HR: 12:00h
AN: U12A-07    [Abstracts]
TI: Changes in Crystal Structure and Thermo-Elastic Properties of (Mg,Fe)SiO₃ across the Post-Perovskite Transition
AU: * Shim, S
EM: sangshim@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Catalli, K
EM: krystle@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Hustoft, J
EM: hustoft@mit.edu
AF: Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States
AU: Kubo, A
EM: akubo@cars.uchicago.edu
AF: University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637, United States
AU: Caldwell, W
EM: wacaldwell@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, United States
AU: Kunz, M
EM: mkunz@lbl.gov
AF: Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA 94720, United States
AB: Recent studies have proposed intriguing changes in physical properties across the post-perovskite transition which may explain some enigmatic seismic observations at the lowermost mantle. However, most of these predictions are based on first-principles calculations and high-quality measurements have been difficult due to the extreme P-T stability of post-perovskite. We measured diffraction patterns of (Mg_0.91Fe_0.09)SiO₃ post-perovskite over wide P-T conditions (37-126 GPa at 300 K and 135 GPa at 2300-2700 K), some of which are directly relevant to the conditions expected for the D" layer, under an argon pressure medium and the gold pressure scale. Through Rietveld refinement, we confirmed the proposed crystal structure of post-perovskite, which provides a critical test for the first-principles predictions. Combined with our measurements on perovskite, we found that density increases by 1.8± 0.1% and bulk modulus decreases by 6.5± 2.0%, resulting in a 3.9± 1.5% decrease in bulk sound speed across the post- perovskite transition, which is consistent with first-principles predictions. This implies that variations in mineralogy between perovskite and post-perovskite may result in anti-correlation between the bulk sound speed and shear wave velocity anomalies combined with the predicted shear wave velocity increase. Our high- temperature data suggest that Grüneisen parameter decreases by 21± 15% across the post-perovskite transition, which would influence the dynamic stability of the post-perovskite patches reported by recent seismic studies.
DE: 3919 Equations of state
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Union [U]
MN: 2007 Fall Meeting