Soil CO2 emission and stable isotopes (δ13C, δ18O) of CO2 and calcites reveal the fluid origin and thermal energy in the supercritical geothermal system of Krafla, Iceland

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Bini, Giulio, Chiodini, Giovanni, Ricci, Tullio, Sciarra, Alessandra, Caliro, Stefano, Mortensen, Anette K, Martini, Marco, Mitchell, Andrew, Santi, Alessandro, Costa, Antonio
• Other Authors: Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Bologna, Bologna, Italia, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione Roma1, Roma, Italia, Istituto Nazionale di Geofisica e Vulcanologia (INGV), Sezione OV, Napoli, Italia, Landsvirkjun, Háaleitisbraut 68, 103 Reykjaviḱ , Iceland, West Systems, via Don Mazzolari 25, 56025 Pontedera, Italy, Lancaster Environment Centre, Lancaster University, LA1 4YQ Lancaster, United Kingdom
• Format: Article in Journal/Newspaper
• Language: English
• Published: Elsevier 2024
• Subjects: Iceland
• Online Access: http://hdl.handle.net/2122/16935; https://doi.org/10.1016/j.jvolgeores.2024.108032

The Krafla geothermal system is located within a volcanic center that periodically erupts basaltic lavas, and has recently attracted an economic interest due to supercritical fluids forming near a shallow magma intrusion (~ 2 km depth). Here, we discuss new soil CO2 flux and stable isotope data of the CO2 efflux (δ13C) and hydrothermal calcites (δ13C, δ18O) of drill cuttings to estimate both the current magmatic outgassing from soils and the thermal flows in the geothermal system. Soil CO2 emission is controlled by tectonics, following the NNE-SSW fissure swarm direction and a WSW-ENE trend, and accounts for ~62.5 t/d. While the δ18O of the H2O in equilibrium with deep calcites is predominantly meteoric, both the δ13C of the soil CO2 efflux and of the fluids from which calcite precipitated have a clear magmatic origin, overlapping the δ13C estimated for the Icelandic mantle (–2.5 ± 1.1 ‰). Estimates based on the soil CO2 emission from the southern part of the system show that these fluxes might be sustained by the ascent and depressurization of supercritical fluids with a thermal energy of ~800 MW. Such significant amount of energy might reach 1.5 GW if supercritical conditions extended below the whole investigated area. Finally, we report an increase in the soil CO2 emission of about 3 times with respect to 14 years ago, likely due to recent changes in the fluid extracted for power production or magmatic activity. Pairing the soil CO2 emission with stable isotopes of the efflux and calcite samples has important implications for both volcano monitoring and geothermal exploration, as it can help us to track magmatic fluid upflows and the associated thermal energy. Published 108032 OSA5: Energia e georisorse JCR Journal