Collaborative Research: Evaluating Ancestry of the Tibet Plateau: Did a Mesozoic Proto-plateau Exist?

尽管进行了大量的研究，但青藏高原何时以及如何达到其海拔高度是地球科学中一个尚未解决的重大问题。这部分是由于高原生长的早期历史是未知的。近年来，许多研究者强调了早新生代印度-亚洲碰撞对青藏高原抬升时间的影响；然而，这种海拔升高的力学模拟需要改进对印度与亚洲碰撞之前存在的初始边界条件的约束。该项目采用多学科检验假设，即在印度与亚洲碰撞之前，沿羌塘地体边界的中生代大陆-大陆碰撞系统导致地壳增厚，从而形成了原始高原。运用沉积学、地层学、构造学、稳定同位素古高程、地球化学、年代学、盆地模拟等方法，对西藏东南部中生代昌都盆地进行了印度碰撞前藏东上地壳构造重建。沉积研究的古环境资料揭示了干旱化模式，并与指示高原发育的模式进行了比较。通过对比昌都盆地沉积物源与周边构造高地的岩性及邻近变形带的构造运动学历史，模拟了该地区的构造演化和地表形态。利用古土壤碳酸盐的氧同位素组成来评估该地区的古高程历史，并发现可能的高原上升事件。记录青藏高原早期的演化历史，是解决若干具有科学和社会重要性的突出问题的必要条件。首先，研究结果提供了对初始输入参数的约束，这将改善高原发育力学模型的校准，以及该地区后来开始挤压构造的阈值条件。此外，青藏高原的地质历史被认为与气候模式的重大变化和海洋化学的大规模长期变化密切相关，这些变化是由于流入青藏高原的河流的化学物质造成的。由于岩石的化学侵蚀消耗了大气中的二氧化碳，对西藏高原广泛隆起地区的侵蚀，加上季风气候的加剧，是全球变冷的潜在驱动因素。最后，形成西藏地区的板块构造过程与今天运行的板块构造过程最相关，这些板块构造过程控制着全球主要地震、火山和滑坡灾害的分布，2008年以青藏高原东部边缘为中心的汶川地震凸显了这一点。本项目除科学目标外，还支持培养STEM学科的2名博士生和3名本科生。西弗吉尼亚大学（美国）、阿拉巴马大学（美国）和南京大学（中国）师生之间的科学合作是该项目的重要组成部分。

Despite much investigation, when and how the Tibet plateau attained its elevation is a major unresolved problem in Earth science. This is partly due to the fact that early history of plateau growth is unknown. In recent years, many researchers have emphasized the effects of early Cenozoic India-Asia collision on the timing of increased elevation of the Tibet plateau; however, mechanical modeling of this increase in elevation requires improved constraints on the initial boundary conditions that existed prior to the impingement of India with Asia. This project employs a multi-disciplinary test of the hypothesis that a proto-plateau resulted from crustal thickening due to Mesozoic continent-continent collisional systems along the Qiangtang terrane borderlands prior to the collision of India with Asia. Reconstructing the upper crustal configuration of eastern Tibet prior to the Indian collision is performed using methods in sedimentology, stratigraphy, structure, stable isotope paleoaltimetry, geochemistry, geochronology, and basin modeling of the Mesozoic Qamdo basin in southeastern Tibet. Investigations of paleoenvironmental data from study of sedimentary deposits reveal patterns of aridification to compare with those indicative of plateau development. Comparison of sedimentary provenance of Qamdo basin deposits with lithologies of surrounding structural highlands and the structural kinematic history of adjacent deformation belts is used to model tectonic evolution and surface configuration of the region. Oxygen isotopic composition of paleosol carbonates is employed to assess paleoelevation history of the area and detect possible episodes of plateau rise. Documenting this early history of Tibet plateau evolution is required to address several outstanding issues of scientific and societal importance. First, research results provide constraints on initial input parameters that will improve the calibration of mechanical models of plateau development, as well as the threshold conditions under which extrusion tectonism was later initiated in the region. Also, the geological history of the Tibet plateau is thought to be tightly linked to major changes in climate patterns and wholesale secular changes in ocean chemistry due to chemical influx from the rivers that drain the Tibet plateau. Because chemical erosion of rocks consumes carbon dioxide from the atmosphere, erosion of the widespread uplifted region of the Tibet plateau, enhanced by a monsoonal climate, is a potential driver of global cooling episodes. Finally, the plate tectonic processes that formed the Tibet region bear the most relevance to the plate tectonic processes operating today that control the distribution of major seismic, volcanic, and mass wasting (e.g., landslide) hazards around the globe, as highlighted by the 2008 Wenchuan earthquake centered on the eastern Tibet plateau margin. In addition to the scientific objectives of this project, it is supporting the training of two Ph.D. students and three undergraduate students in a STEM discipline. Scientific collaboration between students and faculty at West Virginia University (U.S.), the University of Alabama (U.S.), and Nanjing University (China), is an important component of this project.