Petrologic and Chronologic Evaluation of Himalayan Tectonic Models in Southern Bhutan

In this project, the pressure-temperature-time evolution of metamorphic rocks exposed in southern Bhutan is being investigated to test models of collisional orogenesis. In most areas of the Himalaya, low-grade Tethyan rocks are juxtaposed with high-grade Greater Himalayan rocks along a ductile extensional structure, the South Tibetan Detachment. In the Shemgang region of Bhutan, however, a recent study instead proposes an intact stratigraphic section from Greater Himalayan to Tethyan rocks. If correct, this model strongly limits the importance of two models of crustal deformation behavior during collisional orogenesis, and further implies a normal chronologic, thermal and baric gradient across the Greater Himalayan - Tethyan contact. New data are being collected on pressure-temperature conditions from garnet-bearing rocks, and on metamorphic ages from monazite-bearing rocks. The new data will identify whether the section is indeed chronologically and metamorphically intact, testing the stratigraphic model, and provide crucial new constraints on Himalayan metamorphism and deformation behavior.

This research addresses the fundamental problem of how continental crust behaves during collisions: does it flow (in a pipe-flow sense) weakly towards areas of focused erosion, or does it behave in a stronger more rigid fashion? While this debate originated in the Himalaya and is actively studied there, it has been widely applied to other collisional mountain belts. Thus new results are of broad interest to the geologic community. New chronologic and petrologic methods of investigating metamorphic rocks are being more generally developed, expanding applications to other rock types and orogens.

This project supports the post-doctoral training of a recent female PhD, improving representation of women in the geosciences.