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Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
Swedish Museum Nat Hist, Dept Geosci, Stockholm, Sweden..
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Physics (GEOVOL), University of Las Palmas de Gran Canaria, Las Palmas de Gran Canaria, Spain. (CEMPEG)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of Geological Science, Stockholm University, Stockholm, Sweden. (CEMPEG)
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2015 (English)In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 7, 2127-2146 p.Article in journal (Refereed) Published
Abstract [en]

Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles, because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. The parental water content of a magma is usually measured through melt inclusions in minerals such as olivine, a method which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapment changes in their water content. An alternative way to reconstruct the water content of a magma is to use nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogen as a function of the magma's water content. During magma degassing and eruption, however, NAMs may dehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrysts from the Western Canary islands (n=28) through rehydration experiments followed by infrared and Mossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experiments were used to calculate parental water contents of 0.710.07 to 1.490.15 wt % H2O for Western Canary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreement with calculated water contents using plagioclase-liquid-hygrometry, and with previously published data for mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs in combination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which we anticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

Place, publisher, year, edition, pages
2015. Vol. 16, no 7, 2127-2146 p.
Keyword [en]
Canary Islands, NAMs, clinopyroxene, hydrogen, magmatic water content
National Category
Geophysics Geochemistry
Research subject
Earth Science with specialization in Mineral Chemistry, Petrology and Tectonics
Identifiers
URN: urn:nbn:se:uu:diva-263041DOI: 10.1002/2015GC005800ISI: 000360247200007Scopus ID: 2-s2.0-84938855029OAI: oai:DiVA.org:uu-263041DiVA: diva2:857486
Funder
Swedish Research CouncilThe Royal Swedish Academy of SciencesSwedish Research Council
Available from: 2015-09-29 Created: 2015-09-24 Last updated: 2017-12-01Bibliographically approved
In thesis
1. Hydrogen in nominally anhydrous silicate minerals: Quantification methods, incorporation mechanisms and geological applications
Open this publication in new window or tab >>Hydrogen in nominally anhydrous silicate minerals: Quantification methods, incorporation mechanisms and geological applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The aim of this thesis is to increase our knowledge and understanding of trace water concentrations in nominally anhydrous minerals (NAMs). Special focus is put on the de- and rehydration mechanisms of clinopyroxene crystals in volcanic systems, how these minerals can be used to investigate the volatile content of mantle rocks and melts on both Earth and other planetary bodies (e.g., Mars). Various analytical techniques for water concentration analysis were evaluated.

The first part of the thesis focusses on rehydration experiments in hydrogen gas at 1 atm and under hydrothermal pressures from 0.5 to 3 kbar on volcanic clinopyroxene crystals in order to test hydrogen incorporation and loss from crystals and how their initial water content at crystallization prior to dehydration may be restored. The results show that extensive dehydration may occur during magma ascent and degassing but may be hindered by fast ascent rates with limited volatile loss. De- and rehydration processes are governed by the redox-reaction OH- + Fe2+ ↔ O2- + Fe3+ + ½ H2. Performing rehydration experiments at different pressures can restore the water contents of clinopyroxene at various levels in the volcanic systems. Subsequently water contents of magmas and mantle sources can be deduced based on crystal/melt partition coefficients. This thesis provides examples from the Canary Islands, Merapi volcano in Indonesia and the famous Nakhla meteorite. Using NAMs as a proxy for magmatic and mantle water contents may provide a very good method especially for planetary science where sample material is limited.

The thesis’ second part focusses on analytical methods to measure the concentration of water in NAMs. Specifically the application of Raman spectroscopy and proton-proton scattering are tested. The hydrated mineral zoisite is thoroughly analyzed in order to be used as an external standard material. Polarized single crystal spectra helped to determine the orientation of the OH-dipole in zoisite. Further, Transmission Raman spectroscopy and a new method for the preparation of very thin samples for proton-proton scattering were developed and tested. The results provide new possibilities for the concentration analysis of water in NAMs such as three dimensional distribution and high spatial resolution.                       

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. 64 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1448
Keyword
NAMs, clinopyroxene, hydrogen, hydrothermal pressure, magmatic water content, zoisite, OH-dipole, Raman spectroscopy, FTIR, luminescence, proton-proton scattering
National Category
Geosciences, Multidisciplinary
Identifiers
urn:nbn:se:uu:diva-306212 (URN)978-91-554-9740-8 (ISBN)
Public defence
2016-12-14, Lilla Hörsalen, Naturhistoriska Riksmuseet, Frescativägen 40, 11418 Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2016-11-21 Created: 2016-10-26 Last updated: 2016-11-28

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Weis, Franz A.Troll, ValentinDeegan, FrancesDahrén, Börje

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