【作者】 王召林；

【导师】 侯增谦； 杨天南；

【作者基本信息】 中国地质科学院 ， 矿物、岩石、矿床， 2009， 博士

【摘要】 青海玉树地区位于我国著名的“三江”铜多金属成矿带的北延部分,具有巨大的成矿潜力。本研究通过对北羌塘陆块内部火山岩和玉树缝合带内花岗岩的锆石LA-ICP-MS U-Pb年代学、地球化学分析,结合构造-岩浆活动和岩相学特征,进行晚古生代—中生代构造单元划分和构造演化研究。在对玉树-囊谦构造带进行新生代构造演化、变形研究的基础上,结合斑岩钼铜矿和铅锌矿的成矿年龄测定,进行三江北段玉树地区新生代构造特征与成矿作用研究。三江北段玉树地区经历了两个关键地质过程的复合叠加,即晚古生代—早中生代俯冲、碰撞造山过程和新生代碰撞转换造山的过程。晚古生代—早中生代主要形成玉树火山杂岩带,在北羌塘陆块基础上形成二叠纪-三叠纪陆缘弧带,火山杂岩带北侧形成巴颜喀拉浊积岩带,新生代碰撞-转换造山阶段形成走滑断裂和大规模逆冲推覆构造。玉树火山杂岩带内岩石经历了强烈挤压和多层次的构造变形,普遍发生绿片岩相的浅变质作用,形成“扇状”推覆体叠盖在两侧构造单元上。带内主要发育褶皱、透镜体、构造面理和小型断裂,反映同碰撞过程中的挤压变形。玉树火山杂岩带广泛分布着已强烈变形的基性岩脉和花岗闪长质侵入体,而代表同碰撞的花岗岩广泛分布于玉树火山杂岩带和巴颜喀拉浊积岩带内,而羌塘地块内部很少发育花岗闪长岩类,这一岩浆岩的时空分布特征可为金沙江洋在玉树地区向南俯冲和构造单元的划分提供很好的佐证。二叠纪俯冲造山在北羌塘陆块形成纳日贡玛-子曲陆缘弧火山岩带,火山岩的锆石LA-ICPMSU-Pb年龄为275.4 Ma、273.3Ma,岩石地球化学特征显示富集大离子亲石元素（LILE）,亏损高场强元素（HFSE）,具有岛弧火山岩的特征,火山岩具有较高的¹⁷⁶Hf/¹⁷⁷Hf和εHf（t）值,指示岩浆源区应具有上涌的亏损软流圈地幔物质加入。三叠纪陆缘活动形成火山岩和岩浆弧花岗岩。东莫扎抓矿区火山岩锆石LA-ICPMS U-Pb年龄为236.6±1.9Ma和238.3±4.0Ma,火山岩地球化学和锆石稀土元素、Hf同位素特征显示具有陆缘弧火山岩的特征。岩浆弧花岗岩侵入于玉树火山杂岩中,两件黑云母花岗岩锆石U-Pb年龄分别为235.2±1.2Ma和228.7±1.2Ma,除个别外,样品普遍富硅和碱质组分,贫P₂O₅和TiO₂等组分,总体属钙碱性系列,三件花岗岩样品主量元素特征具有很好的相关性,显示明显的结晶分异作用,样品微量元素特征和稀土元素分布形式与岩浆弧花岗岩相似,岩石从闪长岩→石英闪长岩→花岗闪长岩→黑云母花岗岩,稀土元素呈现轻稀土越来越富集,重稀土越来越亏损,稀土分馏越来越明显的特点,认为该花岗岩类是金沙江洋俯冲阶段的产物。与二叠纪和三叠纪活动陆缘有关的陆缘弧火山岩带反映金沙江洋壳发生消减、洋-陆构造体制转换和大陆地壳向北增生的过程。但是,晚古生代—早中生代的造山作用在三江北段玉树地区并没有大量发育类似于三江构造带中-南段弧后扩张（裂谷）环境的“双峰式”岩石组合,没有发育大规模碰撞造山阶段的火山岩和后碰撞伸展作用,可能对晚古生代—早中生代的成矿作用不利。新生代碰撞-转换造山作用在三江北段形成两种构造变形样式,即走滑拉张和挤压汇聚,在走滑拉张的背景下形成走滑断裂、走滑拉分盆地和富碱质侵入岩、钾质-超钾质火山岩,挤压汇聚背景下形成大型逆冲推覆构造系统,逆冲推覆构造系统在逆冲方向上由南向北分为根带、中带和前锋带,各带之间分别以主逆冲断裂相隔。对应于两种构造变形样式,研究区形成两套成矿系统,即晚碰撞阶段走滑断裂控制的斑岩成矿系统和逆冲推覆构造控制的热液成矿系统,前者形成纳日贡玛斑岩型钼铜矿床,其成矿年龄为40.86±0.85Ma（Re-Os法）,并呈现出整个三江地区由北向南斑岩侵位年龄和成矿年龄逐渐变新的趋势;逆冲推覆构造控制的热液成矿系统形成东莫扎抓和莫海拉亨铅锌矿床,矿床形成于逆冲推覆构造的前锋带内,矿体多产在叠瓦状逆冲断层的上（下）盘破碎带或反冲断层附近,成矿年龄为35.03±0.89Ma和34.0±1.1Ma（Rb-Sr法）。更多还原

【Abstract】 Qinghai Yushu area,with huge metallogenic potential,is located in the northern segment of the famous Sanjiang copper polymetallic mineralization belt.This thesis’s objective is to research the division of tectonic units and tectonic evolution of late Palaeozoic early Mesozoic through zircon LA-ICP-MS U-Pb chronology and geochemical analyses for volcanic rocks in North Qiangtang block and granites in Yushu suture zone,as well as study on tectono-magmatic activities and petro-graphic features.Based on the study of Cenozoic evolution and deformation in Yushu- Nangqian structural belt,combining metallogenic age determination of molybdenum（copper） porphyry deposits and lead zinc deposits,we explore the relationships betweeen Cenozoic structural characteristics and metallogenesis in Yushu area.Multiple superimposion was experienced because of two key geological processes,which are subduction of oceanic crust and collision orogeny of late Palaeozoic-early Mesozoic.The Yushu volcanic complex was formed during late Palaeozoic-early Mesozoic;the Pero-Triassic epicontinental arc volcanic rock belt was formed on the basis of North Qiangtang Block.To the north of the volcanic rock belt developed the Bayankala turbidite belt;Cenozoic collisional transformation orogen developed the strike-slip fault and large-scale thrust nappe.The volcanic rock belt in Yushu has experienced strong contraction deformation,thus the green schist phase of low-degree metamorphism was widely developed and the fanlike nappe overlapped the tectonic units on both sides.Within the belt,folds,lens,structural foliation and small faults are developed and indicates the syn-collision contraction.Besides,strongly deformed mafic dikes and granodiorite intrusions are also widely distributed in the belt;while the syn-collision granits occur both in the volcanic belt and Bayankala turbidite belt.In contrast,granodiorite rarely occurs in the Qiangtang Block.Such distribution of granodiorite generally supports the southwards subduction of Jinshajiang Ocean and tectonic division.The Permian subduction produced the Narigongma-Ziqu epicontinent arc volcanic belt in the North Qiangtang Block.The LA-ICPMS U-Pb age of the zircon in these volcanic rocks are 275.4 Ma,273.3Ma. Geochemical features demonstrate that these rocks are of arc volcanic by being rich in large ion lithophile elements（LILE）,and poor in high field strength elements（HFSE）.These rocks are also rich in ¹⁷⁶Hf/¹⁷⁷Hf andεHf（t）,which indicate that the source region of magma may have materials from defective upwelling asthenosphere mantle.The epicontinental activities resulted in volcanic and magmatic arc granites.The zircon ages of volcanic rocks in Dongmozhazhua diposits are 236.6±1.9Ma and 238.3±4.0Ma.The epicontinental arc volcanic feature was indicated by the characteriscs of geochemical data,REE elements and Hf isotope of zircon.Magmatic arc volcanic intruded the Yushu volcanic belt and the zircon ages of two biotite granites are 235.2±1.2Ma and 228.7±1.2Ma.Most of the specimens generally belong to the calc-alkaline series, which are rich in Silicon and alkaline components and poor in P₂O₅和TiO₂.The major elements feature of three granite specimens are closely related and suggest obvious crystallization differentiation.The distribution characteristics of trace elements and rare earth elements for granites form are similar with magmatic arc granites.From diorite through quartz diorite,granodiorite to biotite granite,rare earth elements show increasing enrichment in LREE,gradually depleting in HREE,LREE fractionation characteristics become increasingly evident that the granite should be products of the subduction of Jinshajiang ocean. The epicontinental arc volcanics related to the Permo-Triassic activities suggest the subduction of the Jinshajiang oceanic crust,and the ocean-continent tectonic regime transformation and the northward accretion of continental crust.Within the Yushu area,these is neither large quantity of rocks which are similar to the "bimodal" volcanic rocks formed in the back-arc spreading environment such as those in the middle-southern segment of Sanjiang tectonic belt,nor volcanic rocks in the environment of large-scale orogenic collision and post-collision extension,which maybe be unfavorable influence for metallogenesis in late Paleozoic-early Mesozoic.Cenozoic collisional transformation orogen is expressed in two deformation styles,i.e.strike-slip spreading and compressional convergence.The former resulted in strike-slip faults,pull-apart basins and alkaili-rich intrusive rocks,potassic to ultra-potassic volcanic rocks;and the compressional convergence produced the large-scale thrust faults system.This system could be divided from the south to the north into root thrust zone,middle thrust zone and front thrust zone,which are separated by main thrust faults. Corresponding to these two deformation styles,two ore-forming system are developed in the studied area. One is late-collision porphyry ore-forming system（40.86±0.85Ma in age of Re-Os）,which is controlled by strike-slip faults,produced the Narigongma porphyry molybdenum-copper deposits and the ages of porphyry intrusions and mineralization ages become increasingly young from the north to the south in Sanjiang area.The other is hydrothermal ore-forming system which is controlled by thrust faults system and produced Dongmozhazhua and Mohailaheng lead-zinc deposits.These two deposits occurs in the front thrust zone of the thrust faults system at 35.03±0.89 Ma and 34.0±1.1Ma（in age of Rb-Sr） respectively and their orebodies are formed in fracture zones or back thrust areas in the upper or lower plate of the imbricate thrust faults.更多还原