Lithospheric Dripping in Central Tibet: Underappreciated Factor in Orogenic Plateau Development?

西藏中部岩石圈滴水：造山高原发育过程中被低估的因素？

• 批准号: 2048656
• 负责人: Paul Kapp
• 金额: $ 44.32万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-06-15 至 2025-05-31
• 项目状态: 未结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2048656&HistoricalAwards=false
• 关键词: Lithospheric; Dripping; Central; Tibet; Underappreciated

The lower part of a continental plate is more dense than underlying asthenosphere. If it gets thickened as a result of plate convergence, such as within the India-Asia collision zone, it may become gravitationally unstable and sink into the deeper mantle as a large sheet or smaller-sized drips. This project will test the hypothesis that 45-20 million year old elliptical-shaped basins in central Tibet formed above sinking lithospheric drips, while mantle-derived volcanic rocks simultaneously erupted along the basin-bounding topographic bulges. If validated, the lithospheric drip theory would provide an appealing mechanism to explain the multitude of enigmatic elliptical basins found in all of Earth’s major orogenic plateaus. In collaboration with the University of Arizona’s Assistant Dean of Military and Veteran Engagement, this project will engage three undergraduate-student veterans in geological field and laboratory research. Military veterans are returning from active duty to college in increasing numbers and are underrepresented in the Science-Technology-Engineering-Math workforce. The effectiveness of the student-veteran engagement program will be assessed, along with which factors influence veteran career pathways, by delivering entrance and exit surveys. The project will also train two graduate students and facilitate continued academic, scientific, and cultural exchange among people and institutions in the United States, China, and Tibet.In addition to the lithospheric drip theory, the project will test the alternative hypotheses that Cenozoic shortening, volcanism, and basin formation in central Tibet are manifestations of (i) southward propagation of regional (600 km long) thrust systems and lithospheric thickening followed by lithospheric root removal or (ii) long-lived (active from Eocene through early Miocene time) ~200-250-km-long thrust belts and associated flexural loading across central Tibet, with unrelated mantle processes generating localized volcanic highlands. The hypotheses make distinct predictions about the temporal-spatial distribution of shortening, age of shortened basin fill relative to the age of adjacent volcanic rocks, basin geometries and the nature of their margins, and sedimentary provenance and dispersal patterns. A combination of geological mapping, basin analysis, structural analysis and restorations, and U-Pb igneous and detrital zircon geochronology will be employed to test these predictions. Field research will include the principal investigators, graduate students, undergraduate student-veterans, and collaborators from the Institute of Tibetan Plateau Research in Beijing, and will focus on Cenozoic geology within and between three basins in central Tibet. The spatial coverage will permit assessment of whether (i) shortening structures are localized to the basins or extend regionally along strike, (ii) the basins were previously integrated as long and narrow E-W or more regional basins, or developed throughout their history as isolated depocenters, and (iii) maximum basin subsidence and shortening were coeval with eruption of adjacent volcanic rocks. Ultimately, insofar as Tibet is the world’s archetypical collisional plateau, project results will have relevance for other orogenic plateaus worldwide.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.

大陆板块的下部比下面的软流圈更致密。如果它由于板块汇聚而变厚，比如在印度-亚洲碰撞带内，它可能会变得重力不稳定，以大片或小水滴的形式下沉到地幔深处。该项目将检验这样一种假设，即西藏中部4500万-2000万年前的椭圆形盆地形成于下沉的岩石圈滴上方，而地幔火山岩同时沿着盆地边界的地形隆起喷发。如果得到证实，岩石圈水滴理论将提供一个吸引人的机制来解释地球上所有主要造山带高原上发现的众多神秘的椭圆盆地。该项目与亚利桑那大学负责军事和退伍军人事务的助理院长合作，将邀请三名本科生退伍军人参与地质领域和实验室研究。越来越多的退伍军人从现役回到大学，他们在科学-技术-工程-数学劳动力中的代表性不足。通过提供入学和离职调查，将评估学生-退伍军人参与计划的有效性，以及影响退伍军人职业道路的因素。该项目还将培养两名研究生，促进美国中国和西藏人民和机构之间持续的学术、科学和文化交流。除了岩石圈滴流理论外，该项目还将检验另一种假说，即西藏中部的新生代缩短、火山作用和盆地形成是(I)区域性(600公里长)逆冲系统的南向传播和岩石圈增厚，然后岩石圈根部剥离或(Ii)长达200-250公里的逆冲带和相关的挠曲载荷横跨西藏中部，与之无关的地幔过程产生局部火山高地。这些假设对缩短的时空分布、缩短的盆地充填相对于邻近火山岩的年龄、盆地几何形状及其边缘的性质以及沉积物源和扩散模式做出了明确的预测。将结合地质填图、盆地分析、构造分析和恢复，以及U-Pb火成岩和碎屑锆石年代学来验证这些预测。实地研究将包括来自北京青藏高原研究所的首席研究员、研究生、本科生退伍军人和合作者，并将重点研究西藏中部三个盆地内部和之间的新生代地质。空间覆盖范围将使我们能够评估：(1)缩短构造是局限于盆地还是沿走向在区域上延伸；(2)盆地以前是作为狭长的东西向或更多的区域盆地整合在一起的，或者在其整个历史上作为孤立的沉积中心发展的；(3)最大盆地沉降和缩短与邻近火山岩的喷发是同时发生的。最终，由于西藏是世界典型的碰撞高原，项目成果将与世界各地的其他造山高原相关。该奖项反映了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，被认为值得支持。

项目成果

Where did the Arizona‐Plano Go? Protracted Thinning Via Upper‐ to Lower‐Crustal Processes

• DOI: 10.1029/2021jb023850
• 发表时间: 2022-03
• 期刊: Journal of Geophysical Research: Solid Earth
• 作者: G. Jepson;B. Carrapa;S. George;L. Reeher;P. Kapp;G. Davis;S. Thomson;C. Amadori;C. Clinkscales;Sean Jones;A. Gleadow;B. Kohn