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Hydrogen analysis in nominally anhydrous minerals by transmission Raman spectroscopy
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Department of GeosciencesSwedish Musuem of Natural HistoryStockholmSweden.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics.ORCID iD: 0000-0001-9992-8009
Department of GeosciencesSwedish Musuem of Natural HistoryStockholmSweden.
2018 (English)In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 45, no 7, p. 597-607Article in journal (Refereed) Published
Abstract [en]

We present a new approach for the analysis of water in nominally anhydrous minerals using transmission Raman spectroscopy. Using this approach, the laser was shone through thin, nearly transparent samples of clinopyroxene, garnet and synthetic rhyolite glass. To remove mineral-induced background and to improve the quality of the OH spectral region, specifically for clinopyroxene, a reference spectrum of a dehydrated crystal was measured and subtracted. Water contents of all clinopyroxene samples were previously determined by Fourier transformed infrared spectroscopy (FTIR). The application of transmission Raman spectroscopy and a reference spectrum of a dry sample revealed a noticeable improvement in the quality of spectra and thus the detection limit, compared to the standard backscattering configurations. We show that the quality of transmission spectra and the detection limit depend on the sample thickness, and that the thickness has to be taken into account when measuring and comparing OH-integrated intensity and water content if the results are used for OH quantification.

Place, publisher, year, edition, pages
2018. Vol. 45, no 7, p. 597-607
National Category
Geosciences, Multidisciplinary
Identifiers
URN: urn:nbn:se:uu:diva-306207DOI: 10.1007/s00269-018-0945-2ISI: 000436406600001OAI: oai:DiVA.org:uu-306207DiVA, id: diva2:1040096
Funder
Swedish Research CouncilAvailable from: 2016-10-26 Created: 2016-10-26 Last updated: 2018-09-06Bibliographically 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. p. 64
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1448
Keywords
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, FranzLazor, Peter

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