Equation of state of the postperovskite phase synthesized from a natural (Mg,Fe)SiO 3 orthopyroxene

Proceedings of the National Academy of Sciences of the United States of America - Tập 103 Số 9 - Trang 3039-3043 - 2006
S. R. Shieh1, Yue Meng2, Atsushi Kubo2, Guoyin Shen3, Vitali B. Prakapenka3, Nagayoshi Sata4, Kei Hirose5, Yasuo Ohishi6
1Department of Earth Sciences, National Cheng Kung University, Tainan 701, Taiwan
2Department of Geosciences, Princeton University, Princeton, NJ 08544;
3GeoSoilEnviroCARS, University of Chicago, Chicago, IL 60637;
4Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-Cho, Yokosuka-city, Kanagawa 237-0061, Japan
5**Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8550, Japan; and
6Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan

Tóm tắt

Using the laser-heated diamond anvil cell, we investigate the stability and equation of state of the postperovskite (ppv, CaIrO 3 -type) phase synthesized from a natural pyroxene composition with 9 mol.% FeSiO 3 . Our measured pressure-volume data from 12–106 GPa for the ppv phase yield a bulk modulus of 219( 5 ) GPa and a zero-pressure volume of 164.9( 6 ) Å 3 when K ′ 0 = 4. The bulk modulus of ppv is 575( 15 ) GPa at a pressure of 100 GPa. The transition pressure is lowered by the presence of Fe. Our x-ray diffraction data indicate the ppv phase can be formed at P > 109( 4 ) GPa and 2,400(400) K, corresponding to ≈400–550 km above the core-mantle boundary. Direct comparison of volumes of coexisting perovskite and CaIrO 3 -type phases at 80–106 GPa demonstrates that the ppv phase has a smaller volume than perovskite by 1.1( 2 )%. Using measured volumes together with the bulk modulus calculated from equation of state fits, we find that the bulk sound velocity decreases by 2.3(2.1)% across this transition at 120 GPa. Upon decompression without further heating, it was found that the ppv phase could still be observed at pressures as low at 12 GPa, and evidence for at least partial persistence to ambient conditions is also reported.

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Proceedings of the National Academy of Sciences of the United States of America

Tập 103 Số 9

3039-3043

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