大别山变质岩锆石微区稀土元素和Th,U特征

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

对进行过微区UPb定年和阴极发光成像研究的大别山辛店榴辉岩、双河榴辉岩、黄镇榴辉岩和双河硬玉石英岩中锆石,进行了微区核部与边部稀土元素测定。结合UPb年龄和CL图象,探讨了超高压变质过程中稀土元素从原岩锆石到变质锆石的变化。结果表明,原岩锆石和变质锆石有很不相同的稀土元素含量,它取决于变质锆石是由变质重结晶还是变质增生作用形成及形成时间。一般说来,边部变质锆石比原岩锆石亏损稀土元素,特别是重稀土,并且有更低的Th/U比。变质锆石的稀土元素和Th/U比可以为变质锆石形成时的物理化学环境和变质锆石成因提供重要信息。

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 to the metamorphic zircon dating, during we studied the zircon REE composition change from the protolith inherited zircon 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.