Geomagnetic Signature and Depth Estimate of Basement Rock around Iseyin Area (Ado-Awaiye), Ibadan, Southwestern Nigeria

Abstract

Ground geomagnetic survey was conducted around Iseyin Area, part of Ado-Awaiye in order to map and ascertain the nature of variability in the magnetic signature of the subsurface rock, structure of the magnetic basement as well as the depth to basement top. This was aimed at revealing the subsurface basement configuration, lithology and its mineralization. Total field intensity were measured and recorded at each station with the value of the magnetic anomaly ranging from 30446.47 nT to 33536.10 nT (nanotesla). Regional-residual separation and half - width methods were applied and after necessary data processing, the results were presented in form of magnetic map and profiles. Qualitative and quantitative interpretations were made based on the maps and profiles. Variation in the magnetic data reveals variation in the basement lithology with the higher value corresponding probably to the amphibolite (basic) component and the lower value corresponding to the granitic or gneissic component of the migmatite-gneiss (the area is underlain by migmatite-gneiss as revealed by surface outcrop). The magnetic character and signature varies being higher at the west and lower at the east. The result also reveals that the magnetic basement is shallow (2.5 m) at some places and relatively deep (22.0 m) at some other places with few basement lineament, suprabasement block and intrabasement block (basement depression). The lineament and intrabasement block can be exploited for groundwater development.