Zircon REE and Th,U Characteristics of Metamorphic Rocks from the Dabie Mountains

Micro-scale in situ REE analyses of zircon cores and rims have been carried out for eclogites from Xindian, Shuanghe, Huangzhen and jadeite quartzite from Shuanghe, Dabie Mountains. Combining with the CL internal structure and U-Pb dating, we studied the zircon REE composition change from the protolith inherited zircon to the metamorphic zircon during the ultra-high pressure metamorphism. The results show that the inherited core and metamorphic rim have quite different REE contents. It depends on how metamorphic zircon forms, overgrowth or recrystallization of protolith zircon. In general, the metamorphic zircon rims have lower REE contents compared with the protolith cores, especially in HREE. The metamorphic rims also have lower Th/U ratio than that of the cores. Detailed comparative study on REE and Th/U ratio of inherited zircon cores and metamorphic zircon rims may provide important information on forming process of metamorphic zircons and physico-chemical environment when it forms.