青藏高原东缘数字高程剖面及其对晚新生代河流 下切深度和下切速率的约束*

文章利用数字高程剖面将青藏高原东缘分为4个大尺度地貌单元,即青藏高原地貌区、龙门山高山地貌区、山前冲积平原区(成都盆地)和四川盆地东部隆起区。根据数字高程剖面中的最高海拔高程点剖面与最低海拔高程点剖面之间的高差,定量计算了该地区河流下切深度;结合成都盆地岷江最古老冲积扇沉积物提供的青藏高原东缘河流形成的时间(3.6MaB.P.),定量计算了河流下切速率为1.29mm/a;在约束局部侵蚀基准面和气候变化对河流下切速率控制作用的基础上,建立了青藏高原东缘河流下切速率与表面隆升速率之间的定量关系,结果表明河流下切速率约为表面隆升速率的4倍。基于龙门山在表面隆升速率和下切速率等方面均大于青藏高原内部,认为青藏高原东缘的边缘山脉是剥蚀隆升和构造隆升两者叠加的产物。

PROFILES OF DIGITAL ELEVATION MODELS (DEM) CROSSING THE EASTERN MARGIN OF THE TIBETAN PLATEAU AND THEIR CONSTRAINTS ON DISSECTION DEPTHS AND INCISION RATES OF LATE CENOZOIC RIVERS

Based on Digital Elevation Model(DEM) analysis,the large-scaled geomorphology of eastern margin of the Tibetan Plateau can be divided into four zones,the Tibetan Plateau,the Longmen Mountain,the Chengdu Basin,and the Uplift Zone of Eastern Sichuan Basin.we used DEM to reconstruct the profiles of maximum,minimum,and mean elevations from the Tibetan Plateau to Eastern Sichuan Basin,and calculated the depth of dissection across the eastern margin of Tibetan Plateau.The river incision rate is calculated as 1.29mm/a,based on the depth of dissection and the age(3.6MaB.P.) of the oldest Minjiang fan deposit in Chengdu Basin.Based on these data,we established the Late Cenozoic coupling relationship between incision rate and surface uplift rate,and found out that the incision rate is four times more than the surface uplift rate.As the incision rate and surface uplift rate in Longmen Mountain are much higher than those in the Tibetan Plateau,we inferred that the Longmen Mountain was the result from the combination of erosion uplift and tectonic uplift.