2026-10-09 大阪大学
SiO₂相、AlOOH相、および両者の間に形成される固溶体の模式図。鉱物を構成する原子の置き換わりを概念的に示している。
＜関連情報＞
- https://www.sci.osaka-u.ac.jp/ja/topics/17340/
- https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2026GL124407
下部マントルSiO₂ – AlOOH相における圧力増強型含水-無水固溶体のその場観察 In Situ Observation of Pressure-Enhanced Hydrous–Anhydrous Solid Solution in Lower-Mantle SiO2–AlOOH Phases
M. Nishi, K. Takahashi, H. Dekura, K. Kawano, H. Koike, K. Nakamura, T. Kondo, H. Kuwahara, S. Kakizawa, N. Tsujino, Y. Higo
Geophysical Research Letters Published: 29 September 2026
DOI:https://doi.org/10.1029/2026GL124407
Abstract
Water plays a critical role in Earth’s mantle dynamics and evolution, yet lower-mantle storage mechanisms remain debated. δ-AlOOH and SiO2 phases have been independently proposed as high-pressure water hosts. Here, we conducted in situ synchrotron X-ray diffraction experiments with a multi-anvil apparatus and sintered diamond anvils to investigate phase relations in the SiO2–AlOOH system up to 45 GPa and high temperatures. We found that SiO2 and δ-AlOOH form extensive, stable CaCl2-type solid solutions across a broad compositional range under lower-mantle conditions. The solid-solution extent increases strongly with pressure, indicating enhanced H2O storage in dense SiO2-rich phases and stabilization of SiO2-enriched AlOOH-rich hydrous phases at greater depths. These results suggest that water released from less favorable peridotitic hosts during lower-mantle transport can be redistributed into subducted crustal lithologies, where pressure-stabilized complementary CaCl2-type phases serve as water hosts.
