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Published online on June 30, 2005, 10.1073/pnas.0503737102
PNAS | July 12, 2005 | vol. 102 | no. 28 | 9751-9753


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GEOPHYSICS
Iron-rich silicates in the Earth's D'' layer

Wendy L. Mao *, {dagger}, {ddagger}, Yue Meng §, Guoyin Shen ¶, Vitali B. Prakapenka ¶, Andrew J. Campbell *, ||, Dion L. Heinz *, **, Jinfu Shu {dagger}, Razvan Caracas {dagger}, Ronald E. Cohen {dagger}, Yingwei Fei {dagger}, Russell J. Hemley {dagger}, and Ho-kwang Mao *, {dagger}, §, **

*Department of the Geophysical Sciences and ||Chicago Center for Cosmochemistry, University of Chicago, 5734 South Ellis Avenue, Chicago, IL 60637; {dagger}Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road Northwest, Washington, DC 20015; §High Pressure Collaborative Access Team, Advanced Photon Source, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439; and Center for Advanced Radiation Sources and **James Franck Institute, University of Chicago, 5640 South Ellis Avenue, Chicago, IL 60637

Contributed by Ho-kwang Mao, May 6, 2005

High-pressure experiments and theoretical calculations demonstrate that an iron-rich ferromagnesian silicate phase can be synthesized at the pressure–temperature conditions near the core–mantle boundary. The iron-rich phase is up to 20% denser than any known silicate at the core–mantle boundary. The high mean atomic number of the silicate greatly reduces the seismic velocity and provides an explanation to the low-velocity and ultra-low-velocity zones. Formation of this previously undescribed phase from reaction between the silicate mantle and the iron core may be responsible for the unusual geophysical and geochemical signatures observed at the base of the lower mantle.

core–mantle boundary | high pressure | mineral physics | post-perovskite

Author contributions: W.L.M. and H.-k.M. designed research; W.L.M., Y.M., G.S., V.B.P., A.J.C., J.S., R.C., and Y.F. performed research; W.L.M., Y.M., R.C., and R.E.C. analyzed data; W.L.M., D.L.H., R.C., R.E.C., R.J.H., and H.-k.M. wrote the paper; and D.L.H. helped with revisions.

Abbreviation: ppv, postperovskite.

{ddagger} To whom correspondence should be sent at the * address. E-mail: wmao{at}uchicago.edu.

© 2005 by The National Academy of Sciences of the USA


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