Collaborative Research: A late Cenozoic record of restraining bend initiation and evolution along the Denali Fault at Mount McKinley, Alaska

Major intracontinental strike-slip faults around the world display discrete bends, fault intersections, and other geometric complexities, and these are often associated with the development of significant topographic elements adjacent to the fault. Understanding how strain is partitioned into horizontal and vertical components as material is advected through a structural asperity, is an ongoing focus of research in tectonics. Constraining both the initiation and subsequent evolution of strike-slip fault structural complexities is critical to the deconvolution of the influence of near-field boundary conditions on topographic development in transpressional orogens. In particular, techniques need to examine these transpressional zones on time scales of 103 - 106 years to determine how a fault bend evolves. The Denali fault, a major right-lateral strike-slip fault, displays characteristics typical of many strike-slip faults as well as tracing out a continuous arc across southern Alaska. The highest mountain in North America, Mount McKinley (6,196 m), is situated on the inside of a ~17° bend in the mapped trace of the Denali fault. On the outside of this bend and opposite Mount McKinley is Peters Dome, which at 3,221 m is the highest point in the vicinity north of the Denali fault. The topography to the north decreases in elevation and relief both away from the Denali fault, and laterally along the fault away from Peters Dome. The age of initiation of a rapid exhumation event at Mount McKinley is well-constrained to ~6 Ma, but knowledge on the spatial patterns of exhumation and fault displacement along the restraining bend is limited. The proposed study will apply apatite U-Pb dating, K-feldspar 40Ar/39Ar, apatite fission-track and apatite helium dating in 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. Multiple techniques that cover overlapping time and spatial scales will contribute to a comprehensive and complementary model for the formation, evolution and persistence of the Mount McKinley restraining bend. Key aspects of this process will include understanding the topographic evolution and strain-partitioning as material is advected through this major structural complexity. 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 be a fundamental comparison to the structural complexities along other strike-slip faults such as the San Andreas and Alpine faults and help further our understanding of how crustal blocks interact within broad deforming zones of continental crust and the recognition of transient and persistent uplift/exhumation phenomena in the geologic record. Broader Impacts: The results of this study will complement the recent NSF-funded STEEP project in the St. Elias Mountains, provide inboard controls on regional tectonics resulting from plate boundary processes to be studied by the upcoming GeoPRISMS initiative, and anticipate the movement of EarthScope's USArray program to Alaska. Integration of this work with these initiatives will be facilitated through coordinated fieldwork, presentations at professional meetings, and collaborative participation in data acquisition, interpretation, and manuscript development. This project will support one PI in the second year as an assistant professor (Bemis) and one PI who is a new research associate (Benowitz). Graduate and undergraduate students will be fully integrated in this research, receiving hands-on experience with remote, challenging field work, training in advanced lab procedures and data processing for Quaternary dating methods, and thermochronologic techniques, and provided the opportunity to present results at scientific meetings. 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 & Preserve staff, with the fundamental goal of broadening our scientific understanding of the recent tectonic development of the centerpiece of the park. Additionally, through public lectures for the Murie Science and Learning Center and development of interpretive materials, this project will help provide answers to the general public for the question that has been asked countless times: "How did Mount McKinley (Denali) get there?"