日本地球惑星科学連合2019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-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-P14] Fate of water in subducted hydrous sediments deduced from stability fields of FeOOH and AlOOH up to 20 GPa

*芳野 極1Edward Baker2Kyle Duffey3 (1.岡山大学惑星物質研究所、2.オックスフォード大学、3.プリンストン大学)

キーワード:水、堆積物、脱水、含水鉱物、沈み込み帯

Fe- and Al-hydroxides (FeOOH and AlOOH) in sedimentary rocks form the top part of the subducted oceanic lithosphere and are known to be stable along a normal geotherm in the lower mantle. Banded Iron Formations (BIFs) and bauxite ore deposits formed in the Earth’s oceans can transport significant amount of water into the Earth’s deep interior by subduction of FeOOH and AlOOH and may occasionally serve water to the core. However, stabilities of these hydrous phases have not been well constrained in upper mantle conditions. We determined dehydration curves for FeOOH and AlOOH in upper mantle and mantle transition zone conditions (5–20 GPa, 673–1573K)by quench and in situX-ray diffraction to constrain their capability of water transport to the deep mantle. Dehydration temperatures of these minerals increase with increasing pressure. Comparison between our results and geothermal gradients of subducting slab surfaces demonstrates dehydration of FeOOH in early subduction stage (around 2 GPa). In most cases, diaspore (AlOOH) also dehydrates in early subduction. Despite the implications of the stability of these phases at high pressure, our results show that the sediments located at the slab surface are unlikely candidates for transporting water to the deep mantle.