Redistribution of REEs during metamorphism and its indicative significance for fluid processes

Detailed REE geochemical studies of the Xingzi Group metasedimentary rocks at Lushan and rock-forming minerals such as garnet have been conducted and the results show that the REEs are partly present in the rock-forming minerals and are dominantly contained in the lattice of accessory minerals. In the process of metamorphism the REEs reached partition equilibrium between garnet porphyroblast and rock and the partitioning of REEs between garnet and host rock is obviously controlled by the chemical composition of the system. The REE compositions of metamorphic veins and their minerals display remarked lanthanide tetrad effects and the element pairs Zr-Hf, U-Th and Y-Ho have also experienced remarkable fractionation with respect to the metamorphic rocks and they can be used as discriminating indicators for the occurrence of fluid processes in the process of metamorphism of the Xingzi Group.