MARGINS Successor Program White Paper: Roots of Arc Volcanoes

We propose the fundamental topic of "Roots of Arc Volcanoes" (RAV) as a major theme for the MARGINS Successor program. This theme is specifically identified in the MARGINS 2009 Review. We envision this initiative as encompassing the arc volcano system from the slab to the surface, involving a comprehensive suite of geophysical, geochemical, and geological studies of submarine and subaerial arc volcanoes over a broad range of spatial and temporal scales. This initiative embodies some of the elements of the original MARGINS program (magma genesis, fluids, and volcanism), but with a change in focus to a specific theme of how arc volcanoes work, from bottom to top. A broad analogy can be made to the vast suite of multidisciplinary, multi-scale studies of the Hawaiian volcanoes and hotspot, funded by multiple NSF programs, and involving: "passive" seismic studies from the scale of Halema'uma'u crater to the mantle plume track; marine seismic profiling and offshore-onshore imaging; deep drilling; petrology and geochemistry of lavas; gravity, magnetic, and electromagnetic field studies; geodesy; and much more. Thus, there is great potential for synergistic work on this theme across disciplinary boundaries. Studies in Cascadia and Alaska can take advantage of recent ARRA initiatives, future USArray deployments, and cooperation with U.S. volcano observatories. The "roots of arc volcanoes" theme also has direct societal relevance in terms of providing a deeper understanding of volcano behavior and hence volcanic hazards and environmental impacts. The potential components of the RAV initiative cut across many earth science disciplines. Overall, the research components for the RAV initiative would largely mirror those of the Subduction Factory, but with a different focus: experimental and theoretical analyses; bathymetry, swath mapping, and dredging; activeand passive-source seismology; drilling; magnetotellurics; heat flow; geodesy; field studies; petrologic, geochemical and isotopic analyses; and database development. The suite of studies would of course vary for submarine volcanoes versus subaerial volcanoes. Considerable debate exists, especially in Cascadia and Alaska, regarding the role of the subducting slab during magma genesis. Geochemical studies of primitive lavas in these arcs indicate that magmas are generated via fluid-flux melting, adiabatic decompression melting of hot, nearly anhydrous mantle, partial melting of the slab, or some combination of these processes. The recent work by Grove et al. (2009) on the primary control that slab dip has on arc volcano location is an example of the type of fundamental issue that requires cross-cutting research that could be supported by the RAV initiative. In this case, a combination of experimental work on chlorite stability, geodynamic modeling of subduction zone thermal structure, and seismic estimates of slab dip led to the conclusion that the melting zone is controlled by the intersection of zones of chlorite dehydration with the (vapor-saturated) peridotite solidus, which in turn is controlled primarily by slab dip and, to a lesser degree, by convergence rate. An ultimate goal is to understand how slab petrology (Figure 1) is linked to its seismic structure and seismicity (Figure 2). Given the recent advances in locating non-volcanic tremor on plate interfaces and relating tremor to fluids, earthquakes, and aseismic slip, there is