包头—二连地区显生宙花岗岩年代学格架、Hf同位素特征及地质意义

发布时间：2018-04-13 00:00

本文选题：包头-二连 + 花岗岩　；参考：《中国地质大学(北京)》2015年硕士论文

【摘要】：包头-二连地区在大地构造上横跨了兴蒙造山带的西段和华北克拉通的北缘。通过对华北北缘小井沟花岗岩和兴蒙造山带额仁淖尔地区花岗岩开展年代学、地球化学和同位素研究,探讨其岩石成因和形成的构造背景,以期为确定古亚洲洋的最终闭合时限提供一些约束;结合最新的研究成果,建立起研究区显生宙花岗岩的年代学格架,在此基础上,总结分析研究区显生宙花岗岩Hf同位素特征,以加深对包头-二连地区深部新老地壳时空分布架构的认识。华北北缘小井沟岩体侵位于二叠纪,侵位年龄为275±1Ma。属于弱过铝质的高钾钙碱性系列,具有类似于I型花岗岩的特征,Hf同位素特征表明华北陆块古元古代的地壳岩石应该是其主要物源,可能有幔源物质的参与。兴蒙造山带额仁淖尔地区卫境岩体形成时代为279±1Ma,查干德勒岩体侵位时代为276±4Ma,均为二叠纪岩体。两者均属弱过铝质的高钾钙碱性系列,暗色矿物中出现角闪石,显示出类似于I型花岗岩的岩石学和地球化学特征,Hf同位素特征表明卫境岩体具有年轻的源区特征,查干德勒岩体应是由古老地壳岩石发生部分熔融形成。高精度的年代学数据统计结果表明,研究区岩浆活动大致可分为5个期次,具体包括奥陶纪-泥盆纪(485~359Ma),石炭纪(359~299Ma),二叠纪(299~252Ma),三叠纪(252~201Ma),侏罗纪-白垩纪(201~114Ma),其中二叠纪岩浆活动最为强烈。花岗岩Hf同位素特征表明,研究区可以索伦-西拉木伦断裂为界划分为差异明显的南北两个带,南带花岗岩类具有负εHf值及老的模式年龄,北带花岗岩总体上表现出正εHf值及年轻模式年龄的特征,局部出现具有负εHf值及老的模式年龄花岗岩,显示可能有古老微陆块存在的信息。从南蒙古到华北克拉通北缘地区,二叠纪不是一个统一的构造体制,具有同时异相的特征。二叠纪南带应该处于由俯冲向碰撞-后碰撞转变的构造背景,而北带应该处于后造山的构造背景,古亚洲洋可能在晚二叠世以前就已闭合。
[Abstract]:The Baotou-Erlian area spans the western part of the Xingmeng orogenic belt and the northern margin of the North China Craton.Based on the geochronology, geochemistry and isotopic studies of the Xiaojinggou granites in the northern margin of North China and the granites in the Eren Nur area of the Xingmeng orogenic belt, the petrogenesis and tectonic setting of the granites are discussed.With a view to providing some constraints for determining the final closure time of the Paleo-Asian Ocean and combining the latest research results, the chronological framework of the Phanerozoic granites in the study area was established, on the basis of which,The HF isotopic characteristics of the Phanerozoic granites in the study area are summarized and analyzed in order to deepen the understanding of the space-time distribution framework of the deep new and old crust in Baotou-Erlian area.The Xiaojinggou intrusion in the northern margin of North China is located in the Permian with an emplacement age of 275 卤1 Ma.It belongs to the weak peraluminous calc-alkaline series, which is similar to the I-type granite. The HF isotopic characteristics indicate that the ancient crustal rocks of the North China block Gu Yuan should be the main source of its material, and may involve the mantle material.The formation age of Weijing rock body and the emplacement age of Chagandler rock body are 279 卤1Maand 276 卤4Marespectively, all of which are Permian rocks.Both belong to a weak peraluminous calc-alkaline series with hornblende in dark minerals, showing petrological and geochemical characteristics similar to I-type granites. The HF isotopic characteristics indicate that the Weijing rock body has a young source area.Chagandler rock body should be formed by partial melting of ancient crustal rocks.The statistical results of high-precision geochronological data show that magmatic activity in the study area can be roughly divided into five periods.These include Ordovician Devonian (485U 359MaA), Carboniferous (359U 299Mag), Permian (299U 252MaA), Triassic (252Cretaceous) 201114MaU, Jurassic-Cretaceous (201114MaN), among which Permian magmatic activity is the strongest.The HF isotopic characteristics of granites indicate that the study area can be divided into two distinct north and south zones, and the southern belt has negative 蔚 HF value and old model age.The granites in the northern belt generally show positive 蔚 HF values and young model ages, and there are negative 蔚 HF values and old model age granites, indicating that there may be information of the existence of ancient microcontinental blocks.From southern Mongolia to the northern margin of North China Craton, Permian is not a unified tectonic system and has the characteristics of simultaneous heterogeneity.The southern belt of Permian should be in the tectonic setting of the transition from subduction to collision-post-collision, while the northern belt should be in the tectonic setting of post-orogeny, and the paleo-Asian ocean may have been closed before the late Permian.
【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】：P588.121;P597

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