内蒙集宁地区孔兹岩系中大理岩的形成时代——长英质片麻岩中LA-ICP-MS锆石U-Pb测年的证据  

Formation Age of the Marble in the Khondalite Series in Jining,Inner Mongolia: Evidence of the LA-ICP-MS Zircon U-Pb Dating of Felsic Gneiss

作　　者：徐仲元[1] 范志伟[1] 刘正宏[1] 李世超[1] 王挽琼[1] 张超[1] 马越 王英男 

机构地区：[1]吉林大学地球科学学院,长春130061 [2]内蒙古自治区烟草公司通辽市公司,内蒙古通辽028000

出　　处：《吉林大学学报（地球科学版）》2013年第3期809-819,共11页Journal of Jilin University：Earth Science Edition

基　　金：中国地质调查局区域地质调查项目(1212011120709);国家自然科学基金项目(41211120171;41272223)

摘　　要：研究区位于华北克拉通西部孔兹岩带东段的集宁一带,区内的孔兹岩系由下部的榴云片麻岩组合和上部的大理岩组合组成。在大理岩组合的底部发现了数层与薄层大理岩互层的长英质片麻岩,岩相学、锆石特征和原岩恢复指示该长英质片麻岩原岩为长石砂岩。对长英质片麻岩进行LA-ICP-MS锆石U-Pb测年分析,在70个锆石颗粒中获取了72组锆石数据。其中:碎屑锆石数据中年龄最小的为(2 091±20)Ma,可以代表长英质片麻岩原岩沉积时代的下限;19组集中在1.8～1.9Ga的变质锆石207Pb/206Pb表面年龄的加权平均值为(1 852±15)Ma(MSWD=0.7),该年龄值可以代表长英质片麻岩原岩沉积时代的上限。结合前人研究成果可以认为:集宁地区孔兹岩系中大理岩形成于(2 091±20)～(1 852±15)Ma的古元古代,并在(1 852±15)Ma遭受了区域变质作用,同时也进一步说明大理岩为孔兹岩系的重要组成部分;横贯西部陆块的孔兹岩带中,孔兹岩系原岩的源区曾存在大规模的花岗质岩浆活动,但是带内各个部位有着不尽相同的物源区;孔兹岩系不是由附近太古宙岩石提供碎屑物质的原地沉积,而是古元古代晚期构造作用叠置与附近太古宙岩石产在一起的外来构造岩片。Our research area is located in Jining,the eastern section of the Khondalite belt in the western block of the North China craton,where the khondalite series is composed of garnet-biotite gneiss in the lower part and marble in the upper part.Several layers of felsic gneiss interbedded with thin marble layers are found,and the parental rock of the felsic gneiss is defined as feldsparthic sandstone by petrographical study,zircon characteristics and restoring the protolithic types.After LA-ICP-MS zircon U-Pb dating of the felsic gneiss,72 zircon data are obtained from 70 zircon grains,among which the youngest detrital zircon data is（2 091±20） Ma that can represent the lower limit of felsic gneiss formation age;And the weighted average 207Pb/206Pb apparent age of the 19 metamorphic zircon concentrated between 1.8-1.9 Ga is（1 852±15） Ma（MSWD=0.7）,can represent the upper limit of deposition age of the original rock of the felsic gneiss.Based on the previous research results,we could conclude that in Jining area,marbles in the khondalite series were formed in the Paleoproterozoic Era between（1 852±15） Ma and（2 091±20） Ma,and underwent the regional metamorphism in（1 852±15） Ma.This suggests that marbles are the important component of the khondalite series;In the Khondalite belt across the western block of the North China craton,a large scale of granitic intrusion had existed in the source region of protolith of the khondalite series.However,there are different material source regions in every part of the belt;the protoliths of the khondalite series is not the in-situ deposition of fragmentary materials provided by the nearby Archean rocks,but alien tectonic rock sheet mingled with the nearby Archean rocks by Late Paleoproterozoic tectonic processes.

关 键 词：孔兹岩系 大理岩 长石砂岩 LA-ICP-MS锆石U-Pb 古元古代 

分 类 号：P597.3[天文地球—地球化学]