美国亚利桑那州立大学 Sang-Heon 和韩国延世大学 Lee, Yongjae 的研究组近日取得一项新成果。他们认为地球最顶部外核中的富氢层来源于深部俯冲的水。该项研究成果发表在2023年11月13日出版的《自然—地球科学》上。

研究报道了在与地核-地幔边界相关的压力-温度条件下，含水物矿物中的水与 Fe-Si 合金之间的反应形成 SiO₂ 和 FeH_x ，并进行了高温高压激光加热金刚石—砧座实验。研究人员表示，如果水是通过俯冲作用被输送到核幔边界的，那么这种反应可能使地幔和地核之间的氢和硅的交换成为可能。由此在最顶部核心形成的富氢、缺硅层，将具有较低的密度，稳定核心顶部的化学分层，并具有较低的速度。研究结果表明，在数十亿年的深层水输送过程中，地核和地幔之间的这种化学交换可能有助于假定的 E' 层的形成。

据悉，地核—地幔边界呈现出从硅酸盐到金属等物质的巨大变化。虽然众多研究人员对它们之间的化学相互作用知之甚少，却在最外层核(E' 层)中提出了一个速度较低的薄层，且难以用单个轻元素的浓度变化来解释。

附：英文原文

Title: A hydrogen-enriched layer in the topmost outer core sourced from deeply subducted water

Author: Kim, Taehyun, ORourke, Joseph G., Lee, Jeongmin, Chariton, Stella, Prakapenka, Vitali, Husband, Rachel J., Giordano, Nico, Liermann, Hanns-Peter, Shim, Sang-Heon, Lee, Yongjae

Issue&Volume: 2023-11-13

Abstract: The Earth’s core–mantle boundary presents a dramatic change in materials, from silicate to metal. While little is known about chemical interactions between them, a thin layer with a lower velocity has been proposed at the topmost outer core (E' layer) that is difficult to explain with a change in concentration of a single light element. Here we perform high-temperature and -pressure laser-heated diamond-anvil cell experiments and report the formation of SiO₂ and FeH_x from a reaction between water from hydrous minerals and Fe–Si alloys at the pressure–temperature conditions relevant to the Earth’s core–mantle boundary. We suggest that, if water has been delivered to the core–mantle boundary by subduction, this reaction could enable exchange of hydrogen and silicon between the mantle and the core. The resulting H-rich, Si-deficient layer formed at the topmost core would have a lower density, stabilizing chemical stratification at the top of the core, and a lower velocity. We suggest that such chemical exchange between the core and mantle over gigayears of deep transport of water may have contributed to the formation of the putative E' layer.

DOI: 10.1038/s41561-023-01324-x

Source: https://www.nature.com/articles/s41561-023-01324-x