Metamorphic and Tectonic Evolution of the Tethyan Himalaya, Central Nepal

In this project, new petrologic methods are being developed to help constrain the pressure-temperature-time evolution of metamorphic rocks of the Tethyan Himalayan Sequence exposed in central Nepal. These rocks are key lithologies for understanding the early history of the Himalayan orogen and for testing tectonic models, but their calcareous compositions have defied previous petrologic and chronologic efforts. Recent petrologic advances, however, indicate that titanite major element, trace element (Zr), and U-Pb isotope geochemistry can simultaneously constrain pressure, temperature and age of formation. Titanite is extremely common in Himalayan calcareous rocks. Crystals exhibit chemically and chronologically distinct sub-grain domains and preserve crystallization conditions to temperatures of about 800 °C. By determining pressure-temperature-time conditions for these different domains, we can for the first time map out the pressure-temperature-time evolution of these rocks. These data will discriminate among models of collisional orogenesis, particularly the degree to which the middle and lower crust flows plastically, and may provide a unique window into the early tectonic history of the Himalaya. Results will also broadly impact investigations of igneous petrogenesis and ages and histories of hydrothermal and ore systems. All data will be permanently archived with MetPetDB.

This research addresses several fundamental problems of how continental crust behaves during plate collisions, especially the degree to which the middle and lower crust flows plastically, and how extensional systems, which thin the crust, can form when the overall forces should cause thickening. Our work will also develop new interpretational methods that will advance research in igneous, hydrothermal and ore-forming processes. In addition to the research goals of the project, a two to three day workshop will be held at Tribhuvan University in Kathmandu to help train Nepalese scientists in analytical and interpretational methods and how these data can be used to discriminate among competing hypotheses. This work will also support the research and training of a new PhD student as well as an undergraduate, who we will seek to recruit from Boise State University?s LSAMP program. The PI leverages educational opportunities in his undergraduate and graduate courses at Boise State University, which reaches a different student demographic than other American universities.