日本地球惑星科学連合2022年大会

講演情報

[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-IT17] 地球型惑星内部での液体の特性とその役割

2022年5月30日(月) 11:00 〜 13:00 オンラインポスターZoom会場 (21) (Ch.21)

コンビーナ:坂巻 竜也(東北大学大学院理学研究科)、コンビーナ:中島 陽一(熊本大学大学院先導機構)、座長:坂巻 竜也(東北大学大学院理学研究科)、中島 陽一(熊本大学大学院先導機構)

11:00 〜 13:00

[SIT17-P01] H2O-induced melting at the uppermost lower mantle

*坂巻 竜也1 (1.東北大学大学院理学研究科)

キーワード:mantle melting、lower mantle、hydrous magma、low-velocity anomaly、high pressure

Seismological low-velocity anomalies have been observed above and below the mantle transition zone, which is a water reservoir in the interior of the Earth. These anomalies can be caused by mantle melting. In the case of the downflow zone at the uppermost lower mantle, a dehydration decomposition of ringwoodite to bridgmanite and ferropericlase results in H2O-induced mantle melting. For a better understanding of the melting phenomena at the top of the lower mantle, melting experiments of hydrous peridotite with 2.0 wt.% H2O have been conducted at 26 GPa and at temperatures from 1673 K to 2023 K. Under the experimental temperature, all recovered samples showed the quenched melt texture. This indicates that the solidus temperature of the hydrous peridotite with 2.0 wt.% H2O is below 1673 K and normal mantle geotherm. This result strongly supports the H2O-induced melting at the top of the lower mantle. The composition of partial melt coexisted with bridgmanite is SiO2-poor and MgO-rich, and is inconsistent with that of dry peridotite system. The water content of the partial melt is about 30-50 wt.%, and the melt is less dense than the surrounding lower mantle. The H2O-rich melt goes upward and the mantle transition zone can be kept in hydrous condition.