TY - JOUR
T1 - Sound velocity of MgSiO3 post-perovskite phase
T2 - A constraint on the D″ discontinuity
AU - Murakami, Motohiko
AU - Sinogeikin, Stanislav V.
AU - Bass, Jay D.
AU - Sata, Nagayoshi
AU - Ohishi, Yasuo
AU - Hirose, Kei
N1 - Funding Information:
We thank B. Mysen, D. Yamazaki, T. Katsura, T. Yoshino, A. Yoneda and E. Ito for their helpful comments, and T. Matsuzaki for help with the photomicropraph. This research was partially supported by the Grant-in-Aid for ‘Stagnant Slab Project’ in Scientific Research on Priority Areas, 2005 by the Ministry of Education, Science, Sports and Culture, Japan (to MM), and by the NSF under grants EAR 0003383, 0002021, and 0135642 (to JDB).
PY - 2007/7/15
Y1 - 2007/7/15
N2 - The discovery of a post-perovskite phase transition in MgSiO3 has significant implications for seismological observations in the D″ region at the bottom of Earth's mantle. The D″ discontinuity, which is manifested as a sharp positive seismic-wave velocity jump 200-300 km above the core-mantle boundary (at pressure of 119∼ 125 GPa), is one of the most enigmatic seismic features in this region. Whether this velocity increase may be due to the formation of a post-perovskite phase at the D″ discontinuity has not, however, been directly addressed by experiments. Here we present the results of aggregate sound velocity measurements of the MgSiO3 post-perovskite phase by Brillouin spectroscopy in the diamond anvil cell (DAC) up to a pressure of 172 GPa, in combination with infrared laser annealing of the sample. Based on these results and our recent high-pressure velocity measurements on perovskite, the aggregate shear wave velocity contrast across the perovskite to post-perovskite phase transition is at most 0.5%. This contrast is much smaller than typically observed across the D″ discontinuity, indicating that the formation of an isotropic aggregate of the post-perovskite phase provides an insufficient velocity increase to explain the D″ discontinuity. Lattice preferred orientation (LPO) of post-perovskite is likely to be crucial for explaining the D″ discontinuity.
AB - The discovery of a post-perovskite phase transition in MgSiO3 has significant implications for seismological observations in the D″ region at the bottom of Earth's mantle. The D″ discontinuity, which is manifested as a sharp positive seismic-wave velocity jump 200-300 km above the core-mantle boundary (at pressure of 119∼ 125 GPa), is one of the most enigmatic seismic features in this region. Whether this velocity increase may be due to the formation of a post-perovskite phase at the D″ discontinuity has not, however, been directly addressed by experiments. Here we present the results of aggregate sound velocity measurements of the MgSiO3 post-perovskite phase by Brillouin spectroscopy in the diamond anvil cell (DAC) up to a pressure of 172 GPa, in combination with infrared laser annealing of the sample. Based on these results and our recent high-pressure velocity measurements on perovskite, the aggregate shear wave velocity contrast across the perovskite to post-perovskite phase transition is at most 0.5%. This contrast is much smaller than typically observed across the D″ discontinuity, indicating that the formation of an isotropic aggregate of the post-perovskite phase provides an insufficient velocity increase to explain the D″ discontinuity. Lattice preferred orientation (LPO) of post-perovskite is likely to be crucial for explaining the D″ discontinuity.
KW - Brillouin scattering
KW - D″ discontinuity
KW - MgSiO post-perovskite
KW - elastic properties
KW - high pressure
KW - sound velocity
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U2 - 10.1016/j.epsl.2007.04.015
DO - 10.1016/j.epsl.2007.04.015
M3 - Article
AN - SCOPUS:34250663072
SN - 0012-821X
VL - 259
SP - 18
EP - 23
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
IS - 1-2
ER -