金沙江攀枝花至凹嘎段水系河道纵剖面形态特征及其对河谷发育的指示

Characteristics of stream longitudinal profiles of the Jinsha River from Panzhihua to Aoga and their implications for valley evolution

基于数字高程模型,利用ArcGIS和MATLAB中的河流纵剖面工具对金沙江攀枝花-凹嘎段水系的河道纵剖面进行了分析,结果显示,该区大多数支流的河道纵剖面呈上凸型,发育一个或多个裂点,将河道分割成若干河段.其中,大部分裂点聚集分布在海拔2 000~2 300, 1 600~1 800和1 400~1 500 m,可以与该区广泛发育的三级夷平面相对应,共同指示了该区地势上的不整合.根据对裂点之上古河道纵剖面的重建,获得了河谷累积的下切量,结合区域侵蚀速率研究,推算这3次强烈的构造事件分别发生在3.47、2.19和1.45 Ma,说明目前的金沙江河谷是从晚上新世以来河流自夷平面上下切而形成的新蚀河谷.

Based on digital elevation modal data,the tributary river longitudinal profiles of the Jinsha River from Panzhihua to Aoga were extracted and analyzed using the Stream Profile tool in ArcGIS and MATLAB and the results showed that the longitudinal profile of most tributaries was far from an equilibrium,characterized by a upwardly convex,with one or more knickpoints which divided the river profiles into several segments.The distribution of these knickpoints grouped at three different elevations,namely2 000-2 300,1 600-1 800 and 1 400-1 500 m,corresponding well to the three planation surfaces(PSs)in this area,indicating the topographic unconformities thereof.Based on the incision amount deduced from projection of the relict river profile on PSs,together with the erosion rates,the time of river incision from the PS1,PS2,and PS3 were estimated to be 3.47,2.19,1.45 Ma,respectively,indicating that the modern valleys of the Jinsha River were slowly incised by the Jinsha River itself from the PSs since the late Pliocene.