologic features in a low latitude crystalline basement complex studied.

Keywords: Ground Magnetic Survey, Subsurface Geology, Joints, Fractures, Rock-Rock contact, Ogbomoso, Nigeria