中蒙边界东南段晚中生代挤压-伸展构造的空间展布、转换过程和时限

Late Mesozoic crustal contraction and extension is one of the most remarkable structural features in NE Asia continent. But the detailed transition process, mechanism and time of the transition from contraction to extension are not clear. Based on our latest progress in the Daqing Shan area, this project selects the Jurassic E-W strike contractional structures, early Cretaceous contractional and extensional structures in the southeastern China-Mongolia border as subjects. According to the study of detailed structural analysis, geochronology and P-T analysis of deformation, we trace the features of structures in key areas, observing the relationships between contraction and extension, and analyze the P-T condition of these shear zones. We try to found suitable deformed markers to study the microstructures and obtain geochronologic data. All these are combined to discuss the geometry, kinematic features, deformation stages and develop sequence for late Mesozoic contractional and extensional structures in study area. Combined with studies of magmatism by other projects, we attempt to discuss the detail process and mechanism of transition of late Mesozoic contraction to extension and tectono-magmatic process, geodynamic in NE Asia.

晚中生代地壳挤压与伸展构造是东北亚大陆最显著的构造特征之一，但对于挤压与推覆的详细过程、时限和机制仍然不清楚。本项目根据在大青山地区所取得的新进展，选择与大青山相邻的中蒙边界东南段地区侏罗纪近东西向挤压构造（推覆与褶皱等）、早白垩世挤压与伸展构造为研究对象，以精细构造解析、构造年代学和变质-变形温度分析为基础，开展关键地区构造延伸形迹、挤压与伸展构造的关系、主要断裂剪切带形成的P-T环境等研究，并寻找合适的变形标志体开展显微构造（重结晶型式、矿物滑移系等）和构造年代学分析，以确定研究区内晚中生代挤压-伸展构造的几何学、运动学特征、变形期次和发育序列、时限。在此基础上，讨论晚中生代挤压增厚向伸展减薄的具体过程和机制，结合其他项目对相关岩浆岩的研究，探讨东北亚地区晚中生代构造-岩浆过程和动力学背景。

晚中生代地壳挤压与伸展构造是东北亚大陆最显著的构造特征之一，但对于挤压与推覆的详细过程、时限和机制仍然不清楚。本项目根据在大青山地区所取得的新进展，以中蒙边界东南段地区多期挤压构造、早白垩世伸展构造为研究对象，以精细构造解析、构造年代学和变质变形分析为基础，厘定了两期主要的地壳挤压加厚事件（晚二叠-早三叠、中-晚侏罗世）的展布、构造样式和变形时限，为伸展的早期加厚提供了依据。更重要的是，新识别了众多的早白垩世（~130Ma）同伸展侵位的花岗岩不对称穹隆，这些穹隆具有统一的伸展极性和伸展时限，同略早发育的变质核杂岩一起，构成了蒙古-鄂霍茨克构造体制下的巨型盆岭构造。结合对相关岩浆作用的研究，进一步揭示了东北亚这种挤压向伸展转换为一个由深部到浅部发育的过程，深部从150~140 Ma开始启动深层次韧性伸展，到130~120 Ma达到高潮。这一个过程与岩浆演变有紧密的关联。