【作者】 张亚峰；

【导师】 裴先治；

【作者基本信息】 长安大学 ， 构造地质学， 2010， 硕士

【摘要】 东昆仑造山带岩浆活动频繁,本文选取东昆仑都兰可可沙地区早古生代侵入岩体为研究对象,通过详细的野外路线调查、重点剖面测制和室内镜下薄片分析,对其野外分布、规模和产状及岩石组合特征、岩相学特征进行了详细研究。同时,初步限定了该套岩体的地球化学属性及形成时代,并分析了岩体成因及形成构造环境,为查明东昆仑造山带东段早古生代复杂的构造演化历史提供了依据。主要取得了以下初步认识：1、东昆仑都兰可可沙地区早古生代侵入岩体主要由辉长岩类、闪长岩类和花岗岩类组成,主体为闪长岩类,普遍经历弱的变形、变质。岩体大部分与古元古代白沙河岩组及中元古代小庙岩组呈侵入接触关系,局部与三叠纪洪水川组呈断层或不整合接触关系。2、岩体中各类岩石基本属于中钾钙碱性岩石,其中辉长岩类低碱,高TiO2、CaO、MgO;花岗岩类高碱,低TiO2、CaO、MgO,属弱过铝质岩石；闪长岩类属偏铝质岩石,主量元素含量大多介于辉长岩类和花岗岩类之间。三类岩石共同特性表现为轻稀土元素富集,重稀土元素相对亏损且轻重稀土元素分馏明显；富集Rb、Ba、Th等大离子亲石元素,相对亏损Zr、Hf、Ta等高场强元素,显著亏损Nb、Y、Ti、P等元素。以上特征表明岩体成因与俯冲作用有关,可能是底侵的幔源岩浆熔融与下地壳物质混合的结果,并且岩浆演化后期发生过明显的结晶分异作用。3、岩体中石英闪长岩LA-ICP-MS锆石U-Pb同位素年龄为(515.2±4.4)Ma(MSWD=2.5),限定了该岩体的主体岩浆结晶时代为中寒武世,确证了东昆仑地区存在早古生代的构造-岩浆事件。4、综合以上研究,结合区域地质背景,推断东昆仑都兰可可沙地区早古生代侵入岩体形成于与洋壳俯冲有关的早期陆缘弧或洋盆俯冲初始阶段的构造环境,该事件可能是原特提斯洋扩张演化在东昆仑地区的响应。更多还原

【Abstract】 Magmatism in the East Kunlun orogenic belt occurred frequently. The Kekesha intrusive rocks of Early Paleozoic in East Kunlun area of Dulan county area is selected as the research object of the study. After detailed wild-field geological survey, key section measuring and indoor study of microscope image, the wild-field distribution, scale, occurrence and assemblage and petrology of the rocks are ascertained, meanwhile, the geological geochemistry characteristics and crystallizing age of the rocks, as well as its forming mechanism and tectonic settings are confined in preliminary, which provides strong evindences for ascertaining the complex tectonic evolutional history of the East Kunlun area in Early Paleozoic. Main cognitions are acquired as follows:1. The Kekesha intrusive rocks of Early Paleozoic in the East Kunlun area are constituted of gabbros, diorites and granitoids rocks, mainly of diorites rocks, both of which generally experienced low-grade deformation and metamorphism. The majority of the rocks intrude in Baishahe Group and Xiaomiao Group which belong to Paleoproterozoic and Mesoproterozoic respectively, and the local rocks emplace in Hongshuichuan Group of Triassic in the contact of fault and unconformity.2. The rocks belong to middle Potassium calc-alkaline series in general, of which the gabbros show the characteristics of low total alkali, high TiO2, CaO and MgO in content and the granites of high total alkali, low TiO2, CaO, MgO in content, classified to weakly peraluminous series, while, the diorites show the feature of metaluminous, and the content of major elements of which is mostly between the content of gabbros and granites. The common characteristics of the three types of rocks are enrichment of LREE and LILE like Rb, Ba and Th, loss of HREE and HFSE like Zr, Hf and Ta relatively, especially Nb, Y, Ti and P. All of these indicate that the rocks may form in relation to subduction of continental margin and is a result of mixing of intrusive mantle magma and the material of lower-crust and occurred distinct fractional crystallization in later evolution of the magma.3. LA-ICP-MS zircon U-Pb isotopic age of quartz diorite is (515.2±4.4) Ma (MSWD =2.5), which confines the crystallizing age of the majority rocks to Middle Cambrian epoch and corroborates the tectono-magmatism event of the East Kunlun region during the early Caledonian.4. Combined with the above study fruites and regional geological setting, it is concluded that the rocks of Paleozoic in Kekesha area of the east Kunlun orogenic belt formed in the setting of initial continental margin arc-zone or the primary subduction stage of oceanic basin, and the event may be a material response to expansion of proto-Tethys ocean in the East Kunlun area.更多还原