How Does the Mid-crust Accommodate Deformation in Large, Hot Collisional Orogens? Insight from the Himalaya-Tibet System

中地壳如何适应大型热碰撞造山带的变形？

• 批准号: 1119380
• 负责人: John Cottle
• 金额: $ 36.64万
• 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: 2011
• 资助国家: 美国
• 起止时间: 2011-07-01 至 2016-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1119380&HistoricalAwards=false
• 关键词: How; Does; Mid; crust; Accommodate

Hot, weak crust is a central component of new hypotheses about the evolution of continent-continent collisions, and in particular may play an important role in accommodating the greater than 3000 kilometers of convergence within the Himalaya-Tibetan collision over the last 50 million years. Models that implicate flow of semi-viscous midcrustal rocks south towards the front of the Himalayan orogen, 'channel flow', are able to account for many geologic observations in the Himalaya. However, alternative models of collision, particularly 'thrust-wedge taper', demonstrate that the observed geology could have formed in the absence of a low-viscosity midcrustal layer. Whether channel flow and thrust-wedge taper models are mutually exclusive or whether they represent a continuum of deformation in time and/or space within a single collisional system is of crucial importance for explaining the evolution of the Himalayan orogen and, by extension, for understanding the evolution of Earth?s many continent-continent collision zones. A key difference in these contrasting models is the location, nature and relationships of thrust faults within the Himalayan foreland; specifically, the spatial and kinematic association of the Main Central Thrust and the Ramargh Thrust. In the channel flow model of the Himalaya, exhumed midcrustal rocks are predicted to act as a pervasively-deformed tectonic package bounded at its base by a single major fault; the Ramgarh and Main Central thrust are synthetic and coeval components of that diffuse structure. In contrast, thrust-wedge taper models interpret the Main Central thrust and Ramgarh thrust to be kinematically distinct, and formed in sequence within a foreland propagating fold and thrust belt. These predictions are being tested by analyzing samples at three key sites across the central to eastern Himalaya via a combination of structural analysis, uranium-thorium-lead accessory phase petrochronology coupled to thermobarometry, detrital thermochronology and bulk rock neodymium isotope geochemistry. These data provide essential information about the timing of the Main Central Thrust and the Ramgarh Thrust, the timing of deformation and metamorphism in the midcrust, and source characteristics of the rocks that give clues as to their pre-Himalaya origins. These data also yield insight into the evolution in time and space of the transition between deep crustal hinterland-style deformation recorded within the core and the shallow foreland-style deformation recorded near the front of the Himalaya. This project supports both graduate and undergraduate students, providing them with hands-on research experience in both field investigation methods and a variety of analytical facilities, particularly taking advantage of state-of-the-art high-resolution and high-precision electron- and ion-beam instrumentation at the University of California, Santa Barbara. The project is also supporting the research efforts of two early career researchers, and is contributing to the broadening of participation of underrepresented groups in the earth sciences. This project is part of an international scientific collaboration, bringing together researchers and students from the University of California, Santa Barbara, Canada, Nepal and India.

热的、弱的地壳是关于大陆-大陆碰撞演化的新假说的核心组成部分，特别是在过去5000万年喜马拉雅-西藏碰撞中容纳超过3000公里的会聚方面可能发挥重要作用。模型，牵连流动的半粘性中地壳岩石向南走向喜马拉雅造山带，“通道流”的前面，能够占许多地质观测在喜马拉雅山。然而，碰撞的替代模型，特别是“逆冲楔锥”，表明所观察到的地质可能是在没有低粘度地壳中层的情况下形成的。无论是通道流和逆冲楔锥模型是相互排斥的，还是它们代表了一个连续的变形在时间和/或空间内的一个单一的碰撞系统是至关重要的解释喜马拉雅造山带的演化，并通过扩展，了解地球的演化？有许多大陆-大陆碰撞带。这些对比模型的一个关键区别是喜马拉雅前陆内逆冲断层的位置、性质和关系;特别是主中央逆冲断层和拉玛逆冲断层的空间和运动学关联。在喜马拉雅山脉的通道流模型中，被挖出的中地壳岩石被预测为在其底部由一个单一的主要断层界定的一个普遍变形的构造包; Ramgarh和主要的中央逆冲断层是该扩散结构的合成和同时代的组成部分。与此相反，逆冲楔锥模型解释主中央冲断层和拉姆加尔逆冲断层是运动学上不同的，并在前陆传播褶皱和冲断带内顺序形成。这些预测正在通过分析样品在三个关键地点横跨喜马拉雅山脉中部到东部，通过结合结构分析，铀钍铅副相岩石年代学结合热压，碎屑热年代学和大块岩石钕同位素地球化学。这些数据提供了关于主中央冲断层和Ramgarh冲断层的时间、中地壳变形和变质的时间以及岩石的来源特征的基本信息，这些岩石的来源特征为喜马拉雅山前的起源提供了线索。这些数据也产生洞察到的时间和空间的演变之间的过渡深地壳内记录的核心和浅前陆式变形记录的喜马拉雅山前附近的变形。该项目支持研究生和本科生，为他们提供实地调查方法和各种分析设施的实践研究经验，特别是利用加州大学圣巴巴拉最先进的高分辨率和高精度电子束和离子束仪器。该项目还支持两名早期职业研究人员的研究工作，并有助于扩大代表性不足的群体对地球科学的参与。该项目是国际科学合作的一部分，汇集了来自加州大学、圣巴巴拉、加拿大、尼泊尔和印度的研究人员和学生。