Sound velocity of MgSiO3 post-perovskite phase: A constraint on the D″ discontinuity

Motohiko Murakami, Stanislav V. Sinogeikin, Jay D. Bass, Nagayoshi Sata, Yasuo Ohishi, Kei Hirose

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Pages (from-to)18-23
Number of pages6
JournalEarth and Planetary Science Letters
Volume259
Issue number1-2
DOIs
StatePublished - Jul 15 2007

Keywords

  • Brillouin scattering
  • D″ discontinuity
  • MgSiO post-perovskite
  • elastic properties
  • high pressure
  • sound velocity

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

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