Descr: We propose to use the eastern syntaxis of the Himalayan orogen to address key questions in the geodynamics of continental collisions: how do orogens and associated plateaus come to an end, how do tectonic and surficial processes interact to shape the crust during orogeny, and how is deformation partitioned at various scales? These issues, enigmatic in older orogens, are resolvable in young and active regions such as the India-Asia collision. Our work will involve testing three linked hypotheses: 1) across the transition from Tibetan Plateau to eastern indentor corner, changes in lithospheric rheology are an important control on changes in topography and lithospheric mechanics; 2) erosion plays an equally important role in controlling lithospheric dynamics, or par with crustal thickening and lateral accommodation and feedbacks between the two ultimately shape the evolution of the orogen; and 3) within the syntaxial region, there is nearly complete decoupling b! etween deformation in the upper cr ust and the deeper lithosphere. To test these hypotheses, we will track the magnitude, rates, and types of mass flexes through the central region of the eastern Himalayan syntaxis. To do this we will use isotopic, geochronologic, geomorphic, GPS, petrologic, seismologic, and structural techniques, fully integrated by three-dimensional modeling. The young structures and active processes in the region will permit us to meaningfully combine short-timescale measurements (e.g. seismological, GPS, geomorphic observations) with measurements made over a longer range of temporal scales (e.g. petrologic, structural, geochronological observations) on material that is moving through the region and hence records a complex time-integrated pressure, temperature, and strain history.
