【作者】 郭坤一；

【导师】 张兴州；

【作者基本信息】 吉林大学 ， 构造地质学， 2004， 博士

【摘要】 横亘中国中部的“中央造山带”地处古亚洲构造域和特提斯构造域的重叠部位，具有复杂的构造演化历史，是中国大地构造的枢纽地带，也是研究青藏高原形成、演化和隆升机制的重要地带。西昆仑造山带位于青藏高原西北部，北邻塔里木板块，南以喀喇昆仑断裂与羌塘地块相接，东部阿尔金断裂将西昆仑与东昆仑和阿尔金山分隔，西段沿帕米尔高原延伸进入伊朗、巴基斯坦境内。它是“中央造山带”的重要组成部分，具有复杂的构造演化历史。长期以来受到中外地质学家的普遍关注。但由于地处中亚腹地的高寒缺氧地区，自然条件恶劣，交通极为不便，野外地质调查工作十分艰难。总体来说，该区地质研究程度较低，存在的主要地质问题概括为以下几个方面： 1、基底及盖层的地质组成及结构特征； 2、不同时期花岗岩的类型及构造环境； 3、构造变形及重大构造一热事件的时代； 4、造山带形成及构造演化机制的变迁。 在全面总结前人资料的基础上，本文以大陆造山带理论为指导，通过对西昆仑东段地质组成(重点是前寒武纪地层序列的建立，震旦纪至中新生代地层沉积建造及层序，各地层的主要岩石类型、变质特征等，以及岩浆岩岩石组合及时代)、结构构造特征(包括构造岩浆带的迁移，前寒武系地层的变形层次、变形序列、变形相，构造置换以及区域上大型构造岩片的相互叠置特征等)加以综合研究，以探索西昆仑东段古元古代以来构造演化体制的变迁和构造演化过程。 本次工作取得的主要研究进展包括： 1、系统整理了前人对西昆仑前寒武纪地层的研究成果，结合野外调查及室内的综合研究，对本区前寒武纪地层进行了全面清理，并从前人划分的三叠系中解体出早前寒武纪红柳滩(岩)群(新建非正式地层单元);系统地划分了西昆仑东段的岩石一构造一地层单元，首次在早前寒武纪红柳滩(岩)群和喀拉喀什(岩)群中发现麻粒岩相变质岩;按照不同的岩石组合，结合变质、变形特征、测年资料，将西昆仑前寒武纪划分为三个大的构造一岩石一地层单元，分别为早前寒武纪(Ar一Pt，)变质表壳岩系构造层、中元古代(PtZ)火山一沉积岩系构造层(沟弧体系)、新元古代一震旦纪(Pt厂Z)造山后盖层;依据同位素测年资料，将前人厘定的古元古代埃连卡特(岩)群的时代归并于中元古代蓟县系. 2、通过对西昆仑东段北缘蓟县系埃连卡特(岩)群的研究表明，该岩群下部为典型的逆向演化的双峰式火山岩组合，上部为复理石，顶部有少量的磨拉石.其沉积组合代表了一个沉积盆地的形成、发展和衰亡的历史.双峰式火山岩的地球化学特征显示，其早期的流纹岩为陆壳部分熔融的产物，夹于流纹岩中的薄层碱性玄武岩具有极高的稀土总量和典型的板内玄武岩的微量元素(TE)特征，双峰式火山岩上部的玄武岩具有大洋拉斑玄武岩(TH)的岩石地球化学特征.综合分析该套双峰式火山岩的地层学及岩石地球化学特征表明，它形成于大陆边缘裂解背景，埃连卡特(岩)群属于弧后盆地的产物. 3、首次在西昆仑东段于田一民丰一带鉴定出中元古代蓟县系岛弧火山岩系列(塔西达坂(岩)群).该套火山岩以(玄武)安山岩为主，夹有极少量的流纹英安岩及大理岩条带.出露厚度在2000m以上.(玄武)安山岩具有极低的稀土总t及典型的岛弧火山岩微量元素(TE)特征，流纹英安岩与(玄武)安山岩相比，稀土总量高，但与玄武安山岩具有极相似的稀土配分模式(轻重稀土分异不明显)，表明流纹英安岩与(玄武)安山岩来自相同源区，推测属于俯冲洋壳与地慢相互作用的产物，这为研究本区中新元古代板块构造演化提供了重要地质依据. 4、通过野外调查及测试资料的综合分析，对前人厘定同时也是认识分歧最大的“库地蛇绿岩”提出不同见解，认为“库地蛇绿岩”中的超镁铁岩是阿拉斯加型环状杂岩体，不属于上地慢变质橄榄岩;库地一些克沟玄武岩及上部的所谓的蛇绿质复理石是一套未变质、弱变形的地层，与西昆仑古生界强烈的构造变形和绿片岩相变质作用差异明显。玄武岩具有高的稀土总量，且变化大，微量元素显示富集大离子亲石元素，这些特征说明一些克沟玄武岩是板内裂解的产物，笔者推测其时代不早于二益纪. 5、以可靠的地层资料及同位素年代学资料论证了西昆仑存在格林威尔期造山率件。西昆仑东段新元古代青白口系以显著的角度不整合直接沉积在中元古代蓟县系及古元古宇之上，部分地区缺失青白口系，但可见到南华系冰积岩直接不整合于蓟县系之上(奥依切克)，这表明在中元古代一新元古代初存在一次重要的构造事件.尤其重要的是在埃连卡特(岩)群变质火山岩中首次获得变质矿物角闪石和黑云母理想的Ar一Ar坪年龄分别为1050Ma和1021Ma，表明火山岩峰期变质的事件发生在1050Ma左右，与区域地层研究所得出的结论完全一致.这一构造事件与全球性的格林威尔期造山事件吻合，表明古塔里木板块属于Rod imi。超大陆的成员，这为确定古塔里木板块在 ROd inia超大陆中的位里提供T重要的地质依据。 6、在上述研究工作墓础上，提出了西昆仑造山带经历了四个主要构造演化阶段，它们是:中元古代一新元古代初格林威尔期板更多还原

【Abstract】 Western Kunlun Orogen is located in the Northwest of Qinghai-Tibet Plateau. It adjoins Tarim Plate on the northward, connects the Qiangtang block with Karakorum Fault on the southward. Altyn Tagh comparts Western Kunlun Orogen stretches into Iran and Pakistan along the Pamir Mountain Area. It is the important part of Central Orogenic Belt of China,has complicated tectonic evolution process, and the important belt on which people research the uplifting and evolution of Qinghai-Tibet Plateau. Because of its abominable natural conditions, it is also one of most important belts in China.This paper is mostly researched on the eastern part of Western Kunlun Orogen, some contents of it come down to the whole Western Kunlun area. The major achievements gained by the author based on the two years studies,are indicated as follows:1. The author clears up the Precambrian strata systematically, based on the former researchers’ studies and our own field and indoor researches. The author set up the early-Precarabrian Hongliutan Group (unofficially stratigraphic unit), and for the first time found the granulite and retreated metamorphic granulite faces metamorphic rock in early-Precambrian Hongliutan Group and Karakorum Group. Based on the rock association,metamorphism anddeformation characteristics, and the age-dating data, the author departs Precambrian of Western Kunlun into three tectonic-rock-stratum units as early-Precambrian (Ar-Pti) metamorphic crustal rock series tectonic unit, Mesoproterozoic (Pt2) volcanic-sedimentary rock series tectonic unit (arc-trench system) and Neoproterozoic-Sinian(Pt3-Z) after-orogenic cover strata. According to the isotopic age-dating data, the author mergers the era of the Paleoproterozoic Ailiankate Group into Mesoproterozoic Jixian period.2. The study on the Jixian period Ailiankate Group of the eastern part of Western Kunlun put forwards that the lower part of the Group is typical converse evolution bimodal volcanic rock association, the upside is flysch, on the top there is a spot of molasses. The sedimentary series denotes the formation, development and vanish of the sedimentary basin. The geochemical characteristics of the bimodal volcanic rock indicate that the early rhyolite comes from partial melting of continental crust. The laminar alkaline basalt, interlining the rhyolite, have high S REE and typical trace element characters of intraplate basalt , and the basalt , locates in the upside of the bimodal volcanic rocks ,has the geochemical characteristics of oceanic tholeiite.Based on the stratigraphical and rock geochemical characteristics,the author points out that the bimodal volcanic rock is formed in the continental margin rifting background. Intergrating flysch’s sedimentary characters,the author indicates that Ailiankate Group is formed in the rear arc basin tectonic background.3.For the first time, the author identifies Mesoproterozoic JLxian period arc volcanic rock series (Taxidaban Group) at Yutian-Minfeng district of Western Kunlun. This arc volcanic series mainly consists of (basaltic) andesite,and thimbleful rhyodacite and marble stripe. The thickness of the crop out is more than 2000m. The (basaltic)andesite has ultra-low EREE and typical arc volcanic rock trace element characters. The rhyodacite has high Z REE and the mighty similar REE chondrite-normalized pattern with that of the (basaltic) andesite,which suggests they both come from the same source region,formed with the interaction between the subduction oceanic crust and mantle material ,and provides important geological evidences for the researching work of the evolution of Mesl-Neoproterozoic plates in this area.4. Based on the detailed field and indoor studies on the testing data, the author brings forward different viewpoints on "Kudi ophiolite", the author considers the ultramafic rock in "Kudi ophiolite" is Alaskan-type annular complex,not the metamorphic peridotite of upper mantle. The basalt at Yixiekegou of Kudi and the upper so-called ophiolitiferous f lysch is a suit of nonmetamorph更多还原