摘要
为探讨滇东南瑶山群的原岩年龄以及后期经历的岩浆-变质-构造事件年龄,开展了SHRIMP锆石U-Pb定年研究。结果表明,阴极发光(CL)分析和光学显微分析显示瑶山群的锆石组成比较复杂,可以分为继承锆石、变质锆石、深熔锆石/岩浆锆石等几大类。除少量测点207Pb/206Pb年龄为新元古代外,继承锆石206Pb/238 U表面年龄变化范围集中在235±1.7Ma^261±3.6Ma,加权平均值为250.8±9.8Ma(N=4,MSWD=4.1);深熔/岩浆锆石206Pb/238 U表面年龄显示出~85Ma和~75Ma两个峰值;变质增生锆石206Pb/238 U表面年龄为49~30Ma,且主要集中在32Ma、37Ma和42Ma左右。结合区域地质情况,初步推测:250.8±9.8Ma的继承锆石峰值年龄表明,瑶山群主体的原岩时代可能不早于二叠纪;变质锆石、深熔锆石/岩浆锆石的206Pb/238 U表面年龄可分为~85Ma、~75Ma、~42Ma、~37Ma和~32Ma等5组,可能代表了红河断裂南段自燕山晚期以来5期较强烈构造-岩浆-变质事件的时限。
The Yaoshan Group locates in the southeastern Ailao Shan-Red River strike-slip fault zone.It has experi-enced high-amphibolite facie metamorphism and chorismitization,thus it was thought as the Precambrian basement of the South China block in SE Yunnan region.In order to determine the ages of the protolithos,later magmatic, metamorphic and tectonic events of the Yaoshan Group,the zircon SHRIMP U-Pb dating was investigated.Ac-cording to CL images and optical microscope analyses,the zircons derived from the Yaoshan Group,which are very complicated with the metamorphosed re-crystal and over-growthing,could be divided into inherited,metamorphic, anatectic or magmatic types.Besides a few analyzed spots with the Neo-Proterozic ages,the inherited zircons main-ly yielded 20 6 Pb/2 3 8 U ages in the range from 235±1 .7 Ma to 261±3.6 Ma,with a weighted mean value of 250.8±9.8 Ma （N =4,MSWD=4.1）.The 20 6 Pb/ 2 3 8 U ages of anatectic or magamatic zircons represented by two peaks of85 Ma and 75 Ma,respectively.The 20 6 Pb/2 3 8 U ages of metamorphic zircons are in the range from 49 Ma to 30 Ma,with three peaks of 32,37 and 42 Ma,respectively.Based on the regional geology,this study suggested that the peak age of inherited zircons （250.8±9.8 Ma）indicated that the major protolithos of the Yaoshan Group might be formed later than the Permian,and that metamorphic,anatectic/magmatic zircons showed five 206 Pb/238 U peak a-ges of -85 Ma,--75 Ma,--43 Ma,-37 Ma and -32 Ma might indicate five important tectonic,magmatic and meta-morphic events in the south part of Red River fault since the later Yanshannian.
出处
《矿物岩石地球化学通报》
CAS
CSCD
北大核心
2014年第2期154-162,共9页
Bulletin of Mineralogy, Petrology and Geochemistry
基金
国家自然科学基金资助项目(40972129)
中国科学院创新项目(KZCX2-YW-136)
国家重点基础研究发展计划项目(2007CB41108)
中国科学院留学基金项目(2003023)
