Application of spectral analysis to determine the magnetic source depths in ibarapa district, oyo state, sw nigeria

Abstract

The method of spectral analysis was applied to the total aeromagnetic intensity data covering the district of Ibapara, located on the Nigeria Basement Complex in Oyo State, SW Nigeria. Prior to the spectral analysis, inclined magnetisation was converted to vertical, reduced to the pole and filtered out in order to more correctly reflect spatial location and morphology of magnetic sources over geological bodies, and enhance the effects of shallower sources over deeper ones. The data was divided into blocks and sub-blocks, and was spectrally analysed for the depths to the deep- and shallow-seated magnetic sources. The Curie-point-depths computed from these depths vary between 20.8 and 32.73 km, indicating that the magnetized basement rocks are at different elevations and are probably block faulted. The correlation of shallow Curie-point-depth with the Older Granites inferred that the low Curie-point-depth is due to magmatic intrusion in the highly deformed migmatite unit, the main geologic unit. The surface heat flows derived from the Curie-point-depths vary between 40.82 and 62.84 with a mean of 50.10 mW m^-2, with areas having high surface heat flow presumed to be areas of recent intrusions where the elevated heat has transformed appropriate minerals to sapphire, tourmaline and aquamarine. Correlations of the surface heat flows and the average geothermal gradients on one hand and the Curie-point-depth on the other, unlike global compilation, yielded close empirical relations that are attributed to homogeneous geology of the area.