近日，美国宾夕法尼亚州立大学Lee R. Kump团队研究了大氧化事件峰值时的陆上氧化铀动员。相关论文于2025年9月2日发表在《美国科学院院刊》杂志上。
氧化还原敏感元素在地球表面氧化还原状态演化的研究中占有重要地位，包括大气中O2的第一次主要上升，即古元古代大氧化事件。然而，大多数前寒武纪岩石经历了多阶段的构造热历史，这增加了对其化学性质的解释的模糊性。
应用U-Th-Pb同位素年代学对~2.06 Ga KuetsjRthemsia佩城加绿岩带火山岩组进行分析，以约束U氧化的年龄和程度。通过对比U和Th主题Pb同位素的相对迁移率，研究组发现喷发后不久就发生了完全或接近完全的氧化和U的去除。他们认为，这可能表明大气中的氧含量相对较高，其中氧化风化和变化产生了一个向海洋输送U的全球脉冲。这一脉冲可以解释~ 2Ga地幔储层U-Th-Pb同位素特征的广泛变化，包括洋中脊玄武岩的232Th/238U比值的降低和高238U/204Pb （HIMU）向洋岛玄武岩的开始，强调了古元古代地表和地球深部氧化还原特征之间的联系。
利用207Pb-206Pb、238U-206Pb、235U-207Pb和232Th-208Pb年代学分析，可以将~2.06 Ga氧化U损失与~1.8 Ga区域变质过程中U的重新引入以及显生宙构造热事件中Pb的损失进行区分。因此，该结果建立了岩石中氧化还原敏感元素行为的复杂历史，强调了这样一个事实，即元素丰度本身不太可能在经历了多阶段地质历史的岩石中获得直接的替代信息。
附：英文原文
Title: Subaerial oxidative uranium mobilization at the culmination of the Great Oxidation Event
Author: Bauer, Ann M., Li, Weiqiang, Rybacki, Kyle S., Roden, Eric E., Kump, Lee R., Johnson, Clark M.
Issue&Volume: 2025-9-2
Abstract: Redox-sensitive elements figure prominently in studies of the evolution of Earth’s surface redox state, including the first major rise in atmospheric O2, the Paleoproterozoic Great Oxidation Event. Most Precambrian rocks endured multistage tectonothermal histories, however, adding ambiguity to interpretation of their chemistry. Here, we apply U-Th-Pb isotope geochronology to the highly oxidized ~2.06 Ga Kuetsjrvi Volcanic Formation, Pechenga Greenstone Belt, Russia, to constrain the age and extent of U oxidation. By contrasting the relative mobility of U and Th using Pb isotopes, we find that complete to near-complete oxidation and removal of U occurred shortly after eruption. We argue that this likely indicates relatively high atmospheric O2, where oxidative weathering and alteration produced a global pulse of U to the oceans. Such a pulse could explain widespread shifts in the U-Th-Pb isotope character of mantle reservoirs at ~2 Ga, including a decrease in the 232Th/238U ratio of the mid-ocean ridge basalt source and inception of the high-238U/204Pb (HIMU) source to ocean island basalts, underscoring the connections between the redox character of the Paleoproterozoic surface and deep Earth. Using 207Pb-206Pb, 238U-206Pb, 235U-207Pb, and 232Th-208Pb geochronology, ~2.06 Ga oxidative loss of U may be distinguished from reintroduction of U at ~1.8 Ga during regional metamorphism, as well as Pb loss during a Phanerozoic tectonothermal event. Our results therefore establish the complex history of redox-sensitive element behavior in the rocks, highlighting the fact that elemental abundances, by themselves, are unlikely to capture straightforward proxy information in rocks that have seen multistage geologic histories.
DOI: 10.1073/pnas.2510289122
Source: https://www.pnas.org/doi/abs/10.1073/pnas.2510289122