Effect of spin transition of iron on the thermal conductivity of (Fe, Al)-bearing bridgmanite

Yoshiyuki Okuda, Kenji Ohta, Ryosuke Sinmyo, Kei Hirose, Takashi Yagi, Yasuo Ohishi

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Thermal conductivity of bridgmanite (Bdg) is the important physical property controlling the heat transfer inside the Earth. Here we report room temperature lattice thermal conductivity of (Fe,Al)-bearing Bdg with chemical compositions of Mg0.848Fe0.090Al0.206Si0.856O3 and Mg0.718Fe0.123Al0.281Si0.878O3 measured up to 125 GPa and 74 GPa, respectively, using the pulsed light heating thermoreflectance technique in a diamond anvil cell. We found that the lattice thermal conductivity of these Bdg samples show abnormal reduction in the pressure range of 20-40 GPa at 300 K, which is probably due to the spin transition of Fe3+ in octahedral Si-site (B-site). We propose that the lattice thermal conductivity of Bdg is reduced by 46 ± 16% when Fe is in the mixed spin state, which may form a thermal insulating layer in the Earth's mid lower mantle. In addition, we provide a thermal conductivity model of Bdg, taking into account the effect of compositional difference and the spin transition of Fe. Our conductivity model indicates that the thermal conductivity of Bdg in the pyrolitic lower mantle is more than twice as high as that in the descending MORB, which is likely to create heterogeneity of lateral heat flux through the Earth's core-mantle boundary.

Original languageEnglish
Pages (from-to)188-198
Number of pages11
JournalEarth and Planetary Science Letters
Volume520
DOIs
Publication statusPublished - 15 Aug 2019

Keywords

  • bridgmanite
  • lower mantle
  • spin transition of iron
  • thermal conductivity

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