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

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 (Mg0.06Fe0.94)O with fit parameters V0 = 9.860 ± 0.007 Å3, K0T = 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 VP:VS reduction ratios relative to the Preliminary Reference Earth Model (PREM), as well as certain 1:3 VP:VS reductions within estimated uncertainty bounds. Our work quantifies the viability of compositionally distinct ULVZs containing magnesiowüstite and contributes to developing a framework for amore » methodical approach to evaluating ULVZ hypotheses.« less

Authors:
ORCiD logo [1];  [1];  [1]
  1. California Institute of Technology (CalTech), Pasadena, CA (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC); National Science Foundation (NSF)
OSTI Identifier:
1596133
Grant/Contract Number:  
AC02-06CH11357; AC02-05CH11231; NSF-CSEDI-EAR-1161046; NSF-EAR-CAREER-0956166
Resource Type:
Accepted Manuscript
Journal Name:
Minerals
Additional Journal Information:
Journal Volume: 9; Journal Issue: 12; Journal ID: ISSN 2075-163X
Publisher:
MDPI
Country of Publication:
United States
Language:
ENGLISH
Subject:
58 GEOSCIENCES; (Mg,Fe)O; ultralow velocity zones; core–mantle boundary; equations of state; finite strain analysis; inverse model; X-ray diffraction; synchrotron Mössbauer spectroscopy

Citation Formats

Dobrosavljevic, Vasilije V., Sturhahn, Wolfgang, and Jackson, Jennifer M.. Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones. United States: N. p., 2019. Web. https://doi.org/10.3390/min9120762.
Dobrosavljevic, Vasilije V., Sturhahn, Wolfgang, & Jackson, Jennifer M.. Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones. United States. https://doi.org/10.3390/min9120762
Dobrosavljevic, Vasilije V., Sturhahn, Wolfgang, and Jackson, Jennifer M.. Sun . "Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones". United States. https://doi.org/10.3390/min9120762. https://www.osti.gov/servlets/purl/1596133.
@article{osti_1596133,
title = {Evaluating the Role of Iron-Rich (Mg,Fe)O in Ultralow Velocity Zones},
author = {Dobrosavljevic, Vasilije V. and Sturhahn, Wolfgang and Jackson, Jennifer M.},
abstractNote = {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 (Mg0.06Fe0.94)O with fit parameters V0 = 9.860 ± 0.007 Å3, K0T = 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 VP:VS reduction ratios relative to the Preliminary Reference Earth Model (PREM), as well as certain 1:3 VP:VS 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.},
doi = {10.3390/min9120762},
journal = {Minerals},
number = 12,
volume = 9,
place = {United States},
year = {2019},
month = {12}
}

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