近日，以色列耶路撒冷希伯来大学Weiss, Yaakov团队研究了富镍金刚石包裹体记录的深部上地幔氧化还原状态。2025年9月22日出版的《自然—地球科学》杂志发表了这项成果。
地幔的氧化还原状态受铁和碳的氧化状态控制，并影响地幔的关键物理和化学参数。地幔捕获体、实验和热力学研究表明，氧逸度随深度的增加而减少，下降到~250km。进一步的适度下降与富镍金属合金在250-300公里处的预期稳定有关。然而，250-500Km之间的石榴石记录了更多的氧化条件，并且在这些深度中没有富镍合金被报道作为预测的自然证据。
研究组报道了来自南非Voorspoed矿的两颗钻石中的镍铁金属纳米夹杂物和富镍碳酸盐微夹杂物。各种压力指标证实它们起源于上地幔深部或浅层过渡带（280 ~ 470 km）。富镍金属与碳酸盐共存，表明氧化的碳酸盐岩熔体与还原的含金属橄榄岩发生反应，导致镍富集和金刚石生长。这个反应捕捉了交代动力学的快照，包括可能在以后反应的中间产物的形成。这些钻石提供了富镍合金在地幔预测深度存在的直接证据。它们还表明存在深部碳酸盐-硅熔体，这些熔体偶尔氧化小体积的地幔，并在金伯利岩和碱玄武岩的形成中起作用。
附：英文原文
Title: Redox state of the deep upper mantle recorded by nickel-rich diamond inclusions
Author: Kempe, Yael, Remennik, Sergei, Tschauner, Oliver, Navon, Oded, Holland, Tim J. B., Weiss, Yaakov
Issue&Volume: 2025-09-22
Abstract: The redox state of Earth’s mantle is governed by the oxidation state of iron and carbon and influences key physical and chemical mantle parameters. Mantle xenoliths, and experimental and thermodynamic studies reveal a decrease in oxygen fugacity with depth, down to ~250km. A further more modest drop is linked to the predicted stabilization of nickel-rich metallic alloy at 250–300km. However, garnets from 250–500km record more oxidized conditions, and no nickel-rich alloy has been reported from these depths to account as natural evidence for the predictions. Here we report nickel–iron metallic nanoinclusions and Ni-rich carbonate microinclusions in two diamonds from the Voorspoed mine, South Africa. Various pressure indicators confirm their origin in the deep upper mantle or the shallow transition zone (280–470km). The coexistence of nickel-rich metal and carbonate indicates a reaction between oxidized carbonatitic melt and reduced metal-bearing peridotite that led to nickel enrichment and diamond growth. This reaction captures a snapshot of the dynamics of metasomatism, including the formation of intermediate products that may later react. The diamonds provide direct evidence for nickel-rich alloy at its predicted depth within the mantle. They also indicate the presence of deep carbonatitic–silicic melts, which episodically oxidize small volumes of the mantle and play a role in the formation of kimberlites and alkali basalts.
DOI: 10.1038/s41561-025-01791-4
Source: https://www.nature.com/articles/s41561-025-01791-4