Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle

Suyu Fu; Jing Yang; Yanyao Zhang; Takuo Okuchi; Catherine McCammon; Hyo Im Kim; Sung Keun Lee; Jung Fu Lin

doi:10.1029/2018GL077764

Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle

Suyu Fu, Jing Yang, Yanyao Zhang, Takuo Okuchi, Catherine McCammon, Hyo Im Kim, Sung Keun Lee, Jung Fu Lin

Institute for Planetary Materials

Research output: Contribution to journal › Article › peer-review

26 Citations (Scopus)

Abstract

We measured the effect of pressure on the compressional and shear wave velocity (V_P, V_S) as well as density of Fe-bearing bridgmanite, Mg_0.96(1)Fe²⁺ _0.036(5)Fe³⁺ _0.014(5)Si_0.99(1)O₃, using impulsive stimulated light scattering, Brillouin light scattering, and X-ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of V_P by ~6(±1)% is observed between 42.6 and 58 GPa, while V_S increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while V_S increases by ~3(±1)% above ~40 GPa compared to MgSiO₃-bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe-bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe³⁺ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid-lower mantle may be due to a spin transition of Fe in Fe-bearing bridgmanite.

Original language	English
Pages (from-to)	4725-4732
Number of pages	8
Journal	Geophysical Research Letters
Volume	45
Issue number	10
DOIs	https://doi.org/10.1029/2018GL077764
Publication status	Published - May 28 2018

Keywords

bridgmanite
elasticity
lower mantle
spin transition

ASJC Scopus subject areas

Geophysics
Earth and Planetary Sciences(all)

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10.1029/2018GL077764

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@article{0ff58b5537aa4a31beef10c1f3e483d6,

title = "Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle",

abstract = "We measured the effect of pressure on the compressional and shear wave velocity (VP, VS) as well as density of Fe-bearing bridgmanite, Mg0.96(1)Fe2+ 0.036(5)Fe3+ 0.014(5)Si0.99(1)O3, using impulsive stimulated light scattering, Brillouin light scattering, and X-ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of VP by ~6(±1)% is observed between 42.6 and 58 GPa, while VS increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while VS increases by ~3(±1)% above ~40 GPa compared to MgSiO3-bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe-bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe3+ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid-lower mantle may be due to a spin transition of Fe in Fe-bearing bridgmanite.",

keywords = "bridgmanite, elasticity, lower mantle, spin transition",

author = "Suyu Fu and Jing Yang and Yanyao Zhang and Takuo Okuchi and Catherine McCammon and Kim, {Hyo Im} and Lee, {Sung Keun} and Lin, {Jung Fu}",

note = "Funding Information: The authors thank V. Prakapenka and E. Greenberg for their assistance with X- ray diffraction experiments at 13ID-D, GSECARS. J. F. Lin acknowledges sup port from Geophysics, Instrumentation and Facilities, and CSEDI Programs of the U.S. National Science Foundation, the Visiting Professorship Program of the Institute for Planetary Materials, Okayama University, and Center for High Pressure Science and Technology Advanced Research (HPSTAR). T. Okuchi acknowledges support from JSPS KAKENHI (17H01172). GSECARS was supported by the National Science Foundation (EAR-0622171) and U.S. Department of Energy (DE-FG02-94ER14466) under contract DE-AC02-06CH11357. APS is supported by DOE-BES, under contract DE-AC02- 06CH11357. Experimental sound velo city data from BLS and ISLS measure ments and volume data from XRD results are listed in Tables S1 and S2, respectively. A more detailed discussion of the methodology can be found in the supporting information. Publisher Copyright: {\textcopyright}2018. American Geophysical Union. All Rights Reserved.",

year = "2018",

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doi = "10.1029/2018GL077764",

language = "English",

volume = "45",

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journal = "Geophysical Research Letters",

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T1 - Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle

AU - Fu, Suyu

AU - Yang, Jing

AU - Zhang, Yanyao

AU - Okuchi, Takuo

AU - McCammon, Catherine

AU - Kim, Hyo Im

AU - Lee, Sung Keun

AU - Lin, Jung Fu

N1 - Funding Information: The authors thank V. Prakapenka and E. Greenberg for their assistance with X- ray diffraction experiments at 13ID-D, GSECARS. J. F. Lin acknowledges sup port from Geophysics, Instrumentation and Facilities, and CSEDI Programs of the U.S. National Science Foundation, the Visiting Professorship Program of the Institute for Planetary Materials, Okayama University, and Center for High Pressure Science and Technology Advanced Research (HPSTAR). T. Okuchi acknowledges support from JSPS KAKENHI (17H01172). GSECARS was supported by the National Science Foundation (EAR-0622171) and U.S. Department of Energy (DE-FG02-94ER14466) under contract DE-AC02-06CH11357. APS is supported by DOE-BES, under contract DE-AC02- 06CH11357. Experimental sound velo city data from BLS and ISLS measure ments and volume data from XRD results are listed in Tables S1 and S2, respectively. A more detailed discussion of the methodology can be found in the supporting information. Publisher Copyright: ©2018. American Geophysical Union. All Rights Reserved.

PY - 2018/5/28

Y1 - 2018/5/28

N2 - We measured the effect of pressure on the compressional and shear wave velocity (VP, VS) as well as density of Fe-bearing bridgmanite, Mg0.96(1)Fe2+ 0.036(5)Fe3+ 0.014(5)Si0.99(1)O3, using impulsive stimulated light scattering, Brillouin light scattering, and X-ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of VP by ~6(±1)% is observed between 42.6 and 58 GPa, while VS increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while VS increases by ~3(±1)% above ~40 GPa compared to MgSiO3-bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe-bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe3+ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid-lower mantle may be due to a spin transition of Fe in Fe-bearing bridgmanite.

AB - We measured the effect of pressure on the compressional and shear wave velocity (VP, VS) as well as density of Fe-bearing bridgmanite, Mg0.96(1)Fe2+ 0.036(5)Fe3+ 0.014(5)Si0.99(1)O3, using impulsive stimulated light scattering, Brillouin light scattering, and X-ray diffraction, respectively, in diamond anvil cells up to 70 GPa at 300 K. A drastic softening of VP by ~6(±1)% is observed between 42.6 and 58 GPa, while VS increases continuously with increasing pressure. A significant reduction in Poisson's ratio from 0.24 to 0.16 occurs at ~42.6–58 GPa, while VS increases by ~3(±1)% above ~40 GPa compared to MgSiO3-bridgmanite. Thermoelastic modeling of the experimental results shows that the observed elastic anomaly of Fe-bearing bridgmanite is consistent with a spin transition of octahedrally coordinated Fe3+ in bridgmanite. These results challenge traditional views that Fe enrichment will reduce seismic velocities, suggesting that seismic heterogeneities in the mid-lower mantle may be due to a spin transition of Fe in Fe-bearing bridgmanite.

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KW - spin transition

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Abnormal Elasticity of Fe-Bearing Bridgmanite in the Earth's Lower Mantle

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