【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。更多还原

【Abstract】 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 relevant to its crystal structures and the degree of metamictization. Writers have discovered that:① because 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.② Because 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—Cambrian boundary. We have firstly pointed out a quantitative relationship between the degree of crystallization and Raman 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.更多还原