TECTONICS OF NORTH AMERICA'S GREATEST MOUNTAIN RANGE: RESULTS OF THE ST. ELIAS EROSION AND TECTONICS PROJECT (STEEP) AND ITS IMPORTANCE TO WRANGELL-ST. ELIAS, KLUANE, AND GLACIER BAY NATIONAL PARKS

These three national parks comprise the largest wilderness preserve on earth, the world’s greatest rise from sea level (Mt. St. Elias), and North America’s greatest mountain range, yet within the general public there is widespread ignorance of even the existence of this region. The St. Elias Erosion and tectonics Project (STEEP) is working to show the importance of this region through an integrated study of the orogen at scales ranging from mantle imaging to outcrop scale geology and time scales from the geologic history to determination of ongoing deformation and erosion rates. Some of the key science results of the project can be seen in Session T70 of this meeting, but this presentation will emphasize some general results that can be carried to a broader audience: 1) Recognition that the Yakutat microplate carries a thick crust that is being subducted in flat-slab mode provides a general framework that can explain most of the young orogenesis in southern Alaska in the context of the collision of the Yakutat microplate; 2) passive seismic data provide the first images of the subducted flat slab as well as the roll-over at the edge of the slab that produces the Wrangell volcanic arc; 3) Numerous observations indicate the orogen has been dramatically reshaped by glacial erosion and offshore deposition, shifting deformation patterns as glacial erosion and deposition destroyed orogenic topography faster than tectonics could rebuild it—in a human terms, erosion rates of ~0.2-0.5m in a lifetime are common, and underneath some glaciers erosion rates are as much as 1m in a lifetime. 4) Although basement convergence appears to be relatively simple, the response of cover as it is stripped from basement is a complex response of erosion/tectonic interactions recognized in both surface geology and geodetics. 5) A local “tectonic hot-spot” in the Logan-St. Elias area is recognized from thermochronology and appears to be a juvenile “tectonic aneurysm” comparable to features in the Himalaya.