Collaborative Research: Did the Pamir Gneiss Domes and Salient form by Northward Underthrusting of India or Southward Subduction and Rollback of Asia?

合作研究：帕米尔片麻岩穹丘和突出部是印度向北俯冲形成还是亚洲向南俯冲和回滚形成的？

• 批准号: 1419751
• 负责人: Bradley Hacker
• 金额: $ 17.38万
• 依托单位: University of California-Santa Barbara
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2014
• 资助国家: 美国
• 起止时间: 2014-09-01 至 2017-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1419751&HistoricalAwards=false
• 关键词: Collaborative; Research; Did; Pamir; Gneiss

The aim of this project is to better understand how the moving plates that compose the outer rigid shell of the solid Earth behave. These plates may be composed of dense oceanic rock that underlies the deep oceans and/or more buoyant continental rock that makes up landmasses. For decades, it has been recognized that oceanic plates readily sink (subduct) into the Earth along subduction zones, which produce planar zones of earthquakes at depth. More recently, it has been appreciated that continental plates can also subduct deep into the Earth, but how they do so and what drives this process are poorly understood. The best example of active continental subduction is where the Indian plate is moving northward and colliding with the Eurasian plate, resulting in continued development of the Himalaya Mountains, Tibetan Plateau, and Pamir Mountains to the west. East of the Pamir Mountains, there is growing evidence that India is subducting northward beneath Eurasia, but there are only rare earthquakes at depths commonly observed in oceanic subduction zones. The only subduction-like zone of seismicity within a continent on Earth is located beneath the Pamir Mountains, which is the focus of this study. Unlike the case to the east, however, the seismicity is suggestive of southward subduction of the Eurasian plate. In this study, the principal investigators will test two hypotheses for why the Eurasian plate is subducting southward. The first is that the Indian plate has inserted itself into the Eurasian plate, like a wedge splitting a piece of wood, forcing the lower part of the Eurasian plate to subduct. The second hypothesis is that one of several processes could have abruptly increased the density contrast between the the Eurasian plate and deeper Earth beneath it, causing it to subduct rapidly, perhaps initially at rates greater than the rate of the northward motion of India. These hypotheses make contrasting predictions for the geological history of the high Pamir in Tajikistan, which we will test by quantifying the history of faulting, determining the age of the rocks and when and how fast they were brought from depth to the surface, and constraining where the rocks came from. Both of the hypotheses are novel compared to those that have been raised previously for the Pamir or India-Eurasia collision zone to the east. Validating either would thus provide documentation of an underappreciated behavior of continental subduction. In addition to the scientific goals of the project, the proposal contains educational and outreach components that are multifaceted and of societal relevance. They include the training and mentoring of graduate and undergraduate students in a STEM discipline, which will contribute to workforce development in a field (geosciences) that is expanding to address important national needs and challenges. The project is also facilitating scientific exchange between people and institutions in the United States and Tajikistan?the most impoverished country in central Asia whose stability depends heavily on foreign investment. The project is promoting cross-cultural understanding between American and Tajiks and geographic and scientific awareness by giving presentations in multiple venues that encompass culture, geography, and Earth science to local communities. The project will also support outreach activities aimed at advancing scientific understanding and sustainability for Americans for the local Tucson community, including lectures and field trips into the mountains for secondary school students and teachers and constructing an exhibit to be displayed at the University of Arizona's Flandrau Science Center, and for the annual Tucson Gem and Mineral Show--the largest show of its kind in the world.This project is investigating the metamorphic, structural, and magmatic evolution of Cenozoic gneiss domes in the Pamir to test their potential linkages with Miocene to Recent development of the Pamir salient, northward underthrusting of India, and southward subduction of Asian lithosphere. The Pamir orogen is distinguished by a pronounced, northward-convex salient and a spatially extensive, orogen-parallel suite of gneiss domes. Both the salient and gneiss domes are thought to have developed synchronously, largely since Oligo-Miocene time. The thick crust (greater than 65 kilometers) of the Pamir is underlain in the south by a high-velocity mantle interpreted to be northward underthrust Indian lithosphere, and in the north by a southward-dipping zone of intermediate-depth seismicity that has been attributed to intracontinental subduction of Asian lithosphere. This project is testing two end-member 'tectonic drivers' that may genetically link all of these features: (1) A short-lived phase of rapid northward rollback/retreat of a southward-subducting slab of Asian lithosphere, during which the Pamir gneiss domes were exhumed by significant North-South horizontal extension (approximately 140 kilometers) and growth of the Pamir salient. (2) A protracted phase of northward underthrusting/wedging of Indian lithosphere that forced vertical exhumation of Asian mid-crust above it and southward subduction of Asian lithosphere beneath it. These two end-member hypotheses are not mutually exclusive, nevertheless, they make contrasting orogen-scale predictions that can be tested with geologic investigations. We are testing the predictions for the kinematic, metamorphic, and magmatic evolution of the gneiss domes. Our approach integrates geologic mapping and structural analysis to constrain the kinematics of gneiss-dome exhumation; metamorphic petrology, U/Th-Pb geochronology + trace element analyses to quantify the history of prograde and retrograde metamorphism; moderate- and low-temperature thermochronology to quantify the history of exhumation; and U-Pb geochronology and isotope analysis of zircon (hafnium) and titanite (neodymium) to constrain the history and sources of Cenozoic magmatism.

该项目的目的是更好地了解如何构成固体地球外壳的移动板。这些盘子可能由茂密的海岩组成，其构成了深海和/或构成陆地的浮动大陆岩的基础。几十年来，人们已经认识到，海洋板很容易沿着俯冲带沿俯冲带中沉入地球，后者在深度产生地震的平面区域。最近，人们对大陆板也可以深入地球上的俯冲，但是它们是如何做到的，而驱动这一过程的驱动方式也很少理解。主动大陆俯冲的最好例子是印度板块向北移动并与欧亚板块相撞，从而导致喜马拉雅山，藏族高原和帕米尔山的持续发展。在帕米尔山（Pamir Mountains）以东，有越来越多的证据表明印度在欧亚大陆下方向北俯冲，但在海洋俯冲带中通常观察到的深处只有罕见的地震。地球上一个大陆内唯一的地震性带位于帕米尔山（Pamir Mountains）下方，这是本研究的重点。但是，与东方不同，地震性暗示着欧亚板块的南向俯冲。在这项研究中，首席研究人员将检验两个假设，说明为什么欧亚板块向南俯冲。首先是印度板将自己插入欧亚板块，就像楔形的一块木头一样，迫使欧亚板的下部到达托运。第二个假设是，几个过程之一可能会突然增加欧亚板块和更深的地面之间的密度对比度，从而使其迅速降低，也许最初以大于印度北部运动速度的速度大。这些假设对塔吉克斯坦高帕米尔的地质历史进行了对比预测，我们将通过量化断层的历史，确定岩石的年龄，何时以及它们从深度带到表面的速度以及约束岩石的来源来测试。与先前为东部的帕米尔或印度 - 欧洲碰撞区提出的假设相比，这两个假设都是新颖的。因此，验证这两个都将提供有关大陆俯冲行为不足的文档。除了该项目的科学目标外，该提案还包含多方面和社会相关性的教育和外展成分。其中包括在STEM学科中对研究生和本科生的培训和指导，这将有助于在一个领域（地球科学）中发展以应对重要的国家需求和挑战的领域（地球科学）。该项目还促进了美国和塔吉克斯坦人民与机构之间的科学交流？中亚最贫穷的国家，其稳定在很大程度上取决于外国投资。该项目通过在涵盖文化，地理和地球科学的多个场所进行演讲，促进美国和塔吉克人之间的跨文化理解以及地理和科学意识。该项目还将支持旨在促进美国图森当地社区的科学理解和可持续性的宣传活动，包括讲座和实地考察中学生和老师的山脉，并在亚利桑那大学的弗兰德拉大学的弗兰德拉科学中心以及为年度图森宝石和矿物展览会上展出的展览，并在弗兰德拉斯大学的范围内进行了调查。帕米尔（Pamir）在帕米尔（Pamir）中岩浆片麻岩圆顶的岩浆进化，以测试其与中新世的潜在联系，以与帕米尔（Pamir）显着发展，印度北部北部的北部以及亚洲岩石圈的俯冲。 Pamir造山基因以明显的，北向凸的显着性和空间广泛的片麻岩圆顶植物套件来区分。显着和片麻岩的圆顶都被认为是同步发展的，这主要是自寡新世时代以来。帕米尔（Pamir）的厚地壳（大于65公里）在南部的底线是由高速披风解释为向北的印度印度岩石圈北部，而在北部，北部倾斜的中间深度地震倾向是归因于室内膨胀层岩石层的内在俯冲。该项目正在测试两个可能在遗传上链接所有这些特征的末端“构造驱动器”：（1）亚洲岩石圈的南向南倒退/撤退的短暂阶段的短期阶段，在此期间，pamir片麻岩域被大量的北向延伸水平延伸（大约140 kilote）和pamir salient uniention demir note nortiage。 （2）印度岩石圈北向北向上镇定/楔形的旷日持久的阶段，在其上方迫使亚洲中壳的垂直发掘，并在其下方的亚洲岩石圈向南俯冲。这两个结束的假设不是相互排斥的，但是，它们做出了对比的基质规范预测，可以通过地质研究进行测试。我们正在测试对片麻岩圆顶的运动学，变质和岩浆演化的预测。我们的方法整合了地质图和结构分析，以限制片麻岩挖掘的运动学；变质岩石学，U/TH-PB地质学 +痕量元素分析，以量化进一步和逆行变质的历史；中等和低温热量学，以量化挖掘史；以及锆石（Hafnium）和钛铁矿（Neododymium）的U-PB地质学和同位素分析，以限制新生代岩浆作用的历史和来源。