Stability of CaCl<sub>2</sub>‐type and α‐PbO<sub>2</sub>‐type SiO<sub>2</sub> at high pressure and temperature determined by in‐situ X‐ray measurements

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  • Motohiko Murakami
    Department of Earth and Planetary Sciences Tokyo Institute of Technology Tokyo Japan
  • Kei Hirose
    Department of Earth and Planetary Sciences Tokyo Institute of Technology Tokyo Japan
  • Shigeaki Ono
    Institute for Frontier Research on Earth Evolution Japan Marine Science and Technology Center Kanagawa Japan
  • Yasuo Ohishi
    Japan Synchrotron Radiation Research Institute Hyogo Japan

書誌事項

公開日
2003-03
権利情報
  • http://onlinelibrary.wiley.com/termsAndConditions#vor
DOI
  • 10.1029/2002gl016722
公開者
American Geophysical Union (AGU)

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説明

<jats:p>Here we report the phase boundary between CaCl<jats:sub>2</jats:sub>‐type and α‐PbO<jats:sub>2</jats:sub>‐type silica at high pressure and temperature up to 151 GPa and 2500‐K determined by in‐situ X‐ray measurements in a laser‐heated diamond anvil cell. Amorphous silica was used as starting material, and the sample was heated for more than 1.5 hr to examine the kinetic effects. The results demonstrated that the CaCl<jats:sub>2</jats:sub>‐type silica is a post‐stishovite phase and that it undergoes further transition to the α‐PbO<jats:sub>2</jats:sub>‐type structure above 121 GPa at 2400‐K. Present data together with previous first‐principles calculations indicate that the phase boundary between CaCl<jats:sub>2</jats:sub>‐type and α‐PbO<jats:sub>2</jats:sub>‐type silica is represented by a linear equation P (GPa) = 98 + (0.0095 ± 0.0016) * T (K). The α‐PbO<jats:sub>2</jats:sub>‐type silica can be present in the deep portion of the lower mantle in the silica‐saturated bulk compositions. This phase transition might contribute to the seismic wave velocity anomalies observed in the D″ region.</jats:p>

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