The Chugach-Prince William terrane is an extensive accretionary complex that formed along the western margin of North America during subduction (under-thrusting) of oceanic lithosphere in the Cretaceous to Eocene. It was intruded by near-trench igneous rocks inferred to be related to the subduction of an oceanic ridge (where new ocean crust is formed), but the location of this terrane at the time of ridge interaction is under considerable debate. There are two prevailing hypotheses for its position at the time of formation: 1) The Chugach-Prince William terrane formed more or less in place and ridge interaction was related to the now-subducted Resurrection plate; or 2) the Chugach-Prince William terrane formed far to the south, was intruded by near-trench igneous rocks near a latitude of 48-49°N, and was subsequently translated along the continental margin to Alaska by strike slip faults similar to the San Andreas fault in California. The possible formation of the Chugach-Prince William terrane far to the south and subsequent translation along the continental margin is a defining event in western North American tectonics and makes testable predictions for the origin and thermal evolution of these rocks. We use geochronology, stratigraphy, petrology, structural geology, and geophysics to unravel the source region of this accretionary complex and subsequent thermal history. Together, these data are yielding important constraints on the accretion and translation history of the Chugach-Prince William terrane and has implications for the history of flanking basins such as the hydrocarbon-rich Cook Inlet basin.

This research directly addresses several key problems in North American tectonics related to terrane formation, translation, accretion, and basin formation, and is helping advance geochronologic methods used for tracking the origin and thermal evolution of sedimentary rocks. The results from this work are providing a better tectonic framework for understanding the timing and nature of basin formation (including hydrocarbon-rich strata), and the timing and extent of precious metals deposits (gold) associated with intrusive rocks. This project also has a strong educational component aimed at increasing the number of students in the geoscience pipeline and ultimately the workforce, and our effort is partly focused on recruiting students under-represented in the Geosciences. We are involved in the direct training, mentoring, and assessment of undergraduate students through the Keck Geology Consortium. Students are recruited, and assessed through the existing framework of the Consortium and this effort includes involvement of 30% of the students from non-Keck schools. There is a strong commitment to increasing the number of under-represented students in the Geoscience pipeline (this group includes African American, Hispanic, and Native American) and the new diversity initiative at the Keck Geology Consortium guarantees greater participation by this cohort. The Keck Consortium is dramatically increasing the number of under-represented student participation by several strategies including internal recruitment and external partners. The Keck Geology Consortium plays a leading role in the research training of promising students, and the majority of these students pursue a MSc and/or PhD in the geosciences. Thus the Consortium supplies the geoscience pipeline with bright, talented, well-trained students and many become leaders in the field. It is well known that research active faculty provide a successful and productive learning environment, and that student research at the undergraduate level provides students with the motivation, capability, and preparation for graduate school that typically leads to a productive career in the geosciences.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Stephen S. Harlan
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Carleton College
United States
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