Abstract: River longitudinal profile can reflect various geomorphic and landform characteristics of its drainage basin. This study is focused on the profile of the 10 mainstreams of the northern Tianshan. SL index(SL) and gradient index (SL/K) are examined for concavity studies of each profile. They are compared with the bedrock distribution, active structures, and geomorphic features to clarify the activity of the northern Tianshan. The results illustrate that, after millions of years of tectonic evolution, the main factor to cause the landform of the drainage basin is tectonic uplifting, instead of what proposed by Davis's graded river theory. The third episode of the Himalayan movement affects the trailing edge of the deformation belt, and the movement at the end of the early Pleistocene leads the southern margin of the Junggar Basin to deform completely. Gradient index increases as each river meeting with the southern margin fault of the Junggar basin in district Ⅱ. Therefore, in a large-scaled view of gradient index, tectonic fault exhibits a strong influence on river profile in the study area. The difference of the lithology and the afflux of the tributaries also make a great influence on gradient index in a subbasin-scaled view.

Key words: river longitudinal profile, stream length-gradient index (SL index), Hack profile, tectonics, Tianshan

摘要： 在构造运动活跃地区的流域范围内, 构造运动及地貌特征能有效地反映在河流纵剖面、河流坡度等因素上。针对北天山地区 10 条河流, 提取河流 Hack 剖面、河长坡降指标( SL) 以及标准化坡降指标( SL/K) 等地形指标, 进行量化分析。研究表明北天山地区河流受到持续且快速的构造抬升运动影响, Hack 剖面呈上凸形态, 并且与河长坡降指标峰值、河流纵剖面变化具有很强的关联性。北天山地区河流标准化坡降指标( SL/K) 以依连哈比尔尕断裂带和准噶尔南缘断裂带为界限呈带状(Ⅰ, Ⅱ, Ⅲ区) 的分布, 在构造运动影响下, 流经两大断裂带的河长坡降指标明显升高, 揭示了在河流剖面坡度变化较大且河长坡降指标大的地区多为构造运动活跃的区域。同时, 在小流 域尺度内, 岩性改变与支流汇入也容易使局部地区出现河长坡降指标的峰值。

关键词: 河流纵剖面, 河长坡降指标, Hack剖面, 构造运动, 天山