THERMOCHRONOLOGIC CONSTRAINTS ON THE UPLIFT AND FORMATION OF DENALI MOUNT MCKINLEY, CENTRAL ALASKA BASED ON APATITE U-TH/HE DATING

Denali (Mt McKinley) at ~6194 m is America's highest mountain and dominates the central Alaska Range. This range lies in the apex of the Denali fault, an intracontinental dextral strike-slip fault, one of a family of such faults in southern Alaska. Samples collected from top to bottom of Denali (relief of 4 km) were previously analyzed using apatite fission track (AFT) thermochronology. The AFT age vs. elevation relationship clearly defines the timing (5-6 Ma) of the initiation of surface uplift, rock uplift and denudation associated with the formation of the range (Fitzgerald et al., 1993, 1995). In conjunction with regional geological information, the AFT data also allowed the magnitude of rock and surface uplift as well as denudation to be constrained and hence the average rates of rock uplift, surface uplift and denudation to be constrained. We are applying apatite (U-Th)/He dating, a lower temperature, and usually higher precision, technique to this same set of samples from Denali. This should allow us to better constrain the timing and rates of uplift and denudation of the central Alaska Range. In addition, the combination of the two techniques may allow the paleogeothermal gradient to be constrained. Using the new data, the project will re-evaluate the driving mechanism behind the uplift and formation of the central Alaska Range, ultimately leading to an improved understanding of the formation of mountain belts along a strike-slip fault system.