【作者】 李龚健；

【导师】 邓军；

【作者基本信息】 中国地质大学（北京） ， 矿物学、岩石学、矿床学， 2014， 博士

【摘要】 三江地区地处特提斯构造域东段以及青藏高原东南侧，先后经历了特提斯增生造山以及印度-欧亚陆陆碰撞造山两大阶段。多个微地块于此齐聚一堂，展现出中腰拢合、两侧散开的独特构造格局。本文在前人工作基础上，系统解析了典型古特提斯后碰撞型岩浆岩的成因及其大地构造意义；复原了早古生代微地块分布古地理格局并重新界定了哀牢山缝合带位置；建立了特色大型矿床成矿模式并探讨了其构造驱动机制；研究了三江增生造山/碰撞造山演化过程；初步构建了三江特提斯成矿系统时空格架。对哀牢山缝合带北部镇沅地区花岗岩体进行了全岩微量元素、锆石U-Pb年代学和Hf同位素地球化学研究。结果表明晚二叠世（248-255Ma）石英斑岩和花岗斑岩形成于哀牢山古特提缝合带后碰撞伸展转换背景下。综合哀牢山缝合带俯冲型和碰撞型岩浆的年龄数据，得出其闭合时限为晚二叠世（~260Ma）。通过地层对比分析，以及晚二叠世岩浆岩继承锆石和地层碎屑锆石U-Pb年代学、Hf同位素地球化学研究与年龄谱线对比工作。结果表明镇沅地区含蛇绿岩套残片的晚古生代地层属于思茅地块的一部分。本文由此在镇沅地区东边界沿着蛇绿岩套的分布新拟定了哀牢山缝合线的位置，认为其夹持于西边的雅轩桥火山弧与东边的金平峨眉山玄武岩之间，并沿着古生代地层的西界向南与马江缝合带衔接。对三江各微地块地层碎屑锆石进行了系统的U-Pb年代学分析，通过全面的年龄谱线比照工作，提出：早古生代时期，华南地块、印支地块（思茅地块）、西羌塘地块和东羌塘地块靠近于印度陆块北部边缘；拉萨地块和滇缅泰马地块（腾冲-保山地块）靠近澳大利亚西北部边缘。对老厂VMS型Pb-Zn-Ag-Cu矿床和镇沅造山型Au矿床进行了系统的地质与地球化学研究。老厂Pb-Zn-Ag-Cu矿床围岩沉积记录、矿体结构、矿石组构和矿物组合反映块状硫化物集聚于海底局部的还原环境中。结合流体包裹体以及S-Pb和H-O-C同位素数据认为矿床形成与岩浆释气作用相关。老厂矿床成生于古特提斯大洋晚密西西比阶（~320Ma）洋岛火山环境。火山岩与矿体的Pb-Zn等贱金属的富集与深俯冲地壳物质回返过程相关，其机制可能为早石炭世末期古特提斯大洋板块的初始俯冲作用或者晚寒武世-志留纪原特提斯洋的俯冲作用。镇沅Au矿床S-Pb同位素结果结合前人报导的含金流体He-Ar-C-H-O同位素数据，表明成矿流体主要系下地壳变质流体。矿石矿物组合、元素富集特征、富CO2流体包裹体和S-Pb同位素特征均与造山型金矿床相吻合。结合大地构造背景认为，华南岩石圈在渐新世（~30Ma）发生西向俯冲作用，挤压导致区域载金变质流体被驱逐并汇聚，最终发生金属卸载并形成了造山型金矿床。系统开展了地层、蛇绿岩套、弧岩浆岩和碰撞型岩浆岩等多方面综合研究，全面阐释了增生造山期原、古、中、新特提斯旋回的时空演化历程。古特提斯洋俯冲伊始时间（早二叠世）与中特提斯洋开启时间相同，而古特提斯洋闭合时间（早三叠世），与中特提斯俯冲伊始以及新特提斯洋的开启时间也能很好吻合，反映板块扩张为大洋俯冲消减的驱动机制。基于碰撞造山期构造变形、岩浆活动、盆地充填和成矿作用综合研究，首次提出青藏高原陆陆侧向碰撞带四期构造变形史，即挤压褶皱期（>45Ma）、拆沉伸展期（44～32Ma）、挤压走滑期（31～13Ma）和伸展旋钮期（12～0Ma）。基于增生造山/碰撞造山构造演化过程，建立了增生造山原、古、中、新特提斯成矿系统和碰撞造山挤压褶皱、拆沉伸展、挤压走滑与伸展旋钮期成矿系统的时空构架与演化。构造体制转换对三江区域成矿作用的类型与时空分布具有显著的控制作用。叠加成矿在三江地区表现突出，可划分为火山成因块状硫化物－岩浆热液叠加、沉积－热液叠加以及多期热液叠加三种类型。更多还原

【Abstract】 The Sanjiang region in SE Tibet Plateau and NW Yunnan is known to haveformed by amalgamation of Gandwana-derived continental blocks and arc terranes asa result of oceanic subduction in the Paleozoic. During Cenozoic, intense intraplatedeformation, episodic magmatism and diverse mineralization occurred overprintingthe Pre-Cenozoic tectonic framework of the region.The paper report zircon U-Pb dating, Hf isotopic compostion and bulk chemistryof the granite porphyry and quartz porphyry from the Zhenyuan area in the northAilaoshan suture zone. The results show that these granitic rocks having206Pb/238Uweighted mean age of255-248Ma have intruded under the post-collisional extensivesetting after the closure of Ailaoshan Paleo-Tethys ocean. It was summarized that thetransition from subduction-related to collision-related magmatisms along theAilaoshan suture was at~260Ma. The exact location of the Ailaoshan suture betweenthese Simao and Yangtze continental blocks has been contested. The age distributionpattern of detrital and inherited-xenocrystic zircons from the Zhenyuan-Mojiangsuspect terrane is similar to that of detrital zircons from the Simao block but differentfrom that of those from the Jianshui area in the western margin of the Yangtze block.This indicates that the Zhenyuan-Mojiang suspect terrane belongs to the Simao block.The actual location of the suture between the Simao and Yangtze blocks is suggestedto superimpose the Ailaoshan late-Devonian to early-Carboniferous ophiolite beltwithin the suspect terrane.The age distribution pattern of detrital zircons from the continental blocks in theSanjiang region suggested that the South China, Simao (north of the Indochina),Western Qiangtang and Eastern Qiangtang blocks located along the Indian Gondwanamargin at Early Paleozoic, whereas the Lhasa and Tengchong-Baoshan (north of theSibumasu) located along the Australian margin.The Laochang ore deposit was a Pb-Zn-Ag-Cu volcanic-sediments hostedmassive sulfide (VHMS) deposit formed in the Late Mississippian (~320Ma) oceanic island. The deposit geology, sedimentary facies and fossil records evidenced that themassive sulfides accumulated on the sea floor and the ore-forming fluids formedtheir own local anoxic environment in the oxic bottom water conditions. The localanoxic conditions together with fluid inclusions and S-Pb and H-O-C isotopic dataare more supportive to the magmatic degassing model. The hosted volcanic rocks(OIB) are sourced from an enriched mantle, which was mingled with subductedupper continental crust component. This process possibly occurred during theshrinking of the Proto-Tethys ocean in Late Cambrian-Silurian or the possible initialsubduction of Paleo-Tethys oceanic plate in latest of Early Carboniferous. Byconsideration of the Zhenyuan Au deposit, the S and Pb isotopic compositionsobtained in this paper, together with the analysis on the previously publishedH-O-He-Ar isotopic data of the auriferous fluid, support that the ore fluid is mainlymetamorphic fluid with subordinate mantle fluid. The mineralization age wasindicated by the previous Ar-Ar isochrone age~27Ma of phlogopite in themineralized lamprophyre, which implies the South China block subducted westwardat Oligocene. The continental subduction induced the release gold-chargedmetamorphic fluid and facilitated the shearing of the Ailaoshan fault.In the Sanjiang region, the Paleo-Tethys comprised a main ocean and threebranches, Ailaoshan, Jinshajiang and Garzê–Litang. They were bounded byGondwana-derived continental blocks and were consumed by oceanic subductionfrom Earliest Permian to late Triassic. Hereafter, the evolution of the Baoshan andTengchong blocks was largely influenced by eastward oceanic subduction of theMeso-and Neo-Tethys from late-Permian to middle-Cretaceous and fromlate-Cretaceous to~50Ma, respectively. From Late Paleozoic, various continentalblocks separated and northwards migrated from Gondwana occurred in three periodslinked with the successive opening and closure of three intercalated Tethyan oceans,the Palaeo-Tethys (Devonian to Triassic), Meso-Tethys (Earliest Permian to LateCretaceous) and Ceno-Tethys (Late Triassic to Paleogene). The oceanic subductionwas coupled with the birth of a new ocean. This implies that oceanic subduction wasthe main driving force of geodynamics in the Sanjiang Tethys region. The four main phases for the Cenozoic evolution of the Sanjiang region arefirstly proposed:(1) Subduction of Neo-Tethys oceanic plate caused lithosphereshortening, and emplacement of magmatic intrusions in Tengchong block andCu-dominated ore deposits within Lanping basins resulting from the India-Eurasiasoft collision (>45Ma);(2) Intra-plate mafic rocks in the Thengchong block inducedby the breakoff of Neotethys oceanic plate and potassic magmatic rocks along theJinshajiang-Ailaoshan suture by the delamination (45-32Ma);(3) South china platedetachment-underthrusting and Simao-Indochina block extrusion due to thesustained compression from the India-Eurasian continental collision (31-13Ma);(4)Extensions and volcanic eruption induced by the oceanic slab subduction of Indianoceanic plates (12Ma-present).Many important ore deposits in the Sanjiang region are linked to the evolution ofthe Tethys oceans in Paleozoic–Mesozoic and the Indian-Asian continental collisionin Cenozoic. In this paper, the metallogenic system comprising the ore depositdistributings on time and space in the Sanjiang region is constructed based on theregional tectonic evolution. The transformation of tectonic regime plays a decisiverole in the formation of important deposits in the Sanjiang region. The multipleepisodes of metallogenesis located in the different time and tectonic backgroundoccurred in one orefield or ore deposit, causing various types of superposed deposits.These deposits can be categorized into three types, that is:(Type1) superposition ofmagmatic hydrothermal deposit on the previous VMS deposit;(Type2)superposition of magmatic hydrothermal deposit on the previous sedimentary deposit;(Type3) superposition of between multiple episodes of magmatic hydrothermaldeposit.更多还原