关键词: 河流纵剖面, 河长坡降指标, Hack剖面, 构造运动, 天山

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