Deep magma degassing and volatile fluxes through volcanic hydrothermal systems: Insights from the Askja and Kverkfjöll volcanoes, Iceland

• Published in: Journal of Volcanology and Geothermal Research
• Main Authors: Ranta, Eemu, Halldórsson, Sæmundur A., Barry, Peter H., Ono, Shuhei, Robin, Jóhann Gunnarsson, Kleine, Barbara I., Ricci, Andrea, Fiebig, Jens, Sveinbjörnsdóttir, Árný E., Stefánsson, Andri
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2023
• Subjects: ddc:550; Iceland
• Online Access: http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/78906; https://nbn-resolving.org/urn:nbn:de:hebis:30:3-789062; https://doi.org/10.1016/j.jvolgeores.2023.107776; http://publikationen.ub.uni-frankfurt.de/files/78906/container.zip

Highlights • New fumarole and thermal water data for Askja and Kverkfjöll volcanoes, Iceland. • Data compared to modelled compositions and fluxes of magmatic gas. • Fumarole compositions compatible with origin of CO2 and S from degassing intrusions. • Intrusive magmatic fluxes sufficient to sustain hydrothermal fluxes of CO2 and S in Iceland • Magma degassing insignificant/minor source of H2O and Cl to Icelandic hydrothermal fluids Abstract Mantle volatiles are transported to Earth's crust and surface by basaltic volcanism. During subaerial eruptions, vast amounts of carbon, sulfur and halogens can be released to the atmosphere during a short time-interval, with impacts ranging in scale from the local environment to the global climate. By contrast, passive volatile release at the surface originating from magmatic intrusions is characterized by much lower flux, yet may outsize eruptive volatile quantities over long timescales. Volcanic hydrothermal systems (VHSs) act as conduits for such volatile release from degassing intrusions and can be used to gauge the contribution of intrusive magmatism to global volatile cycles. Here, we present new compositional and isotopic (δD and δ18O-H2O, 3He/4He, δ13C-CO2, Δ33S-δ34S-H2S and SO4) data for thermal waters and fumarole gases from the Askja and Kverkfjöll volcanoes in central Iceland. We use the data together with magma degassing modelling and mass balance calculations to constrain the sources of volatiles in VHSs and to assess the role of intrusive magmatism to the volcanic volatile emission budgets in Iceland. The CO2/ΣS (10−30), 3He/4He (8.3–10.5 RA; 3He/4He relative to air), δ13C-CO2 (−4.1 to −0.2 ‰) and Δ33S-δ34S-H2S (−0.031 to 0.003 ‰ and −1.5 to +3.6‰) values in high-gas flux fumaroles (CO2 > 10 mmol/mol) are consistent with an intrusive magmatic origin for CO2 and S at Askja and Kverkfjöll. We demonstrate that deep (0.5–5 kbar, equivalent to ∼2–18 km crustal depth) decompression degassing of basaltic intrusions in Iceland results in CO2 and S fluxes of ...