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Science 13 March 1998:
Vol. 279. no. 5357, pp. 1698 - 1700
DOI: 10.1126/science.279.5357.1698
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Reports

The Postspinel Phase Boundary in Mg2SiO4 Determined by in Situ X-ray Diffraction

Tetsuo Irifune, Norimasa Nishiyama, Koji Kuroda, Toru Inoue, Maiko Isshiki, Wataru Utsumi, Ken-ichi Funakoshi, Satoru Urakawa, Takeyuki Uchida, Tomoo Katsura, Osamu Ohtaka

The phase boundary between spinel (gamma  phase) and MgSiO3 perovskite + MgO periclase in Mg2SiO4 was determined by in situ x-ray measurements by a combination of the synchrotron radiation source (SPring-8) and a large multianvil high-pressure apparatus. The boundary was determined at temperatures between 1400° to 1800°C, demonstrating that the postspinel phase boundary has a negative Clapeyron slope as estimated by quench experiments and thermodynamic analyses. The boundary was located at 21.1 (±0.2) gigapascals, at 1600°C, which is ~2 gigapascals lower than earlier estimates based on other high-pressure studies.

T. Irifune, N. Nishiyama, K. Kuroda, T. Inoue, M. Isshiki, Department of Earth Sciences, Ehime University, Matsuyama 790, Japan.
W. Utsumi, Japan Atomic Energy Research Institute, Kamigori, Ako-gun, Hyogo 678-12, Japan.
K. Funakoshi, Japan Synchrotron Radiation Research Institute, Kamigori, Ako-gun, Hyogo 678-12, Japan.
S. Urakawa, Department of Earth Sciences, Okayama University, Okayama 700, Japan.
T. Uchida, Institute for Solid State Physics, University of Tokyo, Roppongi, Tokyo 106, Japan.
T. Katsura, Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-01, Japan.
O. Ohtaka, Department of Space and Earth Sciences, Osaka University, Toyonaka 560, Japan.

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