锆石微区喇曼光谱研究及成因标型意义

通过对岩浆和变质成因锆石的微区喇曼光谱研究,揭示出岩浆和变质成因锆石从晶体核部至边缘在喇曼光谱峰强度上存在不同的变化趋势,即岩浆成因锆石由晶体核部至边缘喇曼峰强度逐渐减弱,而变质成因锆石则相反或不变化。这是由于它们形成时晶体中的U、Th分带趋势不同造成,具有重要的成因标型意。

A RAMAN SPECTROSCOPIC STUDY OF ZIRCONS ON MICRO SCALE AND ITS SIGNIFICANCE IN EXPLAINING THE ORIGIN OF THE ZIRCONS

The magmatogenic and metamorphogenic zircons were investigated by Raman microprobe analysis.We found that there are notable diffrences between the two kinds of zircons in the variation trend of Raman peak intensity from core to rim of a crystal. In magmatogenic zircons,the Raman peak intensity and Δ(=H/W) values gradually decrease from core to rim of a crystal,which is caused by the increasing metamictization and suggeits an increase in U and Th concentrations from core to rim. In metamorphogenic zircons,there are two kinds of crystals according to their Raman data:the first group of zircons exhibits a variation trend opposite to that of magmatogenic zircons,tending to increase in the Raman peak intensity and Δ values from core to rim,which is caused by the decreasing metamictization and shows a decrease of U and Th concentrations from core to rim of a crystal.The second group of zircons exhibits no change in Raman peak intensity and Δ values in a crystal.The data of infrared and Raman spectra of these crystals show that they are well crystallized and have no lattice destruction by metamictization,and are considered to crystallize in high temperature stage of metamorphism.During this stage,the U and Th ions have been moved by the metamorphic fluid from the parent rock of these zircons. The other diffences between them is the background level of their Raman spectra,which is higher in magmatogenic zircons than that of metamorphogenic zircon.The is because the former have more impurities with fluorescent radiation due to a higher crystallization temperature than that of the latter. These diffrences between magmatogenic and metamorphogenic zircons can be used to identify the genesis of zircons and understand the origin and history of their parent rocks.