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

最近的模型表明，由于西藏和印度之间的地形差异，青藏高原下的中地壳向南流向印度；这些模型进一步表明，这种挤压物质出现在地球表面喜马拉雅山脉的高侵蚀地区。这些模型对水流的大小和方向如何随深度变化做出了具体的预测。这个项目使用构造地质学和地质年代学来测试这些预测，看看这些模型是否正确，如果不正确，如何改进这些模型。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Jeff Lee、加州大学圣巴巴拉分校的Bradley Hacker和他们的学生将利用结构岩石学、有限应变分析、电子背散射衍射（EBSD）和变质单脱石年代学，研究西藏南部北喜马拉雅片岩穹顶中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。这项研究的动机是最近制定的热、机械通道流动/挤压模型，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、韧性物质，分别由同期的正常剪切带和逆冲剪切带包围，向南流动和挤压。通道内的流动范围可以从纯库埃特流到泊泽维尔流，或者是两者的组合。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，为藏南中部地壳岩石的变形和流动提供一个全面的空间、热和时间历史。这些研究，结合类似的已发表的和正在进行的喜马拉雅高海拔地区的研究，将提供一个前所未有的视野，在50到100公里的距离上平行于运输方向的中部地壳流动。

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.