The Saint Elias orogen of southcentral Alaska and the adjacent region of Canada contains one of the highest coastal mountain ranges on earth and over half of the 25 highest peaks in North America. This superlative topography is a result of the collision of the Yakutat block with southern Alaska. Nearly 45 mm/yr of NW-SE directed convergence from this collision is accomodated within the Saint Elias orogen. The locations of the structures taking up the convergence remain uncertain. As part of the Saint Elias Erosion/Tectonics Project (STEEP), a project designed to elucidate the complex tectonics of the region, we re-occupied 30 campaign GPS sites throughout the orogen during the summer of 2007 and used the data to generate velocities at each site. The velocities show a remarkable degree of Fairweather fault-parallel motion. Since the Yakutat block motion is also parallel to the Fairweather fault, the velocities show that the Yakutat block is the dominant tectonic influence within the orogen. The influence of the subducting Pacific plate is not clearly seen until the western edge of the orogen and Prince William Sound. Velocities along the edges of Icy Bay indicate that over 7 mm/yr of convergence occurs over a distance of 11 km, producing a strain rate of -0.6 microstrains/yr. Contraction rates in the Nepal Himalaya are less than a fifth of this value while rates in the eastern Kenai Peninsula in Alaska only reach half of the Icy Bay rate. The strain rate between Yakutat Bay and the eastern edge of Icy Bay is only -0.0419 microstrains/yr. We use elastic dislocation models to describe the tectonic elements in the area and evaluate two possible end member models. The observed velocities may be due to a creeping fault that comes to the surface in Icy Bay. If this is the case, Icy Bay is the current locus of permanent deformation and mountain building in the orogen. On the other hand, the velocities may be able to be explained by a shallow thrust fault beneath the region that has the down dip end of its locked zone centered under Icy Bay.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1209 Tectonic deformation (6924);
- 1240 Satellite geodesy: results (6929;
- 8158 Plate motions: present and recent (3040)