Variations Along a Continental Convergent Margin: Seismic imaging of the western margin of South America

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Convergent margins, where an oceanic plate dives under the edge of a continental plate, are the sites of many fundamental Earth processes and features that include the world?s largest earthquakes, the longest volcanic chains with some of the youngest supervolcano eruptions, and one of the world?s longest mountain ranges, the Andes. The subduction of the (Pacific) oceanic plate beneath the western margin of South America constitutes the largest ocean-continent convergent margin system on Earth, and hence, is an ideal location to study these important processes and features. We propose to study a large portion of the South American convergent margin by taking advantage of existing seismic data from over 1000 permanent and portable seismic stations that span over 4000 km of the central Andes. We will use modern computational techniques to generate seismic images of the subsurface beneath the Andes to depths as great as 1000 km. By using these new seismic images, our specific scientific goals are to improve our understanding of how earthquakes and volcanoes are building and destroying the mountains, and whether and how water is transported to great depths in the Earth. This project will build on and synthesize two decades of work in the region by the seismology group at the University of Arizona and our scientific collaborators in Peru, Bolivia, Chile, Argentina, and Brazil. The broader impacts include training graduate students in modern seismic techniques and strengthening our international collaborations in South America. Seismic methods potentially provide the highest resolution images of the Earth from the upper crust to the lower mantle. We will use Surface Wave Tomography, Finite-Frequency Teleseismic Travel Time Tomography (P- & S-wave and Vp/Vs), Receiver Functions and a joint inversion of Surface Wave Data and Receiver Functions to produce uniform seismic images of the western margin of South America. Using our newly developed seismic images, our specific scientific goals are to:? Evaluate the along strike role of delamination in the building of the Andes.? Investigate the along strike variability in lower crustal accommodation of crustal shortening, including pure shear thickening, lower crustal flow, and high-angle Moho-cutting faults.? Revisit the question of the importance of magmatic addition in the thickening of the Andean crust. ? Investigate the deformation of the subducted Nazca slab as it penetrates the mantle transition zone, and the role of deeply subducted fluids in the mantle transition zone and below the slab.This project will increase our knowledge about mountain building, crustal deformation and the subduction process by producing a uniform set of high-resolution seismic images of a large along-strike region of the western margin of South America. With uniform seismic images, we can better evaluate different mechanisms that create high elevations and the causes of along-strike variability. Our last goal is related to improving our understanding of the deeper structure of the Nazca slab and the surrounding mantle. Our improved seismic images will help us evaluate the presence of and pathways for water in the mantle transition zone.