[论文解读] 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 0

一句话总结

本研究使用一种新的深层水合地幔熔融模型，通过二维 THMC 模拟显示水引起的浮力推动含水地幔在 MTZ 上升，可能造成瞬时水储存，进而影响地表海洋质量。

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.

研究动机与目标

• 在现实地幔动力学下，MTZ 水储库是否会填满或不填满？
• 评估水含量与温度如何影响 MTZ 中浮力驱动的地幔上挤。
• 探索含水羽流与尖晶石–橄榄石相变及潜在熔融的相互作用。

提出的方法

• 开发深层含水地幔熔融的新经验模型。
• 实现二维热-水-力学-化学（THMC）地幔模型。
• 模拟 MTZ 中水动力学与浮力驱动的上升。
• 分析在转变为橄榄石时娃德斯石（wadsleyite）释放水是否触发熔融。
• 比较 MTZ 下部边界与俯冲板块的脱水引发熔融过程。

实验结果

研究问题

• RQ1 MTZ 储层中的水含量是否会产生浮力驱动的上升，进入尖晶石–橄榄石转变区？
• RQ2 在相变时娃德斯石释放水是否能触发含水熔融并产生浮性熔体？
• RQ3 与瞬时 MTZ 水储存相关的时间尺度和水预算是什么？
• RQ4 少量水含量如何影响 MTZ 羽流的稳定性与动力学及背向熔体透镜？

主要发现

• 水引起的浮力触发 MTZ 中的含水固态地幔上升。
• 在数千万年尺度上，这些羽流上升并与尖晶石–橄榄石相变相交，随着娃德斯石释放水，可能触发含水熔融。
• 形成的熔体密度低于固体基质，向上以岩核体或孔隙波形式上升。
• 含水向下回落的过程，如俯冲板块，亦可在 MTZ 下边界生成上升的浮性熔体 diapirs。
• MTZ 作为瞬时水储库运行，水含量和存在时间尺度可达到几十到几百万年级别。