Interpretation of Aeromagnetic Data Around Nsukka Area, South Eastern Nigeria

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Abstract

The Nsukka area is a sedimentary basin within the Anambra basin which is part of the lower Benue trough. The Nsukka sheet (covering the aeromagnetic data of Nsukka) lies between latitudes 6030΄ and 7000ʹNorth and longitudes 7000ʹ and 7030ʹEast. The IGRF corrected aeromagnetic data of Nsukka sheet, southeastern Nigeria has been interpreted using the standard Euler deconvolution, source parameter imaging, forward and inverse modelling methods with the objectives of determining the depth/thickness of the sedimentary basin, magnetic susceptibilities and type of mineral present. Oasis montaj software and potent software were used in the data analysis. The forward and inverse modelling depths of the sedimentary basin are 1200m, 1644m, 1972m, 2193m and 2285m for the five profiles used. We also obtained that the susceptibility values of the magnetic materials causing the anomalies are 0.0031, 0.0073, 1.4493, 0.0069 and 0.0016 which are typically sandstones and ironstones or oxides of iron which are magnetic in nature. Source parameter imaging depth ranged from 151.6m minimum (shallow magnetic source bodies) to 3082.7 m maximum (deep lying magnetic source bodies). Euler depth result for SI=0.5 shows the depth of contact body ranging from 9.47m to 124.02m; for SI=1, depth of dyke, sill and thin sheet body ranged from 22.51m to 125.29m, for SI=2, depth of line source ranges from 39.05m to 120.30m. For SI=3 depth of spherical and compact body ranged from 7.99m to 128.93m. Euler depths for the four different structural index ranged from 7.99m to 128.93m are depths of shallow magnetic sources resulting from lateritic bodies in the outcrops within the study area. The depth for shallow magnetic material is ranged from 42.10 m to 79.10 m with an average depth value of 60.6 m, for deep lying magnetic material depth ranged from 233.95 m to 3082.73 with an average depth value of 1658.34 m. Depths of 1600m to 3082.7m show thick sediments for possible hydrocarbon accumulation.

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