蒙古东北部克鲁伦缝合带大地构造组成与演化

Located in the northern portion of the eastern Central Asian Orogenic Belt (CAOB), the NE Mongolia (NEM) and the northern Great Xing'an Range (NGXR) as a whole is a key area for understanding the early-stage evolutin of the Paleo-Asian Ocean. However, due to intensive forest covering in the NGXR and considerably poor geological investigations in the NEM, understanding of temporal-spatial tectonic relationships of between the NEM and NGXR has long been hampered. The Kherlen suture zone in the NEM, likely containing ophiolites of Cambrian and Neoproterozoic periods, provides us a unique object for studying and synthesizing the Neoproterozoic-Early Paleozoic tectonic evolution of the eastern CAOB. This project is designed to carry out comprehensive studies of field geology, structural geology, petrology, geochemistry and isotope geochronology for the Kherlen suture zone, with aims to distinguish types, formation ages and forming environments of the tectonic units that constitute the suture zone, to establish the temporal and spatial evolutionary framework and to determine the tectonic attribute of the suture, and then to restore the Neoproterozoic-Early Paleozoic orgenic regimes of the region and attest the tectonic relationship of the suture with the Yilehuli ophiolitic belt in the NGXR, which will place robust constraints on the early-stage tectonic evolutionary history of the eastern CAOB.

蒙古东北部和我国北兴安岭处于中亚造山带东段北部，是认识古亚洲洋东段早期演化的关键地区。北兴安岭地区森林覆盖严重而蒙古东部地质研究程度很低，长期制约对该区域大地构造时空关系的认识。蒙古东北部克鲁伦缝合带可能含有寒武纪与新元古代两个时代的蛇绿岩，是解析中亚造山带东段新元古代-早古生代造山演化难得的研究对象。本项目拟通过野外地质、构造地质、岩石学、地球化学和同位素年代学等系统研究，查明克鲁伦缝合带主要构造单元类型、形成时代与形成构造环境，厘定其形成演化时空框架与大地构造性质，恢复该区域新元古代-早古生代造山体制，确证其与我国北兴安岭伊勒呼里蛇绿岩带的大地构造关系，为全面认识和深入理解中亚造山带东段早期构造演化提供有力约束。

蒙古东北部与我国大兴安岭北部毗邻，均属中亚造山东部北部，是古亚洲洋早期发育的地区，同时又受到蒙古-鄂霍茨克洋构造体制的叠加改造。由于这一地区，特别是我国北兴安岭地区森林植被发育，加之中新生代火山岩及沉积物的覆盖，古生代岩石露头十分稀少，故在这一地区研究恢复古亚洲洋早期演化难度较大，也使得人们对该地区构造演化细节不清，古生代的区域构造框架不明。因此本项目以我们前期厘定的克鲁伦缝合带为主要研究对象，通过对克鲁伦缝合带的组成及结构、主要组成构造单元的性质、时代和形成环境、缝合带演化年代学格架和演化历史等的研究，提出克鲁伦缝合带代表一条早古生代的弧-陆缝合带，即其北侧艾伦达瓦古陆块与南侧伊德莫格岛弧地体的缝合线，并在此基础上将克鲁伦缝合带及北侧古陆块的演化历史划分为新元古代被动陆缘发育阶段（<1.0 Ga--550 Ma）、寒武-奥陶纪活动陆缘发育阶段（550--450 Ma）、志留纪克鲁伦洋盆闭合阶段（440--430 Ma），亦即弧-陆碰撞拼合阶段、泥盆纪碰撞造山后伸展阶段（420--400 Ma）：石炭世至中生代蒙古-鄂霍茨克构造体制叠加改造阶段（370--140 Ma）。这些认识成果对解决该地区存在的区域地质问题具有重要学术价值，对认识蒙古-鄂霍茨克造山带的构造演化也具有重要启示意义，同时也对认识区域成矿规律及找矿方向具有重要参考价值。