Intellectual Merit. Continental magmatic arcs are the site of massive additions of mantle derived magmas which serve to drive melting, thickening, and reorganization of the crust. Much of what we know about Cretaceous and older continental magmatic arcs results from studies of the physics and chemistry of plutonic rocks, and the derivative data strongly influence models of crustal growth and evolution. In contrast to modern arcs where single eruptive units may be analyzed, plutons record a much richer, albeit complex, history and represent a much greater percentage of the total magmatic flux than volcanic rocks alone. Critical questions concern how and at what rate intermediate composition magmas move through the crustal column, and how the crust accommodates these potentially large fluxes? Key to answering these questions is to understand how large masses of crystallized magmas or plutons and batholiths are constructed. To address these questions, collaborative research is proposed to better understand sub-arc magmatic plumbing systems. This project focuses on the roots of a continental magmatic arc in the North Cascades that comprises three well-exposed intrusive bodies emplaced at different depths in the crust. Integrated field mapping, structural analysis, mineral geochemistry, high-precision geochronology and coupled isotopic studies will be employed to [1] determine the degree to which plutons represent single magma batches or complex mixtures of partially crystallized magmas of different origins, [2] estimate magma flux rates and timescales for melt generation, transport, and eruption of intermediate composition magmas, and [3] evaluate potential linkages between regional tectonic strain and magma formation. This multidisciplinary collaborative research is expected to contribute significantly to understanding of magma plumbing systems and the formation of plutons in continental magmatic arcs.
Broader Impacts. This research will support Ph.D. students at MIT and USC, and at least 2 M.S. students at SJSU, and multiple undergraduate student assistants at all 4 institutions. Bpth SJSU PIs have supervised 2 B.S. research projects supported by their most recent grants, and Paterson teaches a formal research class at USC that has involved >20 undergraduates in NSF-supported research. Graduate students from SJSU and USC will visit Kent's lab at OSU to conduct their own analyses, and the MIT graduate student will visit SJSU and assist in SHRIMP analyses. Four M.S. students at SJSU have gone to MIT to carry out U-Pb dating under the tutelage of PI Bowring and his students, and this type of interaction is expected to continue. All of the PIs routinely incorporate their research in class lectures and use research samples in lab courses. Most importantly, The PI's are demonstrating to a large cross section of new students the power of strongly interdisciplinary and collaborative work.
This project studying the processes that lead to formation and modification of the Earth's crust. Specifcally the continental crust - the portion of the crust that almost all people live on, that provides us with metals and other important resources, and where hazards like earthquakes and volcanic eruptions are produced. In the north Cascade region mountain building and erosion has lead to exposure of rocks from very deep in the crust at the surface. Our research has taken advantage of this to study rocks that would otherwise be quite innaccessible. By mapping out the distribution of various rock units and by studying the chemistry of the rocks, and the minerals that occur within them we have been able to understand more about the processes that form magma, that inject magma into the crust and how the crust responds to this. The research points to the important role of the lower parts of the Earth's crust in shaping how magma evolves. We can see indications of magma cooling within the crust and changing as it does this. In addition the cooling hot magma causes the surrounding crust to also melt. Magma from all these sources eventually gets intruded to shallow crustal levels, and in some cases also can form volcanic eruptions. In many cases this complicated mix is difficult to decipher, our work identified several locations where we were able to obtain samples that help us see these processes in greater detail. This research addresses important fundamental questions about how the Earth's crust forms and also provides insight into how mineral deposits might form and where magma for volcanic eruptions might ultimately come from. Almost all human activities rely on the Earth's crust for resources, however we know relatively little about it. Our research also provided important training for graduate and undergraduate students, and allowed researchers from a number of different institutions and with different specialities to come together to study these issues. Training includes work in the field, where mapping the distribution of rock units is paramount, and in the laboratory where chemical and other analyses are done.
