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Science 28 September 2001:
Vol. 293. no. 5539, pp. 2437 - 2440
DOI: 10.1126/science.1061235
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Reports

Stability and Structure of MgSiO3 Perovskite to 2300-Kilometer Depth in Earth's Mantle

Sang-Heon Shim,1*dagger Thomas S. Duffy,1 Guoyin Shen2

Unexplained features have been observed seismically near the middle (~1700-kilometer depth) and bottom of the Earth's lower mantle, and these could have important implications for the dynamics and evolution of the planet. (Mg,Fe)SiO3 perovskite is expected to be the dominant mineral in the deep mantle, but experimental results are discrepant regarding its stability and structure. Here we report in situ x-ray diffraction observations of (Mg,Fe)SiO3 perovskite at conditions (50 to 106 gigapascals, 1600 to 2400 kelvin) close to a mantle geotherm from three different starting materials, (Mg0.9Fe0.1)SiO enstatite, MgSiO3 glass, and an MgO+SiO2 mixture. Our results confirm the stability of (Mg,Fe)SiO3 perovskite to at least 2300-kilometer depth in the mantle. However, diffraction patterns above 83 gigapascals and 1700 kelvin (1900-kilometer depth) cannot presently rule out a possible transformation from Pbnm perovskite to one of three other possible perovskite structures with space group P21/m, Pmmn, or P42/nmc.

1 Department of Geosciences, Princeton University, Princeton, NJ 08544, USA.
2 CARS, University of Chicago, Chicago, IL 60637, USA.
*   To whom correspondence should be addressed. E-mail: sangshim{at}uclink.berkeley.edu

dagger    Present address: Department of Earth and Planetary Science, University of California, Berkeley, CA 94720-4767, USA.

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