Radiogenic heat production in granitoids from the Sierras de Córdoba, Argentina

One of the most important processes of heat generation from the Earth's interior is the radioactive decay of isotopes. The main hosts of the major radiogenic elements U, Th and K in the crust are granitoids. The Sierras de Córdoba are formed of dissimilar granitic intrusions emplaced by a series of magmatic events that occurred during the Paleozoic. The different granitoids are classified as A-type, I-type, and S-type, and there is also a magmatic expression corresponding to the Famatinian period which exhibits TTG-type characteristics. In this work, the geochemical concentrations of the radiogenic elements of the granitic intrusions making up the Sierras de Córdoba were compiled in a single database. The radiogenic heat production of the Sierras de Córdoba granitoids was evaluated, making this the first study of radiogenic heat generation in the area. The radiogenic heat production showed variability for the different events, with the highest values found in Achalian magmatism and early Carboniferous magmatism, which are represented by A-type granitoids. The Capilla del Monte pluton has the highest heat production rate, with a value of 4.54 ± 1.38 µW/m3. The lowest values were found in the TTG-type granitoids and in the S-type granitoids, all of which belong to the Famatinian magmatic event. The range of values for this magmatic event goes from 0.26 ± 0.05 µW/m3 for the San Agustin pluton to 1.19 ± 0.50 µW/m3 for the La Playa pluton. An empirical ternary model is presented for the Sierras de Córdoba that involves the concentrations of the elements U, Th and K, and the radiogenic heat production, with a distinction for the petrogenetic types according to the S-I-A-M classification. The thermal manifestations located on the Capilla del Monte pluton could be related to the radioactive heat generation of the intrusion, involving both the neotectonic activity of the area and the radiogenic heat production. The results provide new opportunities for studying temperature variation within some of these intrusions and to evaluate the geothermal potential of the granitoids of Córdoba.

Radiogenic heat production of S-type and I-type granite rocks in Bangka Island, Indonesia

Radiogenic heat production (RHP) has been investigated from widely types of rocks based on regional setting and metamorphism grade. In this study, we analyze the abundance of heat producing elements (U, Th, K) and Radiogenic Heat Production (RHP) on I-type and S-type granite rocks in Bangka Island, one of the main provinces in Tin Belt Island. The average U, Th and K concentrations for both S-type and I-types granite are 10.27 ppm, 79.6 ppm, 3.1% and 87.79 ppm, 99.2 ppm and 1.93 % respectively. The highest concentration of U (681.22 ppm) and Th (99.2 ppm) are found in Pangkal Pinang and K (3.79%) in West Bangka. We analyze that RHP average for I-type granite is higher with 27.87 (N=17, range from 12.97 to 550.28) than S-type with 8.43 (N=11, range from 4.93 to 12.64). The Th/U ratio shows an exponential correlation with RHP and classifies S-type granite tectonic discriminant as continental collision and I-type granite as continental arc.

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

The area which transcends the Precambrian basement complex onto the Sokoto sector of the Iullemme-den 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 com-plex 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.