Title: Elasticity of ferropericlase and seismic heterogeneity in the Earth’s lower mantle

Abstract

Deciphering the origin of seismic heterogeneity has been one of the major challenges in understanding the geochemistry and geodynamics of the deep mantle. Fully anisotropic elastic properties of constituent minerals at relevant pressure-temperature conditions of the lower mantle can be used to calculate seismic heterogeneity parameters in order to better understand chemically and thermally induced seismic heterogeneities. In this study, the single-crystal elastic properties of ferropericlase (Mg_0.94Fe_0.06)O were measured using Brillouin spectroscopy and X-ray diffraction at conditions up to 50 GPa and 900 K. Additionally, the velocity-density results were modeled using third-order finite-strain theory and thermoelastic equations along a representative geotherm to investigate high pressure-temperature and compositional effects on the seismic heterogeneity parameters. Our results demonstrate that from 660 to 2000 km, compressional wave anisotropy of ferropericlase increased from 4% to 9.7%, while shear wave anisotropy increased from 9% to as high as 22.5%. The thermally induced lateral heterogeneity ratio (R_S/P = ∂lnV_S/∂lnV_P) of ferropericlase was calculated to be 1.48 at ambient pressure but decreased to 1.43 at 40 GPa along a representative geotherm. The R_S/P of a simplified pyrolite model consisting of 80% bridgmanite and 20% ferropericlase was approximately 1.5, consistent with seismic models at depths from 670 tomore » 1500 km, but showed an increased mismatch at lower mantle depths below ~1500 km. This discrepancy below mid-lower mantle could be due to either a contribution from chemically induced heterogeneity or the effects of the Fe spin transition in the deeper parts of the Earth's lower mantle.« less

Authors:

Yang, Jing  ^[1];

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• Search DOE PAGES for ORCID "0000-0001-8572-4048"

Lin, Jung-Fu  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-0163-5329"

Jacobsen, Steven D.  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-9746-958X"

Seymour, Nikki M.  ^[1];

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• Search DOE PAGES for ORCID "0000-0003-0040-063X"

Tkachev, Sergey N.  ^[4];

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• Search DOE PAGES for ORCID "0000-0002-7686-4484"

Prakapenka, Vitali B.  ^[5]

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• Search DOE PAGES for ORCID "0000-0001-9270-2330"

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+ Show Author Affiliations

1. Univ. of Texas, Austin, TX (United States)
2. Univ. of Texas, Austin, TX (United States); Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China)
3. Northwestern Univ., Evanston, IL (United States)
4. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources (CARS)
5. Center for Advanced Radiation Sources, University of Chicago, Chicago Illinois USA

Publication Date:

Fri Dec 16 00:00:00 EST 2016

Research Org.:

Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Org.:

National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences, and Biosciences Division

OSTI Identifier:

1343130

Grant/Contract Number:  

FG02-94ER14466; EAR-0748707; EAR-1128799

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Geophysical Research. Solid Earth

Additional Journal Information:

Journal Volume: 121; Journal Issue: 12; Journal ID: ISSN 2169-9313

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

ENGLISH

Subject:

58 GEOSCIENCES; Brillouin spectroscopy; ferropericlase; elasticity; lateral heterogeneity