内蒙古巴林左旗九井子蛇绿岩锆石U-Pb定年:对西拉木伦河缝合带形成演化的约束  

Zircon U-Pb dating of the Jiujingzi ophiolite in Bairin Left Banner, Inner Mongolia: Constraints on the formation and evolution of the Xar Moron River suture zone

作　　者：刘建峰[1,2] 李锦轶[1] 孙立新 殷东方[1] 郑培玺[2,4] LIU Jian-feng;LI Jin-yi;SUN Li-xin;YIN Dong-fang;ZHENG Pei-xi(Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;Key laboratory of Mineral Resources Evaluation in Northeast Asia, Ministry of Land and Resources, Changchun 130061, Jilin,China;Tianjin Center of Geological Survey, China Geological Survey, Tianjin 300170, China;College of Earth Science, Jilin University, Changchun 130061, Jilin, China)

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]东北亚矿产资源评价国土资源部重点实验室,吉林长春130061 [3]中国地质调查局天津地质调查中心,天津300170 [4]吉林大学地球科学学院,吉林长春130061

出　　处：《中国地质》2016年第6期1947-1962,共16页Geology in China

基　　金：国家自然科学基金项目(41102029;41472055);中国地质调查局地质调查项目(12120115069301;DD20160201-01)联合资助~~

摘　　要：本文对位于西拉木伦河蛇绿岩带东段的九井子蛇绿岩中辉长岩脉以及蛇绿岩的围岩开展了锆石U-Pb定年。结果表明辉长岩的形成时代为（274.7±1.7）Ma，MSWD=0.079，属于早二叠世晚期；结合前人地层、古生物、岩浆岩等方面的资料，表明内蒙古东南部早二叠世晚期还可能存在大洋盆地。与九井子蛇绿岩呈断层接触的粉砂岩碎屑锆石年龄大致构成4个峰值：2350~2700Ma、1700~2100Ma、370~470Ma和250~290Ma，通过与区域构造热事件的对比分析，表明其物源主要来自中朝古板块的北缘。粉砂岩中最小的锆石年龄为晚二叠世末—早三叠世初（（249±4.7）Ma），该年龄与内蒙古东南部海相地层消失的时代、安加拉植物群和华夏植物群出现混生的时代、西伯利亚和中朝古板块古纬度曲线收敛的时代以及区域上与碰撞相关的岩浆岩形成时代大致相同，据此本文认为九井子蛇绿岩的构造侵位时代应为晚二叠世末—早三叠世初，同时也可能代表古亚洲洋的最终闭合时代。The Jiujingzi ophiolite belongs to the eastern segment of the Xar Monron River ophiolite belt in southeastern InnerMongolia. In this paper, the authors carried out zircon U-Pb dating of a gabbro dike of the Jiujingzi ophiolite and the surrounding siltstone that is in fault contact with the ophiolite. The results indicate that the gabbro dike was formed in late Early Permian (274.7±1.7 Ma, MSWD=0.079). Considering previous geological data on strata, paleontology and magmatic rocks, the authors hold thatthere was still an ocean basin in late Early Permian in southeastern Inner Mongolia. The detrital zircons of the adjacent siltstoneconstitute four age peaks: 2350-2700 Ma, 1700-2100 Ma, 370-470 Ma and 250-290 Ma. A comparison with regional tectonothermalevents shows that the provenance of the siltstone was mainly from the north margin of the Sino-Korean paleoplate. The ageof the youngest zircon is late Early Permian-early Early Triassic (249±4.7 Ma), which is similar to the ages of the disappearance ofthe marine strata in southeastern Inner Mongolia, the mixing between the Cathaysian and Angaran floras, the convergence of thepalaeolatitude curves of the Siberian and Sino-Korean paleoplates and the formation of the collision-related magmatic rocks. It isthus suggested that the tectonic emplacement of the Jiujingzi ophiolite might have occurred in late Early Permian- early EarlyTriassic, which might represent the final closure time of the Paleo-Asian Ocean.

关 键 词：内蒙古东南部 西拉木伦河蛇绿岩 构造演化 古亚洲洋 锆石U-PB定年 

分 类 号：P597.3[天文地球—地球化学] P542[天文地球—地质学] P588