The Synthetic Analysis Of The Differential Uplifting In The Eastern Himalayan Syntaxis Region Through Geomorphology Method

The eastern Himalayan syntaxis is located in the southeast of the Tibetan plateau where the Eurasian plate and the Indian plate collide together,and multiple geological structure converge here.Faults and tectonics develop well in this region,and the faulted blocks move in different way.Earthquakes occurred frequently in this region,and 1950 M8.5 earthquake near Chayu which is the biggest earthquake of the Chinese mainland also happened here.Therefore,the eastern syntaxis is the research focus of the tectonic geology all the time.The research of differential uplifting in this region is crucial to understand the regional tectonic deformation mechanism,establish the tectonic model of faulted block and analyze the regional seismic risk.The existing research about the differential uplifting is mainly based on the analysis of the different bedrock exposed age and denudation rate gained by means of the Thermochronology.Due to the limitation of the spatial distribution range of sample collection,it is difficult to extend the Thermochronology method to the whole region,but the research of the watershed and the layered geomorphology can make up for this shortage.Watershed is sensitive to the variation of neotectonics,lithology and climate,and the watershed index can usually indicate the evolution characteristic and reveal tectonic controlling factor.Watershed index is usually obtained or calculated based on the Digital Elevation Model(DEM),and the tectonic inversion through the watershed index quantitative analysis is more and more popular in the active tectonic field since recent years.Similarly,the layered geomorphology(including the planation surface,the river terrace,the alluvial or pluvial terrace,etc.)can record the long time scale tectonic movement since Quaternary,and can directly reflect the deformation pattern and the cumulant of the controlling active tectonic movement,and therefore the cumulative deformation on the layered geomorphology is widely used to study active tectonic by a lot of scholars.In this paper,based on the GIS platform and the ASTER-30m DEM data,combining with field geological investigation,we use the multiple watershed index quantitative analysis method and the layered geomorphology deformation analysis method(including the planation and the river terrace)to study the differential uplifting around the eastern Himalayan syntaxis and attempt to find its tectonic controlling factors.In the aspect of watershed index,we calculated the Hypsometry Index(HI),the Bifurcation Ratio(Rb).the Steep Index(Ksn).the Asymmetry Index(T-factor),the Geomorphic Information Entropy(H).etc.,and analysis the distribution pattern of the index value.In the aspect of the planation,we extracted the highest level planation surface in the study area,and analysis its tectonic deformation pattern.In the aspect of river terrace,we interpreted several grades of terraces on both side along segment of the Yarlung Zangbo river from Milin to Pai,established the river terrace sequence and analysis its tectonic deformation combining with field geological investigation.Through the synthetic study of several aspects above,we identity five strong uplifting area.The first area is located on the right side of the Cuona-Woka rift valley which lies at the easternmost of the Southern Tibet Detachment System(STDS),and it resulted from the uplifting of the tilted end of the faulted block which controls the right marginal normal fault of the Cuona-Woka rift.The second and third area are respectively located at the bothsides of the big bend of the Yarlung river,and they resulted from NE strong pushing of the eastern horn of the Indian Plate.The fourth area is located at the converge end of the Jiali and the Nujiang fault.and it resulted from the compression at the converge area of two fault with the same right lateral slip.The fifth area is located between the Indus-Tsangpo Suture(ITS)and the south branch of the eastern segment of the Jiali fault,and it resulted from the squeezing out and uplifting of relative terrane during the subduction of the NE projecture part at the east of the Indian Plate.Through the research of this paper.we found that the watershed index can indicate regional differential uplifting to a certain degree.and synthetic quantitative analysis of multiple indices can distinguish differential uplifting well.The watershed index and the layered geomorphic surface usually correlate well to each other.In the strong uplifting region,if the layered geomorphic surface bends upward or uplift.then the watershed index will increase or will be abnormal.and vice versa.Therefore,the synthesis of the watershed index quantitative analysis and the layered geomorphic surface deformation analysis can effectively identify the scale,degree and pattern of the strong or weak uplifting zones in the region.