Testing Jura-Cretaceous Terrane Displacement Hypotheses - a Critical Piece of the Cordilleran Puzzle

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Collision of crustal fragment at convergent plate boundaries (subduction zones) is a fundamental mountain building process called accretionary orogenesis. It is important for us to better understand this process because it gives rise to expansive mountain belts (orogens), profoundly influencing long-term global climate patterns, hosts multiple styles of ore deposits, and creates some of the most hazardous geologic environments on Earth. The North American Cordillera is a classic accretionary orogen that is a product of protracted oblique convergence with oceanic plates along the continent's western margin for >200 million years. Changes in the obliquity over time led to tectonic settings that switched between compressional and extensional regimes, both accompanied by varying degrees of left-handed (sinistral) and right-handed (dextral) lateral shearing. This shearing imparted southward and then northward displacements of outer western portions of the Cordilleran orogen. Many of the structures and other geological relationships used to assess these displacements have been obscured by younger overprinting events. The resulting uncertainty in estimates for these displacements (100's to 1000's km) hinders our ability to reconstruct the geologic evolution of western North America and is one of the most controversial aspects of Cordilleran geology. The long-term vision of my research program is to apply my research strengths in innovative ways to unravel complex and enigmatic processes involved in mountain building and facilitate analysis of secular changes of tectonic processes throughout Earth history. Over the next 5 years, the proposed research will focus on testing hypotheses that suggest >800 km southward displacement of the outer western portion of the Cordillera in Late Jurassic-Early Cretaceous time. Short-term objectives involve dating of structural and petrologic processes coupled with detailed field investigations within southwest BC and Yukon where critical geological relationships will be carefully analyzed using state-of-the-art techniques. Specifically, we will: 1) Test hypotheses that invoke significant southward displacement of western portions of the Cordillera in Late Jurassic-Early Cretaceous time, and (2) Evaluate alternative hypotheses that suggest the western Cordillera is separated by a Cretaceous suture zone from the more inboard portion of the Cordillera. Our findings will provide a more sophisticated understanding of Cordilleran mountain building processes. This will benefit a broad base of researchers working on similar problems in the Cordillera and worldwide. Canadian Industry will also benefit from the additional insight that can help inform exploration strategies for ore deposits in Yukon and BC.