小流域化学风化及迁移过程中Y、Ho分异机制研究

Due to Y/Ho ratio is one of the important parameters in REE geochemical studies for tracing matter transportation, in recent years, the geochemists are interest in the fractionation mechanism between Y and Ho during geochemical processes in terrestrial waters. According to the seawater Y/Ho molar ratios are approximately two times higher than the crustal and shale value, the geochemist think that the fractionation between Y and Ho must take place somewhere, such as during weathering and riverine transport or in the marine environment. In the early studies, Nozaki et al. concluded that the fractionation between Y and Ho principally occur through marine biogeochemical processes within the ocean itself. By contrast, Bau et al. have demonstrated differential partitioning of Y and Ho in the dissolved and particulate phases between surface and deep waters, and suggested that the major fractionation between Y and Ho must occur outside the ocean, i.e. the estuarine zone. The main reason of their divergence is that there were lack of the fractionation mechanism between Y and Ho during geochemical processes in terrestrial waters. In the present study, we will investigate the Y/Ho composition in river water and suspended matter in the local drainage basins by using ICP-MS and TIMS determination and sequential extraction methods for discussing the fractionation mechanism between Y and Ho during geochemical processes in terrestrial waters and its contribution for water cycle of the world.

Y/Ho比值在地球科学物源和过程地球化学研究中是重要的示踪指标，对于表生过程中Y、Ho分异机制的探讨是稀土元素地球化学理论体系建设的重要组成部分。目前研究者对于海水Y/Ho比值明显大于陆壳的结果，到底来自于稀土自陆到海迁移的哪个环节还有较大的分歧，主要是缺乏对陆地化学风化和迁移过程中Y/Ho分异机制的系统认识。本研究拟采用ICP-MS和TIMS等分析技术，并结合颗粒物相态提取以及粒度分级提取等方法，通过对特定岩性的代表性小流域风化剖面、水/岩相互作用和水/土相互作用以及水体中Y/Ho分异行为进行研究，探讨小流域化学风化及物质迁移过程中Y/Ho比值的变化特征和可能的Y、Ho分异机制，判断小流域化学风化过程中对Y和Ho分异行为起控制作用的关键环节。最终为地表物质循环过程中Y/Ho分异机制的认识及其地球化学意义提供可供参考的研究结果，是对稀土元素地球化学示踪理论的适当补充。

Y/Ho 比值在地球科学物源和过程地球化学研究中是重要的示踪指标，对于表生过程中Y、Ho 分异机制的探讨是稀土元素地球化学理论体系建设的重要组成部分。目前研究者缺乏对陆地化学风化和迁移过程中Y/Ho 分异机制的系统认识。本研究采用ICP-MS测定，并结合颗粒物相态提取以及粒度分级提取等方法，通过对特定岩性的代表性小流域风化剖面、水/岩相互作用和水/土相互作用以及水体中Y/Ho分异行为进行了研究，探讨了小流域化学风化及物质迁移过程中Y/Ho 比值的变化特征和可能的Y、Ho 分异机制。研究结果显示：1）碳酸盐岩和硅酸盐两个不同流域河流的Y和Ho的浓度差异明显，Y/Ho比值也明显不同，Y/Ho分异显示了一定的来源控制特征。乌江小流域和赣江水体的Y/Ho 摩尔比值分别在80 和45左右。河流沿程变化规律显示，吸附/解吸过程对Y/Ho的分异有一定影响，同时，河流稀释作用也会引起Y/Ho比值的沿程变化。2）中到微碱性水体环境中，随着河水的迁移，颗粒物会逐渐吸附REE元素，使之进入颗粒物。水库水体的溶解态REEs浓度明显低于其上游来水和下泻水中的REE浓度，说明河流建库对包括REEs在内的微量元素，尤其是颗粒物强控制型微量元素的河流地球化学行为及其生物地球化学循环有明显影响，水库建设可以降低流域溶解态微量元素的河流输送。这对于我们今后讨论REE的河水化学，以及河流REE入海通量都有重要意义。3）小流域河流水体输运过程中，吸附/解吸能力不同的重稀土元素和轻稀土元素之间的分异比较明显，说明河流水体系统中因为吸附/解吸过程而引起的Y/Ho分异不可忽视，这对于我们认识陆地水体中Y/Ho分异机理至关重要。该课题赞助标注论文10篇，其中SCI 收录9篇。