Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO 2-H2O system

Tatsuhiko Kawamoto, Kyoko N. Matsukage, Kenji Mibe, Maiko Nishibori, Koshi Nishimura, Naoki Ishimatsu, Shigeaki Ono

Research output: Contribution to journalArticle

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Abstract

Direct observation of aqueous fluids coexisting with MgSiO3 (enstatite) and/or Mg2SiO4 (forsterite) was performed at 0.5-5.8 GPa and 800-1000 °C with an externally heated diamond-anvil cell and synchrotron X-rays. At 1000 °C in the MgSiO 3-H2O system, forsterite crystallizes below 3 GPa but not above that pressure. At 1000 °C in the Mg 2SiO3-H2O system, forsterite congruently dissolves into the aqueous fluids up to 5 GPa. These observations suggest that the aqueous fluids coexisting with enstatite and forsterite have Mg/Si < 1 below 3 GPa and 1 < Mg/Si < 2 above that pressure. Comparison with the previous studies reporting Mg /Si ratios of the aqueous fluid coexisting with enstatite and forsterite indicates that the Mg/Si ratios change rapidly from SiO2-rich to MgO-rich at around 3 GPa and 1000 °C. This change can be related to possible structural changes of liquid water under these conditions. The aqueous fluids coexisting with enstatite and forsterite do have Mg /Si ratios similar to those found in the partial melts of H 2O-saturated peridotite. Somewhere within the upper mantle, these two fluids unite to form a single regime and cannot be distinguished from each other.

Original languageEnglish
Pages (from-to)1433-1437
Number of pages5
JournalAmerican Mineralogist
Volume89
Issue number10
DOIs
Publication statusPublished - Jan 1 2004
Externally publishedYes

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enstatite
forsterite
Fluids
fluid
fluids
diamond anvil cell
peridotite
Diamond
anvils
structural change
upper mantle
Synchrotrons
synchrotrons
Earth mantle
diamonds
melt
liquid
X rays
liquids
cells

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Geochemistry and Petrology

Cite this

Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO 2-H2O system. / Kawamoto, Tatsuhiko; Matsukage, Kyoko N.; Mibe, Kenji; Nishibori, Maiko; Nishimura, Koshi; Ishimatsu, Naoki; Ono, Shigeaki.

In: American Mineralogist, Vol. 89, No. 10, 01.01.2004, p. 1433-1437.

Research output: Contribution to journalArticle

Kawamoto, Tatsuhiko ; Matsukage, Kyoko N. ; Mibe, Kenji ; Nishibori, Maiko ; Nishimura, Koshi ; Ishimatsu, Naoki ; Ono, Shigeaki. / Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO 2-H2O system. In: American Mineralogist. 2004 ; Vol. 89, No. 10. pp. 1433-1437.
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