11:45 〜 12:00
[SMP26-11] Assessment of natural radioactivity and radiogenic heat production in the bedrock of Rundvågshetta in Lützow Holm complex, East Antarctica
キーワード：Radioactive elements, Radiogenic heat production, Gamma-ray spectroscopy
Radiogenic heat production (RHP) is a major contributor to the thermal structure of the Earth's interior, primarily driven by the decay of radioactive elements. This study presents RHP data from the Rundvågshetta region, analysed using high-purity germanium (HPGe) gamma-ray spectroscopy. Rundvågshetta, located on the Sôya Coast near Lützow-Holm Bay, East Antarctica, is predominantly composed of Precambrian high-grade metamorphic rocks. The region is chiefly underlain by pyroxene gneisses, with intercalated garnet-biotite gneisses being more prevalent in the northern area. Despite its geological significance, the natural radioactivity of this region remains largely unexplored.
This study aims to determine the concentration of radionuclides and quantify radiogenic heat production rates across different lithologies. Previous research indicates that the metamorphic rocks of the Lützow-Holm Complex are derived from igneous protoliths, highlighting the need for a detailed assessment of their radiogenic properties. The heat produced by the decay of uranium (U), thorium (Th), and potassium (K) within crustal rocks plays a critical role in governing lithospheric heat flow. The relative contribution of these elements to total heat production varies significantly among different rock types.
For instance, the highest concentration of 238U (20 ppm) is observed in granitic gneiss, whereas pyroxene gneiss exhibits the lowest concentration (0.16 ppm). Similarly, 232Th is most enriched in garnet gneiss (3.68 ppm) and least concentrated in hornblende granulite (0.8 ppm). Additionally, felsic gneiss has the highest 40K concentration (4.78 wt%), while pyroxene granulite records the lowest (0.16 wt%). The radiogenic heat production rates in the bedrock of Rundvågshetta range from 2.30 microwatts per cubic meter in granitic gneiss, indicative of U and Th enrichment during magmatic differentiation, to 0.15 microwatts per cubic meter in pyroxene gneiss.
These findings reveal substantial variability in RHP across different lithologies, strongly influenced by mineralogical composition. The presence of potassium feldspar, plagioclase, biotite, and trace radioactive minerals such as zircon and monazite significantly impact radionuclide concentrations. Understanding these variations is essential for refining regional heat flow models and assessing the role of geochemical differentiation in controlling radiogenic heat production. Moreover, the study underscores the importance of detailed heat production mapping for geothermal energy exploration.
Currently, heat generation maps based on radioactive decay are being developed, and we look forward to presenting them at the forthcoming conference.
References :
Akingboye, A. S., Ogunyele, A. C., Jimoh, A. T., Adaramoye, O. B., Adeola, A. O. and Ajayi, T, Radioactivity, radiogenic heat production and environmental radiation risk of the Basement Complex rocks of Akungba-Akoko, southwestern Nigeria: insights from in situ gamma-ray spectrometry, Environmental Earth Sciences, 80, 1-24, 2021.
Clauser, C, Radiogenic heat production of rocks, In Encyclopedia of solid earth geophysics, 1304-1310, 2021.
Haenel, R., et al. Handbook of Terrestrial Heat-Flow Density Determination. Springer Science & Business Media, 6 Dec. 2012.
Hasterok, D., et al. “On the Radiogenic Heat Production of Metamorphic, Igneous, and Sedimentary Rocks.” Geoscience Frontiers, vol. 9, no. 6, Nov. 2018, pp. 1777–1794, Accessed 8 Oct. 2020.
Sanchez, G, et al. “PetroChron Antarctica: A Geological Database for Interdisciplinary Use.” Geochemistry Geophysics Geosystems, vol. 22, no. 12, 1 Dec. 2021, Accessed 8 Mar. 2024.
This study aims to determine the concentration of radionuclides and quantify radiogenic heat production rates across different lithologies. Previous research indicates that the metamorphic rocks of the Lützow-Holm Complex are derived from igneous protoliths, highlighting the need for a detailed assessment of their radiogenic properties. The heat produced by the decay of uranium (U), thorium (Th), and potassium (K) within crustal rocks plays a critical role in governing lithospheric heat flow. The relative contribution of these elements to total heat production varies significantly among different rock types.
For instance, the highest concentration of 238U (20 ppm) is observed in granitic gneiss, whereas pyroxene gneiss exhibits the lowest concentration (0.16 ppm). Similarly, 232Th is most enriched in garnet gneiss (3.68 ppm) and least concentrated in hornblende granulite (0.8 ppm). Additionally, felsic gneiss has the highest 40K concentration (4.78 wt%), while pyroxene granulite records the lowest (0.16 wt%). The radiogenic heat production rates in the bedrock of Rundvågshetta range from 2.30 microwatts per cubic meter in granitic gneiss, indicative of U and Th enrichment during magmatic differentiation, to 0.15 microwatts per cubic meter in pyroxene gneiss.
These findings reveal substantial variability in RHP across different lithologies, strongly influenced by mineralogical composition. The presence of potassium feldspar, plagioclase, biotite, and trace radioactive minerals such as zircon and monazite significantly impact radionuclide concentrations. Understanding these variations is essential for refining regional heat flow models and assessing the role of geochemical differentiation in controlling radiogenic heat production. Moreover, the study underscores the importance of detailed heat production mapping for geothermal energy exploration.
Currently, heat generation maps based on radioactive decay are being developed, and we look forward to presenting them at the forthcoming conference.
References :
Akingboye, A. S., Ogunyele, A. C., Jimoh, A. T., Adaramoye, O. B., Adeola, A. O. and Ajayi, T, Radioactivity, radiogenic heat production and environmental radiation risk of the Basement Complex rocks of Akungba-Akoko, southwestern Nigeria: insights from in situ gamma-ray spectrometry, Environmental Earth Sciences, 80, 1-24, 2021.
Clauser, C, Radiogenic heat production of rocks, In Encyclopedia of solid earth geophysics, 1304-1310, 2021.
Haenel, R., et al. Handbook of Terrestrial Heat-Flow Density Determination. Springer Science & Business Media, 6 Dec. 2012.
Hasterok, D., et al. “On the Radiogenic Heat Production of Metamorphic, Igneous, and Sedimentary Rocks.” Geoscience Frontiers, vol. 9, no. 6, Nov. 2018, pp. 1777–1794, Accessed 8 Oct. 2020.
Sanchez, G, et al. “PetroChron Antarctica: A Geological Database for Interdisciplinary Use.” Geochemistry Geophysics Geosystems, vol. 22, no. 12, 1 Dec. 2021, Accessed 8 Mar. 2024.