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Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region

Wicks, J. K. and Jackson, J. M. and Sturhahn, W. (2010) Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region. Geophysical Research Letters, 37 . Art. No. L15304. ISSN 0094-8276.

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The sound velocities of (Mg_(.16)Fe_(.84))O have been measured to 121 GPa at ambient temperature using nuclear resonant inelastic x-ray scattering. The effect of electronic environment of the iron sites on the sound velocities were tracked in situ using synchrotron Mössbauer spectroscopy. We found the sound velocities of (Mg_(.16)Fe_(.84))O to be much lower than those in other presumed mantle phases at similar conditions, most notably at very high pressures. Conservative estimates of the effect of temperature and dilution on aggregate sound velocities show that only a small amount of iron-rich (Mg,Fe)O can greatly reduce the average sound velocity of an assemblage. We propose that iron-rich (Mg,Fe)O be a source of ultra-low velocity zones. Other properties of this phase, such as enhanced density and dynamic stability, strongly support the presence of iron-rich (Mg,Fe)O in localized patches above the core-mantle boundary.

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Additional Information:© 2010 by the American Geophysical Union. Received 22 April 2010; accepted 21 June 2010; published 10 August 2010. We thank H. Yavas, J. Beckett, D. Zhang, C. Murphy, and A. Wolf for assistance with the measurements and NSFEAR 0711542 and CSEDI EAR‐0855815 for financial support. Use of the Advanced Photon Source was supported by the U.S. D.O.E., O.S., O.B.E.S. (DE-AC02-06CH11357). Sector 3 operations are partially supported by COMPRES (NSF EAR 06-49658). The Advanced Light Source is supported by the Director, O.S., O.B.E.S., of the U.S. D.O.E. (DE-AC02-05CH11231). Microprobe analyses were carried out at the Caltech GPS Division Analytical Facility (funded in part by the MRSEC Program of the NSF under DMR-0080065).
Funding AgencyGrant Number
Cooperative Studies Of The Earth's Deep Interior (CSEDI) EAR-0855815
Department of Energy (DOE)DE-AC02-06CH11357
Consortium for Materials Properties Research in Earth Sciences (COMPRES) NSF EAR 06-49658
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:ULVZ; core-mantle boundary; (Mg,Fe)O
Record Number:CaltechAUTHORS:20100907-154808644
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Official Citation:Wicks, J. K., J. M. Jackson, and W. Sturhahn (2010), Very low sound velocities in iron-rich (Mg,Fe)O: Implications for the core-mantle boundary region, Geophys. Res. Lett., 37, L15304, doi:10.1029/2010GL043689.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:19815
Deposited By: Tony Diaz
Deposited On:15 Sep 2010 21:28
Last Modified:26 Dec 2012 12:24

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