Did Channel Flow Drive the Thermo-mechanical Evolution of the Eastern Himalaya? A Field-based Test in Northeast Bhutan

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The Himalayan range and Tibetan Plateau represent the world?s tallest mountain range and largest area of elevated land, and are the type-example of a mountain belt that formed as a result of continent-continent collision. This system is still actively growing; therefore, study of these mountains provides a unique opportunity to understand how the crust evolves during this type of plate collision. Across much of the Himalayan range, rocks that have been buried to depths as much as approximately 35 km below Earth's surface and taken to temperatures hot enough to partially melt are observed at the surface today. These rocks have been studied in many parts of the Himalaya, and there is currently a vigorous debate over how these rocks were exhumed to the surface. The channel flow model predicts that these deeply buried rocks lost much of their strength after partially melting, and were then translated southward and towards the surface. In comparison, other proposed models argue that faults and shear zones were responsible for their exhumation, and are less focused on the driving force being the weakness of the rocks. In this project, we propose to test the applicability of these different models to rocks in the kingdom of Bhutan, which lies in the eastern part of the Himalayan range. We will do this by collecting rock samples during field expeditions, and determining the pressure, temperature, timing, and evolution of deformation that they experienced. In the past, Bhutan has been relatively isolated for geologic researchers so the majority of the rocks exposed in Bhutan have not been well studied.The results of this project will make a valuable contribution to the debate over how continental crust evolves during collisional mountain building. In addition, multiple graduate students will be trained in the field and laboratory, including one Bhutanese citizen and current employee of Bhutan's geologic survey. After he finishes his degree, he will return to Bhutan to take on a leadership role in the study of natural resources, natural hazards, and public policy. Undergraduate students will also be involved with laboratory analyses and will obtain training, education, and research experience. Finally, this study will support the research efforts of two early career researchers, as well as foster valuable international collaboration between UNR and scientists at Bhutan?s geological survey.