龙门山前缘新生代沉积不均匀性的动力学机制模拟研究

As the mark of the eastern margin of the Tibetan Plateau, Longmen Shan orogenic belt has high steep landform, strong tectonic activity. However, the foreland basins, corresponding to the intense tectonic uplifts since the Cenozoic Era, have relatively few sediments with a maximum thickness of 500 m or less. The Cenozoic sediments are only developed along the middle and southern segments of the Longmen Shan fault zone, almost disappeared along the northern segment, which is significantly different from other margins of the Tibetan Plateau. What dynamic mechanism determines the non-homogeneity of Cenozoic sediments in the front of Longmen Shan? With the constraints of observation conditions such as lithospheric structure and surface geology, this study plans to explore the deep dynamic process of lithospheric deformation by a two-dimensional profile model, the effect of surface denudation on the Cenozoic sediments by a two-dimensional planar model, the coupling between the surface process and deep dynamics by a three dimensional model. With these series studies, we try to discuss the dynamic mechanism of lithospheric deformation in the eastern margin of the Tibetan Plateau and the non-homogeneous Cenozoic sediments in the front of the Longmen Shan. We will further discuss the lateral expansion mode of the Tibetan Plateau and provide reference for the disaster prevention and major construction in this area.

龙门山造山带以高陡的地貌特征、强烈的构造活动性使其成为青藏高原东缘边界带的标志。然而，与其新生代以来强烈构造隆升相对应的新生代前陆盆地沉积物则相对较少，最大厚度处不超过500m，而且山前新生代沉积只沿着龙门山断裂带中段和南段发育，沿着北段的前缘几乎缺失，这与高原其它边缘有着显著差异。是什么动力学机制决定了龙门山前缘新生代沉积的不均匀性？本研究计划在深部结构和地表地质等观测条件的约束下，通过构建二维剖面有限元模型探讨跨越龙门山北段和南段岩石圈变形的深部动力学过程，二维地表构造地貌模型探讨地表剥蚀作用对其新生代沉积的影响，三维数值模型探讨地表过程和深部动力耦合作用，以此来探讨青藏高原东缘岩石圈变形和龙门山前缘新生代沉积不均匀的动力学机制。在此基础上讨论青藏高原的横向扩展方式，为该区的防灾减灾和重大工程建设提供参考。

龙门山造山带是青藏高原向东扩展遇到四川盆地的阻挡而形成的边界地带，其高陡的地貌和强烈的地震活动性是这一边界带的重要特征。然而，与其新生代以来强烈构造隆升相对应的新生代前陆盆地沉积物则相对较少，最大厚度处不超过500m，而且山前新生代沉积只沿着龙门山断裂带中段和南段发育，沿着北段的前缘几乎缺失，这与高原其它类似高陡地貌的边缘有着显著差异。是什么动力学机制决定了龙门山前缘新生代沉积的不均匀性？本研究在深部结构和地表地质等观测条件的约束下，通过构建二维剖面有限元模型探讨跨越龙门山北段和南段岩石圈变形的深部动力学过程，二维地表构造地貌模型探讨地表剥蚀作用对其新生代沉积的影响，三维数值模型探讨边界条件差异和岩石圈结构不均匀性的影响，以此来探讨青藏高原东缘岩石圈变形和龙门山前缘新生代沉积不均匀的动力学机制。研究结果表明，从青藏高原向东扩展边界条件的不均匀性来看，龙门山断裂带南段逆冲、北段走滑更有利于南段地壳缩短增厚、北段走滑剪切，这样为造山带南段提供了更为充足的沉积物源；从流变强度不均匀性看，强度较高的龙门山造山带南段窄、北段宽，而且南段前陆盆地存在较厚的中生代沉积，这样更有利于新生代沉积发生在南段；从沉积环境看，南段形成的龙门山-龙泉山山前沉积盆地更有利于沉积物的保留，而北段在高侵蚀率的情况下可能很难保留新生代的沉积物。以上结果是结合了深部动力和地表过程而进行的综合解释。项目的研究有助于深入理解深部动力和地表过程相互作用下龙门山地区的岩石圈变形，同时本研究有助于地球系统科学多圈层耦合模式的发展和完善。