ACTIVE DEFORMATION AND ALONG STRIKE VARIATION IN STRUCTURAL STYLE WITHIN THE YAKUTAT TERRANE, SAINT ELIAS MOUNTAINS, ALASKA

The Saint Elias Mountains in southern Alaska provide an important field laboratory to investigate current terrane accretion and collision, a process that is integral in the evolution of most if not all orogens. In the eastern segment of the Yakutat terrane, deformation is dominated by strike-slip motion, while the central segment is characterized by underthrusting of the Yakutat terrane beneath the North American plate. The structural style in the western segment is more complex and structural trend is approximately perpendicular to the fold and thrust belt to the east. Recent field mapping, geomorphic analyses and preliminary cross-sections attempt to work out the mechanism by which the fold and thrust belt is deformed in the western segment. A north-south cross-section through the Chaix Hills highlights the role of the Malaspina fault, thought to be the northern extension of the offshore Pamplona zone and an active deformation front separating the eastern and central segments. The Malaspina fault cuts across the foreland fold and thrust belt represented by the section through the Duktoth River area. To the west, composite sections from the Bering glacier to Ragged Mountain document the change in structural style and orientation. Identification of active faults and folds are the key to understanding structural changes across the terrane. Early results from field work suggest variation in strike and dip and possible offset of the Chugach-St. Elias fault across the Bering glacier. In addition, the western segment contains numerous scarps which are likely related to faulting, flexural slip folding or slope failure. Future work will focus on locating active faulting, loci of deformation and the nature of the scarps in the western segment.