The Cenozoic elevation history of the southeast margin of the Tibetan Plateau

Tuesday, 16 December 2014: 4:15 PM
Gregory D Hoke, Syracuse University, Earth Sciences, Syracuse, NY, United States, Michael T Hren, University of Connecticut, Center for Integrative Geosciences, Groton, CT, United States, Jing Liu-Zeng, Institute of Geology, China Earthquake Administration, Beijing, China, Gregory Wissink, Syracuse University, Syracuse, NY, United States and Carmala N Garzione, University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY, United States
The shallow topographic gradient of the southeastern margin of the Tibetan Plateau has captured the attention of Earth scientists for decades. The area is host to a complex system of long-lived stike slip fault systems, including the Red River fault system. Likewise, the large areas of low-relief landscapes are perched above deeply incised rivers. Both have been proposed to hold clues related to the timing and magnitude of topographic growth of the southeast margin. The presence of the low relief landscape, in concert with the low topographic gradient led to the interpretation of late Miocene lower crustal flow as the mechanism for surface uplift. Surface uplift was also linked to regional drainage reorganization. This study examines the topographic evolution of the southeast margin of the Tibetan Plateau throughout the Cenozoic using stable isotope paleoaltimetry of pedogenic carbonates and leaf waxes preserved in Cenozoic basins extending from the northern to the southern portions of the SE margin of the Tibetan Plateau (Yunnan and Sichuan Provinces, China). Isotope– elevation relationships are determined from a modern sampling transect along the Lancang (Mekong) River and an estimated Eocene Rayleigh fractionation model that was randomly resampled. Paleoelevations are calculated using a Monte Carlo simulation of the normally distributed uncertainties in each parameter used to calculate elevations from the oxygen isotopic value of pedogenic carbonate and hydrogen isotopic value of plant waxes. Elevations calculated by each method indicate the SE margin of Tibet was at its present elevation as early as the late Eocene, with elevations of 3.3 km as far south as the northern third of China’s Yunnan Province. This result expands the extent of the Eocene Tibetan Plateau more than 1000 km east of that previously known and precludes Miocene surface uplift via lower crustal flow in the area of SW Sichuan and Northern Yunnan as a driver for drainage reorganization and an observed middle to late Miocene pulse of rapid exhumation. Elevation estimates from the southern two thirds of the study area parallel to the Red River Fault suggest approximately 1 km of post late Miocene surface uplift, consistent with estimates from previous geomorphic studies in the Red River.