Sound velocity of MgSiO 3 post-perovskite phase: A constraint on the D ″ discontinuity

Details Sound velocity of MgSiO 3 post-perovskite phase: A constraint on the D ″ discontinuity Sound velocity of MgSiO 3 post-perovskite phase: A constraint on the D ″ discontinuity

Jul 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007e%26psl.259...18m&link_type=abstract

Earth and Planetary Science Letters, Volume 259, Issue 1-2, p. 18-23.

Computer Science

Sound

17

Mgsio 3 Post-Perovskite, D ″ Discontinuity, Sound Velocity, Brillouin Scattering, Elastic Properties, High Pressure

Scientific paper

Abstract The discovery of a post-perovskite phase transition in MgSiO 3 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 MgSiO 3 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.

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