云南前寒武系—寒武系界线锆石激光拉曼光谱研究及意义  

Raman Microspectroscopic Studies of Zircon from Precambrian— Cambrian Boundary in Yunnan and Its Significances

作　　者：王银喜[1,2] 张明生[1] 周建新[1] 王哓宇[1] 王媛媛[3] 陈强[1] 宋彪[4] 张开均[5] 杨杰东[1,2] 李惠民[1] 

机构地区：[1]南京大学现代分析中心,南京210093 [2]南京大学内生金属矿床成矿作用国家重点实验室,哈尔滨150030 [3]东北农业大学成栋学院,北京100037 [4]北京离子探针中心,中国地质科学院地质研究所,广州510640 [5]中国科学院广州地球化学研究所

出　　处：《地质论评》2007年第1期22-30,共9页Geological Review

基　　金：国家自然科学基金项目(No40072075);中国百人计划合作研究成果;南京大学开放测试基金(0303Y302-2004)资助

摘　　要：本文通过对8个澳大利亚TEM标准锆石和近百枚云南梅树村剖面前寒武系—寒武系界线M5层斑脱岩火山成因锆石进行了不同入射方位的激光拉曼光谱分析和对比研究。证实正常锆石拉曼光谱各峰的出现、强度与拉曼光束的入射方位有关,同时也发现晶化度差的异常锆石其拉曼光谱各峰的出现、强度与拉曼光束的入射方位无关或有很小的关系。这类异常锆石在四个不同方位上并不产生特征拉曼谱峰,就是有其强度也非常小。可以认为这些异常锆石的激光拉曼光谱特征与其晶体结构及蜕晶化的程度是有密切关系的。笔者等发现:①产在新鲜的火山灰M5层中约有80%的锆石因为高铀钍含量已发生不同程度蜕晶化,5%的锆石为滚圆状的继承老锆石,均为不适合铀-铅离子探针质谱(SHRIMP)和热电离同位素质谱(ID-TIMS)定年的异常锆石;②因为低铀钍含量该M5层中仅有15%的锆石没有发生蜕晶化,为适合SHRIMP和ID-TIMS同位素定年的正常锆石,只有这类锆石的年龄才能代表前寒武系—寒武系界线的年龄。首次提出火山成因锆石晶化度与锆石拉曼光谱的定量关系。使用这项显微拉曼光谱新技术方法可以对寒武系底界M5层火山灰或其它火成岩和变质岩锆石晶体的晶化状况作出了快速判断。对U-Pb定年来讲是一种简单易行并且十分有效的重要制约手段。This paper studies the laser Raman spectrum of zircons at different scatter angles, including 8 standard TEM zircons in Australia and about 100 volcanic zircons from the M5 bentonites of Precambrian-- Cambrian boundary at the Meishucun section in Yunnan, China. It was confirmed that the emergence and relative intensity of Raman peaks for the normal zircons are related to the difference angle of incidence. While these characteristic Raman peaks of abnormal zircons were disappeared or very weak, they didn＇t show relevant relationship with incidence angle as that of normal zircons. It can be thought that the Raman characteristic of the abnormal zircons germanely rel- evant to its crystal structures and the degree of metamictization. Writers have discovered that：①because of the content of the high uranium and thorium ,about 80% of the zircons from the fresh volcano ash M5 layer had already taken place the metamictization in the different degrees. About 5% of the zircons from the fresh volcano ash M5 layer are the roll shape and inherit of the old zircons. These zircons are all abnormal ones and not suitable for U-Pb isotope dating of the SHRIMP and ID-TIMS. ②Because of the content of the low uranium and thorium, only about 15% of zircons in the M5 layer are not metamict. These zircons are all normal ones and suitable for U-Pb isotope dating of the SHRIMP and ID-TIMS. Only the ages of these zircons can represent the ages of Precambrian--Cam- brian boundary. We have firstly pointed out a quantitative relationship between the degree of crystallization and Ra- man spectra for the volcano zircons. This new technique, using Raman spectroscopic analysis to study the degree of crystallization of zircon from the geological samples, has significant value for requiring the absolute age of zircons from the Procambrian--Cambrian boundary. It is also an important simple effective way to the constrain of U-Pb dating method.

关 键 词：激光拉曼光谱 Eg和Alg的特征峰 锆石晶化度 前寒武系一寒武系界线 云南梅树村剖面 

分 类 号：P588.1[天文地球—岩石学]