The Yakutat block is a terrane in the process of accreting to the North American continent. It has been displaced about 600 km northward since the Cenozoic along the Queen Charlotte-Fairweather fault system. The collision of the Yakutat terrane with North America has contributed to the building of the Fairweather, Chugach, and St. Elias Ranges. The Yakutat block is presently bounded on the northeast by the strike-slip Fairweather fault, and on the north by a system of thrust and possibly strike-slip faults in the Chugach and St. Elias mountains. The Yakutat block is bounded on its southwest (oceanic) side by an obvious bathymetric and seismogenic feature known as the Transition Zone, although questions remain about whether the Transition Zone is a presently active structure. Global Positioning System (GPS) measurements made over the last several years show that the Yakutat block has a significant velocity relative to both the Pacific and North American plates. This makes it a terrane in the process of accretion rather than a block already welded to the Pacific or North American plate. Relative to North America, the Yakutat block moves at a rate of about 45 mm/yr NNW, parallel to the onshore portion of the Fairweather fault. This is essentially the entire projection of the Pacific - North America convergence vector onto the Fairweather fault direction. There is about 20 mm/yr of contraction between the Yakutat block and the Pacific plate, which must be accommodated on an offshore structure. South of Yakutat Bay, the boundary between the Yakutat block and the North American plate is purely strike slip, or close to it. The component of convergence across the Fairweather fault is small enough that it is not yet resolvable in the GPS data. North of Yakutat Bay, the relative motion of the Yakutat block drives a very young collisional orogen. Between Yakutat Bay and the Copper River/Wrangell Mountains region, about 40 mm/yr of contraction must be accommodated within a distance of about 200 km or less. This contraction must be accomodated on faults within the continental crust and all or mostly on land, and the convergence rate is among the highest in the world within the continental crust. For comparison, this rate is 2-3 times higher than the convergence rate for the Himalaya.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- 1206 Crustal movements: interplate (8155);
- 1208 Crustal movements: intraplate (8110);
- 8102 Continental contractional orogenic belts;
- 8158 Plate motions: present and recent (3040)