西藏亚东淡色花岗岩Rb-Sr和Sm-Nd同位素研究——关于其年龄和源岩的证据  

Studies on Rb-Sr and Sm-Nd Isotope of Yadong Leucogranite in Tibet: Constraint on Its Age and Source Material

作　　者：杨晓松[1] 金振民[1] 

机构地区：[1]中国地质大学地球科学学院

出　　处：《地质论评》2001年第3期294-300,共7页Geological Review

基　　金：国家自然科学基金(编号49574225);原地质矿产部行业基金(编号95012012);博士点基金(编号 96014003)

摘　　要：对西藏亚东淡色花岗岩Rb-Sr和Sm-Nd同位素的详细研究表明,亚东淡色花岗岩Rb-Sr和Sm-Nd同位素组成十分不均匀,其初始Sr值和ε-(Nd)(13 Ma)分别介于0.756～0.775和-11.6～-16.3。由于存在着显著的同位素变异,而难以获得其全岩Rb-Sr等时线年龄。但研究获得了12.9±0.95Ma矿物—全岩Rb-Sr等时线年龄,其锶初始值为0.7744±0.0008,该年龄可以与高喜马拉雅带其他淡色花岗岩的年龄对比。Rb-Sr和Sm-Nd同位素组成显示亚东淡色花岗岩的源岩很可能是聂拉木群副变质岩。年龄统计分析表明,喜马拉雅淡色花岗岩是在地壳伸展和快速隆起背景下形成的,因此它的形成年龄是碰撞造山后地壳强烈活动和快速隆起的重要标志。The detailed Rb-Sr and Sm-Nd isotopic studies of Yadong leucogranite show that it is characterized by large Rb-Sr and Sm-Nd isotopic variations. Its initial Sr isotopic ratios and εNd, calculated at its age of 13 Ma, are in the range 0. 756 ~0. 775 and -11. 6~ -16. 3, respectively. Because these values match the isotropic composition of the paragneisses in Nielamu Group distributed along High Himalayas, they are regarded as the most probable parental rocks of Yadong leucogranite. The Rb-Sr and Sm-Nd isotopic variations make it difficult to obtain a whole-rock Rb-Sr isochron. However, a mineral-whole rock Rb-Sr isochron age of 12. 9±0. 95 Ma with initial Sr isotopic ration of 0. 7744±0. 0008 was obtained, which is comparable well with that of other granitic plutons within Himalayan leucogranite zone. That the formation of Himalayan leucogranite is statistically consistent with the age of the crustal detachment and the rapid uplift of Tibetan Plateau implies leucogranites is an important sign of crustal movement and rapid uplift in post-orogenic period.

关 键 词：亚东淡色花岗岩 聂拉木群 同位素 内部等时线年龄 铷-锶 钐-钕 

分 类 号：P597[天文地球—地球化学]