摘要
利用新近公布的SRTM数字高程模型(DEM),选取青藏高原北部及高原内、外流区域进行大尺度定量地貌分析。分析表明,青藏高原不同地区的地貌差异反映了它们在地貌演化上的阶段性。在高原北部的祁连山地区,局部地区绝对高程增加的同时,地势起伏反而变缓。这些地区水系的发育程度普遍较低,剥蚀物质往往只经过近距离的搬运仍滞留在逆冲褶皱带内,山间盆地和平地成为山间小河的侵蚀堆积基准,因此“削高填低”的过程有效地降低了局部地形起伏。高原平坦地势是伴随着造山过程及之后的高海拔侵蚀基准和内流型水系条件下“削高填低”剥蚀过程的结果。我们认为高原内部为现今仍在承受剥蚀的地势平坦面。它的形成具穿时性,是内流型水系河流下切侵蚀能力弱化的结果,不直接反映海拔的高低。如果平坦侵蚀面的形成与海拔高程无必然的关联,或侵蚀面可以在任何海拔高度形成,而不一定代表以海平面为基准的准平原,那么它就不能作为一个可靠的参照面用于直接示踪和约束高原的抬升量和抬升时间。
In this paper, we quantify the bulk topographic characteristics of selected regions of the Tibetan plateau, using SRTM DEMs. Regional differences in geomorphology of the Tibetan plateau may be understood as an evolutionary sequence through surficial processes and drainage efficiency in particular. In the Qilian Shan region, local relief decreases with time while elevation increases. In this area, the drainage network is mostly limited in extent. Thus, eroded material from mountain ranges is mostly deposited locally in adjacent intramountain basins. Basin filling due to this limited drainage network has played a major role in smoothing out the tectonically generated structural relief during topographic build-up of the Tibetan plateau. In the plateau interior, passive filling further smoothes the local relief in areas where tectonic uplift had ceased millions of years ago and where internal drainage systems had dominated. Our analysis thus suggests that the plateau interior is a low-relief surface that formed diachronously, due to the much-reduced down-cutting ability of internally drained rivers. This low relief does not directly reflect on the elevation change of the plateau. In this scenario, the ＂flat＂ Tibetan plateau interior does not necessarily imply an initial near-sea-level ＂peneplain＂, and thus cannot be used as a reliable horizontal reference datum to directly constrain the amount and timing of plateau uplift.
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2006年第5期285-299,共15页
Earth Science Frontiers
基金
中国科学院知识创新工程重要方向项目(KZCX3-SW-143)
国家重点基础研究发展计划"973"项目(2002CB412602)
