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Title: Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle

Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear–wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core–mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure–induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe–bearing bridgmanite to 120 GPa using optical pump–probe spectroscopy. The conductivity of Fe–bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure–induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid–lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermalmore » conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. In conclusion, the CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.« less
Authors:
ORCiD logo [1] ; ORCiD logo [1] ; ORCiD logo [2] ; ORCiD logo [3]
  1. Academia Sinica, Taipei (Taiwan)
  2. Okayama Univ., Misasa (Japan)
  3. Univ. of Texas at Austin, Austin TX (United States)
Publication Date:
Grant/Contract Number:
FG02-94ER14466
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 122; Journal Issue: 7; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Research Org:
Univ. of Chicago, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; thermal conductivity; bridgmanite; geodynamics
OSTI Identifier:
1474280

Hsieh, Wen -Pin, Deschamps, Frédéric, Okuchi, Takuo, and Lin, Jung -Fu. Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle. United States: N. p., Web. doi:10.1002/2017JB014339.
Hsieh, Wen -Pin, Deschamps, Frédéric, Okuchi, Takuo, & Lin, Jung -Fu. Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle. United States. doi:10.1002/2017JB014339.
Hsieh, Wen -Pin, Deschamps, Frédéric, Okuchi, Takuo, and Lin, Jung -Fu. 2017. "Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle". United States. doi:10.1002/2017JB014339. https://www.osti.gov/servlets/purl/1474280.
@article{osti_1474280,
title = {Reduced lattice thermal conductivity of Fe-bearing bridgmanite in Earth's deep mantle},
author = {Hsieh, Wen -Pin and Deschamps, Frédéric and Okuchi, Takuo and Lin, Jung -Fu},
abstractNote = {Complex seismic, thermal, and chemical features have been reported in Earth's lowermost mantle. In particular, possible iron enrichments in the large low shear–wave velocity provinces (LLSVPs) could influence thermal transport properties of the constituting minerals in this region, altering the lower mantle dynamics and heat flux across core–mantle boundary (CMB). Thermal conductivity of bridgmanite is expected to partially control the thermal evolution and dynamics of Earth's lower mantle. Importantly, the pressure–induced lattice distortion and iron spin and valence states in bridgmanite could affect its lattice thermal conductivity, but these effects remain largely unknown. Here we precisely measured the lattice thermal conductivity of Fe–bearing bridgmanite to 120 GPa using optical pump–probe spectroscopy. The conductivity of Fe–bearing bridgmanite increases monotonically with pressure but drops significantly around 45 GPa due to pressure–induced lattice distortion on iron sites. Our findings indicate that lattice thermal conductivity at lowermost mantle conditions is twice smaller than previously thought. The decrease in the thermal conductivity of bridgmanite in mid–lower mantle and below would promote mantle flow against a potential viscosity barrier, facilitating slabs crossing over the 1000 km depth. Modeling of our results applied to LLSVPs shows that variations in iron and bridgmanite fractions induce a significant thermal conductivity decrease, which would enhance internal convective flow. Our CMB heat flux modeling indicates that while heat flux variations are dominated by thermal effects, variations in thermal conductivity also play a significant role. In conclusion, the CMB heat flux map we obtained is substantially different from those assumed so far, which may influence our understanding of the geodynamo.},
doi = {10.1002/2017JB014339},
journal = {Journal of Geophysical Research. Solid Earth},
number = 7,
volume = 122,
place = {United States},
year = {2017},
month = {6}
}