日本地球惑星科学連合2022年大会

講演情報

[E] 口頭発表

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-IT19] 地球深部科学

2022年5月22日(日) 13:45 〜 15:15 展示場特設会場 (2) (幕張メッセ国際展示場)

コンビーナ:太田 健二(東京工業大学理学院地球惑星科学系)、コンビーナ:河合 研志(東京大学大学院理学系研究科地球惑星科学専攻)、飯塚 毅(東京大学)、コンビーナ:土屋 旬(愛媛大学地球深部ダイナミクス研究センター)、座長:太田 健二(東京工業大学理学院地球惑星科学系)、土屋 旬(愛媛大学地球深部ダイナミクス研究センター)

14:15 〜 14:30

[SIT19-03] Evidence of Superionic Hydrous SiO2 in the Earth’s lower mantle by In-situ High P-T Electrical Conductivity Measurement

*稲田 真子1奥田 善之1岡 健太1廣瀬 敬1 (1.東京大学)


キーワード:超イオン、含水スティショバイト、電気伝導度、沈み込むスラブ

Superionic conductors have been a matter of significant interest and studied in various fields. For example, superionic H2O ice, which is thought to exist underneath a conducting liquid layer inside icy planets such as Uranus and Neptune, has experimentally been observed. The superionic phase is a solid containing ions that are not bonded in a specific position but move in crystals, which is expected to enhance electrical conductivity significantly. It contributes to the formation and maintenance of the planetary magnetic fields of these icy planets.

Subducted slabs are thought to bring water down to the deep mantle. Observing the distribution of water is a key to understanding the bulk water abundance and water-cycling in the Earth’s interior. High-pressure SiO2 phase, one of the major constituent minerals in subducted continental and oceanic crusts, can contain a large amount of water and carry it to the lowermost mantle. The previous molecular dynamics simulations by Umemoto et al. (2016 PEPI) demonstrated a superionic character of the dense SiO2 phase.

The EC of hydrous SiO2 has been reported up to 12 GPa, in which superionic conduction was not observed. Here we performed high P-T EC measurements at lower mantle conditions using a laser-heated diamond-anvil cell (DAC) in order to observe the superionic state of hydrous CaCl2-type SiO2. We employed SiO2 stishovite containing 0.15 wt.% H2O and 4.8 wt.% Al2O3 as a starting material, which was synthesized in a multi-anvil press. The sample resistance was measured using a recently developed method that enables us to obtain the impedance of a laser-heated transparent material in the DAC. We observed a sudden increase in electrical conductivity with increasing temperature around 1500 K, which may indicate the superionic state of hydrous SiO2. We will show the details of our methods and results and discuss the change in the electrical conduction mechanism in the presentation.