【作者】 丁仨平；

【导师】 裴先治；

【作者基本信息】 长安大学 ， 构造地质学， 2008， 博士

【摘要】 本文在区域地质填图及相关科研项目的基础上，重点对西秦岭—祁连造山带（东段）交接部位早古生代的相关蛇绿岩、火山岩及侵入岩开展了详细的岩石学、岩石地球化学及同位素测年研究，在详细了解研究区有关火山岩、侵入岩的岩石地球化学特征的同时，获得了一批测试方法先进、可信度较高的同位素年龄，在此基础上初步建立了以新阳—元龙大型韧性剪切带为界，南北两侧分属不同大地构造单元的两个早古生代“洋—陆”板块构造格局，并探讨了各自的形成演化历史。新阳—元龙大型韧性剪切带以南属西秦岭造山带北缘，发育有以晚寒武世关子镇—武山蛇绿岩组合为代表的洋盆（对应东秦岭商丹洋）的洋壳残片，北侧分别出露有晚寒武世—早奥陶世李子园群岛弧—弧前盆地沉积—火山岩系、奥陶纪草滩沟群岛弧型火山岩及以流水沟、百花中基性岩浆杂岩为代表的岛弧型深成岩浆岩类。在关子镇蛇绿岩的南侧出露有形成于被动陆缘环境的原岩以石英砂岩为代表的早古生代太阳寺岩组浅变质碎屑岩。关子镇—武山蛇绿岩代表的洋盆于早奥陶世发生由南向北的俯冲消减。新阳—元龙大型韧性剪切带以北属祁连造山带东段，发育有以红土堡—葫芦河变基性火山岩为代表的陆内裂陷—小洋盆，北侧依次出露有弧前盆地沉积的晚奥陶世陈家河群碎屑岩组、岛弧环境的晚奥陶世陈家河群火山岩及以阎家店、黄门川为代表的岛弧型花岗岩类。小洋盆于中奥陶世发生向北的俯冲消减，于晚奥陶世—早志留世碰撞造山，其后沉积了以志留纪葫芦河岩群为代表的复理石建造。本文对划分西秦岭与祁连造山带的区域主边界新阳—元龙大型韧性剪切带进行了详细的物质组成、构造变形特征、几何学运动学特征及不同方法的同位素地质年代学研究，通过剪切带剖面测制、宏观及微观构造观察及剪切带中各类糜棱岩面理、线理的统计作图和岩组学分析，获得该剪切带具右行走滑性质的结论。运用LA-ICP-MS法对韧性剪切带内的花岗质糜棱岩进行了锆石U-Pb定年，获得其原岩结晶年龄为914．2～981Ma，显示出均为新元古代早期构造岩浆活动产物，是全球Rodinia超大陆聚合在本区的响应。通过韧性剪切带花岗质糜棱岩中黑云母单矿物的⁴⁰Ar/³⁹Ar同位素测年方法，获得坪年龄（冷却年龄）为347．95～351．70Ma，说明该韧性剪切带在早石炭世发生了一次变质变形事件。可以认为至少在早石炭纪早期该剪切带已横切秦岭与祁连造山带并发生强烈的走滑构造拼贴作用。更多还原

【Abstract】 This dissertation focuses on detailed petrology,petrogeochemistry and isotopicchronology studies on the early Palaeozoic ophiolite,volcanics and intrusive rocks from thejunction (the eastern part) of Qilian Orogenic belt-Western Qinling on the basic of regionalgeological mapping and several related scientific projects.While studying thepetrogeochemistry characters of volcanics and intrusive rocks in the objective areas,weacquire a set of advanced-technique-testing and reliable isotopic ages,on which we establish apreliminary tectonic framework of two early Palaeozoic“Ocean-land”with two sides,thenorth side and the south side,belonging to two different tectonic units and with the large-scaleXinyang-Yuanlong shear zone as boundary.We also discuss the forming and evolution historyfor the two early Palaeozoic“Ocean-land”.In areas to the south of the large-scale Xinyang-Yuanlong shear zone belongs to thenorthern margin of Western Qinling orogenic belt,in which bears the fragments of oceaniccrust(corresponding to eastern Qinling Shangdan Ocean) that represented by late CambrianGuanzizhen-Wushan ophiolite.In the north side of Guanzizhen-Wushan ophiolite,there arelate Cambrian-early Ordovician Liziyuan group volcanic-sedimentary rocks which wereformed in island arc-forearc basin,Ordovician setting a typical represent by Caotangouvolcanics and Liushuigou-Baihua intermediate-basaltic magma complex.In areas to the southof Guanzizhen-Wushan ophiolite,there are early Paleozoic metamorphic detrital rock ofTaiyangsi formation which formed from passive continental margin and represented by quartzsandstone.The Ocean basin,represented by Guanzizhen-Wushan ophiolite,subducted fromsouth to north in early Ordovician.The Xinyang-Yuanlong large-scale shear zone belongs to the eastern part of Qilianorogenic belt,which is mainly known for a intracontinental rifting-small ocean basin coveredby Hongtubao-Huluhe metamorphism basaltic rock.In the north of the shear zone,detritalrock of Chenjiahe group sedimented in forearc basin and island-arc volcanics of Chenjiahegroup in late Ordovician and island-arc granites of Yanjiadian formation and Huangmenchuanformation outcrop in order.This small ocean basin started to dive to the north in middleOrdovician,and collided with orogenic movement in late Ordovician-early Silurian,after then which deposited the Silurian Huluhe group represented by a set of typical flyschconstrction.Through detailed studies on the physical components,structural deformationcharacteristics,Geometry characteristics,kinematics characteristics and different isotopegeochronology research of the large-scale Xinyang-Yuanlong shear zone,the predominateboundary of diving Western Qinling belt and Qilian orogenic belt,we conclude that thejunction is a large-scale dextro-rotational ductile strike-slip shear zone based on the detailedmeasurement of section,macro-micro structural observation and analysis of structural statisticdata.The La-ICP-Ms U-Pb zircon isotopic dating of granitic mylonites from that shear zoneprovides a magma crystallization age of 914.2-981Ma and indicates they are theNeoproterozoic products of tectonic-magmatic thermal events and the responses to theaggregation of Rodinia Super-continent in this area.Through the biotite single mineral40Ar/39Ar isotopic dating,we obtained a plateau age of 351.70Ma,which shows that thisshear zone had a event of deformation with metamorphism in Early Carboniferous.In otherwords,this shear zone had crossed through the orogenic belts and the Qinling-Qilianorogenic belt strike-slip collage was occurred in Early Carboniferous period.更多还原