【作者】 李松彬；

【导师】 陈柏林；

【作者基本信息】 中国地质科学院 ， 构造地质学， 2013， 硕士

【摘要】 研究区喀腊大湾在区域上位于北阿尔金蛇绿混杂岩带的中东段,位于北东向阿尔金走滑断裂与东西向阿尔金北缘断裂夹持的地区,北接塔里木地块,南邻柴达木地块,东临祁连造山带,占据非常重要的大地构造位置。近年来在研究区发现了一批形成于早古生代的大中型铁和铜、金、铅锌多金属矿床,表现出良好的成矿前景。因此选择阿尔金山北缘喀腊大湾地区作为研究区,开展以研究早古生代构造演化为主题的硕士论文工作,对查清该地区早古生代成矿大地构造背景,建立研究区成矿控矿构造体系以及进一步的找矿勘查工作具有重要意义,也对认识阿尔金北缘地区早古生代的区域构造演化具有重要意义。本论文在前人工作的基础上,通过详细的野外地质路线观察,对研究区早古生代火山-沉积岩地层、中酸性火山岩岩石地球化学特征以及构造变形特征进行了分析工作,并辅以锆石SHRIMP U-Pb定年,主要取得的成果及认识如下：1、早古生代的地层剖面显示：喀腊大湾北部地区以中基性火山-岩浆活动为主,中部以喷发-溢流相中酸性火山岩浆活动为主,中南部以深色偏还原环境的细碎屑沉积岩组合为主,南侧以酸性火山岩为主,火山岩的锆石SHRIMP U-Pb年龄显示这套地层形成于(482.3+5.1)Ma-(517+7)Ma,属于中晚寒武世-早奥陶世。2、岩石地球化学研究表明：研究区内的中酸性火山岩以亚碱系列钙碱性火山岩为主,含有少量碱性系列岩石,主要为安山岩-英安岩-流纹英安岩-流纹岩-粗面英安岩组合。总体表现出由低钾向高钾,由钠质向钾质,由钙碱性向碱性演化的趋势,具有活动大陆边缘环境火山岩的特征。自北向南,具有从I型花岗质岩浆向S型花岗质岩浆演化的特征,反映了形成于自北向南的活动大陆边缘俯冲消减带环境。3、初步分析了大平沟地区的褶皱构造,认为其具有全形连续褶皱的特征,是南北向持续挤压作用的结果,结合褶皱期后侵入褶皱核部花岗闪长质侵入体的时代,确定大平沟褶皱作用发生的上限年龄介于467.5+5.4-477.1+4.7Ma,为早中奥陶世；显微组构研究表明喀腊大湾地区韧-脆性变形以压扁占优势的简单剪切变形为主,具有左行逆冲的特征,主压应力近南北向,结合卷入变形带的花岗岩体和成矿作用时代,初步确定其具有487Ma的上限活动年龄,属于早奥陶世。因此认为喀腊大湾地区早古生代的褶皱构造与韧脆性变形构造是研究区早古生代洋盆俯冲-同碰撞阶段的产物。4、初步分析了研究区北侧不整合覆盖在枕状玄武岩岩片上的复成分砾岩-砂砾岩-砂岩-泥岩沉积地层的地质意义,通过对侵入该沉积砾岩的闪长岩体锆石SHRIMP U-Pb定年,间接获得该套砾岩沉积的上限年龄为458+5.4Ma,认为其标志着喀腊大湾地区早古生代洋盆闭合和陆-陆碰撞作用的下限年龄。5、在前人工作的基础上,综合研究区内火山-沉积地层、中酸性火山岩岩石地球化学特征和构造变形特征,结合获得的地质年代数据,建立了喀腊大湾早古生代的构造演化模型。认为研究区早古生代处于活动大陆边缘环境,古洋盆自北向南俯冲消减,经历了早中寒武世(520-500Ma)的早期俯冲增生、晚寒武-早中奥陶世(500-460Ma)俯冲-同碰撞和晚奥陶-志留世(460-410Ma)碰撞-后碰撞三个演化阶段。更多还原

【Abstract】 Kaladawan area is in the central of the ophiolitic melange of the northern Altyn Tagh. It is clamped by the NE Alytn Tagh strick-slip fault and EW Alytn northern margin fault, North tarim basin, south Qaidam basin and the qilian orogenic belt in the east, occupies the very important tectonic position.A number of medium-large-sized Fe,Au-Cu and Pb-Zn polymetallic deposits fonned in early Paleozoic were found in the study area in recent years, showing a good metallogenic prospects. So this paper choose the Kaladawan area as its target, to carry out the research theme about the early Paleozoic tectonic evolution for the master’s thesis work, which is of great significance on the identification of Paleozoic mineralization tectonic background, the establishment of the mineralization ore-controlling structure system and further prospecting work, but also for recognizing the early Paleozoic tectonic evolution of the northern Altyn.This paper carries out detailed geological observation, mainly select the Early Paleozoic volcanic-sedimentary strata, the intermediate-felsic rock geochemistry and tectonic deformation as the analytical work, supplemented by zircon SHRIMP U-Pb dating, and leads to the main achievements are as follows:1. Early Paleozoic stratigraphic section shows:the rock assemblages in the northern Kaladawan is dominated by intermediate-mafic rocks, eruption-overflow phase intermediate-felsic volcanics in the central and dark combination of fine-grained clastic sedimentary rocks which indicates a reducing environment of deepwater in the south. Zircon SHRIMP U-Pb ages of the intermediate-felsic rocks show these strata formed at (482.3±5.1)Ma～(517±7)Ma, belonging to the era of late Cambrian-early Ordovician.2. Geochemical studies show that:the intermediate-felsic rocks geochemically attributed calc-alkaline series, contains small amounts of alkaline rocks, mainly andesite-dacite-rhyodacite-rhyolite-trachy dacite assemblages,with an evolutionary trend from low potassium to high potassium, sodium to potassium and calc-alkaline to alkaline overall, similar to the volcanic rocks formed at an active continental margin. From north to south, the rock suites have a transition character that from I-type to S-type granitics magma evolution, reflects the fonned in the subduction zone at active continental margin.3. Preliminary analysis of the folds in Dapinggou area indicate that:It is the result of a continuous compression from north to south with characteristics of shaped continuous folds. Zircon SHRIMP U-Pb ages of granodiorites intrusived the core of the fold, determine the ages of(467.5±5.4)Ma-(477.1±4.7)Ma as its lower limite age, belonging to early-mid Ordovician; microfabric study shows the ductile-brittle defonnation flattening dominant simple shear defonnation based, with left-thrust characteristics, principal stress near the north-south, combined with the granites and mineralization age involved in the defonnation belts, preliminary determination of its activities with the upper limit of487Ma age, belonging to early Ordovician. Therefore we consider the folds and ductile-brittle deformation structures are the products of oceanic basin closure-syncollision stage in early Paleozoic.4. Polymictic Conglomerate strata which unconformably overlying the pillow basalt chip, Zircon SHRIMP U-Pb dating of the diorite which invasived the conglomerate indirect limit the upper set age of it as(458±5.4)Ma, belonging to the late Ordovician, implying that the ocean basin in Northern Alytn closed and the continent-continent collision begin.5.In previous work, based on the comprehensive study on volcanic-sedimentary strata, the intermediate-felsic rock geochemistry and tectonic deformation characteristics, combined with the geological data obtained, established the tectonic evolution model in early Paleozoic. Kaladawan area was located at an active continental margin in early Paleozoic, the oceanic crust subducted from north to south.The tectonic evolution history can be divided into three stage as the follows:early subduction-accretion (520～500Ma), subduction-sycollision (500～460Ma) and collision orogeny-post collisional (460～410Ma).更多还原