内蒙古东北部晚二叠世-早三叠世构造演化的新证据:尖子山早三叠世磨拉石的识别  

New Evidence for Tectonic Evolution of Late Permian to Early Triassic in Northeast Inner Mongolia:Recognition of Early Triassic Molasse Formation in Jianzishan

作　　者：姜振宁[1] JIANG Zhenning(Geological Institute of China Chemical Geology and Mine Bureau,Beijing 100101)

机构地区：[1]中化地质矿山总局地质研究院,北京100101

出　　处：《地质与勘探》2023年第2期337-352,共16页Geology and Exploration

基　　金：中国地质调查局大兴安岭成矿带矿产调查项目《内蒙古1∶5万兴安敖包(L51E016004);查干保好(L51E016005);塔拉布拉克(L51E017004);杜尔基(L51E017005)幅区域地质调查》(编号:DD20160048-14)资助。

摘　　要：磨拉石是造山带的重要组成部分,利用磨拉石来限定碰撞作用时限是造山带研究的一项重要内容。以内蒙古东北部科右中旗尖子山出露的一套杂色砾岩夹紫红色-灰紫色砂砾岩地层为研究对象,通过对其岩石组合、沉积构造、沉积时代的研究,认为其是一套产于陆内造山背景下前陆盆地的近源磨拉石,地层底部的近源崩塌堆积成因的花岗岩巨砾锆石LA-ICP-MS U-Pb年龄为250±2.9 Ma。结合区域上老龙头组碎屑锆石年龄及三叠纪同碰撞-后碰撞-陆内伸展阶段花岗岩时代的研究,认为该套磨拉石沉积于早三叠世,属下三叠统老龙头组。研究区早三叠世磨拉石的识别,明确了早三叠世存在陆内造山作用,为内蒙古东北部晚二叠世-早三叠世构造演化提供了新证据。Molasse is an important part of orogenic belt,and is an important content of orogenic belt research to limit the time limit of collision.This work selected a set of mixed colored conglomerate with purplish-purple conglomerate strata outcropped in Jianzishan,Keerqingyouyi Middle Banner,northeast Inner Mongolia as the research object.Based on the study of its rock assemblage,sedimentary structure and sedimentary age,it is believed that it is a set of near-source molasse produced in foreland basin under the background of intracontinental orogeny.The LA-ICP-MS U-Pb zircon age of granitic boullies at the bottom of the stratum is 250±2.9 Ma.Combined with the detrital zircon ages of the Laotou Formation in the region and the granite ages of the Triassic syncollision-post-collision-intracontinental extension stages,it is suggested that the molasse was deposited in the Early Triassic,which belongs to the Lower Triassic Laotou Formation.The identification of Early Triassic molasse in the study area confirms the existence of intracontinental orogenesis in the Early Triassic and provides new evidence for the Late Permian-Early Triassic tectonic evolution in northeastern Inner Mongolia.

关 键 词：磨拉石 陆内造山 前陆盆地 兴蒙造山带 老龙头组 尖子山 内蒙古 

分 类 号：P542.2[天文地球—构造地质学]