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EXtreme Tectonics and Rapid Erosion in Mountain Environments

Final Report Summary - EXTREME (EXtreme Tectonics and Rapid Erosion in Mountain Environments)

Tectonic plate corners are hotspots of continental deformation and erosion rates, and associated with geologic hazards including high-magnitude earthquakes, landslides, and extreme climatic gradients. The EXTREME project challenged the prior ‘tectonic aneurysm’ hypothesis which suggested that rapid deformation and erosion at plate corners is initiated from the “top down” by sustained, highly localized erosion. Results from this study support an alternative hypothesis that rapid deformation and erosion at plate corners may (1) be explained by the “bottom up” 3D geometry of the subducting plate; and (2) requires a threshold rate of both “bottom up” deformation and surface erosion to initiate a feedback between climate and tectonics.
Results from this project support our alternative hypothesis that the 3D geometry of the subducting plate exerts a strong control on the pattern of exhumation in the overriding plate. Coupled thermo-mechanical-erosion numerical models predict localized and rapid erosion above plate corner settings, and that the pattern of erosion evolves through time. Paleoclimate model simulations from 4 different plate corner settings document significant global and regional scale changes in climate over the timescales that mountain topography develops. Observed denudation rates from cosmogenic radionuclides and low-temperature thermochronology support a localized exhumation pattern in three of the four study areas, where as the fourth, arid, study area does not clearly support this pattern. Taken together, these results indicate that the subducting plate geometry exerts a primary control on the pattern and rates of erosion, and that a coupling between local climate and rock exhumation is a secondary influence.