Structural Architecture and Evolution of the Southern Flank of the Brooks Range Fold and Thrust Belt, Arctic Alaska

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A broad zone of fault-related deformation, called the Schist Belt, stretches East-West for more than 600 kilometers along the southern side of the Brooks Range in northern Alaska. This fault zone played a fundamental role in the formation of flanking sedimentary basins, the Yukon-Koyukuk Basin to the south and the Colville Basin to the north of the Brooks Range. It is also the main structure separating southern Alaska, with a geologic history tied to the Pacific plate margin, from northern Alaska, whose history is tied to plate tectonics in the Arctic Ocean. Despite its impressive physical extent, questions about its exact age and hypotheses about why and how it developed are debated. This project will study the geology and deformation history of this fault zone, sharing logistics with an international Swedish project aimed at understanding the geology of the Arctic region. The proposed research represents a contribution to basic science that will improve our understanding of the geology of the Arctic, one of the last remaining frontiers on earth. Current global interest in the Arctic makes this region a superb arena for international collaborations and offers a unique opportunity for graduate students to engage in field-based research, learn state-of-the-art analytical techniques and build their careers. Training graduate students in Arctic geoscience and international collaboration contributes to a diverse, globally competitive STEM (science, technology, engineering and mathematics) workforce for the U.S., particularly in the Arctic. International communication and collaboration is a top priority for the U.S. as Arctic nations chart their offshore-extended economic zones based on international treaties. The proposed research will also produce maps and data compilations that will represent contributions that will be useful to a broad cross-section of society as related to natural resources, including both mineral and hydrocarbons, potential geologic hazards and land-use, as well as contributing to knowledge of the geology of the Gates of the Arctic National Park. Greater understanding of the Arctic region is also important to national security considerations. Along its northern side, the Brooks Range orogen of Arctic Alaska is a Jurassic to Early Cretaceous belt of crustal shortening characterized by a classic thrust belt architecture consisting of imbricated passive margin sequences and allochthonous oceanic arc sequences. The structurally deeper, polymetamorphic core of the Brooks Range is now understood to include portions of the Arctic Caledonides and the Baltic Timanides, translated to their current position by the opening of the Arctic Ocean. The Schist Belt is defined as a zone of penetrative deformation whose fabrics and age (based on 40Argon/39Argon geochronology) are interpreted in remarkably different ways by previous workers. Our proposed work will test hypotheses and address questions about the age and origin of this belt. Geologic mapping coupled with meso- and microstructural work, including the study of quartz lattice preferred orientations, will permit along strike comparisons of deformation within the belt and determine if it represents thrust or normal sense shear. Thermochronology transects using 40Argon/39Argon methods and Uranium-Lead dating of metamorphic zircon growth will place brackets on the age of deformation and metamorphism. Apatite fission track dating will allow us to define the geometry of large-scale Cenozoic structures that led to the remarkable and unique exposures of Schist Belt rocks. The proposed work provides a unique opportunity to join efforts with a 5-year campaign funded by the Swedish Research Council and it will contribute to the broad international effort focused on the understanding the origin of the Arctic Ocean. It also offers us the opportunity to collaborate with a substantial scientific mission involving the deployment of EarthScope?s Transportable Array across the state of Alaska, which will ultimately provide a lithospheric context for this study.