Collaborative Research: Resolving thin-skinned and basement-involved deformation within a seismically active broken foreland region, San Juan, Argentina

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The cities of Mendoza and San Juan, Argentina, have been repeatedly damaged or leveled by large-magnitude earthquakes generated by geological structures associated with Andean mountain building. Because active seismicity occurs along faults that can be expressed at or hidden below Earth’s surface, the nature and history of these enigmatic structures remains debated. Several competing geologic models have been proposed that link the seismicity at depth with faults and mountain ranges expressed at Earth’s surface. This project will address these debates through fieldwork to map fault relationships and measurement of associated sedimentary basin deposits that record the uplift and erosion history of actively growing Andean ranges. A variety of geochronologic and low-temperature thermochronologic analytical techniques will be employed to determine the timing and magnitude of deformation across the geological structures. Results will be integrated using computational models to help resolve the debated geologic history for these Andean ranges. New field and analytical records of long-term fault deformation will be integrated with geophysical observations and decades of earthquake data with the help of collaborating Argentinian scientists. This will lead to a better understanding of how tectonic forces are partitioned among deep and surficial geologic structures and which faults may generate large magnitude earthquakes, information that is critical for assessments of Andean earthquake hazards with the potential to impact human populations and infrastructure. In addition to the scientific goals of the research, the award supports the development of infrastructure to support the engagement of diverse and historically underrepresented high school, undergraduate, and PhD-level students in geoscience research and education. This will involve mentoring undergraduate and graduate students at the participating institutions and creating a place-based educational virtual field trip through the western USA and field area in Argentina.Tectonic stresses associated with flat slab subduction have driven deformation 800 km inboard across the broken foreland of west-central Argentina. Ongoing shortening accommodated within the overlapping thin-skinned and basement-involved structural provinces makes this broken foreland region one of the most seismically active places on Earth. However, there is no consensus on the structural or kinematic links between the thin-skinned Central Precordillera, the Sierras Pampeanas basement uplifts, or the enigmatic thrust front of the Eastern Precordillera structural domain. The principal investigators aim to resolve the temporal and kinematic relationships among structures by (1) determining the timing and magnitude of deformation in the Eastern Precordillera thrust front and (2) interrogating how spatial patterns in exhumational cooling and subsidence coincide with predictions based on the various structural geometries and kinematics proposed for the region. Their research plan will integrate geologic and structural mapping, basin analysis, geo- and thermochronology, and flexural thermokinematic modeling to discriminate between hypothesized structural models. Evaluating spatial-temporal relationships among the seismically active, structural domains in Argentina will inform models of subsurface structural geometries, how shortening transfers from lower to upper crustal levels, and the long-term interactions between frontal thrust structures and foreland-basin sedimentation. New results will quantify the effects of enhanced mechanical coupling between the subducting and overriding plate during flat slab subduction, which dictates the thermo-tectonic evolution of orogenesis and topographic growth and decay of mountain belts.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.