INTERPRETATION OF AEROMAGNETIC DATA FOR DELINEATION OF GEOTHERMAL ENERGY AND ITS ATTRIBUTES IN PARTS OF SOUTHWESTERN NIGERIA

SOURCE:

Faculty: Physical Sciences
Department: Applied Geophysics

CONTRIBUTORS:

Chinyem, F. Iwebunor
Onwuemesi A. G.
Anike O. L.

ABSTRACT:

Spectral analysis of aeromagnetic data was applied to aeromagnetic data in order to produce the total magnetic intensity and residual anomaly maps; determine the depth to the Curie-temperature isotherm; determine the geothermal and mantle heat flow values; generate and model the Curie-temperature isotherm; and delineate fault trends and areas with geothermal energy potential and its attributes in parts of Southwestern Nigeria. To achieve the above stated objectives, nine aeromagnetic data sheets from the study area were assembled and analyzed. The aeromagnetic data were acquired as part of a nationwide aeromagnetic survey sponsored by the Nigerian Geological Survey Agency. The methodology involved the assemblage and digitization of nine aeromagnetic maps; production of total magnetic intensity map; separation of the regional and residual map; contouring the digitized data using Surfer 32 contouring software and subsequently analysis and modeling of magnetic anomaly data. The analysis was carried out using computer program designed for analysis of potential field data. Spectral analysis was used to interpret the data; determine the depth to the basement; delineate the Curie-temperature isotherm and mantle heat flow. Finally, the geothermal energy and its attributes were delineated by computation and integration of all the interpretations. The results showed that the total magnetic field and residual anomalies ranged from 7920 to 8080 nT and – 60 to 100 nT respectively. The computed depths to the Curie-temperature isotherm and geothermal gradients ranged from 7.19 – 24.55 km and 22.53 – 76.91 0C/km along Akure – Benin City and Okomu areas respectively. The corresponding mantle heat flow value varied between 192.28 mW/m2 and 56.33 mW/m2 along Akure – Benin City and Okomu areas respectively. The Curie-temperature isotherm showed that the area is undulating rather than being a horizontally flat surface. Two major fault trends were interpreted: Northeast-Southwest (NE-SW) and Northwest-Southeast (NW-SE) directions. Based on the computed geothermal gradient and heat flow values, the Northwestern area was found to have great geothermal energy potential. The attributes of delineated geothermal energy comprised manifestations of warm spring, high geothermal gradient, fault trends and uplifted crust/mantle boundary. The computed results and model provided information on the capabilities of spectral analysis in delineating geothermal energy and its attributes in Northwestern part of the study area and as such could be adapted to other areas with similar geologic framework in Nigeria and environs.