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Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones

Dobrosavljevic, Vasilije V. and Sturhahn, Wolfgang and Jackson, Jennifer M. (2019) Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones. Minerals, 9 (12). Art. No. 762. ISSN 2075-163X. https://resolver.caltech.edu/CaltechAUTHORS:20191209-111123962

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Abstract

The composition of ultralow velocity zones (ULVZs) remains an open question, despite advances in both seismology and experimental work. We investigate the hypothesis of iron-rich (Mg,Fe)O (magnesiowüstite) as a cause of ULVZ seismic signatures. We report new quasi-hydrostatic X-ray diffraction measurements to constrain the equation of state of (Mg_(0.06)Fe_(0.94))O with fit parameters V₀ = 9.860 ± 0.007 ų, K_(0T) = 155.3 ± 2.2 GPa, K’_(0T) = 3.79 ± 0.11, as well as synchrotron Mössbauer spectroscopy measurements to characterize the high-pressure magnetic and spin state of magnesiowüstite. We combine these results with information from previous studies to calculate the elastic behavior at core–mantle boundary conditions of magnesiowüstite, as well as coexisting bridgmanite and calcium silicate perovskite. Forward models of aggregate elastic properties are computed, and from these, we construct an inverse model to determine the proportions of magnesiowüstite that best reproduce ULVZ observations within estimated mutual uncertainties. We find that the presence of magnesiowüstite can explain ULVZ observations exhibiting 1:2 V_P:V_S reduction ratios relative to the Preliminary Reference Earth Model (PREM), as well as certain 1:3 V_P:V_S reductions within estimated uncertainty bounds. Our work quantifies the viability of compositionally distinct ULVZs containing magnesiowüstite and contributes to developing a framework for a methodical approach to evaluating ULVZ hypotheses.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.3390/min9120762DOIArticle
https://www.mdpi.com/2075-163X/9/12/762/s1PublisherSupplementary Materials
ORCID:
AuthorORCID
Dobrosavljevic, Vasilije V.0000-0002-3710-2188
Sturhahn, Wolfgang0000-0002-9606-4740
Jackson, Jennifer M.0000-0002-8256-6336
Additional Information:© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/). Received: 12 November 2019; Accepted: 6 December 2019; Published: 8 December 2019. Author Contributions: Conceptualization, J.M.J. and V.V.D.; methodology, J.M.J., V.V.D. and W.S.; software, W.S.; validation, J.M.J., V.V.D. and W.S.; formal analysis, V.V.D.; investigation, J.M.J. and V.V.D.; resources, J.M.J. and W.S.; data curation, J.M.J.; writing—original draft preparation, V.V.D.; writing—review and editing, J.M.J., V.V.D. and W.S.; funding acquisition, J.M.J. We thank NSF-CSEDI-EAR-1161046 and NSF-EAR-CAREER-0956166 for support of this research. Operations at Sector 3 (APS) and beamline 12.2.2 (ALS) are partially supported by COMPRES. This research used resources of the Advanced Photon Source and of the Advanced Light Source, which are DOE Office of Science User Facilities under contracts DE-AC02-06CH11357 and DE-AC02-05CH11231, respectively. We thank Christine Beavers, as well as Gregory Finkelstein and Natalia Solomatova, for their help with the diffraction experiments. We thank Don Helmberger, Christine Thomas, and Zhongwen Zhan for valuable discussions. We thank June K. Wicks for synthesis of the sample. The authors declare no conflict of interest.
Group:Seismological Laboratory
Funders:
Funding AgencyGrant Number
NSFEAR-1161046
NSFEAR-0956166
Consortium for Materials Properties Research in Earth Sciences (COMPRES)UNSPECIFIED
Department of Energy (DOE)DE-AC02-06CH11357
Department of Energy (DOE)DE-AC02-05CH11231
Subject Keywords:(Mg,Fe)O; ultralow velocity zones; core–mantle boundary; equations of state; finite strain analysis; inverse model; X-ray diffraction; synchrotron Mössbauer spectroscopy
Issue or Number:12
Record Number:CaltechAUTHORS:20191209-111123962
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20191209-111123962
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100240
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:09 Dec 2019 21:37
Last Modified:09 Dec 2019 21:37

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