The collision of India and Asia is the archetype of continent-continent collision in plate tectonics and is responsible for the development of the 5 km high Tibetan Plateau. Most of the Plateau?s margin is bounded by steep, fault-bounded topographic fronts (e.g. the Himalaya), yet the southeastern Plateau margin is a diffuse boundary with major faults that parallel the topographic gradient. A team of researchers from Syracuse University and the University of Rochester, in collaboration with scientists from the Chinese Institute for Tibetan Studies, will utilize sedimentary rocks preserved on the southeastern margin of the Tibetan Plateau to examine the history of regional drainage basin evolution and the formation of high topography in this area, located near Kunming, Yunnan Province, China.
River sandstones are a mixture of sediment from erosional source regions upstream in a watershed. The range of crystallization age and thermal exhumation ages of the mineral zircon, found within sandstones, provides a fingerprint of the areas being eroded. Changes in the signature of zircon ages in sandstones of known depositional age will be used to trace the changes in sediment source as river networks eroded distinct bedrock source areas.
Minerals and plant organic matter record information about earth?s surface conditions over the time in which they formed. The variation in the oxygen isotopic composition of meteoric (precipitation and surface) water is, in part, sensitive to elevation. The isotopic composition of meteoric water is recorded in mineral and plant material, and can be used to decipher the elevation of the ground surface where the plant grew and/or the minerals formed. The organic matter from soil microbes is distinct from that of plants, and the bond arrangement reflects soil temperature, another parameter sensitive to elevation. Over a vertical succession, sedimentary rocks containing appropriate material can be used to reconstruct how elevations changed over time. A principal goal of this research is to reconstruct the elevation history of the SE margin of the Tibetan Plateau over the past 40 million years. Elevation, a key geophysical parameter, is a critical constraint for unraveling the processes by which the earth?s crust evolves.
This research will address a major outstanding question in continental tectonics: how do diffuse margins of plateaus form? One of the leading hypotheses for the formation of the southeastern Tibetan Plateau margin suggests that a weak, plastically deforming lower crust flows from the adjacent high Plateau toward the edges. By unraveling both the change in sediment sources and elevation history it will be possible to constrain the timing, rate and process by which this type of plateau margin develops, while at the same time testing the viability of the lower crustal flow hypothesis. The results of the study will have implications beyond continental tectonics, as it is hypothesized that the Tibetan Plateau has a major influence on global climate.
This project is supported by the Tectonics Program in the Earth Sciences Division and the East Asia and Pacific Program in NSF's Office of International Science and Engineering.
A team of Earth scientists from 3 American Universities and the Chinese Earthquake Administration conducted a 4-year study of the southeastern margin of the Tibetan Plateau located in the Sichuan and Yunnan provinces of China. The southeast Plateau margin represents an anomaly in the overall topographic form of the Tibetan Plateau and has inspired many competing scientific hypotheses for how the Tibetan Plateau developed in time, spatial extent and topography. The overarching goal of the study was the determine the Cenozoic (last 65 million year) topographic evolution of the region as a means for discriminating between the competing models of how the Tibetan Plateau developed. Subordinate scientific goals were a) to determine how the drainage routing changed for the four major rivers running through the study area, in particular, if all the regional rivers were part of a unified river network approaching the scale of the Mississippi River basin? b) how quickly is the landscape eroding in the southeast margin in response to topographic change? c) how quickly is the Yangtze River cutting its valley near its enigmatic, hairpin, first bend? and d) What are the dominant sources of precipitation to the southeastern margin of the Tibetan Plateau and what is its stable isotope signature? Executing the research required a total of 4 months of field study divided into thee separate trips to Yunnan and Sichuan Provinces, China for sample collection and measurement and description of Cenozoic sedimentary rocks. The research team also collected modern river sands, modern river water samples and deployed 12 rainfall collection stations from the border with Vietnam into southeastern part of the Xinjiang Autonomous Region (Tibet). Nearly 400 samples were collected and more than 6000 vertical feet of rock were described. The majority of samples were prepared and analyzed at the University of Rochester and Syracuse University. Additional laboratory facilities were utilized at 4 universities in the United States and international institutions in the European Union. This project successfully achieved its main goal by determining the elevation history of the southeastern margin of the Tibetan Plateau. The research team was able to demonstrate that the northern part of their study area has been at or near its present elevation since ~ 40 Ma (the Eocene Epoch). The southern part of the study area appears to have experienced an increase in the mean surface elevation of ~ 1 km since ~12 Ma (the late Miocene). These results, when combined with other studies from the central portion of the Tibetan Plateau, definitively extend the boundary of the early Tibetan Plateau some 1000 km (600 miles) eastward than previously known. This result implies that at least the southern portion of the Tibetan Plateau grew quickly in response to the collision of the Indian sub-continent with Eurasia. The subordinate scientific goals of the project were also successful. Highlights from these secondary scientific goals include the development of a new research tool for tracking sediment sources and the determination that the entire southeastern margin of Tibet is eroding at a rate of ~ 1 cm per century. This project provided direct training and development opportunities for several personnel at Syracuse University, including 3 undergraduate students, 1 graduate student, 1 postdoctoral scholar and an early career professor of Earth science. Two Syracuse University undergraduates received extensive training in rock sample preparation techniques and the use of geographic information systems to create maps and compile spatial information. One undergraduate traveled to China and participated in field studies with the doctoral student and the principal investigator. The doctoral student’s dissertation topic was molded around objectives to the project and he received thorough mentoring and professional development opportunities throughout the prescribed program of study that will culminate in the production of a versatile PhD level scientist. The postdoctoral scholar received mentoring and training from the project’s principal investigator that built upon that individual’s existing research portfolio. All project participants engaged in direct scientific exchange with Chinese scientists and graduate students while in China and at home, forming the foundation for continued scientific exchange with China. Finally, this project helped the Principal Investigator, an assistant professor at Syracuse University, begin to establish a strong, competitive research program.
