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Title: Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides

Abstract

We explore the effect of Mg/Fe substitution on the sound velocities of iron-rich (Mg 1 - xFe x)O, where x = 0.84, 0.94, and 1.0. Sound velocities were determined using nuclear resonance inelastic X-ray scattering as a function of pressure, approaching those of the lowermost mantle. The systematics of cation substitution in the Fe-rich limit has the potential to play an important role in the interpretation of seismic observations of the core-mantle boundary. By determining a relationship between sound velocity, density, and composition of (Mg,Fe)O, this study explores the potential constraints on ultralow-velocity zones at the core-mantle boundary.

Authors:
ORCiD logo [1];  [2]; ORCiD logo [2]; ORCiD logo [3]
  1. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA USA; Department of Geosciences, Princeton University, Princeton NJ USA
  2. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA USA
  3. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena CA USA; Hawai'i Institute of Geophysics and Planetology, University of Hawai'i at Manoa, 1680 East-West Rd Honolulu HI
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
Sponsoring Org.:
National Science Foundation (NSF)
OSTI Identifier:
1355031
Resource Type:
Journal Article
Resource Relation:
Journal Name: Geophysical Research Letters; Journal Volume: 44; Journal Issue: (5) ; 03, 2017
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES

Citation Formats

Wicks, June, Jackson, Jennifer M., Sturhahn, Wolfgang, and Zhang, Dongzhou. Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides. United States: N. p., 2017. Web. doi:10.1002/2016GL071225.
Wicks, June, Jackson, Jennifer M., Sturhahn, Wolfgang, & Zhang, Dongzhou. Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides. United States. doi:10.1002/2016GL071225.
Wicks, June, Jackson, Jennifer M., Sturhahn, Wolfgang, and Zhang, Dongzhou. Sun . "Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides". United States. doi:10.1002/2016GL071225.
@article{osti_1355031,
title = {Sound velocity and density of magnesiowüstites: Implications for ultralow-velocity zone topography: Sound velocities of Iron-rich Oxides},
author = {Wicks, June and Jackson, Jennifer M. and Sturhahn, Wolfgang and Zhang, Dongzhou},
abstractNote = {We explore the effect of Mg/Fe substitution on the sound velocities of iron-rich (Mg1 - xFex)O, where x = 0.84, 0.94, and 1.0. Sound velocities were determined using nuclear resonance inelastic X-ray scattering as a function of pressure, approaching those of the lowermost mantle. The systematics of cation substitution in the Fe-rich limit has the potential to play an important role in the interpretation of seismic observations of the core-mantle boundary. By determining a relationship between sound velocity, density, and composition of (Mg,Fe)O, this study explores the potential constraints on ultralow-velocity zones at the core-mantle boundary.},
doi = {10.1002/2016GL071225},
journal = {Geophysical Research Letters},
number = (5) ; 03, 2017,
volume = 44,
place = {United States},
year = {Sun Jan 01 00:00:00 EST 2017},
month = {Sun Jan 01 00:00:00 EST 2017}
}
  • The sound velocities of (Mg{sub .16}Fe{sub .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 Moessbauer spectroscopy. We found the sound velocities of (Mg{sub .16}Fe{sub .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 soundmore » 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.« less
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  • Liquid Fe-light element alloys are likely present in the Earth's outer core and the cores (or outer cores) of other terrestrial planets such as Moon, Mercury, and Mars, suggested by geophysical and geochemical observations. In order to determine the abundances of light elements and their effects on the structure, dynamics, and evolution of planetary cores, it is crucial to determine the equation of state for Fe-light element alloying liquids under core conditions. However, density data on liquid Fe-light element alloys at core pressures are very limited and no sound velocity or bulk modulus data are available for these liquids atmore » high pressures. This makes it difficult to extrapolate the equation of state to core pressures. As a result, density data on solid Fe alloys are often used in the literature to compare with seismological observations by making rough corrections for the volume of melting. In this study, we determine the density and sound velocity for Fe-S liquids with different sulfur contents at high pressure and temperature conditions up to 8 GPa and 2173 K using synchrotron X-ray techniques.« less
  • No abstract prepared.