Uplift Of The Eastern Margin Of Tibetan Plateau And Its Impact On River Network Pattern And Landscape Formation

The eastern margin of the Tibetan plateau is characterized by dissected landscape where large rivers incise into the regionally distributed high-elevation,low-relief surfaces which have been elevated due to the continuous convergence between India and Eurasia.Beyond that,this region is also featured by peculiar river patterns where river capture has been proposed to have occurred.In this thesis,the author focuses on the Dadu and Anning Rivers,two major tributaries of the Yangtze River,draining on the eastern plateau margin,aiming to characterize the incision history of the Dadu River,investigate the potential capture between Dadu and Anning Rivers and its impact on the development of the regional topography and to constrain the uplift history of the eastern Tibetan plateau margin.To constrain the incision history of the Dadu River,a combination of bedrock lowtemperature thermochronometers,in particular,Apatite(U-Th)/He(AHe)and Zircon(UTh)/He(ZHe),was used.The AHe and ZHe ages reveal incision of the Dadu River in the Late Miocene which is synchronous with onset of exhumation in other regions on the eastern plateau margin,indicating regional tectonic uplift in triggering river incision.To investigate the potential capture between the Dadu and Anning Rivers,we performed detrital zircon UPb dating on modern sand samples from the Dadu River,Anning River and on the Pliocene samples of the Xigeda formation.The data indicate that the Pliocene sediments deposited along the Anning River have similar U-Pb age pattern as the modern Dadu River,suggesting a connection between the Dadu and Anning rivers during the deposition of the Xigeda formation and a subsequent cutoff of this connection after.By comparing with the regional fault movement history,we infer that this capture is associated with the movement of the Daliang Shan fault.This is further supported by topographic analysis of the Dadu River drainage basin where the spatial patterns of the topographic metrics such as hypsometric curve and hypsometric integral(HI),stream length gradient(SLK),topographic slope,topographic relief reveal rejuvenated landscape either due to temporally and spatially variable uplift rates with high uplifted localized along the Xianshuihe fault or due to river capture.To constrain the uplift history of the eastern Tibetan Plateau margin,a linear inversion approach was used.The results show that acceleration of uplift rate started at 10 Ma in the Dadu river drainage basin and since then uplift rate increased gradually from <0.1 mm/yr to 2.1mm/yr at present.Altogether,our results suggest that the eastern Tibetan plateau margin was uplifted since the Late Miocene(~10 Ma)which has triggered rapid incision of the Dadu River.However,the landscape has also been modified by river capture associated with the movement of the local fault which postdates the regional tectonic history and results in transient landscape.