Collaborative Research: Structure of the Nazca slab and Sierras Pampeanas

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Within subduction zones, one tectonic plate dives beneath another and recycles material back into the mantle. Stresses associated with subduction zones produce some of the highest mountains and largest earthquakes around the Earth. The Nazca plate subducts into the mantle beneath the western portion of South America. In central Argentina, it subducts at a very low angle and remains at shallow depths for 100's of kilometers before sinking into the mantle; this is the most extreme example of present day shallow subduction in the world. The Sierras de Cordoba in the eastern Sierras Pampeanas of central Argentina mark the location where the Nazca slab eventually descends into the mantle. The collocation of this mountain range with the change in slab dip suggests a connection, but the means by which stresses may be transferred from the slab to the overriding plate to uplift the mountains remain elusive. This project is focused on identifying the mechanisms through which forces could be transferred from the descending Nazca plate up though the mantle wedge and into the South American lithosphere. A great deal of active crustal deformation and seismcity occurs in the Sierras de Cordoba region; this study will help characterize the seismic hazards in the vicinity of Cordoba through improved understanding of lithospheric dynamics that will come from this study. The involvement of researchers and students from Argentina, and our resulting collaboration on data analysis, interpretation, and development of new ideas and theories, make the international component of this project one of its major strengths. The funding of this research reflects the prominence of its international component as the Geophysics program, within the Division of Earth Science, supports this project with a contribution from the Office of International Science and Engineering.There is much debate about the mechanics, dynamics, and structure of both the overriding plate and subducting slab related to flat-slab subduction. This project is undertaking a deployment of digital seismograph systems to investigate the deep structure of the eastern Sierras Pampeanas mountain range in central Argentina in order to determine details of their origin. Active basement uplifts within the eastern Sierras Pampeanas, which overlie the shallowly subducting Nazca plate, offer an ideal region to investigate the influence of flat slabs on surface deformation. The scientific goals of this experiment include determining the mechanism and mode by which the overriding South American lithosphere deforms away from its margin and understanding why the subduction angle of the downgoing Nazca plate steepens after traversing 100's of km at a shallow angle. Additionally, the fate of water, and other volatiles, within the slab as it descends into the mantle will be investigated to determine how devolatization may contribute to deformation within the upper plate or influence the coupling between shallowly subducting slabs and the overriding plate. Such knowledge will be applicable to understanding past (Jurrassic to Createcous) deformation in regions of the western United States such as Utah, Colorado, and Wyoming.