兴蒙造山带构造演化的新模式:来自内蒙古中部四期不同类型变质作用的证据  

New model for the tectonic evolution of Xing'an-Inner Mongolia Orogenic Belt:Evidence from four different phases of metamorphism in Central Inner Mongolia

作　　者：张晋瑞 魏春景[2] 初航[3] ZHANG JinRui;WEI ChunJing;CHU Hang(College of Earth Sciences,Jilin University,Changchun 130061,China;School of Earth and Space Sciences,Peking University,Beijing 100871,China;Tianjin Institute of Geology and Mineral Resources,Tianjin 300170,China)

机构地区：[1]吉林大学地球科学学院,长春130061 [2]北京大学地球与空间科学学院,北京100871 [3]天津地质矿产研究所,天津300170

出　　处：《岩石学报》2018年第10期2857-2872,共16页Acta Petrologica Sinica

基　　金：国家自然科学青年基金项目(41702049);科技部"973"项目(2013CB429801);博士后面上基金项目(2016M600854)联合资助

摘　　要：有关中亚造山带东段即兴蒙造山带早古生代以来的构造演化一直倍受关注,其中争议最大的问题是古亚洲洋最终闭合的时间究竟是在泥盆纪还是早中生代?晚古生代的大地构造背景究竟是持续的大洋俯冲还是经历了造山后的伸展裂解过程?以往对内蒙中部地区的研究多数局限于区域内广泛分布的蛇绿岩和各类型岩浆岩的年代学和地球化学,但是通过地球化学的方法来确定一个地区的构造环境往往具有多解性。为建立研究区的构造框架并查明兴蒙造山带构造演化过程,本文详细总结了内蒙古中部地区变质作用的最新研究进展,对兴蒙造山带的演化提出了新的认识。确定了该区域在古生代以来的变质作用可分为四期:第一期为志留纪的高压低温型(430～410Ma),以南、北带的温都尔庙群蛇绿混杂带为代表,发育典型的低温高压型蓝片岩相岩石,记录了洋壳的双向俯冲过程;第二期为早-中泥盆世的中压型(～400Ma),以宝音图群为代表,发育典型的巴罗型变质带,经历以升温升压为特征的前进变质、峰期变质、峰后近等温降压以及随后降温降压的顺时针型P-T演化,指示与地壳加厚有关的碰撞造山过程;第三期为石炭纪的低压高温型(345～309Ma),以锡林郭勒杂岩低压变质岩为代表,发育广泛的混合岩化和基性岩脉的侵入,经历早期升温伴随微弱减压,直至温度峰期后近等压冷却的顺时针P-T演化,指示造山后的陆内伸展过程;第四期为早三叠世(～240Ma)的中-低压低温型,以早三叠世区域低级变质岩系为代表,经历中-低压相系的顺时针P-T演化,指示与有限海盆闭合有关的陆内造山过程。结合已有的研究,内蒙古中部地区晚古生代的火山岩和侵入岩更可能形成于伸展的构造环境,超基性岩和沉积岩系的时空配置与典型大洋的蛇绿混杂岩明显不同,更可能形成于有限海盆的环境。因此,从四�The tect0nic evolution of Xing＇an-Inner Mongolia Orogenic Belt in the southeastern segment of the Central Asian Orogenic Belt has been highly argued： whether the Paleo-Asian Ocean was closed in Devonian or Early Mesozoic and whether the tectonic regimes during Carboniferous and Permian were operated by continuous subduction-arc systems or extension after the orogenic process. Previous studies mostly focus on the geochronology and geochemistry of ultramafic,plutonic and volcanic rocks,however,tectonic discriminations through geochemical data analysis in the previous researches were usually multiple in solutions thus resulted in the above dispute. Comprehensive studies of metamorphism for four metamorphic units in Central Inner Mongolia including the Ondor Sum Group,Baoyintu Group,Xilingol Complex,and Early Triassic metamorphic sequences provide better constraints on the argument points of the XIMOB. Combined with the previous researches,four phases of metamorphism are identified in central Inner Mongolia since the Paleozoic,including（ ⅰ） the Silurian（ 430 - 410 Ma） high P/T metamorphism in the southern and northern Ondor Sum Group,with presence of typical blueschist-facies metamorphic rocks,indicating bidirectional subduction processes;（ ⅱ） the EarlyMiddle Devonian（ - 400 Ma） medium P/T metamorphism in the Baoyintu Group,characterized by a clockwise P-T path including prograde metamorphic stage with increasing temperature and pressure,peak metamorphic stage,isothermal decompression and later cooling and decompression metamorphic stages,suggesting a crustal thickening orogeny process;（ ⅲ） the Carboniferous（ 345 -309 Ma） high temperature-low pressure metamorphism of the Xilingol Complex,characterized by a clockwise P-T path involving prepeak heating with slight decompression,peak and post-peak cooling stages,indicating an extension process of a previous orogen; and（ ⅳ） the Early Triassic（ - 240 Ma） extensive medium-low P/T metamorphism along the Solonker suture zone,charac

关 键 词：变质作用 复合造山模式 索伦缝合带 兴蒙造山带 

分 类 号：P542[天文地球—构造地质学] P588.3[天文地球—地质学]