A composition-independent quantitative determination of the water content in silicate glasses and silicate melt inclusions by confocal Raman spectroscopy |
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| Authors: | Zoltán Zajacz Werner Halter Wim J Malfait Olivier Bachmann Robert J Bodnar Marc M Hirschmann Charles W Mandeville Yann Morizet Othmar Müntener Peter Ulmer James D Webster |
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| Institution: | (1) Department of Earth Sciences, Isotope Geochemistry and Mineral Resources, ETH Zürich, 8092 Zürich, Switzerland;(2) Section des Sciences de la Terre, Université de Genève, Département de Minéralogie 13, rue des Maraìchers, 1211 GENEVE 4, Switzerland;(3) Department of Geosciences, 4044 Derring Hall, Virginia Tech, Blacksburg, VA 24061-0420, USA;(4) Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, USA;(5) Department of Earth and Planetary Sciences, A.M.N.H., Central Park West at 79th Street, New York, NY 10024-5192, USA;(6) Now at: Laboratory of Planetology and Geodynamic, University of Nantes, 2 rue de la Houssiniere, 44300 Nantes, France;(7) Institute of Geological Sciences, University of Bern, Baltzerstr. 1, 3012 Bern, Switzerland;(8) Department of Earth Sciences, Institute for Mineralogy and Petrology, ETH Zürich, 8092 Zürich, Switzerland |
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| Abstract: | A new approach was developed to measure the water content of silicate glasses using Raman spectroscopy, which is independent
of the glass matrix composition and structure. Contrary to previous studies, the compositional range of our studied silicate
glasses was not restricted to rhyolites, but included andesitic, basaltic and phonolitic glasses. We used 21 glasses with
known water contents for calibration. To reduce the uncertainties caused by the baseline removal and correct for the influence
of the glass composition on the spectra, we developed the following strategy: (1) application of a frequency-dependent intensity
correction of the Raman spectra; (2) normalization of the water peak using the broad T–O and T–O–T vibration band at 850–1250 cm−1 wavenumbers (instead of the low wavenumber T–O–T broad band, which appeared to be highly sensitive to the FeO content and
the degree of polymerization of the melt); (3) normalization of the integrated Si-O band area by the total number of tetrahedral
cations and the position of the band maximum. The calibration line shows a ±0.4 wt% uncertainty at one relative standard deviation
in the range of 0.8–9.5 wt% water and a wide range of natural melt compositions. This method provides a simple, quick, broadly
available and cost-effective way for a quantitative determination of the water content of silicate glasses. Application to
silicate melt inclusions yielded data in good agreement with SIMS data. |
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