二连盆地北缘中生代以来盆山体系构造-热演化研究

Clarifying the characteristics of tectono-thermal evolution process between basin and adjacent range is crucial for studying basin and range system on restoring the tectonic evolution process, clearing the coupling relationship and exploring the tectonic mechanism. Multiple approaches in terms of field investigation, apatite fission track, apatite/zircon (U-Th)/He and vitrinite reflectance of organic matter are applied on a typical basin and range system in the north of Erlian Basin, the following questions will be resolved in this project: (1)clarifying the tectono-stratigraphic framework of the basin and range system, (2)restoring the thermal histories of the basin and the adjacent range respectively since Mesozoic times, (3)revealing the spatial features of thermal evolution process in the basin and range system. On the basis, the above data will be used to analyze the relationship between differential exhumation process and structural activities, to build a tectono-erosional model and to reconstruct the coupling relationship between the basin and the adjacent range in the north of Erlian Basin. The expected results will provide new constrains on a better understanding of the tectonic evolution process and its dynamic mechanism since Mesozoic in the critical phase of multiple tectonic domains transformation in the Central Inner Mongolia.

厘清盆缘山地和相邻盆地的构造-热演化特征是恢复盆山体系演化历史、明确盆山耦合关系、探索构造成因机制的关键。选择二连盆地北缘盆山体系为研究对象，拟通过野外地质调查、磷灰石/锆石裂变径迹和（U-Th）/He定年与镜质体反射率多种古温标结合：(1)查明盆山体系的构造-地层格架；(2)恢复中生代以来沉积盆地和盆缘山地的热历史；(3)揭示盆山体系热演化特征的空间变化规律。在此基础上，分析差异剥蚀作用与断裂构造活动的成因联系，构建构造-剥蚀演化模式，重塑二连盆地北缘盆山耦合关系。该研究成果将为清晰认识多构造域叠加转换作用下内蒙古中部中生代以来构造演化进程及其动力学机制提供新的地质证据。

本项目综合野外地质调查、低温热年代学研究、锆石U-Pb定年、镜质体反射率分析等方法，以二连盆地北缘吉尔嘎郎图作为研究区，揭示了盆山系统的构造-热演化特征，分析了构造动力学成因机制，进而阐释了相关地质意义。研究发现，吉尔嘎郎图地区具有东南断、西北超的半地堑构造特征。北部盆缘隆起区与南部盆地沉积区以沉积接触为主，除NE向延伸的主控断层发育外，基岩区还发育NW向延伸的次级断层构造。锆石U-Pb年代学研究表明，盆缘隆起区晚古生代以来岩浆活动主要分四个阶段：早石炭世（ca.336-320Ma）、晚石炭世（ca.311-299Ma）、早二叠世（ca.299-289Ma）和早白垩世（ca.140-135Ma）。基岩的AFT年龄变化范围为128.9~223.4Ma；早白垩世火山岩AFT年龄为85.6Ma；沉积盆地砂岩的AFT年龄为65.9Ma。热史模拟结果显示，研究区主要经历三阶段的快速隆升剥蚀，分别为晚古生代末期、晚侏罗世—早白垩世、晚白垩世，东西向差异剥蚀特征显著。经分析，盆地断陷形成、NW向次级断层发育、中生代岩浆活动扰动以及晚白垩世盆地构造反转等多地质因素影响可能是造成差异剥蚀的原因。综合前期工作，对二连盆地及其周边区域剥蚀演化过程进行重建：晚古生代末期至三叠纪期间，古亚洲洋闭合以及华北板块和扬子板块碰撞，造成了二连地区快速抬升剥蚀；侏罗纪至早白垩世期间，强烈的剥蚀隆升主要发生于宝力格隆起、苏尼特隆起和温都尔庙隆起，受控于蒙古—鄂霍茨克洋闭合以及造山后垮塌伸展，大范围断陷盆地发育形成。晚白垩世期间，古太平洋俯冲角度变化、俯冲作用增强，盆地构造反转，隆升剥蚀过程几乎覆盖整个二连盆地，盆缘隆起区域的强烈剥蚀作用向东扩展至大兴安岭隆起。古新世至始新世期间，二连盆地西部剥蚀作用明显减弱，显著剥蚀已转至大兴安岭隆起及其以东地区。该项工作将为认识我国东北地区晚古生代以来构造演化过程及其动力学机制提供全新的理论依据。