涪江上游流域地貌特征及其对断裂活动性的响应

Geomorphological Characteristics and Its Response to Fault Activity in the Upper Reaches of the Fujiang Drainge Basin,China

对涪江上游流域地貌特征及其与断裂活动的相关性进行分析,有助于深入理解青藏高原东缘晚新生代以来的地貌演化过程,也可为该区域构造活动和河流发育历史研究提供参考依据。基于经空间叠加处理的海拔高程数据和地势起伏度数据,在涪江上游流域划分出15种地貌形态组合,在此基础上结合区域断裂活动状况,从研究区地貌类型、海拔高程、地势起伏度、干流下切深度、河道水平扭错等方面探讨流域地貌特征对断裂活动性的响应,结果表明:(1)虎牙断裂和龙门山断裂带逆冲活动驱动区域性间隙抬升使中海拔地貌区成为涪江上游流域地貌类型的主体;(2)虎牙断裂逆冲作用导致位于上盘的西侧块体具有更高的隆升幅度和海拔高程,并加剧了外营力侵蚀,形成了相对较高的地势起伏形态;龙门山断裂带三条主干断裂的上盘叠瓦式向上推移,使虎牙断裂东侧区域海拔高程和地势起伏度均自北向南逐级降低;(3)涪江上游流域一系列逆断层的差异活动导致位于断裂上盘区域的河道下切深度、下切速率总体上大于下盘区域。涪江干流对流经区域地表的切割,内、外营力的贡献比值大致为1.95∶1;(4)横跨断裂的涪江河道因断裂平移走滑而沿断裂走向发生同步弯曲,龙门山断裂带的区域性右旋作用使涪江干流及其支流的流向在龙门山地区发生系统性转变。

Analysis of geomorphic characteristics and its correlation with fault activity is helpful to understand the geomorphic evolution process of the eastern margin of the Qinghai-Tibet plateau since late Cenozoic in the upper reaches of the Fujiang river.It can also provide reference material for tectonic activity and river evolution history in this area.In this study,the upper reaches of the Fujiang river basin were divided into 15 geomorphic types based on elevation data and relief data,geomorphological characteristics and its response to fault activity were discussed combined with regional fracture activity from the aspects of geomorphologic type,elevation,relief amplitude,incision depth,river channel horizontal dislocation and so on.The results showed that thrust activity of the Huya fault and the Longmenshan fault zone drived regional uplift for a long time,so that middle-elevation landform area became the main landform type in the upper reaches of the Fujiang river.As a result of the thrusting effect of Huya fault,higher uplift amplitude and elevation were generated on the western block of hanging wall,the exogenous erosion was aggravated,and relatively higher topographic relief was formed.The imbricated thrusting of the hanging wall of the Longmenshan fault zone led to the decrease of elevation and relief from north to south in the region.As a result of differential activities of thrust faults,the depth and rate of river incision in the hanging wall were generally greater than that in the footwall.The effect proportion of endogenous forces and exogenous forces to erosion process was about 1.95∶1.Due to the translational strike-slip of the fault,the Fujiang river course was curved synchronously along the faults.The regional dextral action of the Longmenshan fault zone made the flow direction of the main stream of the Fujiang river and its tributaries change systematically in the Longmenshan area.