Estimation of Depth to Magnetic Basement in Ekiti State, South Western Nigeria from Aeromagnetic Data Using Spectral Analysis Technique

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International Journal of Research and Innovation in Applied Science (IJRIAS) | Volume VI, Issue IV, April 2021|ISSN 2454-6194

Estimation of Depth to Magnetic Basement in Ekiti State, South Western Nigeria from Aeromagnetic Data Using Spectral Analysis Technique

Olufemi F Ojo1 and Isaac B Osazuwa2
1 Department of Geology, Ekiti State University, Ado‑Ekiti,Nigeria
2 Department of Geophysics, Federal University Oye-Ekiti, Oye‑Ekiti, Nigeria

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ABSTRACT
Magnetic method is one of the oldest geophys¬ical techniques used to delineate subsurface structure and determine the source of specific anomalies present in a particular area. An estimate of depths to magnetic basement of Ekiti State in Nigeria was carried out using spectral analysis of composite aeromagnetic map of the state. Regional anomaly was removed from the total magnetic intensity data by fitting a plane surface polynomial using Surfer software. The resulting residual was subjected to reduction to equator (RTE) filtering with the aid of Oasis montaj software to remove the asymmetry associated with the low latitude anomalies. Results of the 2-D spectral analysis revealed a two layer depth source model. The depths of shallower magnetic sources vary from 55.9 to 190.4 m, while the depths of deeper magnetic sources vary from 547.2 to 1244 m. The eastern part of the study area has low magnetic relief while the central part of the state has high magnetic relief; hence the overburden thickness towards the east is relatively high as evident from the configuration of the basement topography in the area.Depth estimation of the magnetic basement in Ekiti State indicates the maximum overburden thickness of about 1.2 km which is not sufficient for accumulation of hydrocarbon; therefore, the state can only be explored for solid mineral resources and not petroleum resources.

KEYWORDS: basement topography, contour map, magnetic relief, spectral analysis, total magnetic intensity.

1 Introduction
The study presented in this research concerns the estimation of depth to magnetic basement in Ekiti State from the spectral analysis of aeromagnetic data. The study area is underlain by Precambrian crystalline basement rocks mostly of igneous-metamorphic origin. The prominent rock units in the state include porphyritic granite, fine-medium grained granite, granite gneiss, schist/quartz schist, migmatites and charnockite [1].Magnetic survey explores the subsurface geology on the basis of anomalies in the Earth’s magnetic field resulting from the magnetic properties of the underlying rocks. It gives information which helps in the determination of depth to basement rocks and mapping of the topographic features on the basement surface. Hence, basement structures and depths are accurately delineated and mapped using magnetic data. Aeromagnetic data are routinely interpreted by estimating source depths or locations; consequently, many processing algorithms have been proposed to assist the estimation [2]. The application of 2-D spectral inversion to the interpretation of potential field data is one method that has been used to determine the basement depth, and is now sufficiently well established [3]. Spectral analysis of magnetic data has been used extensively in the past two decades to derive the depth to magnetic basement [4].