Collaborative Research: Investigating Mesozoic Deformation in the Pamir: Implications for Crustal Thickening in the Pamir and the Evolution of the Tibetan Orogen

本研究的目的是了解作为喜马拉雅-西藏造山带西端的帕米尔中南部地区中生代地壳缩短的时间和幅度。喜马拉雅—青藏造山带是印度板块与欧亚板块汇聚而形成的大陆碰撞山带的典型代表。传统的地质认识表明，大部分隆升发生在新生代。相反，主要研究人员假设该地区岩石记录的地壳缩短和增厚大部分发生在晚侏罗世至中白垩世。为了验证这一假设，pi将进行多学科调查，包括地质和构造制图、地层分析、地质年代学和热年代学定年。该项目的研究成果将为了解喜马拉雅-西藏造山带帕米尔地区的构造演化提供新的思路。除了研究的科学目标外，该项目还有助于培养研究生和本科生在地球科学领域的前沿研究，这是一个重要的STEM学科。该项目将有助于扩大代表性不足的群体对地球科学的参与，这是一项重要的社会成果。该项目将促进美国、意大利和塔吉克斯坦研究人员之间的国际合作，并将在两所美国大学之间建立重要的机构合作。该项目将包括外联工作，包括为杜尚别大学的学生举办关于帕米尔地质的讲座和讲习班，以促进这个发展中国家的地球科学教育和科学素养。研究成果将发表在同行评议的科学文献中，并在专业学会会议上发表；同位素和地球化学数据将存档在基于网络的社区数据库中。在过去的十年中，越来越多的证据表明，青藏高原大部分地壳的缩短和增厚发生在白垩纪，早于印度和亚洲之间的新生代碰撞。然而，在整个造山带上，前新生代的缩短和增厚在横向上是多么广泛，或者在空间上是如何变化的，目前还不清楚。这项研究将为青藏造山带西部广大地区地壳缩短的时间和幅度提供重要信息，并解决有关青藏造山带前新生代变形沿走向连续性的重要问题。此外，尽管在中新世至新近片麻岩丘中记录了帕米尔高原新生代地壳增厚，但早期对上地壳缩短幅度的计算被证明明显高估了，这提出了关于新生代地壳增厚机制的重要问题（即逆冲作用与纯剪切增厚）。这一结果也将为理解帕米尔地区地壳增厚的机制提供新的信息。本研究的具体目标包括验证帕米尔高原中南部大部分地壳缩短和增厚发生在中生代（而不是先前解释的新生代）的假设，并代表了西藏记录的广泛的晚侏罗世-中白垩世地壳缩短和增厚的沿走向延续。该项目将包括详细的地质测绘和结构分析，以评价帕米尔高原的地壳缩短；对全区发现的粗大陆源矿床进行地层分析，评价其是否与区域缩短构造同构造；对粗大陆源矿床进行地质年代学（碎屑U-Pb锆石）和热年代学（碎屑白云母40Ar/39Ar定年和碎屑AFT/AHe双定年）分析，确定沉积年龄，评价区域缩短时间；参与区域缩短的基底地体的热年代学分析，以评估与缩短相关的发掘时间。

The objective of this proposal is to understand the timing and magnitude of Mesozoic crustal shortening that has occurred within the Central and Southern Pamir region as the western end of the Himalayan-Tibetan orogenic belt. The Himalayan-Tibetan orogen is the classic example of a mountain belt that has formed by continent-continent collision due to the convergence of the Indian and Eurasian tectonic plates. Conventional geologic understanding suggest that most of the uplift is occurred during the Cenozoic. In contrast, the principal investigators hypothesize that much of the crustal shortening and thickening recorded by rocks in this area occurred during Late Jurassic to middle Cretaceous time. To test this hypothesis, the PIs will conduct a multidisciplinary investigation that will involve geologic and structural mapping, stratigraphic analysis, geochronologic and and thermochronologic dating. The results of this project will provide new insights in to the understanding of the tectonic evolution of the Pamir region of the Himalayan-Tibetan orogenic belt. In addition to the scientific goals of the research, the project is contributing to the training of graduate and undergraduate students in cutting-edge research in the geosciences, an important STEM discipline. The project will contribute to the broadening of participation of underrepresented groups in the geosciences, which is an important societal outcome. The project will facilitate international collaboration between researchers at U.S., Italy, and Tajikistan, and will build important institutional collaborations between two U.S. universities. The project will include outreach efforts that include lectures and workshops on the Geology of the Pamir for students at the University of Dushanbe in order to promote geoscience education and science literacy in this developing country. The outcomes of the research will be published in peer-reviewed scientific literature and presentations at professional society meetings; isotopic and geochemical data will be archived in web-based community databases.Over the last decade, increased evidence has shown that much of the crustal shortening and thickening in the Tibetan plateau is Cretaceous in age, pre-dating the Cenozoic collision between India and Asia. However, it is still unclear how laterally extensive, or spatially variable, pre-Cenozoic shortening and thickening is across the entire orogen. This study will provide important information on the timing and magnitude of crustal shortening over a broad region of the western portion of the Tibetan orogen and address important questions regarding the along-strike continuity of pre-Cenozoic deformation in the Tibetan orogen. Further, while significant Cenozoic crustal thickening in the Pamir has been documented in Miocene to Recent gneiss domes, early calculations of the magnitude of upper crustal shortening have been shown to be significantly overestimated, raising important questions regarding the mechanism of Cenozoic crustal thickening (i.e. underthrusting vs. pure shear thickening). The results of this will also provide new information in understanding the mechanisms of crustal thickening in the Pamir region. The specific goal of this study involves testing the hypothesis that much of the crustal shortening and thickening in the Central and Southern Pamir is Mesozoic in age (rather than Cenozoic, as previously interpreted) and represents the along-strike continuation of extensive Late Jurassic-middle Cretaceous crustal shortening and thickening documented in Tibet. The project will include detailed geologic mapping and structural analysis to evaluate crustal shortening in the Pamir; stratigraphic analyses of coarse terrigenous deposits found throughout the region to evaluate whether the deposits are syntectonic with regional shortening structures; geochronologic (detrital U-Pb zircon) and thermochronologic (detrital muscovite 40Ar/39Ar dating, and detrital AFT/AHe double dating) analyses of coarse terrigenous deposits to determine the age of deposition in order to evaluate timing of regional shortening; thermochronologic analyses of basement terranes involved in regional shortening to evaluate timing of shortening related exhumation.