[論文レビュー] Water-induced buoyancy controls transient water storage in the mantle transition zone

Taras V. Gerya, Nickolas Moccetti Bardi+2 more|arXiv (Cornell University)|Feb 14, 2026

High-pressure geophysics and materials被引用数 0

ひとこと要約

The study uses a new deep hydrous mantle melting model with 2D THMC simulations to show water-induced buoyancy drives hydrous mantle upwellings in the MTZ, potentially creating transient water storage that may affect surface ocean mass.

ABSTRACT

The spinel phase (wadsleyite, ringwoodite) in the mantle transition zone (MTZ), can contain up to 1-2 weight percent of water. However, whether these water reservoirs in the MTZ are filled is debated. Here, we investigate water dynamics in the MTZ numerically by using a newly developed empirical model of deep hydrous mantle melting combined with 2D thermo-hydro-mechanical-chemical (THMC) upper mantle models. Numerical modeling results suggest that water-induced buoyancy triggers the development of hydrous solid-state mantle upwellings in the MTZ. On time scales of some tens of millions of years, they rise to and interact with the spinel-olivine phase transition. Depending on the water content and temperature of these thermal-chemical plumes, this crossing may trigger hydrous melting by water release from the wadsleyite upon its conversion to olivine. The melts are less dense than the solid matrix and continue rising upward in the form of either diapirs or porosity waives. Similar dehydration-induced melting process3 is also documented for the lower MTZ boundary, where hydrous downwellings (such as subducted slabs) generate buoyant melt diapirs rising through the MTZ. We therefore suggest that the MTZ operates as a transient water reservoir. Relatively small amounts of water (less than 0.1 weight percent, smaller than 0.2 ocean masses) and a geologically moderate duration (80-430 Myr) of the transient water storage should be characteristic for the MTZ, which may play a key role in stabilizing the surface ocean mass on Earth and Earth-like rocky exoplanets.

研究の動機と目的

• Investigate whether water reservoirs in the MTZ fill or not under realistic mantle dynamics.
• Assess how water content and temperature influence buoyancy-driven mantle upwellings in the MTZ.
• Explore the interaction of hydrous plumes with spinel–olivine phase transitions and potential melting.

提案手法

• Develop a new empirical model of deep hydrous mantle melting.
• Implement 2D thermo-hydro-mechanical-chemical (THMC) mantle models.
• Simulate water dynamics and buoyancy-driven upwellings in the MTZ.
• Analyze conditions under which wadsleyite-derived water triggers melting upon transition to olivine.
• Compare dehydration-induced melting processes at the MTZ lower boundary and subducted slabs.

実験結果

リサーチクエスチョン

• RQ1 Does water content in MTZ reservoirs create buoyancy-driven upwellings that reach the spinel–olivine transition?
• RQ2 Can water release from wadsleyite upon phase transition trigger hydrous melting and generate buoyant melts?
• RQ3 What are the timescales and water budgets associated with transient MTZ water storage?
• RQ4 How do small water contents affect the stability and dynamics of MTZ plumes and back-melt diapirs?

主な発見

• Water-induced buoyancy triggers hydrous solid-state mantle upwellings in the MTZ.
• Over tens of millions of years these plumes rise to intersect the spinel–olivine phase transition and may trigger hydrous melting as water is released from wadsleyite.
• Melts formed are less dense than the solid matrix and rise as diapirs or porosity waves.
• Hydrous downwellings, such as subducted slabs, can generate buoyant melt diapirs rising through the MTZ at its lower boundary.
• The MTZ can operate as a transient water reservoir with small water contents and durations on the order of tens to hundreds of millions of years.