ADVECTION AND MIGRATION IN THE MOUNT MCKINLEY RESTRAINING BEND OF THE DENALI FAULT, DENALI NATIONAL PARK & PRESERVE, ALASKA

The spatial association of the active Alaska Range orogen with the Denali fault system for more than 600 km and 70 degrees of map-view curvature indicates a clear genetic relationship between these two features. Geologic and geodynamic studies support the model of a highly slip-partitioned Denali fault system acting to localize topographic development along the system, but geologic studies demonstrate that the mechanisms accommodating topographic growth vary along strike. A prominent illustration of this are cooling ages derived from low-T thermochronometers illustrating a heterogeneous distribution of exhumation along the axis of the Alaska Range, whereas the widespread distribution of uplifted foreland basin deposits suggests the processes leading to exhumation heterogeneity is superimposed upon an orogen-scale uplift signal. One region where this pattern varies is the anomalous topography and rock uplift associated with the Mount McKinley restraining bend. Here the strongly localized topographic development of Mount McKinley (Denali) is the result of the horizontal space problem associated with an ~60 km long section of the Denali fault that is oriented 18° counterclockwise relative to the broadly curved trace of the fault to the east. Active thrust faults occur to the north between the eastern and western apices of this restraining bend, corresponding with and parallel to the oblique section of the Denali fault. Simple geometric constraints based upon the style and slip rates of active faults suggest that the eastern apex of the restraining bend is migrating SW. This is supported by the trend of cooling ages becoming progressively older to the NE in the ‘wake’ of the restraining bend migration. Furthermore, measurable Quaternary shortening north of the Denali fault is restricted to the zone adjacent to the oblique Denali fault section, suggesting that the entire stepover zone is migrating. Observations supporting the advection of crustal material through the restraining bend on the south side of the Denali fault include the occurrence of the most deeply exhumed fault rocks west of the current highest topography and Denali fault slip rates outside of the restraining bend being larger than our estimate of the restraining bend migration rate.