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American Mineralogist

Journal of Earth and Planetary Materials

Ed. by Baker, Don / Xu, Hongwu / Swainson, Ian


IMPACT FACTOR 2018: 2.631

CiteScore 2018: 2.55

SCImago Journal Rank (SJR) 2018: 1.355
Source Normalized Impact per Paper (SNIP) 2018: 1.103

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1945-3027
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Volume 100, Issue 5-6

Issues

Very large differences in intramolecular D-H partitioning in hydrated silicate melts synthesized at upper mantle pressures and temperatures

Ying Wang
  • Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, U.S.A.
  • Other articles by this author:
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/ Samantha X. Cody
  • Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, U.S.A.
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/ Dionysis Foustoukos
  • Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, U.S.A.
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/ Bjorn O. Mysen
  • Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, U.S.A.
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/ George D. Cody
  • Corresponding author
  • Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, NW, Washington, D.C. 20015, U.S.A.
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Published Online: 2015-05-12 | DOI: https://doi.org/10.2138/am-2015-4940

Abstract

Hydrated (with D2O and H2O) sodium tetrasilicate glasses, quenched from melts at 1400 °C and 1.5 GPa, are studied using 1H, 2H, and 29Si solid-state nuclear magnetic resonance (NMR) spectroscopy. Whereas D2O and H2O depolymerize the silicate melt to similar degrees, protium and deuterium intramolecular partitioning between different molecular sites within the glasses is very different and exemplified by a strong preferential association of deuterons to sites with short O-D···O distances. This preference is independent of total water content and D/H ratio. Substantially different intramolecular D-H partitioning is also observed in a glass with a model hydrous basalt composition. Such large differences in isotope partitioning cannot result from classic equilibrium fractionation because of the high synthesis temperature. Potential kinetic isotope effects are excluded via a slow quench experiment. The apparent fractionation is likely governed by density/molar volume isotope effects, where deuterium prefers sites with smaller molar volume. Large differences in intramolecular site partitioning in melts could lead to significant differences in D-H partitioning between water-saturated melt and exsolved aqueous fluid (where D/HW,Melt ≠ D/HW,Fluid) during crystallization of Earth’s magma ocean, potentially controlling the D/H content of the Earth’s oceans.

Keywords: Hydrogen isotopes; silicate melts; fractionation

About the article

Received: 2014-02-17

Accepted: 2014-10-29

Published Online: 2015-05-12

Published in Print: 2015-05-01


Citation Information: American Mineralogist, Volume 100, Issue 5-6, Pages 1182–1189, ISSN (Online) 1945-3027, ISSN (Print) 0003-004X, DOI: https://doi.org/10.2138/am-2015-4940.

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© 2015 by Walter de Gruyter Berlin/Boston.

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