内蒙古达茂旗北部包尔汉图群时代及中早-中三叠世变质锆石年龄的启示  

Inspiration from the age of Baoerhantu Group and metamorphic zircon age of middle early middle Triassic in the northern Damao Banner,Inner Mongolia

作　　者：赵利刚 王文龙[1] 高学生[1] 王树庆[1] 许雅雯[1] 胡晓佳[1] ZHAO Ligang;WANG Wenlong;GAO Xuesheng;WANG Shuqing;XU Yawen;HU Xiaojia(Tianjin Center,China Geological Survey(North China Center of Geoscience Innovation),Tianjin 300170,China)

机构地区：[1]中国地质调查局天津地质调查中心(华北科技创新中心),天津300170

出　　处：《华北地质》2024年第2期1-15,37,共16页North China Geology

基　　金：中国地质调查项目“华北地区数据更新及地质编图(DD20230223)”;“温都尔庙-镶黄旗地区区域地质调查(DD20190038)”。

摘　　要：【研究目的】包尔汉图群主要分布于达茂旗北部地区,是研究古亚洲洋早古生代构造演化的关键部位。【研究方法】本文对达茂旗一带包尔汉图中基性火山岩进行岩石学、地球化学、同位素地球化学和年代学研究,以探讨其形成时代和成岩。【研究结果】本次工作在包尔汉图群片麻状斜长角闪岩LA-ICP-MS法锆石U-Pb成岩年龄为495±2.0 Ma,同时在角闪绿帘岩和斜长角闪岩中获得了变质锆石年龄分别为242.3±1.1 Ma和249±3 Ma。【结论】片麻状斜长角闪岩地球化学特征表现为富集Rb、Th等大离子亲石元素,亏损Nb、Ta、P、Ti等高场强元素,表明包尔汉图群在寒武纪(Є3)已有火山喷发,其形成与古亚洲洋由北向南的俯冲作用有关。角闪绿帘岩和斜长角闪岩具MORB型地球化学特征,其中的捕获锆石既有华北板块古老的再循环陆壳物质,又有古生代的新生基性下地壳物质,可以限制古亚洲洋闭合时代应早于249 Ma。This paper is the result of rock geochemistry.[Objective]The Baoerhantu Group is mainly distributed in the northern region of Damao Banner and is a key area for studying the early Paleozoic tectonic evolution of the ancient Asian Ocean.[Methods]This article conducts petrological,geochemical,isotopic geochemical and chronological studies on the basic volcanic rocks in the Baoerhan map of Damaoqi area,in order to explore their formation age and diagenesis.[Results]The LA-ICP-MS zircon U-Pb diagenetic age of the gneiss like plagioclase amphibolite in the Baoerhantu group was 495±2.0 Ma,while metamorphic zircon ages of 242.3±1.1 Ma and 249±3 Ma were obtained in the amphibolite greenstone and plagioclase amphibolite,respectively.[Conclusions]The geochemical characteristics of the gneiss like plagioclase amphibolite are characterized by enrichment of large ion lithophilic elements such as Rb and Th,and depletion of high field strength elements such as Nb,Ta,P,and Ti,indicating that the Baoerhantu Group had volcanic eruptions during the Cambrian(ε3),and its formation is related to the subduction of the ancient Asian Ocean from north to south.The hornblende epidote and plagioclase hornblende exhibit MORB type geochemical characteristics,and the captured zircons contain both the ancient recycled continental crust material of the North China Plate and the newly formed basic lower crust material of the Paleozoic era,which can limit the closure of the ancient Asian Ocean to be earlier than 249 Ma.

关 键 词：兴蒙造山带 包尔汉图群 锆石U-PB年龄 地球化学特征 

分 类 号：P588.1[天文地球—岩石学] P597[天文地球—地质学]