Pan Fabin, Wu Xiang, Wang Chao, Zhang Yanfei, Yang Yiping, He Xiaobo, Jin Chong, Zhou Lian, Zhang Hongfei, He Hongping, Zhang Junfeng
State Key Laboratory of Geological Processes and Mineral Resources, and School of Earth Science, China University of Geosciences, Wuhan, China.
State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China.
Nat Commun. 2025 Jul 1;16(1):5440. doi: 10.1038/s41467-025-60566-y.
Previous high-temperature-pressure experiments predicted metallic iron's potential presence in the deep mantle below 250 km, arising from ferrous disproportionation in silicates, which could profoundly impact the redox environment and physicochemical properties. However, direct natural petrological evidence has been lacking, except scant clues like Fe-alloy inclusions in ultradeep diamonds. Here we present peridotite fragments, found in Cenozoic basalts from eastern China, containing decomposed Na-rich majoritic garnets (from depths of 410-550 km) and olivine with Fe-spinel-bearing inclusions, likely originated from retrograded wadsleyite/ringwoodite. Enriched Zn-Sr isotopic compositions of the decomposed garnet indicate an origin associated with the stagnant Pacific slab in the mantle transition zone. Disproportionation of iron is evidenced by widely distributed submicron-sized spherical Fe-Ni alloys and Fe-rich (Fe/ΣFe = 0.35-0.40) olivine. These findings provide compelling evidence for recycling of stagnant slab components in the eastern Asia big mantle wedge (BMW), and iron disproportionation in the deep mantle.
先前的高温高压实验预测，由于硅酸盐中的亚铁歧化作用，在250公里以下的深部地幔中可能存在金属铁，这可能会深刻影响氧化还原环境和物理化学性质。然而，除了超深钻石中的铁合金包裹体等少量线索外，一直缺乏直接的天然岩石学证据。在此，我们展示了在中国东部新生代玄武岩中发现的橄榄岩碎片，其中含有分解的富钠镁铝榴石（来自410-550公里深处）和带有含铁尖晶石包裹体的橄榄石，这些包裹体可能源自退变的瓦兹利石/林伍德石。分解石榴石的锌-锶同位素组成富集，表明其起源与地幔过渡带中停滞的太平洋板块有关。广泛分布的亚微米级球形铁镍合金和富铁橄榄石（铁/总铁=0.35-0.40）证明了铁的歧化作用。这些发现为东亚大地幔楔（BMW）中停滞板块组分的再循环以及深部地幔中的铁歧化作用提供了有力证据。
