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，弱的外壳是关于大陆碰撞发展的新假设的核心组成部分，尤其是在过去5000万年中，喜马拉雅藏族碰撞内的3000公里融合中可能发挥重要作用。暗示半粘膜中壳岩石向南朝喜马拉雅造山基因“通道流”向南流动的模型能够解释喜马拉雅山中的许多地质观察。然而，碰撞的替代模型，尤其是“推力叶锥”，表明在没有低粘度中间层的情况下，观察到的地质可能形成。通道流量和推力叶状锥度模型是否相互排斥，还是代表单个碰撞系统内的时间和/或空间的连续性，对于解释喜马拉雅造成的演变以及通过延伸而言，对于理解地球的演变而言，至关重要。这些对比模型的关键区别在于喜马拉雅陆境内推力断层的位置，性质和关系；具体而言，主要中央推力和拉马格推力的空间和运动学关联。在喜马拉雅山的通道流量模型中，预测挖掘出的中子岩石是一个普遍形成的构造包装，该构造包裹在其基部被一个主要的断层所束缚。 Ramgarh和主要中央推力是该弥漫结构的合成和共轴成分。相比之下，推力叶状锥度模型将主要的中央推力和拉姆加尔推力解释为运动学上的不同，并在繁殖褶皱和推力带中以序列形成。通过结构分析，铀 - thorium-Lead辅助阶段石化，与热生体测量法，碎屑热力学学和体积岩石NeodyMium Isotope Geemistry相连，通过分析了喜马拉雅东部至中心的三个关键位点的样品来测试这些预测。这些数据提供了有关主要中央推力和Ramgarh推力的时机，中壳中变形和变质的时机的必要信息，以及岩石的源特性，这些岩石特征为其前himalaya起源提供了线索。这些数据还可以深入了解在核心内记录的深层腹地腹地式变形与喜马拉雅河正面附近记录的浅层前陆形变形之间的过渡之间的演变。该项目支持研究生和本科生，为他们提供现场调查方法和各种分析设施的动手研究经验，尤其是利用加利福尼亚大学圣塔芭芭拉分校的最先进的高分辨率高分辨率和高精度电子和离子电子束仪器。该项目还支持两位早期职业研究人员的研究工作，并为扩大代表性不足的团体参与地球科学的参与而做出了贡献。该项目是国际科学合作的一部分，将加利福尼亚大学，圣塔芭芭拉，加拿大，尼泊尔和印度的研究人员和学生汇集在一起​​。