Investigating the Structures within the Lower Benue and Upper Anambra Basins, Nigeria, Using First Vertical Derivative, Analytical Signal and (CET) Centre for Exploration Targeting Plug-In

Abstract

The IGRF-corrected 2009 aeromagnetic data over the Lower Benue and Upper Anambra basins Nigeria was subjected to both Vertical and Horizontal Derivatives, Analytical Signal and CET grid analysis, these digital processing tools were achieved both on map and profile analysis. From the analysis of both the Vertical and Horizontal Derivatives the study area could be divided into two regions based on the degree of distortion to the magnetic signatures the Northern and the Western edge of the area is covered by short wavelength magnetic anomalous signatures that are the characteristic of outcrop and shallow intrusive magnetic bodies, while the remaining part of the study area is characterized by medium to long wavelength magnetic signatures that are attributes of deep sited magnetic rocks in areas of medium to thick sedimentations. Result of the Analytical Signal which is in local amplitude reveals regions with outcrop of magnetic rocks having amplitudes ranging from 0.230 to 0.40 (shown as pink color), area with magnetic rock intruding into sedimentary formations at shallow depths, with amplitudes ranging from 0.094 to 0.229 cycles (shown as red color), while regions with magnetic rock intruding into sedimentary formations at greater depths, having very low amplitudes ranging from -0.085 to 0.055 cycles (shown in yellow to green color). Analyses due to CET grid analysis equally reveal the basement rocks to the North and Southern edge of the study area. Intrusions into the sedimentary formation are also revealed. The research discovered that the lower (southern) part of the area (on Angba and Otukpo area) shows structures (Basaltic rocks) that intrude into the basement which could have predate the sedimentation period, several fracture and fault lines are detected on the CET map, most prominent among them is that at the Southeastern corner of the area which trends NE-SW which can be attributed to an onshore extension of Charcots fault zone , and that which trends N-S is a fault line that controls the course of River Niger. These three features are responsible for the depressions where sediments can accumulate.