TY - JOUR
T1 - Mg/Si ratios of aqueous fluids coexisting with forsterite and enstatite based on the phase relations in the Mg2SiO4-SiO 2-H2O system
AU - Kawamoto, Tatsuhiko
AU - Matsukage, Kyoko N.
AU - Mibe, Kenji
AU - Nishibori, Maiko
AU - Nishimura, Koshi
AU - Ishimatsu, Naoki
AU - Ono, Shigeaki
PY - 2004/1/1
Y1 - 2004/1/1
N2 - 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.
AB - 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.
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U2 - 10.2138/am-2004-1010
DO - 10.2138/am-2004-1010
M3 - Article
AN - SCOPUS:7444227982
VL - 89
SP - 1433
EP - 1437
JO - American Mineralogist
JF - American Mineralogist
SN - 0003-004X
IS - 10
ER -