3D THERMOMECHANICAL MODELING OF THE ST ELIAS TECTONIC ANEURYSM

The nonlinear feedback between tectonics and erosion within the ongoing Yakutat­ - North America collision has shaped the St. Elias orogen of southern Alaska. The associated pattern of deformation is dominated by the affects of the tectonic corner structure characterized by the transition from strike-slip to compressional deformation. Thermochronological data reveal localized rapid exhumation located underneath the Seward Glacier, spatially located within the tectonic corner structure. The results of three-dimensional thermo-mechanical numerical models indicate the strain patterns and uplift/exhumation histories are consistent with the mapped and predicted deformation within the orogen. This deformation pattern is characteristic of oblique convergence within a tectonic corner, recording the transition from transcurrent to compressional strain within a zone spatially consistent with the highest exhumation rates. Modeled P-T histories compare favorably with thermochronological observations, and indicate rocks exhumed within the St. Elias orogen did not surpass upper greenschist facies metamorphic conditions. Finally, the inclusion of an erosion model enhances the uplift and development of a tectonic ‘aneurysm’, but does not drive it. The finding of this study indicate the initial stages of the growth of a tectonic anerurysm are related to tectonics, specifically the relationship between geometry and strain distribution, rather than erosion.