Collaborative Research: A Late Cenozoic Record of Restraining Bend Initiation and Evolution along the Denali Fault at Mount McKinley, Alaska

University Of Alaska Fairbanks Campus, Fairbanks AK

Investigators

Abstract

This project targets the Mount McKinley restraining bend of the Denali fault in Alaska in order to examine the linkages between structural slip rates and regional exhumation rates and how restraining bends can form and evolve in a strain-partitioned transpressional system. The highest mountain in North America, Mount McKinley (6,196 m), is situated on the inside of a 17 degree bend in the mapped trace of the Denali fault. North of the Denali fault, on the outside of this bend, the highest peak is Peter's Dome (3,221 m) with elevations rapidly decreasing away from the Denali fault to an aggradational basin less than 15 km to the north. This topographic asymmetry suggests a strong structural control on local exhumation patterns and that this restraining bend has been a primary control on regional orogenic development for several million years. The study will apply a multi-thermochronometer approach to constraining exhumation rates and timing along the Mount McKinley restraining bend in conjunction with a neotectonic/structural analysis of fault patterns and slip rates. The researchers will employ radiocarbon, optically stimulated luminescence, and in-situ terrestrial cosmogenic nuclide surface exposure dating techniques to provide age control for the major deformed landforms in this study area. Furthermore, insights from this study will be compared to the evolution of complex fault geometries along other strike-slip faults and the recognition of transient and persistent uplift/exhumation phenomena in the geologic record. Major intracontinental strike-slip faults around the world exhibit abrupt changes in the fault geometry over relatively short distances, often occurring as bends or step-over zones between fault segments. These zones of complex fault geometry are often associated with significant uplift or subsidence adjacent to the fault. Understanding how the horizontal displacement along the broader strike-slip system is partitioned into horizontal and vertical components in these complex fault zones is an ongoing focus of research in tectonics. In particular, contractional zones (i.e., restraining bends) that result from a change in fault geometry along a strike-slip fault require significant deformation adjacent to the fault for the crust to continue along the path of long-term horizontal motion. Therefore, it would seem that these zones would evolve toward a straight fault segment: yet restraining bends persist. Developing new slip rate data for the Denali fault and adjacent faults will provide key insights into the modern tectonic framework and constrain potential boundaries of proposed crustal blocks. Furthermore, insights from this study will: 1) allow comparison to the structural complexities along other strike-slip faults such as the San Andreas and Alpine faults; 2) help further understanding of how crustal blocks interact within broad deforming zones of continental crust 3) aid the recognition of transient and persistent uplift/exhumation phenomena in the geologic record. The research team will work closely with educators at the Watershed School in Fairbanks, Alaska, to develop educational plans and materials to foster student interest in science through place-based education. The communication of the scientific advances made through this project will be promoted through close collaboration with Denali National Park and Preserve staff. With numerous previously unknown faults occurring in this seismically-active region, results from this study will contribute significantly to regional seismic hazard assessments.