内蒙古大青山侏罗纪沉积盆地充填和构造古地貌重建
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本文为国家自然科学基金项目(编号:41902116,42022029)和中国地质调查项目(编号:DD20230008)的成果


Jurassic sedimentation and paleogeomorphic reconstruction in the Daqing Mountains area, Inner Mongolia
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    摘要:

    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构造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,碎屑组分中沉积岩岩屑和砾石明显增多,指示构造平静阶段的地貌夷平。至中—晚侏罗世,大青山地区构造属性发生反转,断陷盆地南部开始卷入挤压变形,形成大青山褶皱—逆冲系统雏形。然而,这些新生的挤压构造似乎未能引起地表地形的剧烈起伏,它们主要表现为隐伏状态。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浅层次盖层、火山物质与深层次TTG岩套的的反复剥露抬升。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先存断裂活化密切相关,也是对周缘板块向东亚大陆俯冲汇聚的远程响应。

    Abstract:

    Detailed stratigraphy and provenance analysis have been conducted in the Jurassic Shiguai Basin, with aims at constructing the basin’s depositional architecture and facies distribution, tracing provenance’s tectonic position and uplifting history, and finally discussing the Jurassic geomorphic evolution in the Daqing Mountains area.Methods: Conventional sedimentological methods were applied in this study, including detailed logging in six available sections, restoring paleo-drainage system, and calculating detrital/gravel composition in sandstones and conglomerates. Based on these works, along with published studies of growth strata, isotopic dating and structural deformation, depositional architecture and facies distribution can be well reconstructed.Conclusions:The Shiguai Basin is the most well-preserved Jurassic basin among the Yinshan Mountains belt, whose depositional process and detrital composition document the Jurassic geomorphic evolution of the Daqing Mountains area. The Lower Jurassic Wudanggou Fm. and the Middle Jurassic Zhaogou Fm. constitute the lower part of the basin fill, and record an extensional setting. During the initial rifting, southern part of the basin deposited coarse-grained alluvial fan system duo to adjacent steep topography, and gravel composition within these deposits reveals the unroofing process of proximal high-grade metamorphic terrane. The late stage of rifting was characterized by thermal subsidence, and meanwhile the flooding surface reached its maximum. During the same interval, material sourced from sedimentary rocks increased markedly in the Zhaogou Fm., indicating the ongoing deplanation and the corresponding tectonic quiescence. After then, the Late-Middle Jurassic saw a tectonic inversion occurring in the Daqing Mountains area. This event formed the nearly E-trending Daqing Mountains fold-and-thrust belt which involved the southern part of the previous rifting basin into compressive deformation. However, these young structures were probably blind and their actives seemed not to cause obvious uplifting. On the contrary, basin’s northern margin denudated dramatically at the same time, as evidenced not only by the marginal deposition of the Changhangou Formation and Daqingshan Formation merely occurring in the northern part of the Shiguai Basin, but also by alternative unroofing of the deep and shallow materials in the Yinshan Mountains belt. This character that the north terrane uplifted higher than the south, could be attributed to the reactivation of regional faults beside the Yinshan Mountains belt, and also can be considered as remote response to the Late Mesozoic multi-plate convergence in East Asia.

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王永超,董树文,陈宣华,魏丽娟.2023.内蒙古大青山侏罗纪沉积盆地充填和构造古地貌重建[J].地质论评,69(5):2023050020,[DOI].
WANG Yongchao, DONG Shuwen, CHEN Xuanhua, WEI Lijuan.2023. Jurassic sedimentation and paleogeomorphic reconstruction in the Daqing Mountains area, Inner Mongolia[J]. Geological Review,69(5):2023050020.

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  • 收稿日期:2023-03-22
  • 最后修改日期:2023-06-21
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  • 在线发布日期: 2023-10-19
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