惑星深部物質の熱伝導率に対する水と化学不純物の影響：地球型惑星の熱進化の探求

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Core mantle boundary heat flux, which is governed by the thermal properties of the lowermost mantle minerals, controls the generation of observed magnetic field, geological activity and thermal structure of the terrestrial planets. The purpose of this study is to understand how impurities in minerals affect the thermal evolution of terrestrial planets and to achieve the following projects: (1) Determination of pressure dependence and temperature dependence of thermal conductivity of (Fe, Al)-bearing bridgmanite (2) Determination of pressure dependence and temperature dependence of thermal conductivity of anhydrous and hydrous ringwoodite by pulse heating method.In this fiscal year, we analyzed experimental data of project (1) obtained in the previous fiscal year. The significant decrease of pressure dependence and the absolute value of thermal conductivity of bridgmanite indicates a gradual slowing of the cooling rate of the mantle due to impurities' involvement during the secular cooling after the magma ocean solidification. We have also vigorously pursued project (2). The synthesis conditions of ringwoodite samples with desired compositions and water content have been well mastered. However, we found ringwoodite is very brittle, during cutting into thin slices, it easily breaks into pieces. After many struggles, we decide to decrease the sample diameter to get thin slices of ringwoodite. A new high-pressure thermal conductivity measurement cell for such smaller samples has been developed. The measurements of thermal conductivity of ringwoodite are now undergoing.