Intellectual Merit: This project is a multidisciplinary effort to understand the causes of continental intraplate magmatism. Our project will examine an area that represents one of the most accessible, yet least understood, examples worldwide of voluminous and regionally extensive continental magmatism that is young enough to allow comparison of surface expressions of magmatism with seismically imaged crust and upper mantle structures. We will determine crustal and upper mantle structure beneath the High Lava Plains of eastern Oregon, interpret the imaged structure with input from geochemical, geochronologic, and petrologic data on the young surface volcanism, and combine these observational datasets with geodynamic modeling to understand why this minimally extended part of the Basin and Range has been the most volcanically active region of North America in the late Cenozoic. We believe that this area holds key insight into to such questions as: 1) Is a plume necessary for large-volume intraplate volcanism? 2) Can shallow-dip subduction establish the conditions that lead to active tectonism and magmatism when the subducting plate eventually steepens? 3) Does flow of mantle around the edges of a subducting plate instigate focused volcanism in the overlying crust? 4) What role does "bottom topography" of the lithosphere play in localizing tectonomagmatism in the overlying crust? 5) Is crustal extension the cause or expression of continental magmatism?

We will install a dense array of broadband seismometers across two transects of the High Lava Plains. One extends from the Cascade front over 400 km southeast to the Proterozoic crust of southern Idaho. The other reaches from nonextended crust composed of accreted terranes north of the High Lava Plains 350 km southward to northern Nevada near the first exposures of pre-Cenozoic basement. Embedded within this passive seismometer deployment will be two seismic refraction lines and accompanying gravity measurements to provide high resolution images of crustal structure across these widely varied terranes. The structural information returned from the geophysical components will be combined with the geologic history derived from volcanology-geochemistry-geochronology-petrology data and compared with geodynamic modeling of mantle flow expected for various models of slab and plume behavior in the "dying" continental convergent margin exemplified by the Pacific Northwest. The objective of this synthesis is to better understand the relative roles of lithospheric structure, tectonics, flat-slab subduction, slab roll-back, and plumes as instigators of aerially extensive magmatism that continues from a plate margin well into the interior of a continent.

Broader Impacts: The collaborative nature of this project will allow numerous students to participate in a diverse set of approaches (e.g. geophysical, geochemical, petrologic) to investigate solid earth processes including field data acquisition, data processing, and data analysis. We have found that this experience commonly creates increased interest and motivation in students that lasts throughout their careers. We will interact with Federal Land Management agency representatives at several National Geologic Monuments in this area, adding to a better public understanding and appreciation of the local, still active, geology. This project, particularly in its study of Recent volcanic centers such as Newberry Volcano and the Jordan Valley Volcanic Field, can assist in better definition of the volcanic hazard represented by the ongoing magmatic activity in eastern Oregon. Finally, a significant aspect of the project will be a concerted effort to disseminate databases in accessible forms beyond our own group aided by the participation of several of the PIs of this project in various earth science cyberinfrastructure projects.