碳酸盐岩化学风化过程中Sm-Nd分异研究

钐（Sm）和钕（Nd）是具有相似地球化学性质的轻稀土元素。同时，Sm-Nd之间也构成了两对常用的放射性同位素母子体。通常认为在化学风化过程中Sm-Nd很难活化和分异。因此，Sm/Nd比值、Sm-Nd同位素及Nd同位素模式年龄，经常被用做'指纹'示踪风化壳、风尘及沉积物的母岩或源区。目前，化学风化过程中稀土元素的活动性、轻-重稀土元素间的分异已得到确认。但是，对于化学风化过程中Sm-Nd的行为仍缺乏清晰和科学的认识。本项工作，拟以云贵高原碳酸盐岩--红色石灰土原位风化体系为研究对象；揭示在碳酸盐岩风化及红色石灰土形成过程中，Sm-Nd活化迁移及重新分布规律；评价化学风化过程中Sm-Nd 之间的相对活动性差异；阐明化学风化过程中Sm-Nd分异规律及其形成机制。该项工作不仅对Sm-Nd体系的物源示踪及年代学研究具有重要的意义，而且对深入探索碳酸盐岩风化机理及红色石灰土的形成过程亦有一定的益处。

Samarium (Sm) and neodymium (Nd) are light rare earth elements (LREE) and have very similar geochemical properties. Moreover, the two elements are joined in two parent-daughter relationships by the alpha-decay. They are generally considered to be resistant to mobility and fractionation during chemical weathering of rocks. Thus, Sm/Nd ratio, Sm-Nd isotopic compositions and Nd model ages are used as fingerprints to provide information on the source of weathering crust, eolian dust and sediments as well as to provide age data. Although the mobility of rare earth elements (REE) and fractionation between LREE and heavy rare earth elements (HREE) during chemical weathering of rocks have been documented, the behavior of the Sm-Nd during chemical weathering processes is still not fully understood. In this study, we will focus on the in-situ weathering system of carbonate rocks--terra rossa on the Yunnan-Guizhou Plateau. The purposes are to: (1) reveal the objective regularities of mobility, migration and redistribution of Sm-Nd during in-situ chemical weathering, (2)evaluate the relative mobilities between Sm and Nd under chemical weathering circumstances, and (3) investigate the regularity of Sm-Nd fractionation and its formation mechanism during chemical weathering within the carbonate rock--terra rossa system. This study is very important to reduce errors in Sm-Nd data interpretations of provenance and age of the affected rocks under terrestrial weathering conditions. Furthermore, the knowledge about Sm-Nd behavior during chemical weathering is also of interest for understanding the weathering processes of carbonate rocks and the origin of terra rossa.