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Causes and Mechanisms of Focused Exhumation Along the Denali Fault

Project: Causes and Mechanisms of Focused Exhumation Along the Denali Fault, Eastern Alaska Range

Investigators: Paul Fitzgerald (with SU students and in collaboration with scientists and students from University of Alaska, Fairbanks, and University of California, Davis)

Department: Earth Sciences

Sponsor: National Science Foundation

Amount Awarded: $139,856 (2010-2012)

Background: Since the 2002 Denali earthquake (7.9 magnitude) in the eastern Alaska Range, scientists have focused  on how much slip and convergence occurs along the 1,200-kilometer-long Alaskan Denali Fault system. Similar in part to the San Andreas Fault of California, the Denali Fault features extreme mountainous terrain along parts of its length associated with basins in some areas. The location of these mountains and basins and the timing of their formation with respect to geologic structures and plate boundary forces will be used to determine the distribution of crustal deformation through time. The eastern Alaska Range, one part of the topographic signature of the eastern Denali Fault, rises dramatically from the tundra to sharp glaciated peaks reaching 4,000 meters in height, forming a narrow but high-relief region immediately north of the fault. As the fault continues west, the topography drops significantly, then rises again to form the central Alaska Range, home to Mt. McKinley and Denali National Park. Uplift of the Alaska Range is related to plate boundary processes—such as subduction of the Pacific plate under North America and collision of the Yakutat microplate with southern Alaska. However, when and why the uplift occurs along the eastern Denali Fault remains unclear. The proposed research seeks to understand the time-temperature history of rocks in the eastern Alaska Range and hence determine regional patterns of exhumation and uplift over approximately the last 30 million years. 

Project investigators will undertake a high-resolution multi-technique thermochronological approach combined with mapping of rock types and measurements of structures within the rock units along the eastern Denali Fault. This approach will document variations in exhumation rates, allowing scientists to understand local exhumation patterns in the mountains associated with the shape and location of various faults. Structural studies will focus on the regions with the most extreme exhumation, both in terms of rate and total amount, to understand what controls these patterns with respect to near-field boundary conditions (for example, geometry of the Denali and related faults). Linking the structural history to exhumation rates will permit scientists to evaluate the temporal and spatial influence of such geodynamic drivers as changes in Pacific versus North America plate motion, dip of the subducting slab, and the collision of buoyant Yakutat block. 


Impact: This study has relevance to fundamental problems of major strike-slip fault systems, including what causes localized exhumation and how strike-slip deformation is transferred into the lower crust. By providing a better understanding of contributing factors for the formation of the mountains and hence seismic behavior along the fault, the results will contribute to the region's earthquake hazard predictions and seismic hazard maps. The Trans-Alaska oil pipeline and future $26 billion Alaska gas pipeline cross the eastern Alaska Range and Denali Fault. The pipeline is designed to withstand strike-slip motion, but the effects of a significant vertical component could break the pipeline and be disastrous. Current natural gas exploration in the Tanana Basin, north of the study area, would also benefit from the research because the region's basin development is, in part, a flexural response to mountain building. The outcome of this research is therefore of interest to the public in Alaska and elsewhere and a wide range of Earth scientists. The project also integrates research with teaching, providing training for four young scientists. A science journalist will collaborate with the group on fieldwork and write essays for newspapers and magazines about the remote mountain research experience to bring science to the general public.  

Photo courtesy of Paul Fitzgerald