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Science 28 April 2006:
Vol. 312. no. 5773, pp. 564 - 565
DOI: 10.1126/science.1123442
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Reports

Iron-Rich Post-Perovskite and the Origin of Ultralow-Velocity Zones

Wendy L. Mao,1* Ho-kwang Mao,2,3 Wolfgang Sturhahn,4 Jiyong Zhao,4 Vitali B. Prakapenka,5 Yue Meng,3 Jinfu Shu,2 Yingwei Fei,2 Russell J. Hemley2

The boundary layer between the crystalline silicate lower mantle and the liquid iron core contains regions with ultralow seismic velocities. Such low compressional and shear wave velocities and high Poisson's ratio are also observed experimentally in post-perovskite silicate phase containing up to 40 mol% FeSiO3 endmember. The iron-rich post-perovskite silicate is stable at the pressure-temperature and chemical environment of the core-mantle boundary and can be formed by core-mantle reaction. Mantle dynamics may lead to further accumulation of this material into the ultralow-velocity patches that are observable by seismology.

1 Lujan Neutron Scattering Center, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
2 Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
3 High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
4 X-ray Operations and Research, Advanced Photon Source, Argonne National Laboratory, Argonne, IL 60439, USA.
5 University of Chicago, Chicago, IL 60637, USA.

* To whom correspondence should be addressed. E-mail: wmao{at}lanl.gov

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