SHORTENING AT THE WESTERN END OF THE MOUNT MCKINLEY RESTRAINING BEND: PRELIMINARY SLIP RATE AND ALONG STRIKE CHANGES ASSOCIATED WITH THE CHEDOTLOTHNA FAULT, DENALI NATIONAL PARK & PRESERVE, ALASKA

Except for the Denali fault, no Quaternary-active faults have been mapped to accommodate the expected deformation associated with the tectonically-active region west of Mount McKinley, Alaska. As part of a multi-year investigation in Denali National Park into the evolution of the Mount McKinley restraining bend of the Denali fault, we examined the foothills at the western end of the restraining bend to document evidence for late Quaternary faulting and to determine slip rates and fault geometry wherever possible. A Quaternary-active thrust fault (the Chedotlothna fault) corresponds with the topographic range front of the Alaska Range from near the Straightaway Glacier to the Chedotlothna Glacier. On the west side of the Chedotlothna Glacier valley, this fault offsets a sequence of glacial deposits and landforms, with well-defined vertical displacements of ~24 m and ~55 m. Tentative correlation of glacial deposits with regional and global climate records suggest a late Pleistocene vertical displacement rate of ~0.4-2 mm/yr, and samples for in-situ terrestrial cosmogenic nuclide surface exposure and burial dating techniques are being processed to test these tentative correlations of glacial deposits. The active surface trace of the Chedotlothna fault appears discontinuously across glacial moraines and alluvial fans for ~10 km southwest from the the Chedotlothna Glacier. Beyond this active trace, broad smooth-crested early-mid Pleistocene glacial moraines are not offset across the range front, suggesting that displacement on this fault ceases southwestward or transfers onto other structures. Based upon a lack of geomorphic evidence for additional active faults north of the Denali fault and the geologic relationships established by prior bedrock geologic mapping, we infer that the decrease in fault-normal shortening illustrated by active thrust faults north of the Denali fault are restricted to the most oblique portion of the Denali fault through the restraining bend.