Collaborative Research: Testing Channel-flow Models Using Mid-crustal Rocks of North Himalayan Gneiss Domes

最近的模型表明，由于西藏和印度地形的差异，青藏高原下方的中地壳向南向印度流动；模型进一步表明，这种挤压物质出现在喜马拉雅高侵蚀地区的地表。这些模型对水流的大小和方向随深度的变化做出了具体的预测。该项目使用构造地质学和地质年代学来测试这些预测，以确定模型是否正确，如果不正确，模型可能如何改进。这是一次重要的测试，因为印度-亚洲碰撞是地球上正在进行的最大的大陆碰撞，是观察整个地球历史上发生的更古老的大陆碰撞的重要镜头。中央华盛顿大学的杰夫·李、加州大学圣巴巴拉分校的布拉德利·哈克和他们的学生将利用构造岩石学、有限应变分析、电子背散射衍射(EBSD)和变质独居石年代学，研究暴露在西藏南部北喜马拉雅片麻岩穹隆中的强烈变形的中地壳岩石的运动学、涡度、有限应变和变形温度的时空分布。这项研究是由最近形成的热、机械通道流动/挤压模型推动的，该模型假设暴露在高喜马拉雅和西藏南部的中地壳是一种低粘度、韧性的物质，上下分别被向南流动和挤压的同时代正常剪切带和逆冲剪切带所包围。流道内的流动范围可以是纯Couette流到Poiseuille流，也可以是两者的组合。研究人员和他们的学生将记录韧性流动过程中的变形和时间，以提供藏南中地壳岩石变形和流动的全面空间、热和时间历史。这些研究与高喜马拉雅地区已发表和正在进行的类似研究相结合，将为50至100公里范围内平行于运输方向的中地壳流动提供前所未有的视角。

Recent models suggest that the middle crust beneath the high Tibetan Plateau flows southward toward India because of the difference in topography between Tibet and India; the models further suggest that this extruding material emerges at Earths surface in the high-erosion area of the Himalaya. These models make specific predictions about how the flow varies in magnitude and direction with depth. This project uses structural geology and geochronology to test these predictions to see whether the models are correct, and if they are not, how the models might be refined. This is an important test to conduct because the India?Asia collision is Earths largest ongoing continent collision and serves as an important lens for viewing older continental collisions that happened throughout Earths history.Researchers Jeff Lee of Central Washington University, Bradley Hacker from the University of California Santa Barbara, and their students will investigate the spatial and temporal distribution of kinematics, vorticity, finite strain, and deformation temperature in strongly deformed middle crustal rocks exposed in the North Himalayan gneiss domes, southern Tibet, using structural petrology, finite-strain analysis, electron-backscatter diffraction (EBSD), and metamorphic monazite geochronology. This research is motivated by recently formulated thermal, mechanical channel flow/extrusion models that postulate that the middle crust exposed in the high Himalaya and southern Tibet was a low-viscosity, ductile material, bounded above and below by coeval normal- and thrust-sense shear zones, respectively, that flowed and extruded to the south. Flow within a channel can range from pure Couette flow to Poiseuille flow, or be a combination of the two. The investigators and their students will document the deformation and timing during ductile flow to provide a comprehensive spatial, thermal, and temporal history of deformation and flow in middle crustal rocks in southern Tibet. These studies, combined with similar published and ongoing studies in the high Himalaya, will provide an unprecedented view of middle crustal flow parallel to the transport direction over a distance of 50 to 100 km.