独居石和磷钇矿是用于各类岩石U-Th-Pb定年的重要副矿物，同时也是稀土矿床最主要的矿石矿物。独居石和磷钇矿作为REE、Y、U、Th和Pb等元素的载体矿物，其在热液中的溶解行为约束着稀土元素的富集成矿以及U-Th-Pb年龄的有效性。由于目前有关热液中独居石和磷钇矿溶解行为的基础实验数据还相当匮乏，且存在不一致性，导致对稀土成矿作用的理解以及U-Th-Pb年龄数据的地质解释存在许多困难和混乱。本项目拟以天然以及合成的独居石和磷钇矿为研究对象，采用人工合成包裹体原位流体取样和矿物微区定年等方法，系统研究不同温压下含F-、Cl-、SO42-和CO2热液中独居石和磷钇矿的溶解度以及所含U-Th-Pb体系的封闭性，查明控制热液中稀土元素迁移、分异以及沉淀的关键因素，揭示热液过程中U-Th-Pb年龄重置的机制和特征，为研究稀土元素的选择性富集成矿以及合理解释独居石和磷钇矿的年龄数据提供实验依据和约束。

Monazite and xenotime U–Th–Pb dating has been increasingly used for geochronological studies. Monazite and xenotime are usually accessory minerals but can also be ore minerals of the rare earth element (REE) deposits, representing light and heavy REE minerals, respectively. As a carrier of elements such as RE, Y, U, Th and Pb, the dissolution behavior of monazite and xenotime in hydrothermal fluids constrains the fractionation and enrichment of REE, as well as the usefulness of age determinations by the U-Th-Pb method. However, presently the basic experimental data for the dissolution of monazite and xenotime in hydrothermal fluids are scarce and conflicting, making the understanding of REE mineralization and their U–Th–Pb age results puzzling. In this project, we use both synthetic and natural monazite and xenotime, combining the methods of in-situ synthetic fluid inclusion sampling and in-situ mineral dating, to find out (1) the key physical-chemical factors controlling REE transportation, fractionation and precipitation; (2) U-Th-Pb age reset mechanisms of the monazite and xenotime in hydrothermal fluids. This study could provide direct experimental constraints on REE mineralization and better geological interpretation for monazite and xenotime U-Th-Pb dating.