中祁连马衔山岩群内基性岩墙群锆石LA-ICP-MSU-Pb年代学及其构造意义  

LA-ICP-MS U-Pb Zircon Geochronology of Basic Dikes within Maxianshan Rock Group in the Central Qilian Mountains and Its Tectonic Implications

作　　者：何世平[1] 王洪亮[1] 陈隽璐[1] 徐学义[1] 张宏飞[2] 任光明[1] 余吉远[1] 

机构地区：[1]中国地质调查局西安地质矿产研究所,陕西西安710054 [2]中国地质大学地球科学学院,湖北武汉430074

出　　处：《地球科学（中国地质大学学报）》2008年第1期35-45,共11页Earth Science-Journal of China University of Geosciences

基　　金：中国地质调查局国土资源大调查项目“西北地区重要成矿带基础地质综合研究”(No.1212010510416)

摘　　要：马衔山岩群变质基底岩系中发现大量基性岩墙,作为中祁连造山带东部一次重要的构造-岩浆事件的标志.根据地质-岩石学特征,将马衔山岩群中的基性岩墙分为两期.利用LA-ICP-MS(激光剥蚀等离子体质谱)方法,分别对两期基性岩墙进行单颗粒锆石微区U-Pb同位素测定,并应用CL图像对所测锆石进行了成因研究.获得早期变辉长岩墙的侵入年龄为(441.1±1.4)Ma(早志留世早期),主变质期年龄为(414.3±1.2)Ma(早泥盆世早期);晚期辉绿(玢)岩墙群的侵入年龄为(434±1.0)Ma(早志留世晚期),并保留有曾遭受马衔山岩群混染的信息(捕获锆石的207Pb/206Pb表面年龄为(2325±3)Ma～(2573±6)Ma),以及遭受了加里东晚期构造-热事件的改造的信息(206Pb/238U表面年龄为(400±2)Ma～(429±2)Ma).结合相关研究成果,认为马衔山岩群中的两期基性岩墙群形成于祁连地区由俯冲造山向碰撞造山的转换时期,代表了中祁连地块在区域上遭受北东-南西向强烈挤压的过程中派生北西-南东向扩张作用的地质纪录.A large number of basic dikes which indicate an important tectonic-magmatic event in the eastern part of the middle Qilian orogenic belt were found in the Maxianshan rock group, Yongjing County, Gansu Province, China. According to research on their characteristics of geology and petrology, basic dike swarms, widely intruded in Maxianshan rock group, are divided into two phases. U-Pb isotopes of zircons from the basic dikes of the two phases were determined by LA-ICP-MS respectively in the State Key Laboratory of Continental Dynamics of Northwest University, and the causes of formation of the zircons were studied by using CL images. The formation age of the earlier phase of variational gabbro dikes is （441.1 ± 1.4） Ma （corresponding to the early stage of Early Silurian）, and the age of main metamorphic period is （414.3±1. 2） Ma （corresponding to the early stage of Early Devonian）. The formation age of the later phase of diabase dike swarms is （434±1.0） Ma （corresponding to the late stage of Early Silurian）, and the age of main metamorphic period is （414. 3±1.2） Ma （corresponding to the early stage of Early Devonian）. The captured-zircons from diabase dike swarms retain some information of material interfusion by Maxiashan rock group （^207Pb/^206Pb apparent ages are （2 325±3） Ma-（2 573±6） Ma）, and some zircons from diabase dike swarms also retain information impacted by tectonic thermal event during the late period of Caledonian Movement （^206 pb/^238 U apparent ages are （400 ± 2） Ma- （429 ± 2） Ma）. The study, together with others, suggests that, the basic dikes within Maxianshan rock group formed in the period when Qilian transferred from subductional orogeny towards collisional orogeny, which is the geological record of NW-SE extension during regional NE-SW toward intense compression in the Central Qilian block.

关 键 词：马衔山岩群 基性岩墙群 锆石 La—ICP-MS U-PB定年 志留纪 扩张作用. 

分 类 号：P591[天文地球—地球化学]