河西走廊北山地区构造变形影响下的地貌演化过程研究

Geomorphic evolutions are greatly controlled by forms and processes of tectonic deformation, while how the effect was conducted has been one of the core issues in geomorphology studies. In recent 30 years, a series of geometric models and kinematics of fault-related fold were proposed and widely used in near-surface crust deformation. Besides, different physical models were also widely used in geomorphic process studies, and in the meantime numerical modeling method became popular in studying geomorphic evolutions. In this project, we would apply both tectonic deformation kinematic models and geomorphic evolution models to study the landscape evolution processes along the Beishan Mountains in the north of the Hexi Corridor, trying to answer the question of how tectonic deformation influence geomorphic processes. The Beishan Mountains (including JintaNan Shan and Heli Shan), which is a relatively new mountain series (initial uplifting on Quaternary or late Pliocene), supply us a good natural lab for the geomorphic evolution study because of its relatively simple deforming history and widely distributed geomorphic surfaces and fluvial and alluvial deposits. Thus, we will first study the deformation of strata and geomorphic surfaces, ages of surfaces and Quaternary deposits by cosmogenic exposure and burial dating methods, history of local geomorphic evolution. And then, based on these information, we will build kinematic models of tectonic deforming, and model the processes of geomorphic evolution associated with tectonics by numerical modelling methods.

构造变形模式与过程深刻地影响着地貌演化过程，而它是怎样影响的一直是地貌学关注的主题之一。近30年以来，各种断裂相关褶皱几何学模型与运动学过程不断提出并得到应用，地貌学研究中也开始利用物理模型来描述地貌现象并逐渐引入数值模型的方法模拟地貌演化过程。这两方面研究的发展为构造变形影响下的地貌演化研究提供了新的思路与方法，所以本项目拟以构造变形几何学模型与运动学过程为构造研究内容，以地貌演化物理模型和数值模拟为研究方法，对河西走廊北山地区地貌演化过程进行研究。走廊北山（这里主要研究金塔南山和合黎山）抬升时间较晚（第四纪或晚上新世以来），构造变形历史较短，变形过程相对简单，并有大量的冲、洪积地貌面与沉积物的分布，为实施本研究提供了理想的实验区域。拟通过地层与地貌面变形、宇生核素暴露与埋藏测年、地貌面与沉积物演化序列，获得区域构造变形模式与地貌演化历史，再利用数值模拟方法再现区域地貌演化过程。

构造活动影响着山体的隆升和水系演化过程，决定着活动造山带的地貌格局和地表形态特征。位于青藏高原东北缘的河西走廊北山地区属于干旱区幼年期山体，区域内气候差异较小、构造活动相对简单，是探讨构造活动如何影响地貌演化历史的理想区域。本研究首先通过调查河流阶地变形特征建立了金塔南山地区的褶皱变形几何学模型，发现金塔南山北缘断裂为铲式逆冲断裂，其相关褶皱作用控制着金塔南山阶地面及下伏基岩的变形特征。其次通过阶地序列的详细调查与年代学研究，获得金塔南山西段河流平均下切速率为0.23-0.25 mm/a。最后，基于Landlab平台构建的地貌演化数值模型重现了北山地区局地地形的演化历史，通过模拟地形与真实地形的对比，以准周期性谷间距等地形特征指标为判识标准，推算了北山地区典型区域山体隆升的时代与速率，结果表明北山地区合黎山、金塔南山东段和金塔南山西段的地表隆升速率分别为0.4 mm/a、0.3 mm/a和0.2 mm/a，地表起始隆升时间为1570 ka、305 ka和405 ka。数值模拟结果与本研究实测的河流下切速率、以及前人研究获取的断层活动速率具有较好的一致性，表明通过地貌演化数值模型可以评价年轻山地的隆升速率和起始时代，而准周期性谷间距是研判模拟结果与真实地形相似性的有效工具。