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Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust

Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust


Title: Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust
Author: Kleine, Barbara Irene   orcid.org/0000-0002-9440-2734
Stefánsson, Andri
Halldórsson, Sæmundur Ari   orcid.org/0000-0002-4724-8578
Whitehouse, M.J.
Jónasson, Kristján
Date: 2018-04
Language: English
Scope: 5-11
University/Institute: Háskóli Íslands
University of Iceland
School: Verkfræði- og náttúruvísindasvið (HÍ)
School of Engineering and Natural Sciences (UI)
Department: Jarðvísindastofnun (HÍ)
Institute of Earth Sciences (UI)
Series: Geochemical Perspectives Letters;7
ISSN: 2410-339X
2410-3403 (eISSN)
DOI: 10.7185/geochemlet.1811
Subject: Silicon isotopes; Oxygen isotopes; SIMS; Quartz; Isotope modelling; Hydrothermal fluid; Kvars; Kristallafræði; Jarðskorpa; Jarðhiti
URI: https://hdl.handle.net/20.500.11815/855

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Citation:

Kleine, B. I., Stefánsson, A., Halldórsson, S. A., Whitehouse, M. J., & Jónasson, K. (2018). Silicon and oxygen isotopes unravel quartz formation processes in the Icelandic crust. Geochemical Perspectives Letters, 7, 5-11. doi:/10.7185/geochemlet.1811

Abstract:

Quartz formation processes in the Icelandic crust were assessed using coupled δ18O and δ30Si systematics of silica deposits formed over a wide temperature range (<150 to >550 °C). Magmatic quartz reveals δ18O (-5.6 to +6.6 ‰) and δ30Si (-0.4 ± 0.2 ‰) values representative of mantle- and crustally-derived melts in Iceland. Hydrothermal quartz and silica polymorphs display a larger range of δ18O (-9.3 to +30.1 ‰) and δ30Si (-4.6 to +0.7 ‰) values. Isotope modelling reveals that such large variations are consistent with variable water sources and equilibrium isotope fractionation between fluids and quartz associated with secondary processes occurring in the crust, including fluid-rock interaction, boiling and cooling. In context of published δ18O and δ30Si data on hydrothermal silica deposits, we demonstrate that large ranges in δ30Si values coupled to insignificant δ18O variations may result from silica precipitation in a hydrothermal fluid conduit associated with near-surface cooling. While equilibrium isotope fractionation between fluids and quartz seems to prevail at high temperatures, kinetic fractionation likely influences isotope systematics at low temperatures.

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This work is distributed under the Creative Commons Attribution 4.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

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