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Crustal thermal structure of the Pan-African remobilized basement complex in north-central Nigeria: an integrated and interactive approach for geothermal prospectivity

Aisabokhae Joseph

Acta Geophysica

2024

Vol. 72, no. 1

115--128

In this study, an interactive analysis combined measurements of surface radiogenic heat production (RHP) and sub-surface heat flow data to predict the crustal thermal regime of the area. The radioactive decay of 40 K, 232Th and 238U radionuclides in combination with other processes generate a significant quantity of heat within the earth’s crust which can be utilized to produce green energy. Statistical analysis involving a box-whisker plot was used to optimize the generated RHP data with median RHP value of each lithologic unit presented as 3.2 gW m-3 (diorite), 2.9 gW m-3 (granodiorite), 3.1 gW m-3 (granite) and 2.7 gW m-3 (quartzdiorite). The results are in tandem with similar studies around the globe and are in near approximation to measurements that depict high heat production character. Heat generation predictions were extrapolated from the RHP values and displayed in percentile plots. The study showed that quartzdiorite presented the largest variation (from 5.2740 to 8.7185 HGU) in the region, followed by granite (from 6.1127 to 8.7445 HGU), then diorite (from 6.499 to 8.8975 HGU) and granodiorite (from 5.9870 to 8.3762 HGU). Heat flow measurements in 12 site holes within the granitoid emplacement showed averaged values of 48.5, 40.9, 48.5 and 28.9 mW m-2 for diorite, granodiorite, granite and quartzdiorite plutons, respectively. The analyzed thermal properties in this study suggest that the surface plutons are not deep-seated. An explanation for the high thermal condition of the deep-seated crustal rocks was adduced to tectonic events that distributed radioelements into reactivated inter-rift crustal blocks.

Spatial distribution of radiogenic heat in the Iullemmeden basin – Precambrian basement transition zone, NW Nigeria

Aisabokhae Joseph, Adeoye Moses

Geology, Geophysics and Environment

2020

Vol. 46, no. 3

239--250

The area which transcends the Precambrian basement complex onto the Sokoto sector of the Iullemmeden basin in northwestern Nigeria presents a unique prospect for geothermal exploration research in the absence of regional heat production data, despite its tectonic history and depositional characteristics. In this study, geophysical exploration employing radiometric technique was adopted to classify the petrologic units within the fringes of the Iullemmeden basin and the adjoining crystalline basement complex so as to estimate the radiogenic heat potential within the terrain that may support geothermal considerations. Airborne radiometric measurements acquired over the area were digitized and processed to obtain radioelement concentration maps and the K/Th/U ternary map. Results show that the ranges of measured concentrations of 40K, 238U and 232Th are 4.6 to 18.9%, 0.7 to 4.9 ppm and 4.6 to 18.9 ppm respectively. Radiogenic heat estimation derived from radioelement data within eight petrologic units comprising quaternary sediments, schist, carbonates, shale/clay, younger granites, older granites, gneissic rock and migmatite showed that the lowest radiogenic heat production estimates ranging from 0.27–0.66 µW∙m−3 were recorded in the sedimentary terrain within the quaternary sediments while the highest radiogenic heat production values of between 2.04 to 2.34 µW∙m−3 were recorded in the basement complex within gneissic rocks. The spatial distribution of radiogenic heat in the area showed an increased heat gradient within the basement complex and a diminishing heat gradient over the Iullemmeded basin.