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

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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.