Detrital Zircon geochronology applied to Cordilleran Tectonics

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This 5 year research program is part of a long-term effort to unravel the complex tectonic history of the mountains of western North America (N.A. Cordillera). The N.A. Cordillera is one of the most intensively studied mountain belts on earth and a key natural laboratory for studying feedback relationships between the deep mantle, lithosphere, hydrosphere and atmosphere. Although much is known about the evolution of the N.A. Cordillera, and many workers are focused on its genesis, there are still important fundamental questions and contradictions that remain unresolved or poorly explained. Resolving these, is important to the international earth science community because of North America’s important role as a natural laboratory for research into continental plate tectonics. If we do not understand the best-studied continent on earth then how do we extrapolate to other parts of the world that are less well understood? The most important problems remaining in North American tectonics: 1. The Baja - BC controversy, 2. Terrane processes: How and where are terranes made, transported and accreted? 3. Orogenic and magmatic cyclicity: Why do magmatic arcs shut down and flare up and how is this related to terrane processes 4. Subduction initiation: How does subduction initiate and propagate, what are the rates, and how does this process relate to the terrane processes? These unresolved questions are all central to our understanding of the last half a billion years of western North America’s tectonic evolution. In addition, the answers to theses questions impacts how scientists view continental tectonics in general, at the global scale. A key outcome of the next five years of research by my group is the resolution of the The Baja-BC controversy, which is centered on paleomagnetic data and basic geologic observations. The paleomagnetic data require large-scale south to north transport of terranes whereas the geologic observations are seen as precluding such lateral displacements. We are reconciling the geological and paleomagnetic data via the use of high-resolution detrital zircon geochronology as an independent constraint on the lateral movement of crustal fragments. Success in this area will change the tectonic history of western North America and contribute to resolving questions 2 and 3 above. Another important outcome of this program will be to establish Haida Gwaii as North America’s natural laboratory for subduction initiation. Our research program will provide the first data that records the uplift and erosion associated with the initiation of Pacific plate subduction beneath western North America. We will know when subduction initiated, propagation rate and what the effects on the overriding plate are. This research program is important to Canada because it raises Canada’s profile as a transformative agent in the earth sciences while training Canadian HQP who will transfer knowledge and skills.