EXTREME TOPOGRAPHIC DEVELOPMENT ALONG THE DENALI FAULT STRIKE-SLIP SYSTEM, ALASKA: WHY IS MOUNT MCKINLEY SO BIG?
Preliminary apatite fission track (AFT) cooling ages from samples on both sides of the restraining bend, range from ~8 Ma to ~2 Ma and suggest a pattern of AFT cooling ages younging to the west. This apparent east to west time progressive trend in inferred focus of exhumation is mimicked by an increase in width of the deformation front to the west. In addition, north and south side topographic development increases west towards the bends apex before decreasing further to the west. Therefore, we infer the evolution of the Mount McKinley restraining bend is the dominant control on exhumation patterns in the region, not variations in erosional forcing, basement faults, lithology, and rheology. The Peters Dome area, located north of the bend’s apex, is a region of high seismicity, young cooling ages and multiple active faults, demonstrating significant shortening that is likely accommodating the westward migration of the Mount McKinley restraining bend at a long term rate of 4-6 mm/yr. This rate is > 50% of the bend’s Holocene Denali fault slip rate, but approximates the bend migration rate predicted by kaolin analog experiments (bend migration rate ~50% of master strand slip rate). Hence crustal blocks remain in the region of focused vertical tectonics for an extended period of time, and Mount Foraker with deeply exhumed orthogneiss (~40 Ma protolith age) is likely a paleo-Mount McKinley.