日本地球惑星科学連合2019年大会

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[E] ポスター発表

セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT23] Structure and Dynamics of Earth and Planetary Mantles

2019年5月26日(日) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:中川 貴司(香港大学地球科学専攻)、芳野 極(岡山大学惑星物質研究所)、趙 大鵬(東北大学大学院理学研究科附属地震・噴火予知研究観測センター)

[SIT23-P02] Effect of iron content on thermal conductivity of olivine with implications for cooling history of rocky planets

*Youyue Zhang1Takashi Yoshino1Akira Yoneda1Masahiro Osako2 (1.Institute for Planetary Materials, Okayama University、2.Division of Physical Sciences, National Museum of Nature and Science)

キーワード:Thermal conductivity, Olivine, Heat capacity, High pressure, Mantle

Knowledge of thermal transport properties of mantle materials is essential for understanding the thermal state and dynamics of the Earth and planetary interiors. Previous studies have suggested that temperature and pressure dependences of thermal conductivity can affect mantle convection and plate tectonics involving subduction dynamics. Olivine is the most abundant mineral in the Earth’s upper mantle and chemical composition of olivine in the Earth’s upper mantle is characterized by high forsterite content around Fo90. For other terrestrial planets, Mercury is believed to have a FeO-poor mantle along with end member silicates, whereas olivine in the Martian mantle would be more Fe-rich, speculated to be Fo67. Recent studies suggested that surface of some asteroids is dominated by olivine of composition from Fo49 to Fo70. Hence, the effect of Fe content in olivine on thermal conductivity could be significant for understanding the thermal structure and cooling history of these terrestrial planets and asteroids.

In this study, thermal conductivity and diffusivity of olivine were determined simultaneously by combining multi-anvil high pressure experimental technique and pulse heating method. Thermal properties of olivine with six different Fe contents (Fo, Fo90, Fo70, Fo50, Fo31, Fo0) were measured under the Earth’s upper mantle condition in a 5000-ton Kawai type multi-anvil press. The minimum λ was found to be at composition near Fo31; the absolute λ value of Fo31 is about 65% lower than that of Fo. Small amounts of minor elements can strongly reduce the thermal conductivity at low temperature; λ value of Fo90 is about 50% of Fo at room temperature. As temperature increases, the difference in λ among olivine samples with various Fe contents tends to become smaller. Thermal conductivities of polycrystalline olivine have smaller absolute values and weak pressure and temperature dependences, compared with those of natural single crystal olivine determined by previous studies. Heat capacity of olivine calculated from λ and κ is independent of pressure and is controlled by nearly constant thermal expansion coefficient of Fo70 and Fo50 with increasing temperature. Smaller λ of olivine aggregate with high Fe content would produce thicker crust in the Fe-rich Mars, while heat in the Fe-poor Mercury can escape faster than the other terrestrial planets. Olivine-dominant asteroids with high Fe concentration could have longer cooling history and lower thermal inertia on the surface.