Geological Interpretation of the High Resolution Aeromagnetic Data over Okigwe-Udi Area, Anambra Basin, Nigeria, Using 3-D Euler Deconvolution and 2-D Spectral Inversion Methods

Abstract

Geological interpretation of the high resolution aeromagnetic data over Okigwe-Udi area Southeastern Nigeria, was carried out using 2-D spectral inversion and 3-D Standard Euler deconvolution methods. The objectives of the study are to delineate subsurface geological features, estimate the depth to anomalous magnetic bodies, map basement topography and infer the contribution of the interpreted features to the mineral and hydrocarbon potentials of the study area. The acquired magnetic data was enhanced to separate residual features relative to the strong regional gradients and other more intense magnetic anomalies due to basement features and igneous intrusives. The spectral inversion computational method used in the study transformed the spatial data into the frequency domain and provided a relationship between the radially averaged power spectrum of the magnetic anomalies and the depths to the respective sources. Similarly, the 3-D Standard Euler Deconvolution method examined the shape of the magnetic field within a window and calculated the 3-D source locations based on magnetic structural indices (SI). Results of the 2-D spectral analysis revealed a two layer depth model with the shallower magnetic source depth varying from 0.223 to 1.048 km (d1) with an average depth of 0.641 km while the deeper magnetic source bodies (d2) depth varies from 2.659 km to 3.748 km with an average depth of 3.088 km. Linear features delineated from the study revealed a predominance of NE-SW trending structures within the study area. Structural interpretation using 3-D Euler deconvolution with structural index values of 0 to 3, revealed three dominant structural models which include spheres, horizontal pipes/cylinders and sills/dykes. In addition, magnetic depth estimates made from 3-D Standard Euler deconvolution revealed a depth range of 0 to 3.0 km. Despite the fairly appreciable sedimentary thickness, the hydrocarbon potential of the study area is low owing to the presence of pyroclastics in the area which is a strong indication of previous igneous activities.