地震学研究表明，在地核-地幔边界有许多超低速度带(ULVZs)，它们表现出特殊的物理属性，其组成和起源仍然存在争议。水-铁反应可以在最低地幔条件下生成独特的相，这可能对ULVZs的形成起着至关重要的作用。
通过机器学习技术的第一性原理分子动力学模拟，研究人员确定了水-铁反应产物氢化铁作为超离子相在核-幔边界是稳定的。在最低地幔条件下，超离子氢化铁具有比周围地幔慢得多的速度和更高的密度。
氢化铁的积累，要么是由俯冲的水和铁之间的化学反应产生的，要么是由对流携带的下地幔核心物质的凝固产生的，研究结果可以解释ULVZs的地震观测结果，特别是与俯冲有关的地震观测结果。研究结果强调，水可能在核-幔边界产生地震非均质性方面发挥了重要作用。
附：英文原文
Title: Superionic iron hydride shapes ultralow-velocity zones at Earth’s core–mantle boundary
Author: Zhang, Yu, Wang, Wenzhong, Li, Yunguo, Wu, Zhongqing
Issue&Volume: 2024-8-20
Abstract: Seismological studies have exposed numerous ultralow velocity zones (ULVZs) exhibiting extraordinary physical attributes at Earth’s core–mantle boundary, yet their compositions and origins remain controversial. Water–iron reaction can generate unique phases under lowermost-mantle conditions and likely plays a crucial role in forming ULVZs. Through first-principles molecular dynamic simulations with machine learning techniques, we determine that iron hydride, the product of water–iron reaction, is stable as a superionic phase at the core–mantle boundary. This superionic iron hydride has much slower velocities and a higher density than the ambient mantle under lowermost-mantle conditions. Accumulation of iron hydride, created through either a chemical reaction between subducted water and iron or solidification of core material entrained in the lower mantle by convection, can explain the seismic observations of ULVZs particularly those associated with subduction. This work suggests that water may have a substantial role in creating seismic heterogeneities at the core–mantle boundary.
DOI: 10.1073/pnas.2406386121
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2406386121