内蒙古大青山侏罗纪源—汇系统分析与构造古地貌重建

Structural paleogeomorphy evolution and the “source-to-sink” system have become a hot topic in the earth science field. The Daqingshan area is located in the eastern segment of the Yinshan belt and mainly consists of the southern Daqingshan fold-and-thrust system and the northern Jurassic Shiguai Basin, which is one of the ideal places for studying the Yanshan Movement along the northern margin of the North China Block. Because the stratigraphic and sedimentological studies are currently much weaker than the structural analysis in the Daqingshan area, this project will mainly focus on the Jurassic Shiguai Basin. Based on multidisciplinary studies on stratigraphy, sedimentology, thermochronology and so on, the applicants want to restore different periods of facies distribution and sedimentary filling process, to trace the provenance position, material composition and their dramatic changes, to quantitatively calculate the uplift and exhumation processes of the basin-bounding mountains, and finally to delineate the Jurassic paleogeomorphic evolution and material exchange in the “source-to-sink” system in the Daqingshan area. All of these jobs will contribute to better understanding the initiation of the Yanshan Movement and the transition process of the deep-earth dynamic systems along the northern margin of the North China Block.

构造地貌演化和源—汇系统研究是当前地球科学领域颇受关注的前沿性课题，对传统沉积学研究具有重大的理论指导意义。大青山地处阴山山脉东段，主要由南部的大青山褶皱—逆冲系统和北部的侏罗纪石拐盆地组成，是探讨华北地块北缘燕山期陆内造山过程的理想地区之一。然而，多年来，学者们的目光主要聚焦于大青山褶皱—逆冲系统几何学和运动学方面的研究，忽视了沉积学研究对于揭示盆缘构造活动性的重要作用。鉴于此，本项目将以石拐盆地为重点研究对象，聚焦盆山系统间的源—汇过程和构造地貌演化，通过地层学、沉积学、构造热年代学等多学科的交叉研究，恢复盆地不同时期的沉积充填过程和沉积相分布，示踪源区构造位置、物质组成及其突变过程，定量计算盆缘山脉隆升剥露历史，其目的在于精细刻画大青山侏罗纪构造地貌演化和源—汇系统中的物质交换过程，为深入探讨华北地块北缘燕山期陆内造山启动和深部动力学体系转折过程提供详实可靠的沉积学资料。

石拐盆地是阴山地区保存最完整的侏罗纪盆地，其沉积充填过程和碎屑物质组成为正确认识大青山侏罗纪盆山地貌演化提供了重要约束。石拐盆地形成于伸展断陷环境，依次充填了下侏罗统五当沟组和中侏罗统召沟组。断陷初期，南部地貌陡峭，控制发育了冲积扇沉积体系，碎屑组分记录了近源高级变质地体的剥露过程；晚期以坳陷为主，在召沟组末期形成最大湖泛面，碎屑组分中沉积岩元素明显增多，指示构造平静阶段的地貌夷平。至中晚侏罗世，大青山地区爆发强烈陆内造山，断陷盆地南部普遍卷入挤压变形，形成大青山褶皱—逆冲系统。然而，这些新生的挤压构造多隐伏于地下，未能引起地表地形的剧烈起伏。相反，该时期北部地貌抬升最为显著，不仅体现在中侏罗统长汉沟组和上侏罗统大青山组边缘相沉积均分布在盆地北部，更体现在阴山地体中深浅物质的反复剥露抬升。这种“北高南低”地貌特征的形成与阴山地体持续抬升及其两侧区域性断裂活化密切相关，也是对周缘板块向东亚大陆俯冲汇聚的远程响应。