日本东京大学Tsutsumi, Yutaro和Hirose, Kei团队合作报道了在核-幔边界条件下俯冲板块中的水滞留。该研究于2024年6月21日发表于国际一流学术期刊《自然—地球科学》杂志上。
据悉，水合SiO2相是下地幔俯冲板块中水的主要载体。假设它在核-幔边界以上的高温下脱水，有人推测，在这个神秘的区域和最上面的核中观察到的地震异常可能被归因为板块释放的水。
研究人员报告了在25-144GPa和2900-4100K的核-幔边界条件下的含水玄武岩熔融实验结果。高分辨率成像技术的二次离子质谱测量显示，SiO2相和SiO2-ALOOH固溶体分别含有0.5-3.6Wt%和约3.5wt%的H2O，与含有0.9-2.6wt%H2O的熔体相共存。
在核-幔边界区域的高温下，水对SiO2的高溶解度和高SiO2/熔体分配系数表明，实际上水不会从地幔底部的俯冲板块中逸出。即使核-幔边界温度高到足以熔化俯冲下来的地壳物质，大部分H2O也会留在固体残留物中，而不是部分熔化。因此，先前提出的板块脱水的结果不太可能是，导致最底部地幔和最顶部地核的化学非均质性的原因。
附：英文原文
Title: Retention of water in subducted slabs under core–mantle boundary conditions
Author: Tsutsumi, Yutaro, Sakamoto, Naoya, Hirose, Kei, Tagawa, Shoh, Umemoto, Koichiro, Ohishi, Yasuo, Yurimoto, Hisayoshi
Issue&Volume: 2024-06-21
Abstract: The hydrated SiO2 phase is a main carrier of water in subducting slabs in the lower mantle. Assuming its dehydration at high temperatures above the core–mantle boundary, it has been speculated that seismic anomalies observed in this enigmatic region and the uppermost core might be attributable to water released from slabs. Here we report melting experiments on a hydrous basalt up to conditions of the core–mantle boundary region at 25–144GPa and 2,900–4,100K. Secondary-ion mass spectrometry measurements with high-resolution imaging techniques reveal that the SiO2 phase and SiO2–AlOOH solid solution contain 0.5–3.6wt% and ~3.5wt% H2O, respectively, coexisting with melts holding 0.9–2.6wt% H2O. The high solubility into SiO2 and high SiO2/melt partition coefficient of water at the high temperatures of the core–mantle boundary region suggest that practically water does not escape from subducted slabs at the base of the mantle. Even if the core–mantle boundary temperature were high enough to melt subducted crustal materials, most of the H2O would remain in the solid residue rather than entering a partial melt. Previously proposed consequences of slab dehydration are therefore unlikely to be responsible for chemical heterogeneities in the lowermost mantle and the topmost core.
DOI: 10.1038/s41561-024-01464-8
Source: https://www.nature.com/articles/s41561-024-01464-8