講演情報
[R3-01]Lattice thermal conductivity of dry ringwoodite: implications for mantle dynamics and thermal evolution of stagnant slabs
*Youyue ZHANG1, Takashi YOSHINO2, Masahiro OSAKO3, Steeve Gréaux1 (1. GRC, Ehime Univ., 2. IPM, Okayama Univ., 3. National Museum of Nature and Science)
キーワード：
Ringwoodite、Thermal conductivity、High pressure、Mantle transition zone
Heat transport within the Earth’s interior governs the long-term thermal evolution and dynamic behavior of the mantle. Accurate knowledge of the thermal conductivity of mantle minerals is essential for understanding these processes. Ringwoodite, a high-pressure polymorph of olivine, comprises ~60 vol% of the bottom mantle transition zone (MTZ) (Frost, 2008) and ~80 vol% of subducted harzburgitic lithologies (Irifune & Ringwoodite, 1987), exerting significant control over the thermal state of these regions. Seismic and electromagnetic tomography have revealed thermochemical heterogeneities in the MTZ (Houser, 2016; Goes et al., 2022), with some anomalies potentially linked to water incorporation. The difference in heat transport between dry and hydrous ringwoodite may thus be critical to understanding the origin of these heterogeneities. However, thermal transport properties of ringwoodite remain poorly constrained. Few studies have mainly measured thermal diffusivity or effusivity (Xu et al., 2004; Marzotto et al., 2020), with water-incorporated samples. The thermal properties of dry ringwoodite, a key reference for mantle modeling, are still lacking due to synthesis challenges.
To address this, we synthesized dry (Mg0.9Fe0.1)2SiO4 ringwoodite under deep mantle oxygen fugacity (IW buffer) using a Kawai-type multi-anvil press at 20 GPa and 1775 K. Thermal conductivity and diffusivity were simultaneously measured up to 1100 K using a pulse heating method. Results show that dry ringwoodite has significantly higher thermal conductivity than previously reported hydrous samples, indicating a suppressive effect of water. At the 660 km discontinuity, dry ringwoodite exhibits conductivity ~15% higher than decomposed post-spinel assemblages and ~45% higher than Al, Fe-bearing bridgmanite, while hydrous ringwoodite shows values comparable to the latter. These findings suggest that dry regions near hot plumes may experience faster heating, while wet areas near stagnant slabs may remain cooler, contributing to the observed thermal and chemical heterogeneity in the MTZ.
To address this, we synthesized dry (Mg0.9Fe0.1)2SiO4 ringwoodite under deep mantle oxygen fugacity (IW buffer) using a Kawai-type multi-anvil press at 20 GPa and 1775 K. Thermal conductivity and diffusivity were simultaneously measured up to 1100 K using a pulse heating method. Results show that dry ringwoodite has significantly higher thermal conductivity than previously reported hydrous samples, indicating a suppressive effect of water. At the 660 km discontinuity, dry ringwoodite exhibits conductivity ~15% higher than decomposed post-spinel assemblages and ~45% higher than Al, Fe-bearing bridgmanite, while hydrous ringwoodite shows values comparable to the latter. These findings suggest that dry regions near hot plumes may experience faster heating, while wet areas near stagnant slabs may remain cooler, contributing to the observed thermal and chemical heterogeneity in the MTZ.