日本地球惑星科学連合2018年大会

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[EE] 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-IT22] 核-マントルの相互作用と共進化

2018年5月22日(火) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 7ホール)

コンビーナ:飯塚 毅(東京大学)、渋谷 秀敏(熊本大学大学院先端科学研究部基礎科学部門地球環境科学分野)、土屋 卓久(愛媛大学地球深部ダイナミクス研究センター、共同)、太田 健二(東京工業大学大学院理工学研究科地球惑星科学専攻)

[SIT22-P10] Thermal equations of state of MgSiO4H2 phase H up to 63 GPa determined by in situ X-ray diffraction measurement in a multianvil apparatus

*西 真之1,2土屋 旬1,2有本 岳史1柿澤 翔1國本 健広1丹下 慶範3肥後 祐司3入舩 徹男1,2 (1.愛媛大学地球深部ダイナミクス研究センター、2.東京工業大学地球生命研究所、3.(財)高輝度光科学研究センター )

キーワード:Thermal equations of state、mantle、phase H、multianvil apparatus、water

Hydrous minerals deliver a certain amount of water into the Earth’s interior via subduction of oceanic plates. Following to the theoretical prediction on the thermodynamic stability of MgSiO4H2 phase H at above 35 GPa in 2013 (Tsuchiya 2013), some experimental studies have succeeded to identify the formation of this phase under high pressure and temperature conditions (Nishi et al. 2014; Ohtani et al. 2014; Walter et al. 2015). Phase H is now considered to be the key hydrous phase responsible for the water cycle in the whole mantle as the highest-pressure form of DHMS. However, the qualities of in-situ X-ray diffraction (XRD) profiles of phase H obtained in earlier studies were sometimes not enough to satisfy the precise determination of its cell parameters because phase H easily dehydrates at temperatures where spectroradiometry can be applied in laser-heated diamond anvil cell (DAC) experiments. Therefore, XRD peaks of phase H have been used basically only for its phase identification within very limited temperature ranges. Nishi et al. (2014) succeeded to obtain the cell parameters of phase H from multiple independent XRD peaks by using multianvil apparatus, which can accurately control the temperature of the sample. However, the data in limited pressure ranges of the previous study (32-42 GPa) were not applicable to construct the equation of state (EOS) of MgSiO4H2 phase H.

Here, we have determined the thermal equations of state of phase H by using in situ X-ray diffraction measurements in conjunction with a multi-anvil apparatus through its stability field from 34 to 63 GPa up to 1300 K. We succeeded to expand the experimental conditions up to 63 GPa by state-of-the-art high-pressure technology using sinter diamond anvils and Al2O3 pressure medium, which achieved higher pressures by ~20 % compared to those using the conventional MgO pressure medium in the similar design of the cell assembly used in Nishi et al. 2014. The data analysis based on the Mie-Grüneisen-Debye model using the third-order Burch-Murnaghan equations at the reference pressure of 35 GPa yielded Vref, =49.61±0.01 (Å3), Kref=344.6±4.1 (GPa), Kref’=3.05±0.32, θref=974±146 (K), γref =1.8±0.1, and q =1.79±0.55. The compressibility of phase H observed in this study is in good agreement with that derived by theoretical calculation in the pressure regions where hydrogen bond symmetrisation is predicted to occur.