Are Remnants of the Tibetan Plateau Preserved in the Southern Himalayan Thrust Belt?

University Of Arizona, Tucson AZ

Investigators

Abstract

The Himalaya of Nepal is one of Earth's most rugged and rapidly eroding landscape, with local relief greater than 5,000 meters and a morphology dominated by deep fluvial incision. This regional pattern of relief is broken in western Nepal, where the Bhumichula plateau represents a approximately 250 square kilomter area of low-relief (200-400 meters), but high-elevation (4200-4800 meters) ground isolated amidst surrounding deeply incised topography resembling that of Tibet. This projects investigates how and when the Bhumichula plateau formed. Determining whether the Bhumichula plateau formed as a low-elevation surface that was later uplifted and incised, or whether it was high standing from its earlier stages and part of a larger Tibetan plateau and was later modified by surface processes, is significant for the understanding of the mechanisms forming high topography on Earth. High elevation features such as the Himalaya and Tibet are a product of tectonic processes over geological time, which are responsible today for the location and magnitude of earthquakes. The Himalayas and Tibet also play a significant role on climate by driving the Asian monsoon and thus control the distribution of fresh water on our planet. Important societal outcomes deriving from this project include training of graduate students This project also supports the training of graduate and undergraduate students in an important science, technology, engineering and mathematics discipline (STEM), thereby contributing to the increased economic competitiveness of the United States. The project also contributes to the broadening of underrepresented groups in STEM, thereby promoting diversity in science. and minorities, female research scientists, and promotes diversity in science. It also is supporting the development of an online virtual field trip experiences for general education and upper division classes. This is a muldisciplinary invesgation that uses geological mapping, low-temperature thermochronology, cosmogenic nuclide dating, geomorphological analysis, stable isotope paleoaltimetry, and 40Ar/39Ar geochronology to determine the age of basement rocks, the timing of deformation, erosion/incision and uplift of the Bhumichula plateau in western Nepal. Although other low-relief, high-elevation surfaces have been identified in the Himalaya, none has been investigated with the complete array of methods to be employed in this work. A principal goal of the project is to establish a workflow for how to analyze and interpret these low-relief surfaces in general, which are common features in the Himalaya to the east of Nepal. This study is the first attempt to apply such a wide array of techniques to unravel the history of landscape development in the India-Asia collisional environment, including the first attempt to determine paleoelevation on the southern slope of the Himalaya. Three main hypotheses will be tested: (1) BP formed as a low-elevation surface that was uplifted to high elevation and incised by antecedent and headward eroding rivers; (2) the BP is a remnant of a once much larger paleo-Tibetan landscape that reached nearly to the front of the Himalaya during the Miocene, and has been etched northward by headward erosion since that time; and (3) the BP formed in response to drainage reorganization and feedbacks between drainage area, erosion, and elevation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.