内蒙古克什克腾旗林西组碎屑锆石LA-ICP-MS年代学及其地质意义  

LA-ICP-MS U-Pb Dating of Detrital Zircons from Linxi Formation and Its Geological Implications in Hexigten Qi,Inner Mongolia

作　　者：李红英[1] 张达[1] 周志广[1] 柳长峰[1] 李鹏举[2] 陈利贞 谷丛楠[4] 

机构地区：[1]中国地质大学(北京)地球科学与资源学院,北京100083 [2]四川理工学院经济与管理学院,四川自贡643000 [3]河北省区域地质矿产调查研究所,河北廊坊065000 [4]天津华北地质勘查局,天津300170

出　　处：《吉林大学学报（地球科学版）》2016年第1期146-162,共17页Journal of Jilin University：Earth Science Edition

基　　金：内蒙古自治区国土资源厅矿产调查项目(NMKD2006-05);中国地质调查局地质调查项目(1212010811001;1212011085490;12120114093901;1212011220465)~~

摘　　要：内蒙古克什克腾旗位于西拉木伦河以北，属锡林浩特地块南缘。本文对出露于克什克腾旗北东约5km的一套变质粉砂岩进行了锆石LA—ICP—MSU—Pb测年，其年龄结果主要分为4个区间：258～298Ma（峰值为285Ma）、377～474Mat峰值为430Ma）、1261～1727Ma、1853～2513Ma，此外还含有321Ma和937Ma的锆石各一颗。锆石CL图像显示：258～298Ma的锆石以岩浆锆石为主，响应兴蒙造山带的晚古生代岩浆活动；377-474Ma的锆石中既有岩浆锆石又有变质锆石，表明其源区既有奥陶纪泥盆纪岩浆岩，又有古生代的变质岩；1261～1727Ma的锆石以岩浆锆石为主，少数为变质锆石，暗示中元古代的岩浆岩和变质岩也为该组提供物源；1853～2513Ma的锆石以岩浆锆石为主，反映了华北板块基底的年龄信息。该变质粉砂岩中碎屑锆石的最小谐和年龄是258Ma，限定了其沉积时代的下限为晚二叠世，应属于林西组。年龄峰值既对应华北板块的重要构造热事件，又有与兴蒙造山带地质事件相关的年龄信息，表明林西组具有南北两个物源区，同时也暗示在其形成时华北板块与西伯利亚板块已经拼合。Hexigten Qi is located to the north of Xar Moron River, tectonically on the south margin of Xilinhot massif. The authors conduct the analysis on the detrital zircon LA - ICP - MS U - Pb dating for the metasiltstones of Linxi Formation from a ca. 5 km outcrop in the northeastern Hexigten Qi. The samples yield 4 groups of ages principally at： 258 -298 Ma （peak at 285 Ma）, 377 -474 Ma （peak at 430 Ma）, 1261-1 727 Ma, andl 853-2 513 Ma. Besides, two zircons yield the age of 321Ma and 937 Ma respectively. Zirons aged 258 - 298 Ma show oscillatory zones in CL images, reflecting the magmatic events in Late Paleozoic along Xing＇an- Mongolia orogenic belt. Zircons with 377- 474 Ma ages are featured by both magmatic and metamorphic origins, suggesting that the provenances of Linxi Formation in Hexigten Qi probably were from Ordovician-Devonian magmatic and Paleozoic metamorphic rocks. Zircons yielded ages of 1 261 - 1 727 Ma are dominated by magmatic zircons, with some metamorphic zircons; indicating that the Mesoproterozoic magmatic and metamorphic rocks are also the provenances of Linxi Formation. Most of the Zircons aged 1 853 - 2 513 Ma are of magmatie origin, showing the old age information from North China Craton （NCC）. The youngest age from this metasiltstone is 258 Ma, which constrains the deposition age of Linxi Formation to Late Permian. The broad scope of ages reflects the tectono-magmatic events both in NCC and Xing＇ an - Mongolia orogenic belt, and indicates that Linxi Formation has two provenances, and also implies that NCC and Siberia plate had amalgamated before Linxi Formation deposited.

关 键 词：林西组 碎屑锆石 变质粉砂岩 U—Pb年龄 克什克腾旗 锡林浩特地块 

分 类 号：P588.3[天文地球—岩石学] P597.3[天文地球—地质学]