Japan Geoscience Union Meeting 2025

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[E] Oral

S (Solid Earth Sciences ) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT20] Deep Earth Sciences

Thu. May 29, 2025 10:45 AM - 12:15 PM 105 (International Conference Hall, Makuhari Messe)

convener:Takayuki Ishii(Institute for Planetary Materials, Okayama University), Riko Iizuka-Oku(Department of Earth Sciences, School of Education, Waseda University), Kenji Kawai(Department of Earth and Planetary Science, School of Science, University of Tokyo), Jun Tsuchiya(Department of Earth and Space Science, The University of Osaka), Chairperson:Kenji Kawai(Department of Earth and Planetary Science, School of Science, University of Tokyo), Takayuki Ishii(Institute for Planetary Materials, Okayama University), Jun Tsuchiya(Geodynamics Research Center, Ehime University), Riko Iizuka-Oku(Department of Earth Sciences, School of Education, Waseda University)


11:30 AM - 11:45 AM

[SIT20-22] Our understanding of the CMB heat transport

*Haruhiko Dekura1, Taku Tsuchiya1 (1.Geodynamics Research Center, Ehime University)

Keywords:Lower mantle, Thermal conductivity, CMB heat flux, Fe solid solution effect, Ab initio calculation

The lattice thermal conductivity (κlat) is critical for understanding the energy transport in Earth's deep interior. High-pressure experiments report that only ~7 mol% Fe incorporation drastically reduces the κlat of MgSiO3 bridgmanite (Brg) by ~40% [e.g., Edmund et al., 2024]. However, the experimental pressure (P, T) conditions are limited compared to the actual lower mantle (LM) P, T. Recently, we developed an advanced computational framework to predict the κlat of Fe-bearing systems integrating density-functional theory, anharmonic lattice dynamics, the internally consistent LDA+U method, and the phonon Boltzmann transport theory [e.g., Dekura et al., 2023; 2024]. In this study, we apply this parameter-free approach to κlat of Fe-bearing Brg and post-perovskite (PPv) and construct the LM conductivity profile. The results reveal that ~6 mol% Fe incorporation significantly reduces the κlat of endmembers by ~60% due to drops in phonon group velocity and phonon lifetimes. The effective thermal conductivity (κeff) for the pyrolitic LM aggregate (Brg/PPv:FP = 8:2) is found to vary from approximately ~1 Wm-1K-1 at the uppermost LM to approximately ~4 Wm-1K-1 at the CMB. The spatial CMB heat flux modeled using the obtained κeff shows a significant lateral heterogeneity (~1.0 × 10-2 to ~9.0 × 10-2 Wm-2) and the net CMB heat flow of approximately 7 TW. Our estimation is significantly lower than that calculated for the Fe-free system (approximately 17 TW) [e.g., Dekura et al., 2019], which highlights the critical role of Fe in the LM conductivity. The present estimation for the net flow is substantially lower than that estimated for the outer core (~12-18 TW) [e.g., de Koker et al., 2012]. Potential mechanisms, such as the formation of a thermally stratified layer at the uppermost outer core, contributions from radiative heat transfer, or the effects of chemical heterogeneity near the CMB, may help reconcile the significant discrepancy.