Spectral analysis of high resolution aeromagnetic data for the determination of curie point depths in parts of Chad Basin,Nigeria.
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Date
2014
Authors
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Journal ISSN
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Publisher
Physics,Obafemi Awolowo University
Abstract
The Curie Point Depth (CPD), sedimentary thicknesses and heat flow maps of parts of the Chad Basin, Nigeria were generated through the analysis of radial log power spectral of overlapping square blocks of high resolution aeromagnetic data. This was with a view to evaluating the thermal gradients and associated heat flow beneath the study area.
Nine sheets of High Resolution Aeromagnetic Data (HRAD) of parts of the Nigerian sector of Chad Basin, bounded by Latitudes 11° 30′ to 13° 00′ and Longitudes 12° 00′ to 13° 30′, were acquired from the Nigerian Geological Surveys Agency (NGSA). The HRAD were interpolated onto a uniform grid at 100 m spacing using the minimum curvature gridding method. The regional trend and cultural noise in the data were removed using polynomial surface fitting and upward continuation filtering techniques. The filtered HRAD grid was then subdivided into twenty-five overlapping square blocks with dimensions of 55 km × 55 km. Each block was overlapped by fifty percent with the adjacent blocks. The depth to the centroid ( ) and depth to the top boundary of the basement ( ) were calculated from the power spectrum computed for each block and the values of and were used to determine the CPD. The CPD values and appropriate thermal conductivity were used to estimate the thermal gradients and associated heat flow values. The results were compiled into CPD, sedimentary thicknesses and heat flow maps. 2D forward modelling of profiles taking across the CPD map and the anomalous zones of the Reduced-to-the-Equator map of the filtered HRAD was carried out to obtain five models of the magnetic crust in the study area.
The magnetic anomalies in the study area mainly trend in the NE¬–SW, E–W and ENE–WSW directions, for which the NE–SW orientation predominated. The CPDs ranged between 3.0 km and 16.7 km. Shallow CPD (< 3.5 km) zones were mapped at the extreme edge of the north-western and south-western portion. The sedimentary thicknesses in the study area ranged between 1 km and 3 km. The geothermal gradient range of 34°C/km – 173°C/km and heat flow range of 87 – 446 estimated for the study area indicated that there were high vertical temperature gradients and geothermal heat flow in parts of the Chad Basin. The magnetic forward models revealed the variation of the basement topography with the smoother Curie point isotherm level and the presence of sub-basins in the study area. Basement rocks in regions of shallow CPD were found to have richer magnetic contents than those in regions of deep CPD.
The study concluded that dry wells encountered in the Nigerian sector of the Chad Basin in the past could have been the consequence of high magnitude of geothermal heat flow ( ) resulting from shallow depths to the Curie isotherm in various parts of the study area.
Description
xv, 149p
Keywords
Sedimentary, Curie Point Depth, Geothermal heat flow, Topography, Aeromagnetic data, Geothermal heat flow
Citation
Falade,S.C (2014). Spectral analysis of high resolution aeromagnetic data for the determination of curie point depths in parts of Chad Basin,Nigeria. Obafemi Awolowo University