PARTITIONING OF STRAIN TRIGGERS RAPID EXHUMATION WITHIN THE ST. ELIAS OROGEN, SOUTHERN ALASKA

Three-dimensional thermo-mechanical numerical modeling of the ongoing Yakutat–North America collision identifies the trigger for localized rapid uplift/exhumation that has been observed within the St. Elias orogen of southern Alaska. Thermochronological data reveal localized rapid exhumation beneath the Seward Glacier within the tectonic corner where strike-slip motion to the south changes to shortening to the north and west. The modeled deformation patterns are characteristic of oblique convergence within a tectonic corner, recording the transition from simple shear to contractional strain within a zone spatially consistent with the highest exhumation rates. The models test the relative roles of erosion versus tectonics in the development of this pattern of deformation by varying the surface boundary conditions. Inclusion of an erosion model enhances the uplift and development of a localized rapid exhumation, but does not drive it, indicating the initial stages of the growth of zones of rapid exhumation are related to tectonics (partitioning of strain) rather than erosion.