Integrated Geophysical Investigation of Suspected Structurally Controlled Valleys within the Basement Complex Underlain Federal University Oye-Ekiti, Southwestern Nigeria

摘要

Integrated geophysical investigation was carried out across series of parallel valleys within the Federal University Oye-Ekiti, Ekiti State, Southwestern Nigeria with a view to establishing if the features are structurally controlled or are mere geomorphological features. Total field magnetic intensity and 1D Vertical Electrical Sounding (VES) data were acquired along three traverses that were established approximately normal to the strike of the valleys. The magnetic data were corrected for diurnal variation and offset and presented as residual magnetic profiles and map. The residual data were reduced to the magnetic equator (RTE) and series of data enhancement filters such as the Second Vertical Derivative (SVD) and Total Horizontal Derivative (THD) were applied to the data set.Fifteen Schlumberger VES, whose locations were constrained by the results of the magnetic survey, were occupied. The VES data were presented as VES curves and interpreted quantitatively by partial curve matching and computer assisted 1-D forward modeling using the WinResist software. The VES interpretation results were used to generate geoelectric sections. The magnetic field intensities varied between -10.6 and 111.1 nT with series of low (negative) magnetic peaks, typical of thin and thick dykes, suspected to be geologic structures. These anomalies showed on the residual and RTE maps as isolated and short wavelength signatures whose locations were often displayed away from the valley sites. The general NW-SE anomaly trend was discordant to the strikes of the investigated valleys.Contact enhancement SVD and THD maps revealed discontinuous and isolated contact locations along segments of some of the valley courses. The 2-D geoelectric sections revealed that the study area is underlain by four (4) geologic layers. These include the topsoil, weathered layer, partly weathered/fractured basement and the fresh basement. The partly weathered/ fractured basement rocks are isolated and localized and most time outside the valley axes. This study therefore concluded that the series of parallel valleys are not structurally controlled but mere geomorphological features.