Strongly Anisotropic Magnesiowüstite in Earth's Lower Mantle
The juxtaposition of a liquid iron‐dominant alloy against a mixture of silicate and oxide minerals at Earth's core‐mantle boundary is associated with a wide range of complex seismological features. One category of observed structures is ultralow‐velocity zones, which are thought to correspond to either aggregates of partially molten material or solid, iron‐enriched assemblages. We measured the phonon dispersion relations of (Mg,Fe) O magnesiowüstite containing 76 mol % FeO, a candidate ultralow‐velocity zone phase, at high pressures using high‐energy resolution inelastic X‐ray scattering. From these measurements, we find that magnesiowüstite becomes strongly elastically anisotropic with increasing pressure, potentially contributing to a significant proportion of seismic anisotropy detected near the base of the mantle.
© 2018 American Geophysical Union. Received 12 DEC 2017; Accepted 13 MAY 2018; Accepted article online 18 MAY 2018; Published online 16 JUN 2018. We thank Stephen J. Mackwell for providing the single crystals for this study and Rachel A. Morrison for help in conducting experiments. We are thankful to NSF‐CSEDI‐EAR‐1161046 and 1600956, the W. M. Keck Institute for Space Studies for financial support, and two anonymous reviewers for their helpful comments. G. J. Finkelstein is also partially supported by the Caltech Seismological Laboratory Director's Postdoctoral Fellowship. We acknowledge COMPRES for partial support of Sector 3 and Sector 30 at the Advanced Photon Source (APS). Ruby fluorescence measurements were conducted at GSECARS, which is supported by NSF‐EAR‐1128799 and U.S. DOE, Geosciences (DE‐FG02‐94ER14466. Use of the APS is supported by U.S. DOE, Office of Science (DE‐AC02‐06CH11357). The spectra corresponding to the results reported in this paper are provided in the supporting information.
Supplemental Material - jgrb52824-sup-0001-2017jb015349_s01.pdf