中国地质调查局:内蒙古乌兰沟蛇绿混杂岩带(K49E009020和K49009021图幅之内)1∶50000专题地质图数据库

内蒙古乌兰沟蛇绿混杂岩带专题地质图是""内蒙古锡林郭勒盟朱日和等三幅1∶5万地质矿产综合调查""项目的主要成果,由内蒙古自治区地质调查研究院完成,隶属于中国地质调查局天津地质调查中心实施的二连-东乌旗成矿带地质矿产调查二级项目,工作起止年限为2015年～2017年,野外验收和报告验收均为优秀级。图幅位于西伯利亚板块和华北板块之间的索伦-西拉沐伦对接带上。 本次填图以洋板块地质学和造山带填图方法为指导,采用岩性-构造填图法,新识别出晚古生代乌兰沟蛇绿混杂岩,并精细填绘出其物质组成和结构,明确其与索伦蛇绿岩和西拉沐伦蛇绿岩同属于索伦-西拉沐伦对接带,明确了内蒙中部洋盆最终闭合的位置,恢复了晚古生代洋盆转换的过程。 通过详细的野外地质填图,填绘出晚古生代乌兰沟蛇绿混杂岩主要包括蛇绿岩、洋岛海山岩、蓝闪片岩、岛弧岩浆岩等岩石组合。外来岩块包括早古生代哈尔哈达组硅质岩及大石寨组粉砂质板岩和流纹岩等岩石组合。主要受北西-南东向逆冲推覆构造控制,哈尔哈达组石英岩逆冲推覆于早-中二叠世蛇绿混杂岩之上,上盘发育明显的褶皱构造,下盘平行化片理构造发育。其中晚古生代蛇绿岩岩块包括枕状玄武岩、细碧岩、辉长岩、辉绿岩、超基性岩等,基质主要为硅质泥岩、粉砂质板岩、绢云母片岩、石英片岩和绿泥片岩等。获得多组辉长岩、玄武岩锆石U-Pb年龄（LA-MC-ICP-MS法,下同）,主要集中在267.6～294.7Ma,形成于早-中二叠世的洋中脊构造环境。 在蛇绿混杂岩内识别出了洋岛海山岩,主要岩性为玄武岩、细碧岩、结晶灰岩及碧玉岩等岩石组合,获得玄武岩锆石U-Pb年龄为273.9±2.2Ma。 在该套蛇绿混杂岩内首次识别出了晚古生代蓝闪片岩,主要岩性为蓝闪片岩、蓝闪钠长阳起片岩和绿帘绿泥钠长蓝闪片岩等,位于逆冲推覆构造的下盘。绿泥蓝闪片岩获得的锆石U-Pb年龄为274.3±7.2 Ma,蓝闪片岩获得年龄为254.9±2.0 Ma。推测蓝闪片岩形成于早-中二叠世之后推覆构造作用下的热液交代作用。 另外在该套蛇绿混杂岩内还识别出了早古生代蛇绿岩、蓝闪片岩、岛弧岩浆岩及晚古生代岛弧岩浆岩等岩石组合。 通过以上证据较完整的恢复了古亚洲从洋壳的形成-俯冲到洋内弧、陆缘弧的形成、又在晚二叠世-早三叠世期以乌兰沟蛇绿混杂岩向南俯冲到华北克拉通基底之上的方式完成闭合,最终完成了陆壳泛大陆化的演化历程。该项目取得的成果,为今后开展区域构造演化及解决关键地质问题提供重要线索和直接证据。The thematic geological map of the Wulangou ophiolite mélange zone in Inner Mongolia is the main achievement of the project "Three 1:50000 scale comprehensive geological and mineral surveys including Zhurihe in Xilingol League, Inner Mongolia", completed by the Inner Mongolia Geological Survey Institute. It is subordinate to the second-level project of geological and mineral survey in the Erlian-Dong Ujimqin metallogenic belt implemented by the Tianjin Geological Survey Center of China Geological Survey. The work period was from 2015 to 2017, and both field acceptance inspection and report review were rated as excellent. The map sheet is located in the Solonker-Xar Moron suture zone between the Siberian Plate and the North China Plate. This mapping was guided by oceanic plate geology and orogenic belt mapping methodologies, adopting the lithological-tectonic mapping approach. The Late Paleozoic Wulangou ophiolite mélange was newly identified, and its material composition and structure were finely mapped. It was clarified that this mélange belongs to the Solonker-Xar Moron suture zone together with the Solonker ophiolite and the Xar Moron ophiolite, the final closure position of the central Inner Mongolia ocean basin was determined, and the process of Late Paleozoic ocean basin transformation was restored. Through detailed field geological mapping, it was mapped that the Late Paleozoic Wulangou ophiolite mélange mainly includes rock associations such as ophiolite, oceanic island seamount rocks, glaucophane schist, and island arc magmatic rocks. The allochthonous blocks include rock associations such as Early Paleozoic Haerhada Formation siliceous rocks, Dashizhai Formation silty slate and rhyolite. The mélange is mainly controlled by NW-SE trending thrust nappe structures: the quartzite of the Haerhada Formation thrusts over the Early-Middle Permian ophiolite mélange, with obvious fold structures developed in the hanging wall and parallel schistosity structures developed in the footwall. The Late Paleozoic ophiolite blocks mainly include pillow basalt, spilite, gabbro, diabase, ultrabasic rocks, etc., and the matrix is mainly siliceous mudstone, silty slate, sericite schist, quartz schist, chlorite schist, etc. Multiple groups of zircon U-Pb ages (LA-MC-ICP-MS method, the same below) of gabbro and basalt were obtained, mainly concentrated in 267.6~294.7 Ma, formed in the mid-ocean ridge tectonic setting of the Early-Middle Permian. Oceanic island seamount rocks were identified in the ophiolite mélange, with main lithologies including basalt, spilite, crystalline limestone and jasper, and the zircon U-Pb age of basalt was obtained as 273.9±2.2 Ma. Late Paleozoic glaucophane schist was identified for the first time in this set of ophiolite mélange, with main lithologies including glaucophane schist, glaucophane albite actinolite schist and epidote chlorite albite glaucophane schist, etc., located in the footwall of the thrust nappe structure. The zircon U-Pb age of chlorite glaucophane schist was obtained as 274.3±7.2 Ma, and that of glaucophane schist was 254.9±2.0 Ma. It is speculated that the glaucophane schist was formed by hydrothermal metasomatism under thrust tectonic action after the Early-Middle Permian. In addition, rock associations such as Early Paleozoic ophiolite, glaucophane schist, island arc magmatic rocks and Late Paleozoic island arc magmatic rocks were also identified in this set of ophiolite mélange. Based on the above evidence, the evolution of the Paleo-Asian Ocean was relatively completely restored: from the formation and subduction of oceanic crust, to the formation of intra-oceanic arcs and continental margin arcs, and then the final closure was completed during the Late Permian-Early Triassic when the Wulangou ophiolite mélange subducted southward beneath the North China Craton basement, ultimately completing the evolutionary process of continental crust towards pan-continentalization. The achievements of this project provide important clues and direct evidence for future regional tectonic evolution studies and solving key geological issues.