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

Ranta E, Halldorsson SA, Barry PH, Ono S, Robin JG, Kleine BI, Ricci A, Fiebig J, Sveinbjornsdottir AE, Stefansson A (2023)

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Publication Type: Journal article

Publication year: 2023

Journal

Book Volume: 436

Article Number: 107776

DOI: 10.1016/j.jvolgeores.2023.107776

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 330–5060 and 6–210 kt/yr, respectively, which is sufficient to account for the estimated CO2 flux of Icelandic VHSs (3365–6730 kt/yr), but not the VHS S flux (220–440 kt/yr). Secondary, crystallization-driven degassing from maturing intrusions and leaching of crustal rocks are suggested as additional sources of S. Only a minor proportion of the mantle flux of Cl is channeled via VHSs whereas the H2O flux remains poorly constrained, because magmatic signals in Icelandic VHSs are masked by a dominant shallow groundwater component of meteoric water origin. These results suggest that the bulk of the mantle CO2 and S flux to the atmosphere in Iceland is supplied by intrusive, not eruptive magmatism, and is largely vented via hydrothermal fields.

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APA:

Ranta, E., Halldorsson, S.A., Barry, P.H., Ono, S., Robin, J.G., Kleine, B.I.,... Stefansson, A. (2023). Deep magma degassing and volatile fluxes through volcanic hydrothermal systems: Insights from the Askja and Kverkfjöll volcanoes, Iceland. Journal of Volcanology and Geothermal Research, 436. https://dx.doi.org/10.1016/j.jvolgeores.2023.107776

MLA:

Ranta, Eemu, et al. "Deep magma degassing and volatile fluxes through volcanic hydrothermal systems: Insights from the Askja and Kverkfjöll volcanoes, Iceland." Journal of Volcanology and Geothermal Research 436 (2023).

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