One Dimensional Spectral Analysis and Curie Depth Isotherm of Eastern Chad Basin, Nigeria

Abstract

One dimensional spectral analysis was applied to aeromagnetic data in order to determine the sedimentary thickness variations, depths to the Curie-temperature isotherm and heat flow measurements within the eastern part of the Nigerian Chad Basin. Two depths sources were interpreted in the area namely; the shallower sources have a mean value of 2.21 km while the deeper ones have an average value of 14.07 km. The result of the analysis shows that depths to the centriod and magnetic bodies (sedimentary thicknesses) range from 11.55 to 18.32 km and 1.65 to 5.12 km respectively. The depth to the Curie temperature isotherm in the area varies between 21.45 km at Mafa-Bama area and 31.52 km at Maiduguri-Gwoza area below sea level. The result also shows that the Curie temperature isotherm within the basin is not a horizontal level surface, but is undulating, and the geothermal gradients associated with it range between 17.45 and 25.64^oC/km while the corresponding mantle heat flow is about 46.00 mWm^-2 and 67.60 mWm^-2. It is good to note that areas of high heat flow correspond to high geothermal gradient within the study area. An inverse relationship exists between calculated Curie depths and heat flow within the study area such that high-heat-flow regions correspond to low Curie depths regions. These results correspond to the depths inferred by extrapolating geothermal gradient and heat-flow values, suggesting that the Curie point depth analysis is a useful tool in estimating regional thermal structure. Based on the computed sedimentary thicknesses and the high geothermal gradient, some parts of the study area have been demarcated for detail hydrocarbon exploration.

Keywords: Chad Basin, aeromagnetic data, spectral analysis, Curie point depth, geothermal gradient and Hydrocarbon