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

尼泊尔的喜马拉雅是地球上最崎岖和侵蚀最快的地貌之一，当地地貌起伏超过5000米，地貌以深深的河流切割为主。这种地区性的地貌模式在尼泊尔西部被打破，那里的Bhumichula高原代表着大约250平方公里的低地势(200-400米)，但高海拔(4200-4800米)的地面孤立在与西藏相似的深深切割的地形中。这个项目调查了Bhumichula高原是如何以及何时形成的。确定Bhumichula高原是作为后来被抬升和切割的低海拔表面形成的，还是从早期阶段和更大的青藏高原的一部分形成的高海拔，后来被表面过程改造，对于理解地球上形成高地形的机制具有重要意义。喜马拉雅和西藏等高海拔地貌是地质时期构造作用的产物，这些构造作用决定了今天地震的位置和强度。喜马拉雅山脉和西藏也通过驱动亚洲季风对气候起着重要作用，从而控制着我们星球上淡水的分配。该项目产生的重要社会成果包括对研究生的培训该项目还支持对一门重要的科学、技术、工程和数学学科(STEM)的研究生和本科生进行培训，从而有助于提高美国的经济竞争力。该项目还有助于扩大STEM中代表性不足的群体，从而促进科学多样性。和少数民族，女性研究科学家，并促进科学多样性。这是一项多学科的调查，利用地质制图、低温热年代学、宇宙核素测年、地貌分析、稳定同位素古高度学和40Ar/39Ar年代学来确定尼泊尔西部Bhumichula高原的基岩年龄、变形、侵蚀/切割和隆起的时间。尽管在喜马拉雅山脉已经发现了其他低起伏、高海拔的表面，但还没有一种完整的方法来调查这项工作。该项目的一个主要目标是为如何分析和解释这些低起伏地表建立一个总体工作流程，这些低起伏地表是尼泊尔东部喜马拉雅山脉的共同特征。这项研究是首次尝试应用如此广泛的技术来揭示印度-亚洲碰撞环境中的景观发展史，包括首次尝试确定喜马拉雅南坡的古海拔。将检验三个主要假说：(1)BP形成为低海拔表面，上升到高海拔，并被先前和逆流侵蚀的河流切割；(2)BP是曾经更大的古西藏景观的遗迹，在中新世几乎延伸到喜马拉雅山脉前面，自那时以来一直被逆流侵蚀向北侵蚀；以及(3)BP是为应对排水重组和流域区域、侵蚀和高程之间的反馈而形成的。这一裁决反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，认为值得支持。

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.