Review of variability of radiogenic heat properties of some rock types as a basis for geothermal characterization in Nigeria

Abstract

The southwestern part of Nigeria is one of the three known regions in Nigeria with geothermal prospect. It is characterized by distinctly different thermal state and surface thermal manifestations. Although a number of geophysical explorations have been undertaken, but studies on fundamental geothermal theory remain scarce, including a lack of high-quality heat flow determinations and thermal structure studies. Heat production and heat flow properties play a very critical role in the study of thermal structure in a region. In this report, heat production and heat flow data of rock samples from published studies from some localities in Nigeria was compiled. To optimize this data, the rock-type denominations from the original studies was classified. This was used to characterize the thermal structure of the areas for possible geothermal exploration and radiogenic heat production distribution for the different rock types in the region. This gave some useful guidelines to lithospheric thermal modeling. From the heat production data, there is a wide range in values with igneous rocks having a maximum 11.17 µWm-3 and the metamorphic rocks having 131.37 µWm-3 as maximum value. The metamorphic rocks have higher values than the igneous rocks while the heat flow compiled for the country area has a minimum of 29 mWm-2 and a maximum of 130 mWm-2 with a mean value of 80 mWm-2. The high heat flow observed from data of the southwest zones may suggest the existence of anomalous heat source body in crust due to the radiogenic heat of the solid crust. This work is also an appraisal to direct attention to the lack of thermal properties investigations in the southwestern part of Nigeria and the need to improve on the heat flow database of Nigeria. Hence some parts of the study areas could be further explored for geothermal energy using appropriate geophysical techniques.