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CHARACTERISTICS OF THE HUANGHE RIVER LONGITUDINAL PROFILES AROUND XUNHUA-GUIDE AREA(NE TIBET)AND THEIR TECTONIC SIGNIFICANCE
循化-贵德地区黄河水系河流纵剖面形态特征及其构造意义

Keywords: Tibetan Plateau,Xunhua-Guide region,longitudinal profile,stream-power incision model
青藏高原
,循化-贵德地区,河流纵剖面,河流水力侵蚀模型

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Abstract:

Xunhua-Guide area is a part of Late Cenozoic tectonic orogenic systerm along the northeastern Tibetan Plateau.The section of the Huanghe River in this area provides an ideal site to unravel the process of the plateau uplift and incision of the Huanghe River.Although some terrace studies within this region have shown a coupling pattern between the plateau uplift and Huanghe River incision,more analysises are still needed to test the impact of the ongoing uplift on river evolution.It is known that longitudinal profile can be well adjusted to respond the vertical differential uplift and lithological change along a river thus in this paper we have carried out a study on longitudinal profile of the Huanghe River and its 38 tributaries.By utilizing the digital elevation model database,longitudinal profiles along the Huanghe River around Xunhua-Guide area were extracted and analyzed.Our study indicates that 65.8%(25/38)of the longitudinal profiles are convex up,while 34.2%(13/38)show concave features.Determination of the knickpoint location along the profile indicates that 64.0%(16/25)of the 25 convex profiles have their knickpoints near the basin boundary or the contact between basin and range systerm.On the basis of the stream-power incision model,the tectonic expression on the profile is determined.Our logrithmic slope-area plots for the Huanghe River drainage declare that 68.4%(26/38)are upward-convex and the left are almost near the linear state.Consequent analysis reveals that the upward-convex features of the profiles and slope-area plots can be explained by the elevation of the bedrock profile getting higher and higher and the uplift being beyond the incision around the target area.Additionally,we know that in the areas where the rivers run across the pre-Cenozoic high resistant bedrocks,the longitudinal profiles also show a similar upward-convex feature,which indicates that the differential lithology distribution is also another control of the profile feature.In a general view,the longitudinal profiles of the Huanghe River tributaries are well controlled by the Late Cenozoic tectonics and lithological difference,which indicates that the landscape around Xunhua-Guide area is in the pre-steady state or near to the steady state.Meanwhile,our analysis also agrees,to some degree,that the northeastern Tibetan Plateau is one of the newly uplifted parts in the whole plateau frame.

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