北祁连玉石沟蛇绿混杂岩的组成、时代及成因

发布时间：2018-02-15 15:35

本文关键词： 蛇绿岩蛇绿混杂岩玉石沟构造演化北祁连　出处：《中国地质大学(北京)》2015年硕士论文　论文类型：学位论文

【摘要】：北祁连加里东造山带位于中祁连板块与华北板块西南缘(阿拉善地块)之间,呈北西—南东走向,东与右行走滑的同心一固原断裂相邻,西被左行走滑的阿尔金断裂所截切,北祁连造山带自南向北可以划分为托莱南山北坡的消减洋壳残片、托莱山北坡的俯冲形成的高压变质岩以及增生杂岩、河西走廊南山的岛弧火山岩以及河西走廊弧后盆地等不同的构造单元。根据收集的资料显示,玉石沟蛇绿岩向东可与川刺沟、扎麻什、小八宝蛇绿岩相连,一起构成了大洋扩张脊型蛇绿岩带。通过对玉石沟地区蛇绿混杂岩的野外地质特征、岩石镜下观察、岩石地球化学特征、堆晶辉长岩测年等多方面的详细研究,并结合前人对玉石沟蛇绿混杂岩的研究成果,初步得出以下几点认识:研究区蛇绿混杂岩由堆晶辉长岩、早奥陶世阴沟群基性火山岩、变质橄榄岩、辉长辉绿岩墙及早奥陶世阴沟群深海沉积岩等组成;蛇绿混杂岩北侧逆冲推覆于二叠系窑沟群红泉组(P3h)之上,南侧由北向南逆冲推覆于石炭系羊虎沟组(C2y)与二叠系八音河群大黄沟组(P1—2d)地层之上,西侧与古元古界托赖岩群(Pt1Tb)片岩段成断层接触,向东沿出工作图区外;在蛇绿混杂岩内部不同岩片之间的接触关系为断层接触;获得堆晶辉长岩年龄为513.4±6.4Ma,表明蛇绿岩形成时间大约为早寒武纪到早奥陶世;玉石沟蛇绿混杂岩单元内枕状玄武岩在Zr/Y-Zr和Zr/4-Y-Nb/2的构造判别图解上,均落入洋脊玄武岩区,从N-MORB标准化微量元素配分模式显示出“局部凸起、总体相对平坦”的特征,即在Rb、Ba、Th、Ta、Nb处局部隆起,其他所有元素的丰度相对于N-MORB值不太富集,与典型的洋中脊玄武岩相似(Pearce,1982),总体均表明玉石沟蛇绿混杂岩中的玄武岩是在扩张脊条件下生成的。
[Abstract]:The Caledonian orogenic belt in North Qilian is located between the Middle Qilian plate and the southwestern margin of the North China Plate (Alashan Block), with a NW-SE strike, adjacent to the right-strike-slip concentric Guyuan fault in the east, and cut by the Altun fault of the left strike-slip in the west. The North Qilian orogenic belt can be divided from south to north into subducted oceanic crust fragments on the northern slope of Tolai Mountains, high-pressure metamorphic rocks and accretive complex formed by subduction of the northern slope of Tulaishan. The volcanic rocks of the island arc in the South Mountain of the Hexi Corridor and the back-arc basin of the Hexi Corridor are different tectonic units. According to the collected data, the Yushigou ophiolite can be connected to the Chuan Caigou, Zamashi and Xiaobabao ophiolite to the east. Through the detailed study of the field geological characteristics of ophiolite melange in Yushigou area, the microscopic observation of rocks, the geochemical characteristics of rocks, the dating of heap gabbro, etc. Combined with the previous research results of the Yushigou ophiolite melange, it is concluded that the ophiolite in the study area is composed of heaped gabbro, early Ordovician trench group basic volcanic rocks, metamorphic peridotite. The pyroxene dike is composed of deep-sea sedimentary rocks of the early Ordovician trench group, and the northern side of the ophiolitic melange is thrust over the Hongquan formation of the Permian Yaogou group (P3h). The southern side is thrust from north to south, which is overlaid by the Yanghugou formation of Carboniferous (C2y2) and the P1-2d formation of the Bayinhe Group of Permian. The west side is in contact with the Paleoproterozoic Towlaiyan group (Pt1Tb) schist in fault contact, and out of the working map area along the eastward direction. The contact relationship between different pieces of ophiolitic melange is fault contact, the age of heaped gabbro is 513.4 卤6.4 Ma. it indicates that the ophiolite was formed from early Cambrian to early Ordovician. The occipital basalts in the Yushigou ophiolite melange unit fall into the oceanic ridge basalt area on the structural discriminant diagram of Zr/Y-Zr and Zr/4-Y-Nb/2. From the N-MORB standardized trace element distribution model, the characteristics of "local bulge, overall relatively flat" are shown. In other words, the abundance of all other elements is not enriched relative to N-MORB value at the local uplift of Rb#en0# Ba-Ba-Th Ta-TaNb, and is similar to that of typical mid-oceanic ridge basalts, which shows that the basalts in the Yushigou ophiolite melange were formed under the condition of extensional ridges.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P588

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