阿拉善地块北部雅干断裂带周缘晚古生代花岗岩体特征

发布时间：2018-10-15 08:56

【摘要】：阿拉善地块北部地处内蒙古西缘,中亚造山带南缘中段,是华北板块、塔里木板块和哈萨克斯坦板块等多构造单元的结合部,是研究古亚洲洋闭合过程的重点区域,雅干断裂带是阿拉善地块最北部的一条重要构造分界线。本文从岩相学、岩石地球化学、年代学和火山-沉积建造特征等方面,对雅干断裂带周缘花岗岩的形成年代、源岩类型、成因机制及构造演化开展了研究。位于雅干断裂北侧的楚伦昂高茨岩体具有较高的镁指数和壳幔混合来源特征而区别与雅干断裂带南侧的干江嘎顺岩体和查干陶勒盖东岩体。楚伦昂高茨岩体中的晚三叠世(226.7±1.8Ma和220.5±1.9Ma)二长花岗岩属高钾弱偏铝质钙碱性系列,源岩类型为I型,形成于后碰撞伸展环境;干江嘎顺岩体中的早二叠世(288.5±1.9Ma)闪长岩及二叠纪晚期二长花岗岩属高钾准铝质钙碱性—碱性系列,源岩类型为I型但兼具造山期后A型花岗岩特点,形成于同碰撞向后碰撞转化环境;查干陶勒盖东岩体中的早二叠世(284.2±1.7Ma和269.3±2.4Ma)花岗岩属高硅钾弱过铝质钙碱性系列,源岩类型为I型花岗岩,形成于同碰撞向后碰撞转化环境。明水—小黄山—雅干断裂带(蛇绿岩带)所代表的大洋的构造演化可归纳为以下几个阶段:中奥陶世前,雅干断裂带北侧的洋盆向南俯冲,形成呼和套尔盖构造带中奥陶统火山岩,南侧的珠斯楞—杭乌拉构造带处于后碰撞拉张环境,或可形成早古生代的火山—沉积建造;晚志留世—中泥盆世,明水—小黄山—雅干洋盆向南俯冲;晚泥盆世—早石炭世,洋盆转为北向俯冲形成北山明水—额旗呼和套尔盖—蒙古Harshatewula近东西走向的早石炭世火山弧;本文同碰撞—后碰撞环境形成的早二叠世—晚三叠世花岗岩,说明古亚洲南支在二叠纪早期(288.5±1.9Ma)已经发生碰撞,结束了大洋的演化历程。
[Abstract]:Located in the northern part of the Alashan block in the western margin of Inner Mongolia and the central part of the southern margin of the Central Asian orogenic belt, the Alashan block is the junction of the North China plate, the Tarim plate and the Kazakhstan plate, and is the key area for studying the closure process of the Paleo-Asian Ocean. The Yakan fault zone is an important tectonic boundary in the northernmost part of the Alashan block. In this paper, from the aspects of petrography, petrogeochemistry, geochronology and volcanic-sedimentary formation characteristics, the age of formation, source rock type, genetic mechanism and tectonic evolution of granites in the Yanan fault zone are studied. The Chulunangarz rock body located in the northern side of the Yakan fault has high magnesium index and mixed crust and mantle characteristics and is distinguished from the Ganyanggaoshun rock body and Chagan Tolegaidong rock body in the southern side of the Yagan fault zone. The late Triassic (226.7 卤1.8Ma and 220.5 卤1.9Ma) monzonitic granites in the Chulungangaoc pluton belong to the high-potassium weakly metamorphic calc-alkaline series, and the source rocks are of type I and formed in the post-collision extensional environment. The early Permian (288.5 卤1.9Ma) diorite and the late Permian granites belong to the high-potassium quasi-aluminous calc-alkaline series in the Gangjiang Gashun pluton. The source rocks are of type I but have the characteristics of post-orogenic A-type granites. The early Permian (284.2 卤1.7Ma and 269.3 卤2.4Ma) granites in the Chagan Tulergaidong pluton belong to the calc-alkaline series of high silicon potassium and weak peraluminite, and the source rocks are I-type granites, which were formed in the same collision backward collision transformation environment. The tectonic evolution of the ocean represented by the Mingshuixiaohuangshan-Yagan fault zone (ophiolite belt) can be summarized as follows: before the middle Ordovician, the ocean basin on the north side of the Yakan fault zone subducted south. The volcanic rocks of the Middle Ordovician are formed in the Huhe Tuergai tectonic belt, and the Zhusileng-Hangula tectonic belt on the south side is in a post-collision extensional environment, or it may form an early Paleozoic volcanic-sedimentary formation, and the late Silurian to the Middle Devonian, The late Devonian to early Carboniferous, the oceanic basin subducted to the north to form an early Carboniferous volcanic arc near the east-west direction of Beishan Mingshui-Yakanghu and Thuergai Mongolia Harshatewula. The early Permian-late Triassic granites formed in the same collision-post-collision environment indicate that the southern branch of Paleo-Asia has collided in the early Permian (288.5 卤1.9Ma), ending the evolution of the ocean.
【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】：P588.121

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