Internal Flow, Extrusion and Exhumation History of the Greater Himalayan Slab

大喜马拉雅板块是一个5-30 km厚的向北倾斜的中地壳岩石构造单元，形成喜马拉雅的结晶核，沿着其底部以主中央冲断带为界，沿着顶部以藏南拆离系正断层为界。假设沿着这些地壳尺度的边界剪切带同时或重叠运动，大喜马拉雅板块通常被建模为一个北倾的通道或楔/板的中地壳岩石，开始于早中新世时代，从青藏高原下向南挤出。确定一个纯剪切分量是至关重要的，因为一个显着的纯剪切分量本身将作为一个驱动器的地壳挤压和折返，导致：1）变薄和倾向平行延伸板本身，2）相对于严格的简单剪切，在喜马拉雅结晶核的应变率和挤压/折返率的增加。通道流/挤压模型的测试需要的空间和时间分布的涡域绘制出整个板，并最终还需要一个运动学和压力-温度-时间分析之间的紧密结合，以约束渐进变形和折返路径。结果从以前的工作山。珠峰地区（沿着大喜马拉雅板块顶部）的研究表明，与通道流和挤压模型的预测相反，最高纯剪切分量位于板块底部，可能表明岩石静力载荷的重要性。本项目将完成穿越珠峰地区大喜马拉雅板块的运输平行取样穿越，并在喜马拉雅山脉沿着的关键地区进行一系列类似的运输平行穿越，以便对以下方面进行一级评估：a）水流沿走向的空间和时间变化，B）这些流量变化如何与大喜马拉雅板块的构造演化和折返历史中的沿走向变化相关。在每个横向套件的定向样品将收集基于实验室的涡度分析使用所有适当的微观结构和晶体组构/应变技术。这些不同分析技术提供的数据将与相关微结构和晶体组构所指示的变形温度相联系，从而能够在渐进折返/冷却过程中跟踪流动涡度的变化。喜马拉雅山经常被引用为大陆-大陆碰撞产生的山脉的经典例子，随着印度和亚洲之间的持续碰撞，岩石片一片一片地堆叠在一起，链条逐渐演变。有人提出，形成喜马拉雅变质核的岩石，最初位于青藏高原之下，正在向南挤压和挤压，作为朝向地球表面的板状体，向上推动喜马拉雅山的顶部，这种运动是由垂直载荷的水平梯度驱动的。在该流动通道中的垂直挤压和缩短的程度越大，朝向表面挤出的材料的量越大。如果地表侵蚀跟不上挤压的速度，那么挤压的量越大，地表隆起的量就越大，这就解释了为什么喜马拉雅山的最高峰总是与这片中地壳岩石的露头位置重合。如果材料是通过简单的剪切变形的，这种机制类似于洗牌一副扑克牌，那么岩石不会平行于剪切运动而伸长，就像洗牌时扑克牌不会伸长一样。因此，在简单剪切中，来自中地壳的岩石不会向地表移动很远。然而，如果材料被剪切和垂直缩短（纯剪切），那么岩石将平行于剪切运动延长并向表面移动。该研究项目旨在确定纯剪切驱动的挤压过程是否沿着喜马拉雅山脉的长度运行，或者它们是否是目前山脉最高部分所独有的。

The Greater Himalayan Slab is a 5-30 km thick northward-dipping tectonic unit of mid-crustal rocks that forms the crystalline core of the Himalaya and is bounded along its base by the Main Central Thrust Zone and along the top by the South Tibetan Detachment System of normal faults. Assuming simultaneous or overlapping movement along these crustal-scale bounding shear zones, the Greater Himalayan Slab is often modeled as a north-dipping channel or wedge/slab of mid-crustal rocks that, beginning in Early Miocene times, was extruded southward from beneath the Tibetan plateau. Identification of a pure shear component is critically important because a significant pure shear component will itself act as a driver for crustal extrusion and exhumation, resulting in: 1) thinning and dip-parallel extension of the slab itself, 2) relative to strict simple shear, an increase in both strain rates and extrusion/exhumation rates of the Himalayan crystalline core. Testing of channel flow/extrusion models requires that spatial and temporal distributions of vorticity domains be mapped out across the slab, and ultimately also requires a close integration between kinematic and pressure-temperature-time analyses in order to constrain progressive deformation and exhumation paths. Results from previous work the Mt. Everest region (along the top of the Greater Himalayan Slab) suggests that, in contrast to predictions from channel flow and extrusion models, the highest pure shear components are located towards the base of the slab, possibly indicating the importance of lithostatic loading. This project will complete transport-parallel sampling traverse across the Greater Himalayan Slab in the Everest region and undertake a series of similar transport-parallel traverses in key areas along the length of the Himalaya in order to make a first order assessment of: a) along-strike spatial and temporal variations in flow and, b) how these variations in flow may be related to along-strike changes in the structural evolution and exhumation history of the Greater Himalayan Slab. In each traverse suites of oriented samples will be collected for laboratory-based vorticity analyses using all appropriate microstructural and crystal fabric/strain techniques. Data provided by these different analytical techniques will be linked to deformation temperatures indicated by associated microstructures and crystal fabrics, hence enabling changes in vorticity of flow to be tracked during progressive exhumation/cooling.The Himalaya is frequently cited as the classic example of a mountain chain produced by continent-continent collision, with the chain progressively evolving as sheets of rock are stacked up on top of one another during continued collision between India and Asia. It has been proposed that rocks forming the metamorphic core of the Himalaya, originally located beneath the Tibetan Plateau, were being squeezed and extruded southwards as a slab-shaped body towards the Earth's surface, driving upwards the crest of the Himalaya, and that this movement is driven by horizontal gradients in vertical load. The greater the degree of vertical squeezing and shortening in this flowing channel, the greater the amount of material extruded towards the surface. If surface erosion cannot keep pace with extrusion, then the greater the amount of extrusion the greater the amount of surface uplift, hence explaining why the highest Himalayan peaks always coincide with the outcrop position of this slab of mid-crustal rocks. If the material is deforming by simple shear, a mechanism similar to shuffling a pack of playing cards, then the rocks won't lengthen parallel to the shearing motion, just as a playing card doesn't lengthen when the deck is shuffled. So, in simple shear, rocks from the middle crust won't move very far towards the surface. However, if material is both sheared and vertically shortened (pure shear) then the rocks will lengthen parallel to the shearing motion and move towards the surface. This research project aims to determine if the pure shear driven extrusion processes have operated along the length of the Himalaya, or if they are unique to the currently highest part of the mountain chain.