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Impact of fluid-rock interaction on water uptake of the Icelandic crust: Implications for the hydration of the oceanic crust and the subducted water flux

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dc.contributor Háskóli Íslands
dc.contributor University of Iceland
dc.contributor.author Kleine, Barbara Irene
dc.contributor.author Stefansson, Andri
dc.contributor.author Halldorsson, Saemundur
dc.contributor.author Barnes, J.D.
dc.date.accessioned 2020-12-01T11:02:37Z
dc.date.available 2020-12-01T11:02:37Z
dc.date.issued 2020
dc.identifier.citation Kleine, B. I., Stefánsson, A., Halldórsson, S. A., & Barnes, J. D. (2020). Impact of fluid-rock interaction on water uptake of the Icelandic crust: Implications for the hydration of the oceanic crust and the subducted water flux. Earth and Planetary Science Letters, 538, 116210. doi:https://doi.org/10.1016/j.epsl.2020.116210
dc.identifier.issn 0012-821X
dc.identifier.uri https://hdl.handle.net/20.500.11815/2263
dc.description Pre-print (óritrýnt handrit)
dc.description.abstract Oceanic crust is a major transport medium of water into the mantle wedge and the convecting mantle. Yet, the water content of the oceanic crust remains uncertain. Active geothermal systems situated at on-land spreading centers provide a unique opportunity to study the hydration of the oceanic crust, with well constrained systems and boreholes reaching depths of >4 km. Here, we present hydrogen isotope data of geothermal fluids and altered basalt for three Icelandic geothermal systems: the meteoric water fed system at Krafla and the seawater fed systems at Reykjanes and Surtsey. The bulk rock δD values of altered and hydrated basalts from these localities, which exhibit significantly higher water contents (up to 8.9 wt.%) than magmatic (non-hydrated) basalts, vary greatly from −125 to −96 at Krafla, from −80 to −46 at Reykjanes and from −78 to −46 at Surtsey. The corresponding fluids have δD values of −84.1 to −81.1 at Krafla, −23.1 to −14.9 at Reykjanes and +2.1 to +4.3 at Surtsey. Comparison of isotope modeling results to the natural data reveals that hydration of the Icelandic crust and corresponding hydrogen isotopic characteristics are controlled by (1) the isotope composition of the source fluid, (2) isotope fractionation between the aqueous geothermal fluids and the alteration minerals formed, and (3) the type and quantity of alteration minerals formed. These factors in turn depend on the extent of fluid-rock interaction and temperature. Using the same modeling approach and expanding it to datasets available for the oceanic crust, we assessed the hydration state and δD values of the oceanic crust as a function of depth. We show that 1400 to 1650 Tg H2O/yr is added to the igneous oceanic crust upon alteration by seawater and that the upper part (<2 km) of oceanic crust hosts almost 50% of the added water. The corresponding hydrogen isotope composition of the hydrated crust was calculated to an average of −55 ±6 . Upon subduction and subsequent dehydration, 80–90% of water with δD values of −35 to −10 will be released to the crustal forearc and mantle wedge. The remaining dehydrated slab with δD values of ∼−160 to −85 is expected to be transported to deeper levels modifying the mantle’s water budget and isotopic composition.
dc.description.sponsorship This project was financially supported by NordVulk, the International Continental Scientific Drilling Program (ICDP) through a grant to the SUSTAIN project, and the Icelandic Research Fund (project number: 163083-051). SAH acknowledges support from the Icelandic Research Fund (project number: 196139-051). HS Orka and Landsvirkjun kindly provided access to the drill cuttings. J. Cullen, T. Larson, R. Ólafsdóttir and Á.E. Sveinbjörnsdóttir are thanked for assistance during sample preparation and data acquisition. BIK is particularly grateful of being part of this project as without the project-related lab work she would have never met her future husband E.W. Marshall IV. We thank four anonymous reviewers for their constructive comments and suggestions to an earlier version of this manuscript. Louis Derry is thanked for careful editorial handling of this study.
dc.format.extent 116210
dc.language.iso en
dc.publisher Elsevier BV
dc.relation.ispartofseries Earth And Planetary Science Letters;538
dc.rights info:eu-repo/semantics/openAccess
dc.subject Jarðhiti
dc.subject Jarðskorpa
dc.subject Hydrogen isotopes
dc.subject Water cycling
dc.subject Oceanic crust
dc.subject Fluid-rock interaction
dc.title Impact of fluid-rock interaction on water uptake of the Icelandic crust: Implications for the hydration of the oceanic crust and the subducted water flux
dc.type info:eu-repo/semantics/article
dc.identifier.journal Earth And Planetary Science Letters
dc.identifier.doi 10.1016/j.epsl.2020.116210
dc.contributor.department Jarðvísindastofnun (HÍ)
dc.contributor.department Institute of Earth Sciences (UI)
dc.contributor.school Verkfræði- og náttúruvísindasvið (HÍ)
dc.contributor.school School of Engineering and Natural Sciences (UI)

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