Thrust Belt Exhumation and Duplex Development in the Sikkim Himalaya

Colliding tectonic plates create high uplifting landscapes that exhibit diverse spatial patterns of active deformation, affect global climate, and ultimately regulate the flux of sediment and water to the oceans. Past research shows these mountain belts grow both outward and upward in complex ways across space and time. However, major questions remain about how and why different parts of mountain belts evolve differently and what role various internal and external forcings may play in the process. Duplexes are stacks of thrust-bounded rock bodies that represent regions of intense shortening that result in focused crustal thickening and uplift rather than expansion outward. An emerging view is that a large duplex has become an important, widespread component in the frontal portion of the Himalayan chain that may be a response to concentrated monsoon precipitation and erosion. In the Sikkim Himalaya in India, the Lesser Himalayan Duplex is well exposed by river incision, the geologic structure is well documented, and hence various structural models are proposed for how it may have developed. This research project will determine the exhumation patterns of the region using bedrock cooling ages and computer models informed by the geologic structure, to quantify the integrated history of duplex deformation and exhumation. The results will determine the chronology and magnitude of Lesser Himalayan Duplex growth and erosion, address the hypothesized structural models for Lesser Himalayan Duplex development, and test the fidelity of this approach to tackling complex deformation processes throughout the world's active mountain belts and ultimately the mechanisms that drive them.

This research confronts the reality that increasingly complicated deformation processes are being recognized in mountain ranges and tackles that challenge by advancing the ways we integrate geologic data and computer models to comprehend active mountain system behavior. Improved knowledge of the processes that localize mountain deformation, climate, and erosion has important implications for seismic hazards and the generation, transport, and delivery of fluid and debris to adjacent lowlands where a large portion of the Earth?s population resides. This project also represents a synergy of integrated research and education between North American and Indian geoscientists, educators, and students. Combined approaches and results from this project and a complimentary one in India will be discussed at the Indian Institute of Technology Bombay and University of North Carolina. A future US science teacher will participate in the research and translate the results into educational material for K-12 Earth Science courses and the public. This award is designated as a Global Venture Fund Award and is being co-funded by NSF?s Office of International Science and Engineering.