Evaluation of the depth to the bottom of magnetic sources and heat flow from high resolution aeromagnetic (HRAM) data of
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ORIGINAL PAPER
Evaluation of the depth to the bottom of magnetic sources and heat flow from high resolution aeromagnetic (HRAM) data of part of Nigeria sector of Chad Basin T. O. Lawal 1 & L. I. Nwankwo 1
Received: 26 April 2016 / Accepted: 8 August 2017 # Saudi Society for Geosciences 2017
Abstract Understanding the thermal distribution within the crust and rheology of the earth’s lithosphere requires the knowledge of the Depth to the Bottom of Magnetic Sources (DBMS). This depth is an important parameter in this regard, which can be derived from aeromagnetic data and can be used as a representation for temperature at depth where heat flow values can be evaluated. In this work, high-resolution aeromagnetic (HRAM) data of part of Chad Basin (covering about 80% of the entire basin), an area bounded by eastings 769,000 and 1,049,900 mE and northings 1,200,000 and 1,500,000 mN, were divided into 25 overlapping blocks and each block was analyzed using spectral fractal analysis method. The spectral analysis method was used to obtain the Depth to the Top of Magnetic Source (DTMS), centroid depth, and DBMS. From the calculated DBMS, the geothermal gradient and heat flow parameters were evaluated and the result obtained shows that DBMS varies between 18.18 and 43.64 km. Also the geothermal gradient was found to be varying between 13.29 and 31.90 °C/km and heat flow parameters vary between 33.23 and 79.76 mW/m2, respectively. The heat distribution of this area is one of the key parameters responsible for various geodynamic processes; therefore, this work is important for numerically understanding the thermal distribution in Chad Basin, Nigeria since rock rheologies depend on temperature, which is a function of depth.
Keywords Aeromagnetic data . Spectral analysis method . DBMS . Heat flow . Chad Basin . Nigeria * T. O. Lawal [email protected]
1
Department of Physics, University of Ilorin, Ilorin, Nigeria
Introduction Magnetic methods are employed for direct and indirect mapping of hydrocarbon reservoirs, geological structures, and thermal state of the crust (Glenn and Badgery 1998). The method measures variations in the magnitude of the earth’s magnetic field resulting from the magnetic properties of the underlying rocks. Due to the inaccessibility and inability to cover a wide range of areas, airborne magnetic survey has been applied to acquire subsurface data in the past decades. Such data gives information about the Depth to Bottom of Magnetic Sources (DBMS), location, and extent of sedimentary basins that are required in understanding the thermal distribution in the area. Suitable information about the thermal structure of the lithosphere is necessary because of an extensive multiplicity of geodynamic examinations. These examinations include rock deformation, hydrocarbon maturation, mineral phase boundaries, rates of chemical reactions, electrical conductivity, magnetic susceptibility, seismic velocity, and mass density (Ross et al. 2006) and information about the thermal structure could only be obtained i
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