Post-spinel transition in Mg2SiO4 determined by high P - T in situ X-ray diffractometry

Tomoo Katsura, Hitoshi Yamada, Toru Shinmei, Atsushi Kubo, Shigeaki Ono, Masami Kanzaki, Akira Yoneda, Michael J. Walter, Eiji Ito, Satoru Urakawa, Kenichi Funakoshi, Wataru Utsumi

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Abstract

The phase boundary of the post-spinel transition in Mg2SiO4 was re-investigated by means of high P - T in situ X-ray diffractometry with a gold pressure marker in a Kawai-type apparatus. Rapid and continuous temperature changes were conducted to initiate dissociation of spinel, which tends to be inert after long annealing. Isothermal decompression at high temperature was conducted to form spinel from perovskite plus periclase. The phase boundary is located at ca. 22 GPa in the temperature range from 1550 to 2100 K, which is 1-1.5 GPa lower than the 660 km discontinuity. This discrepancy might be explained in terms of the pressure effect of thermocouple emf and inaccurate equation of state (EOS) for the pressure maker. The transition is found to be less sensitive to temperature than reported previously, with a Clapeyron slope ranging from -2 to -0.4 MPa/K. This small Clapeyron slope implies that the post-spinel transition would not be an effective barrier to mantle convection.

Original languageEnglish
Pages (from-to)11-24
Number of pages14
JournalPhysics of the Earth and Planetary Interiors
Volume136
Issue number1-2
DOIs
Publication statusPublished - Apr 15 2003

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Keywords

  • 660 km discontinuity
  • High pressures and temperatures
  • In situ X-ray diffractometry
  • Mantle
  • MgSiO
  • Post-spinel transition

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Geophysics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science

Cite this

Katsura, T., Yamada, H., Shinmei, T., Kubo, A., Ono, S., Kanzaki, M., Yoneda, A., Walter, M. J., Ito, E., Urakawa, S., Funakoshi, K., & Utsumi, W. (2003). Post-spinel transition in Mg2SiO4 determined by high P - T in situ X-ray diffractometry. Physics of the Earth and Planetary Interiors, 136(1-2), 11-24. https://doi.org/10.1016/S0031-9201(03)00019-0