Determination of depth to basement using spectral analysis of aeromagnetic data over Azare segment of Chad Basin

Abstract

The high-resolution aeromagnetic data over part of the Bornu basin (sheet 84) north eastern (NE) Nigeria, was processed and interpreted using spectral analysis to determine the depth to the basement. The study area is bounded between longitude 10⸰ 00’ 00’’E to 10⸰ 30’ 00’’ E and latitude 11⸰ 00’ 00’’ N to 12⸰ 00’ 00’’. Regional residual separation of the total magnetic field intensity (TMI) was performed using polynomial fitting method. The residual map was divided into nine square spectral blocks using the filtering tool of Microsoft excel software. The Microsoft excel program employed Fast Fourier Transform (FFT) technique. It transforms the magnetic field data into the radial energy spectrum for each block. Then the average radial energy spectrum is computed in MATLAB. The result shows that depth to the deeper magnetic source ranges from 4503.9m to 1948.3m. However, it can be observed that NN, NE, and NW are having less deep magnetic sources ranging from 1948m to 2459.7m. The deepest sources happened at the major towns of interest which are Bidawa , Matsango , Yakiri and Fatara areas, Katagum Bauchi state ranging from 2632.8m to 4503.9m The maximum depth of the sedimentary unit was estimated as 4.5km because the isolated value beyond this depth cannot be connected , and this depth occurs around Matsango and Bidawa. The shallow depth magnetic source map shows that SS, SW, SE are having least shallow depth, central to northern part of the study area are having shallowest depth to the magnetic source.