颗粒破碎铀同位素年代技术的发展及其在风尘系统中的应用

As one of the rapid developing isotopic tracing methods in recent years, the composition of radiogenic uranium isotope of fine particles records the time since of the grain breaking, which has great potentials in tracing the land surface processes. However, the uranium comminution age has not been tested by geological records yet and its application is limited by complicating factors such as weathering dissolution, surface characterization, and precipitation of authigenic phases. The loess deposits in China could provide an ideal material for testing and developing the uranium comminution age due to its accurate age constrain and the extensive geochemical investigations conducted on its dust source, weathering and pedogenesis. Furthermore, eolian system is an important component of the land surface systems, which has great influences on the critical zone processes. Production and transportation of eolian dust is critical to understand its environmental functions and to interpret the paleo-records in the eolian deposits. One of the major challenges of current eolian research is associated with the traditional geochemical tools that could only reflect the composition or ages of the eroded rocks but can hardly discriminate the differing production mechanisms and transportation pass ways for the dust with the same petrological source. This project will test and develop the uranium isotope comminution age based on the eolian loess deposits in China, which may provide a new tool to resolve the production and transportation of eolian dust.

细粒物质的放射性铀同位素组成记录了颗粒自破碎以来的时间，具有示踪地表过程的巨大潜力，是近年来快速发展的同位素示踪新方法。但铀同位素破碎年龄学还未被地质记录所验证，其应用受风化溶解、表面表征、次生沉淀等复杂因素限制。中国黄土沉积年龄精准，物源、风化、成壤等基础地球化学研究深入，是验证与发展铀同位素破碎年龄学的绝佳材料。同时，风尘系统是陆地表层系统的重要组成部分，对诸多关键带过程有着重要作用。风尘的产生机制与搬运过程对理解风尘的环境功能和解读风尘沉积的古气候记录至关重要。以往传统地球化学方法只能反映最终剥蚀区的岩石成分或年龄，无法区分相同岩石学物源背景下不同粉沙产生机制和搬运中间过程，是当前风尘研究的最大挑战之一。放射性铀同位素组成与岩石成分无关，可反映不同搬运和粉沙产生机制所对应的破碎年龄。本项目以中国风成黄土为核心，验证和发展铀同位素破碎年龄学，为解决风尘的产生机制和搬运路径提供新手段。

铀同位素破碎年代学具有示踪地表物质循环的巨大潜力，是近年来我国科学家主导发展的新型同位素方法体系之一。该方法面临放射性破坏晶格中234U优先溶解影响、234U弹射反冲系数难以限定和缺乏应用推广三方面的难题。本项目围绕铀同位素破碎年代学的基础理论、技术方法和应用拓展三方面开展了系统研究，取得如下重要进展：.（1）在基础理论方面，利用我国青藏高原周缘天然剥蚀梯度水化学特征和贡嘎冰川地区独特的强风化冰川沉积物，揭示放射性破坏晶格优先溶解对地表过程铀同位素分异影响有限，提出近饱和溶解限制放射性破坏晶格优先溶解的化学机制，为铀同位素破碎年代学的广泛应用奠定了理论基础；.（2）在技术方法方面，广泛分析了各类沉积物样本，开发了不破坏表面的系统清洗方案，开发了利用久期平衡样品并结合电成型筛精准粒度控制和比表面积测量的234U弹射反冲系数定量测量方法；.（3）在应用推广方面，建立了铀同位素示踪“源-汇”过程指标体系，为黄土风尘物源、考古遗址古洪水事件等具有重大争论的问题提供了证据，建立了铀同位素剥蚀速度计，为解析高原抬升剥蚀风化动力学过程提供了新的手段。.这些研究完善了铀同位素破碎年代学理论模型，提升了方法精度，推动了应用研究，并被国内外同行广为采用，相关成果在《Geology》、《EPSL》、《JGR》等刊物上发表学术论文20篇以上。

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