| The topography,geomorphology and uplift pattern of the southeastern margin of the Tibetan Plateau as well as the evolution of the topography since Cenozoic are closely related to the continuous collision between the Indian plate and the Eurasian plate.As one of the most tectonically active regions in the southeastern margin of the Tibetan Plateau,Yunnan-Zhongshan is regarded by geologists as the best place to understand the uplift evolution and climate change of the Tibetan Plateau At present,there are two widely accepted models of the Tibetan Plateau uplift and tectonic deformation mechanism: one is the rigid block lateral extrusion model proposed by Tapponnier and the other is the lower crust pipeline flow model proposed by Royden.The rigid block lateral extrusion model emphasizes the tectonic deformation and stress accumulation at the block boundary on the large strike-slip fault,while the lower crust pipeline flow model holds that the stress and strain are evenly distributed in the block,and the deformation is uniform and continuous.The two geodynamic models have been debated since they were proposed.The southeast margin of the plateau has experienced many uplifts,and the geomorphic response in different uplifting periods is also controversial.As the most basic unit in geomorphology and most susceptible to tectonic activity,river provides a very important help for understanding the bedrock uplift mode.The hydrodynamic erosion mode is a very advantageous means.The normalized steepness index(ksn)of bedrock channel usually increases with the increase of rock uplift rate In this paper,about 320 watercourses were extracted from the central Yunnan massif using SRTM data with a resolution of 90 m.The required geomorphic parameters of these watercourses were extracted using Arc GIS and Matlab software(including the steepness index(ksn)of the watercourses and the concave index(θ).A series of landform parameters,such as the slope of the elevation channel at the location of the split point),and the longitudinal profile of the river in the middle block of Yunnan was extracted and analyzed.After extraction,the ksn of the thrust fault zone was relatively high,while the ksn of the striking fault channel in the middle block of Yunnan was relatively low In this study,a comparative analysis of sediment content between ksn and annual lithologic precipitation shows that there is a low correlation between channel steepness index(ksn)and rock erosion resistance and climate in the central Yunnan massif.In addition,no correlation between ksn and basin area is found The variation of channel steepness index(ksn)is controlled by tectonic activities rather than by non-tectonic factors such as climatic conditions and lithology.It is found that the uplift rate in the central Yunnan block is evenly distributed However,due to the influence of the inverse Yalong-Yulong thrust belt,the uplift rate of the northern part of the central Yunnan block is relatively high.The relative intensity of tectonic activity(Iat)of 98 small basins in Yalong-Yulong thrust belt was extracted by Arc GIS and 30 m resolution digital elevation model(DEM),and some non-tectonic factors(lithologic precipitation)are calculated After excluding the non-structural factors,we evaluated the degree of tectonic activity(Iat)in the middle of Yunnan Province.Finally,the investigation showed that the structural activity of Yalong-Yulong thrust belt has the characteristics of segmental,and the areas with high degree of tectonic activity decreased from north to south.The conclusions obtained by the two methods point to the lateral extrusion model of rigid block. |
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