洮河水系流域地貌特征及其构造指示意义

Geomorphology of the Taohe River drainage system and its structural implications

通过数字高程模型(DEM)的空间分析技术,系统提取研究区洮河水系流域盆地典型的河流地貌参数,并利用活动造山带地区发育的基岩河道纵向剖面形态等典型参数,分析洮河水系流域盆地地貌发育不对称性特征及洮河在岷县流向的急剧转变成因。研究表明洮河上游南岸水系较北岸水系形状指数高、流域面积大、水系发育更成熟,下游东岸河流河长较短、流域面积小、形状指数低于西岸,西岸水系更发育,且上游流域要比下游河道平缓,水系的相对落差更低,发育更成熟,表明上游河道形成时间早于下游河道。临潭—宕昌断裂带的逆冲隆升作用是造成洮河上、下游水系形态差异的主要原因。岷县东侧山脉的快速隆起致使古洮河被截断,之后被东北侧河流溯源侵蚀,切穿西秦岭北缘构造带,进行河流袭夺,从而形成了现今的洮河。最后探讨了对青藏高原东北端晚新生代以来的构造响应。

In order to study the geomorphologic asymmetric characteristics of the Taohe River drainage basin and discuss the evolution of the Taohe River and the reason of the stream direction sharply changing at Minxian County,a DEM based topographic analysis of mountain belts has been done to extract much drainage and sub-basin information and the drainage geomorphic parameters of the Taohe River. Taohe River drainage sub basins and longitudinal channel profiles of the main bedrock channels of different active orogens show that the southern and northern tributaries of the Taohe River are of obviously asymmetry. Almost all the parameters of the upstream northern and downstream eastern basins are smaller than those of the upstream southern and downstream western ones,respectively. And upstream basins are smooth,low relief and mature,which may have formed earlier than the downstream ones. The rapid uplift of the mountain range in the east of Minxian County interrupted the paleo Taohe River,and later on,the river from the northeast cut through the West Qinling Fault zone by headwater erosion,and then captured the paleo Taohe River near Minxian County and formed the new Taohe River. The structural implications of the geomorphologic asymmetric characteristics of the Taohe River drainage basin for the northeast margin of the Tibetan Plateau within the Late Cenozoic have been discussed.