蒙古国扎门乌德地区古生代沉积过程、岩浆作用及其对兴蒙造山带构造演化的意义  

Paleozoic sedimentary processes and magmatism in Zamenwude area,Mongolia,and their implications for tectonic evolution of the Xingmeng orogenic belt

作　　者：周建磊 徐备 李文博 周佳安 胡邦超 ZHOU JianLei;XU Bei;LI WenBo;ZHOU JiaAn;HU BangChao(Hebei Key Laboratory of Strategic Critical Mineral Resources,Hebei GEO University,Shijiazhuang 050031,China;Hebei Province Collaborative Innovation Center for Strategic Critical Mineral Research,Shijiazhuang 050031,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China)

机构地区：[1]河北省战略性关键矿产资源重点实验室,石家庄050031 [2]河北省战略性关键矿产研究协同创新中心,石家庄050031 [3]北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2023年第5期1353-1369,共17页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(42172248、42042029)资助.

摘　　要：兴蒙造山带属于中亚造山带的东段,关于其演化过程存在两种主要观点:一种观点认为它是由古亚洲洋经历整个古生代的连续俯冲-碰撞过程后在早三叠世形成;另一种观点则认为古亚洲洋在晚泥盆世之前就通过俯冲-碰撞过程闭合,形成早-中古生代造山带,随后在石炭-二叠纪又经历了从陆内伸展到再次闭合的过程,并形成陆内造山带。蒙古国东南部扎门乌德地区出露各类古生代沉积岩和岩浆岩,可以为解决上述争议提供典型研究实例。本文通过沉积学、年代学和地球化学等多种手段综合研究,取得以下研究成果:(1)根据年代学和岩性特征,在该地区识别出三类古生代岩石组合,第一类是以黑云母二长花岗岩为代表的中志留世侵入岩,第二类是中泥盆世大套的粗碎屑岩-火山岩沉积旋回,第三类是不整合地沉积于早期造山带之上的二叠纪巨厚火山-沉积岩系。这三类岩石组合分别属于俯冲阶段的大陆边缘岛弧带岩浆岩、碰撞造山后期的上叠盆地以及叠加在早期造山带岩石圈之上的晚古生代陆内伸展时期的裂谷盆地的沉积。(2)利用研究区所有古生代碎屑锆石和岩浆岩全岩资料,揭示了该地区古生代时期地壳厚度变化趋势如下:500~425Ma的俯冲-碰撞过程造成地壳加厚;425~375Ma的碰撞造山后伸展过程使地壳变薄;375~350Ma地壳再次加厚,可能与造山带物质堆叠有关;350~275Ma地壳再次减薄,对应于广泛而强烈的晚石炭世-早二叠世火山岩,证明此时期岩浆活动的构造背景是区域伸展而不是挤压作用。(3)根据研究区出现的三类岩石组合特点,结合研究区以南的艾力格庙地区已有的研究成果,可以划分出五个早-中古生代造山带构造单元和两个叠加其上的晚古生代陆内造山带构造单元,揭示蒙古国扎门乌德地区经历了早-中古生代加积造山带和晚古生代陆内造山带等两个构造演化过程�The Xingmeng orogenic belt is the eastern part of the Central Asian Orogenic Belt,and there are two main views on its tectonic evolution:one is that it was formed in the Early Triassic after the continuous subduction-collision process of the Paleo-Asian Ocean during the whole Paleozoic;the other is that it was an intracontinental orogenic belt evolved from an early Middle Paleozoic orogenic belt formed by a subduction-collision process during the closure of Paleo-Asian Ocean before the Late Devonian,which experienced an intracontinental extension and closure in the Carboniferous-Permian Period.The occurrence of various Paleozoic sedimentary and magmatic rocks in the Zamenude area in the southeastern Mongolia can provide a typical case for resolving the above disputes.In this paper,sedimentary and magmatic rocks exposed in Zhamenwude area are studied through comprehensive methods such as sedimentology,geochronology and geochemistry,and the following results are obtained:(1)According to the geochronology and lithology characteristics of the main rock assemblages in the study area,they can be divided into three types:the first type is the Middle Silurian intrusive rocks represented by biotite monzogranite;the second type is a set of coarse clastic-volcanic sedimentary cycles in the lower part of the Middle Devonian stratigraphic sequence;the third one is the Permian thick volcanic-sedimentary series unconformably deposited on the early orogenic belt.Tectonically,the three-rock assemblages are formed in a continental marginal arc during the subduction stage,a superimposed basin during the collisional stage,and a rift basin during the Late Paleozoic intracontinental extension superimposed on the previous orogenic lithosphere,respectively.(2)The Paleozoic crustal thickness trends estimated from detrital and magmatic zircons in the study area reveal that the subduction-collision processes can be divided into four stages:a thickened crust during 500~425Ma;a thinned crust caused by the post-collision extension process dur

关 键 词：兴蒙造山带 陆内造山带 构造演化 扎门乌德 蒙古国东南部 

分 类 号：P588.12[天文地球—岩石学] P588.2[天文地球—地质学] P597.3