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Book Chapter

Discovery of post-perovskite phase transition and implications for the nature of the D″ layer of the mantle

By
Kei Hirose
Kei Hirose
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
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Katsuyuki Kawamura
Katsuyuki Kawamura
Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
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Published:
January 01, 2007

MgSiO3 perovskite is a principal mineral in the upper part of the lower mantle, but its stability and possible phase transition at greater depths have long been uncertain Recently, a new high-pressure MgSiO3 polymorph called “post-perovskite” was discovered above 125 GPa and 2500 K on the basis of X-ray diffraction measurements in a laser-heated diamond anvil cell (LH-DAC). Crystal structure of post-perovskite was first determined to be orthorhombic (space group: Cmcm) by molecular dynamics (MD) calculations. The first-principles theoretical calculations also confirmed the stability of this new phase. These results suggest that MgSiO3-rich post-perovskite is a predominant mineral below 2500–2700 km depth near the base of the mantle. The D″ layer has long been the most enigmatic region in Earth's interior. The post-perovskite phase can account for the large seismic anomalies observed in the D″ region, such as D″ discontinuity, polarization anisotropy, and anticorrelation between S-wave and bulk sound velocities. The long-term enigma may be explained with this newly discovered crystal.

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Contents

GSA Special Papers

Advances in High-Pressure Mineralogy

Eiji Ohtani
Eiji Ohtani
Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Tohoku University, Sendai 980-8578, Japan
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Geological Society of America
Volume
421
ISBN print:
9780813724218
Publication date:
January 01, 2007

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