CAREER: Shallow angle subduction and tectonic underplating of magmatic arc root zones: a recipe for high-flux magmatism?

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This project evaluates the hypothesis that shallow-angle subduction of material beneath a continent, and sticking that material to the base of the overriding plate, can cause a "flare-up" in igneous activity (i.e., more voluminous volcanic eruptions and subsurface intrusions). This hypothesis predicts that subduction should shortly precede an uptick in upper plate igneous activity and that upper plate magmatism should spatially overlap the underplated region. To test this hypothesis, this research focuses on two sites where subduction-related rocks underlie volcanic-plutonic materials: the Klamath Mountains (northern California-southern Oregon) and the central California Coast Ranges. This work has the potential to transform understanding of the relationships between shallow-angle subduction and upper plate magmatism. This research addresses the globally significant question of whether shallow-angle subduction is a net producer or destroyer of continental crust, which has implications for how the crust grows (or shrinks) over time. This project: 1) provides a field-based research experience and instructor-student and peer-student mentoring for approximately 54 students, increasing the likelihood that these students will pursue continued study and careers in the STEM (science, technology, engineering and mathematics) fields; 2) exposes two underrepresented minority undergraduate researchers and one post-baccalaureate researcher per year to modern analytical techniques and active researchers across the United States; 3) accelerates the career development of the principal investigator as a teacher-scholar, building new and enhancing existing collaborations; 4) produces recruitment and promotional materials aimed at increasing the visibility of underrepresented groups in STEM fields; and 5) sustains an active outreach program with elementary school students of the greater Twin Cities, Minnesota region. This project aims to clarify the processes that control the long-term stability of continental crust through investigation and mass balance of system inputs (e.g., tectonic and magmatic underplating) and outputs (tectonic erosion and delamination). Sites of shallow angle (i.e., a dip of less than 30 degrees) subduction, representing about 10% of active subduction zones, are a particular focus of this project, as rapid crustal growth and destruction characterize these areas. For example, melt-fertile forearc materials are likely conveyed into arc root zones during the slab shallowing process, providing a possible catalyst for high-flux magmatism in the overriding plate. With this in mind, the research objective of this work is to test the hypothesis that tectonic underplating of forearc materials directly beneath active arcs during shallow subduction events can trigger episodes of high-flux magmatism prior to arc shutoff. The scientific merits of this research include: 1) the potential to transform our understanding of the relationships between shallow subduction, tectonic underplating, and arc magmatism; 2) constraining the rates of tectonic erosion and underplating in exhumed shallow subduction systems for comparison with modern systems; and 3) clarifying the original positions of, and lithologic correlations within, the central California Coast Ranges and the central Klamath Mountains.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.