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Professor Michael E. Oskin from the University of California, Davis visits our institute for exchange

2019/11/28 15:12:54

At the invitation of distinguished researcher Liu Jing of the State Key Laboratory of EarthquakeDynamics, Professor Michael E. Oskin from the University of California, Davis visited our institute for exchange from October 12 to 24, 2019. During the visit, he and the members of Liu Jing’s working group conducted a field geological survey of the active faults, river and lacustrine deposition, and geomorphology in the Jinsha River Basin, as well as a river terrace in the Lancang River Basin.

Figure.1 Field photographs of lacustrine and fluvial deposits preserved along the Jinsha River

The southeastern edge of the Qinghai–Tibet Plateau is a slow-falling plateau boundary, which has developed as antransient landform with a high altitude, a low relief residual landform, and a deep valley. It is a natural laboratory for studying the geomorphology, morphology, and evolution of an active orogenic belt, as well as the interaction between structure, surface processes, and climate. Liu Jing’s working group has carried out structural geomorphology research in the region, including digital geomorphology analysis, paleoheight reconstruction, quantification of erosion rates on different time scales (including investigation of low-temperature thermal chronology, river terraces, and the concentration of 10Be of the cosmogenic nuclide in the modern river sand), and numerical simulation of geomorphological evolution. Research results have been published in Earth and Planetary Science Letters, Tectonics, Geophysical Research Letters, Tectonophysics, Lithosphere, and other international journals. The relationship between the evolution of the water system in southeast Tibet and active faults has always been controversial; this time, we performed a collaborative study.We investigated the late Cenozoic activity of active faults across the Jinsha River, and we also investigated the filling records of lacustrine and fluvial facies valleys and river terraces preserved along the Jinsha River, carried out a targeted field investigation, and discussed the dating scheme of sediment burial time and geomorphic surface abandonment time. Michael E. Oskin suggested that we conduct detailed field mapping of the study area; in addition, he provided many constructive suggestions on the identification, division, and spatial correlation of lake-related shorelines and underwater sediments, with qualitative identification based on the terrace soil profile and the relative sequence of terrace division.

Since 2014, Zhang Jinyu and colleagues have carried out field investigation and dating of river terraces along the Lancang River, and obtained a relatively reliable rate of river cutting from Mangkang to Deqin. However, the Lancang River in the section from Lanping to Yunlong has a wide channel, multistage river deposits on both banks and the broad terraces, and a complex history of river aggradation and downcutting; thus, dating work has encountered a bottleneck, and it has not been possible to determine the downcutting rate of the river reliably. During the joint expedition, Professor Michael E. Oskin examined the sedimentary features of the bedrock and terrace sediments, dating samples, and other details, and proposed a systematic sampling scheme to help determine the formation time of these terraces.

The success of this joint investigation has laid a good foundation for further research on active structures and river landforms in this area, and the two parties have confirmed their intentions to continue cooperating closely in the follow-up cooperative research and joint training of talent.