Jura-Cretaceous Sinistral Displacement of Terranes Along the Northern Cordilleran Margin

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One of the most controversial aspects of North American geology concerns the degree to which rocks extending from California to Alaska have been transported south and then north along the continental margin due to convergence and translation between the North American and ancestral Pacific tectonic plates during Late Cretaceous-Paleogene time. Some relationships suggest limited mobility - geologic features remain close to where they formed. In contrast, other data sets suggest thousands of kilometers of transport - rocks in much of Alaska, British Columbia, Washington, and Oregon first moved south to the latitude of Mexico, and then moved back north to their present positions. The uncertainty in coast-wide transport hinders our ability to reconstruct the geologic evolution of western North America and to understand the origin (and future discovery) of important energy and mineral resources located in these regions. This project focuses on determining the amount of southward motion accommodated on fault systems that extend from northwestern Washington to southern Alaska. In addition to the scientific goals of the project, the award is supporting important societal outcomes by training students in an important discipline that is contributing to the development of a diverse, globally competitive STEM workforce. The research project also involves collaboration with researchers from the British Columbia Geological Survey.This project involves field and laboratory analysis of fault systems that may have accommodated up to 1600 km of southward motion of rock assemblages. The investigators will conduct detailed structural analyses to determine the amounts of displacement on recognized faults, map areas between recognized faults to evaluate continuity, and collect samples that will constrain when motion occurred. Field studies will focus on faults in coastal British Columbia given that these are the best-known segments of the faults - their extensions into Alaska and Washington are not well constrained. The scientific objectives of the project include: 1) testing the hypotheses that each of these two fault record approximately 800 kilometers of Late Jurassic-Early Cretaceous sinistral motion, (2) evaluating the alternative interpretation that the Insular and Intermontane tectonostratigraphic terranes are separated by an Early Cretaceous suture zone, (3) using this new information to evaluate current models for Cordilleran paleogeography, and (4) establishing the sinistral faults as world-class examples of shear zones operating within an active magmatic arc during oblique subduction. Field and laboratory analyses will be conducted in large part by undergraduate students at the University of Arizona in an effort to provide opportunities to learn techniques of geologic mapping in a frontier area, and to perform geochronologic and geochemical analyses using state-of-the-art instruments at the Arizona LaserChron Center (University of Arizona). Each student will be sufficiently engaged in the field and laboratory studies that they will be able to prepare a manuscript for publication that includes detailed and regional geologic maps, descriptions of critical structural/intrusive relations, large geochronologic and geochemical data sets, and interpretations of broad significance.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.