吉林大学王枫和许文良教授团队近日取得一项新成果。经过不懈努力，他们的最新研究提出了地表水再循环进入地幔过渡带的钾同位素证据。2024年5月14日出版的《自然—地球科学》发表了这项成果。
本研究报道了东北亚一组特征良好的新生代火山岩中的钾同位素数据。数据显示，钾同位素比值(-0.83‰至-0.36‰)低于原始地幔(-0.42‰至±0.08‰)，表明了地壳钾输入和俯冲板块物质对地幔过渡带的改造作用。钾同位素与放射性成因Sr-Nd-Pb同位素的解耦，再加上地球物理上确定的过渡带上方的低电阻率异常，需要从停滞俯冲板块向过渡带输入地表水。这些水可以在东北亚火山中循环回到地表。
据悉，全球水循环涉及地球内部和地表环境之间的相互作用。地球物理和矿物物理学的研究表明，地幔过渡带是含水的，至少是局部含水的。然而，对于过渡带中的水是来自内部的原始物质还是通过来自地球表面与俯冲有关的过程，目前还没有明确的限制。东北亚新生代火山活动是由停滞的太平洋板块上方的湿热上升流引发的，并产生了地幔过渡带衍生的火山岩。钾元素在岩浆过程中的地球化学行为与水相似，因此可以用于限制地幔过渡带中水的性质。
附：英文原文
Title: Potassium isotopic evidence for recycling of surface water into the mantle transition zone
Author: Xing, Kai-Chen, Wang, Feng, Teng, Fang-Zhen, Xu, Wen-Liang, Wang, Yi-Ni, Yang, De-Bin, Li, Hong-Lin, Wang, Yan-Chao
Issue&Volume: 2024-05-14
Abstract: Global water cycling involves interactions between Earth’s interior and its surface environment. Geophysical and mineral physics studies have suggested that the mantle transition zone is hydrous, at least locally. However, there are poor constraints on whether water in the transition zone is sourced internally from primordial materials or from Earth’s surface via subduction-related processes. Cenozoic volcanism in Northeast Asia is triggered by hot and wet upwelling flows above the stagnated Pacific slab and has produced mantle transition zone-derived volcanic rocks. Potassium behaves geochemically similarly to water during magmatic processes, and hence can potentially be used to constrain the nature of water in the mantle transition zone. Here we report potassium isotopes in a set of well-characterized Cenozoic volcanic rocks in Northeast Asia. Their K isotope ratios (-0.83‰ to -0.36‰) are lower than primitive mantle (-0.42‰±0.08‰), suggesting crustal potassium inputs and modifications of the mantle transition zone by subducted slab materials. Decoupling of potassium isotopes from radiogenic Sr–Nd–Pb isotopes, combined with a geophysically identified low-resistivity anomaly above the transition zone, requires the input of surficial water from the stagnated subducted slab into the transition zone. This water can then be cycled back to the surface in Northeast Asian volcanics.
DOI: 10.1038/s41561-024-01452-y
Source: https://www.nature.com/articles/s41561-024-01452-y