大兴安岭阿尔山迈罕特乌拉蛇绿混杂岩形成时代及其地质意义  

Geochronology and regional implication of Manhantewula ophiolitic mélange in Arxan,the Great Xing'an Range

作　　者：冯志强[1,2] 刘永江 李伟民 李小玉[6] 蒋立伟 梁琛岳 邵学峰[7] Feng Zhiqiang;Liu Yongjiang;Li Weimin;Li Xiaoyu;Jiang Liwei;Liang Chenyue;Shao Xuefeng(Department of Earth Science and Engineering,Taiyuan University of Technology,Taiyuan 030024;MNR Key Laboratory of Mineral Resources Education in Northeast Asia,Changchun 130026;MOE Key Lab of Submarine Geosciences and Prospecting Techniques,Institute for Advanced Ocean Study,College of Marine Geosciences,Ocean University of China,Qingdao,Shandong 266100;Laboratory for Marine Mineral Resources,Qingdao National Laboratory for Marine Science and Technology,Qingdao,Shandong 266237;College of Earth Sciences,Jilin University,Changchun 130061;Heilongjiang Geological Science Institute,Heilongjiang,Haerbin 150080;Liaoning Institute of Geological Exploration,Dalian,Liaoning 116100)

机构地区：[1]太原理工大学地球科学与工程系,太原030024 [2]自然资源部东北亚矿产资源评价重点实验室,长春130026 [3]中国海洋大学海底科学与探测技术教育部重点实验室,海洋高等研究院,海洋地球科学学院,山东青岛266100 [4]青岛海洋科学与技术国家实验室海洋矿产资源评价与探测技术功能实验室,山东青岛266237 [5]吉林大学地球科学学院,长春130061 [6]黑龙江省地质科学研究所,哈尔滨150080 [7]辽宁省地质勘查院,辽宁大连116100

出　　处：《地质科学》2021年第2期508-532,共25页Chinese Journal of Geology(Scientia Geologica Sinica)

基　　金：国家自然科学基金项目(编号:42072230,41602235);博士后基金项目(编号:2019M661060);山西省创新项目(编号:2019L0126,2019L0054);国家重点研发计划项目(编号:2017YFC0601300‑01);泰山学者计划项目(编号:ts20190918);青岛市创新领军人才计划项目(编号:19‑3‑2‑19‑zhc);国家重点基础研究发展计划“973”项目(编号:2013CB429802)资助。

摘　　要：基性岩年代学及地球化学精细研究有助于判别蛇绿岩套的类型及构造背景,在追溯和重建古洋盆的构造演化过程中发挥着重要作用。本文报道了新近在阿尔山西北部发现的迈罕特乌拉蛇绿混杂岩中基性单元的初步定年工作。对选自3件枕状玄武岩以及1件变质辉长岩进行了LA‑ICP‑MS U‑Pb定年。结果表明,它们的年龄和锆石内部结构复杂多样,包含少量的热液锆石和大量捕获锆石,基性特征锆石次之并被定为玄武岩和变质辉长岩的自生锆石,形成时代为晚二叠世—早三叠世。枕状玄武岩地球化学特征具有LREE富集,类似E‑MORB的稀土配分模式,而相对于E‑MORB又富集大离子亲石元素,轻度亏损Ta、Zr等高场强元素。结合枕状玄武岩及变质辉长岩中锆石普遍来自陆壳成因的特点,我们推测迈罕特乌拉蛇绿混杂岩产自古亚洲洋封闭后,由于岩石圈拆沉导致的伸展环境,可能为时空规模都有限的新生陆内小洋盆代表。The detailed analysis of chronology and geochemistry analysis of mafic rocks into an orogenic system can not only key distinguish the nature and type of ophiolite,but also can provide important insights into the evolution of involved tectonics.Recent found pillow lava basalts and metagabbros in the Maihantewu ophiolitic mélange,the Northwest Arxan,and its preliminary dating has been reported here.73 zircons of three samples from the pillow lava basalts and 64 zircons of one sample from the metagabbro have been dated using LA‑ICP‑MS.The distribution of ages and internal structures of these zircons are complicated,including the basic magmatic zircon,most capturing zircons,and a few metamorphic zircons.One of the basic magmatic zircons have been believed as the autogenetic zircons of mafic rocks,the ages of these zircons range from the end of Permian to the Early Triassic.The chondrite‑normalized REE patterns of the mafic rocks of the pillow lava basalts are of characteristics of LREE enrichment,similar to E‑MORB,while the spider diagram shows the enrichment of the large iron lithosphite elements and weak depletion of high field strength elements.Referring to the most zircons of continental crust in the pillow basalt and metagabbros,we speculate that the Maihantewula ophiolitic mélange were likely formed in the extensional tectonics resulting from the delamination of the lithosphere after the closure of the Paleoasian Ocean,and related to the representing a tectonic setting of limited intra‑continental ocean basin.

关 键 词：大兴安岭 迈罕特乌拉蛇绿混杂岩 古亚洲洋 锆石 LA‑ICP‑MS 

分 类 号：P542[天文地球—构造地质学] P597[天文地球—地质学]