兴蒙造山带新发现的构造混杂岩时空关系及其大地构造意义

There are several ophiolitic mélange zones developed in the Xingmeng Orogenic Belt, which has the fundamental implication for the closure of the Paleo-Asian Ocean, and the evolution and formation process of the orogen. Despite this importance, no consensus has been reached on the issues of the plate tectonic framework and evolution of these ophiolitic mélange zones, and the tectonic attribute during the Late Carboniferous-Early Permian, as a result that there is still debate on the plate tectonic pattern of Xingmeng Orogenic Belt in the Late Paleozoic. In recent years, we have newly found the E-W extending Weijing, Bulitai, Zhunmubutai, and Dashizhai tectonic mélanges, which are characterized by similar distribution as the Late Carboniferous-Early Permian marine sedimentary - volcanic strata and Suzuoqi-Xiwuqi magmatic belt. We will focus on the material composition, field occurrence, precise chronology, tectonic significance of these tectonic mélange and the relationships between the Late Carboniferous-Early Permian strata. Moreover, we will further discuss the spatial-temporal relationships between Wenduermiao-Tulinkai, Daqingmuchang-Diyanmiao, Erlian-Hegenshan, and Solonker-Xar Moron ophiolitic mélanges. These works will provide better constraints on the plate tectonic evolution of the Xingmeng Orogenic Belt and its tectonic attribute during the Late Carboniferous-Early Permian, then will further help to give new research supports for the closure process of the Paleo-Asian Ocean and the mechanism of continental crust accretion.

兴蒙造山带发育多条蛇绿混杂岩带，为研究古亚洲洋闭合及造山带形成与演化提供了珍贵的地质资料，由于各蛇绿混杂岩带的板块构造意义以及晚石炭-早二叠世的大地构造属性至今仍未达成共识，导致兴蒙造山带晚古生代的板块构造格局存在争议。申请人近年来新发现了近东西向展布的卫境、补力太、准木布台和大石寨4处构造混杂岩，它们与晚石炭世-早二叠世海相沉积-火山地层及苏左旗-西乌旗岩浆岩带具近一致的空间展布特征。本立项拟研究4处构造混杂岩的物质组成、野外产状、精准的年代学、大地构造意义及其与上石炭统-二叠系的关系，探讨其与温都尔庙-图林凯、达青牧场-迪彦庙、二连-贺根山、索伦山-西拉木伦河蛇绿混杂岩的时空关系，为研究兴蒙造山带板块构造演化及晚石炭世-早二叠世的构造属性提供新的约束，进而对古亚洲洋闭合模式和陆壳增生机制提供研究支撑。

项目围绕着兴蒙造山带不同地区发育的构造混杂岩的物质组成、时空关系，及其与华北板块的构造关系和增生机制开展研究。选择大石寨、柯单山、准木布台、小苇塘和卫境等构造混杂岩，采用野外地质调查、岩石地球化学和同位素年代方法，论证了不同构造混杂岩的时空关系和形成的大地构造背景，提出中二叠世研究区由伸展体制向挤压体制转换，认为兴蒙造山带晚古生代经历了5个不同构造体制的演化。大石寨晚古生代盆地研究提供了重要支撑。选择内蒙北部地区发育的中生代侵入岩开展大地构造背景研究，提出兴蒙造山带受到了晚侏罗世鄂霍茨克洋闭合形成陆缘弧的改造，早白垩世经受了古太平洋构造域和鄂霍茨克洋构造域的共同作用。通过系统研究新元古代至中生代岩浆岩的同位素地球化学和年代学，结合沉积地层的碎屑锆石年代学方法，认为大别造山带北部130-116 Ma古太平洋岩石圈俯冲回撤导致了区域地壳伸展。依据项目野外调查新发现的古元古代武川超镁铁质混杂岩和丰宁县永利碳酸岩体，采用岩石学、同位素地球化学、年代学及区域构造解析等方法，提出华北克拉通北缘造山带新太古代至古元古代经历了2.68-2.5 Ga与俯冲作用有关的弧岩浆岩侵入，2.50-2.45 Ga弧陆碰撞与广泛的变质作用，2.40-2.35 Ga发生造山后伸展，2.3 - 2.0 Ga形成弧后盆地，2.2 - 1.9 Ga华北克拉通与西伯利亚克拉通或其他地块发生俯冲-碰撞及1.88 Ga左右的角闪岩相变质作用，以及1.87-1.78 Ga处于造山后伸展环境等演化阶段。总之，项目研究系统地论证了兴蒙造山带的形成与演化，完成了项目的目标任务。