兴蒙造山带中东部蛇绿混杂岩带对比研究

发布时间：2018-05-15 09:15

本文选题：蛇绿岩 + 蛇绿混杂岩带　；参考：《中国地质大学(北京)》2017年硕士论文

【摘要】：研究区位于内蒙古自治区中部,大地构造位置上位于华北板块与西伯利亚板块之间的兴蒙造山带中东部地区。研究区内存在三条蛇绿混杂岩带,由北向南分别是贺根山蛇绿混杂岩带、迪彦庙—达青牧场蛇绿混杂岩带、西拉木伦蛇绿混杂岩带。本文通过野外地质调查,重点区域地质样品采集及室内分析,并结合前人对兴蒙造山带内蛇绿岩的研究成果,运用区域大地构造学、沉积学、岩石学、岩石地球化学、年代学等方法进行研究,发现兴蒙造山带中东部在晚古生代时期具有多期次的构造活动特征。贺根山蛇绿混杂岩带中存在两种构造环境中形成的玄武岩,一种为变质玄武岩,稀土和微量元素具有IAT和N-MORB特征,为贺根山蛇绿岩的组成成分,其形成年龄为403Ma-354Ma,该时期并没有岛弧岩浆记录,因此推测其形成于洋中脊环境,受到早期古亚洲洋俯冲板片的影响而具有岛弧的性质。另一种玄武岩的稀土元素特征为轻稀土富集的右倾型,该特征类似于陆壳型(C-crust型)玄武岩。因此表明其形成大陆裂谷环境。其形成年龄约为300Ma-292Ma。迪彦庙—达青牧场蛇绿混杂岩带中,迪彦庙蛇绿岩具有IAT和N-MORB型的特征,并且发现有玻安岩的存在,推测其形成于岛弧环境,根据本文采集的迪彦庙堆晶辉长岩所测得的年龄为345.6±2.3Ma,结合前人的研究成果,推测迪彦庙蛇绿岩的形成时代为早石炭世早期—早石炭世晚期(356Ma-320Ma)。达青牧场蛇绿岩中具有两种类型的玄武岩:一种为枕状玄武岩,其岩石地球化学特征类似于N-MORB。另一种为片理化玄武岩,其玄武岩中REE总量极低,微量元素特征类似于陆壳型(C-crust型)玄武岩,推测其形成于大陆裂谷环境。西拉木伦蛇绿混杂岩带中,小苇塘蛇绿岩的蚀变玄武岩具有N-MORB型玄武岩的特征,上覆岩系中含有放射虫硅质岩,推测小苇塘蛇绿岩形成于洋中脊环境。硅质岩中发现有中二叠世的放射虫化石及伴生的牙形石,因此推测该区蛇绿岩形成时代应该在早—中二叠世。兴蒙造山带中东部三条蛇绿混杂岩带中蛇绿岩的年龄由北向南具有依次变年轻的特征,可能代表了兴蒙造山带中东部由北向南,大洋依次开合的过程。
[Abstract]:The study area is located in the central part of Inner Mongolia Autonomous region, and the tectonic position is located in the central and eastern part of the Xingmeng orogenic belt between the North China Plate and the Siberian Plate. There are three ophiolite melange belts in the study area, from north to south, they are Hegen Mountain ophiolite melange, Diyanmiao Dachingshan ophiolite melange and Xilamurun ophiolite melange. Based on the field geological survey, the collection and laboratory analysis of geological samples in key regions, and the previous research results on ophiolite in the Xingmeng orogenic belt, this paper applies regional geotectonics, sedimentology, petrogeochemistry, etc. By means of chronology and other methods, it is found that the central and eastern part of the Xingmeng orogenic belt is characterized by multiple tectonic activities in the late Paleozoic. There are two kinds of basalts formed in the Hegenshan ophiolite melange belt, one is metamorphic basalt, rare earth and trace elements have IAT and N-MORB characteristics, and they are the composition of Hegenshan ophiolite. The age of its formation is 403Ma-354Ma.There is no island arc magma recorded in this period, so it is assumed that it formed in the middle ridge environment of Yu Yang and was influenced by the early paleo-Asian ocean subduction plate and has the character of island arc. Another type of basalt is characterized by LREE enriched right-dip type, which is similar to the continental crust type (C-crust type) basalt. Therefore, it shows that it formed a continental rift environment. The age of formation is about 300Ma-292Ma. In the Dianmiao-Dachingshan ophiolite melange belt, the ophiolite has the characteristics of IAT and N-MORB type, and the existence of Boyanite is found, which is supposed to be formed in the island arc environment. According to the age of 345.6 卤2.3 Ma. obtained from the Diyan Miao crystal gabbro collected in this paper, combined with the previous research results, it is inferred that the age of formation of the ophiolite is 356Ma-320Maan in the early Carboniferous to the late early Carboniferous. There are two types of basalts in the ophiolite of Dachingchang: one is pillow basalt, and its geochemical characteristics are similar to those of N-MORB. The other is schistatic basalt, in which the total amount of REE is very low, and the trace element characteristic is similar to that of continental crust type (C-crust) basalt, which is supposed to be formed in the continental rift environment. In the Xilamurun ophiolite melange, the altered basalts of the ophiolite in Xiaolitang have the characteristics of N-MORB type basalts, and the overlying rocks contain radiolarian siliceous rocks. It is inferred that the ophiolite formed the Yu Yang middle ridge environment. There were radiolarian fossils and conodonts associated with the Middle Permian in siliceous rocks, so it is assumed that the ophiolite was formed in the early and Middle Permian. The ages of ophiolite in the three ophiolite melange belts in the central and eastern part of the Xingmeng orogenic belt are younger from north to south, which may represent the process of opening and closing from north to south in the central and eastern part of the Xingmeng orogenic belt.
【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】：2017
【分类号】：P587

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