Crustal thermal regime of Ikogosi warm spring, Nigeria inferred from aeromagnetic data
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ORIGINAL PAPER
Crustal thermal regime of Ikogosi warm spring, Nigeria inferred from aeromagnetic data M. O Olorunfemi & A. A Adepelumi & D. E Falebita & O. A Alao
Received: 5 August 2011 / Accepted: 11 November 2011 / Published online: 26 November 2011 # Saudi Society for Geosciences 2011
Abstract Spectral analysis method was applied to aeromagnetic data obtained for Ikogosi warm spring (IWS) area of southwestern Nigeria. This was done with the objective of determining the bottom of the magnetized crust called Curie point depth (CDP) and understand the nature and extent of the local geothermal system at depth beneath IWS. The depth to the centroid, Zo, of the deepest distribution of the magnetic dipoles was obtained by computing least-squares fit to the lowest-frequency segment of the azimuthally averaged log power spectrum. The average depth to the top of the deepest crustal block was computed as the depth to the top, Zt, of the second lowestfrequency segment of the spectrum. The depth to the bottom of the deepest magnetic dipoles, the inferred Curie point depth, was then calculated from Zb =2Zo −Zt. The Curie depth estimates for IWS range between 4.68 and 11.38 km (below sea level). We also estimate the heat flow and Curie temperature using a one-dimensional conductive heat transport model. The average heat flow, 42 mW m−2, and geothermal gradient, 32°C/km, obtained suggest a low enthalpy thermal regime. The Curie temperature for the region varies between 153°C and 350°C. Also, an inverse linear relationship between heat flow and Curie depths was determined. Good agreement between the Curie point depths derived from heat flow data and magnetic data suggests that the Curie point depth analysis is useful to estimate the regional thermal structure and the tectonic settings.
M. O. Olorunfemi : A. A. Adepelumi (*) : D. E. Falebita : O. A. Alao Department of Geology, Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria e-mail: [email protected]
Keywords Spectral analysis . Spring . Magnetic . Curie point depth . Nigeria
Introduction Geothermal energy is currently meeting an increasing proportion of the world’s energy requirements. For example, in 2007, over 12,000 MW of electricity was produced from some 250 geothermal power plants in 22 countries around the world. These plants provide reliable base-load power for well over 60 million people, mostly in developing countries. In Africa, Kenya, Algeria, Tunisia, and Zambia have significant installed capacities of geothermal energy. However, geothermal manifestation in Nigeria is scarce except for two warm springs named Ikogosi and Wikki located in the southern and northern part of Nigeria. The Ikogosi warm spring (IWS) being investigated in this study is located in Ikogosi-Ekiti, a small agrarian village (longitude 7°30′ N–7°45′ N and latitude 5°00′ E–5°15′ E) that is about 300 km from Lagos, the former Federal capital of Nigeria. It has both warm and cold water coming out from seven different sources. Oral history and mythology suggest that the Ikogosi warm spr
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