Shortening, extension, and drainage reorganization in the Andean fold-thrust belt and broken foreland basin of northern Patagonia, Argentina

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The Andes Mountains of South America are a key location for mountain building along convergent plate tectonic boundaries where an overriding continental plate is deformed above a subducting oceanic plate. Although Andean mountain building is generally associated with regional collision and shortening of continental crust, recent studies point to important examples of extensional deformation. This research project will address the long-term history of crustal deformation in the northern Patagonian Andes, where alternations between shortening and extension appear to have influenced the generation of topography, erosion, river drainage systems, and sedimentary basins. The project will utilize a variety of analytical techniques, including sedimentary basin analysis, geochronology, and structural geology to determine the age, duration, and depositional processes within the Patagonian basin of southern Argentina. The project will help define processes within the Earth's crust and at the surface that influence the formation of sedimentary basins produced by both shortening and extensional deformation. The study will have implications for understanding the fundamental geologic processes and associated geohazards along ocean-continent plate boundaries, offering societal benefits in the form of information that will enable improved risk assessment and infrastructure planning. In addition, the project will initiate international scientific collaborations between academic and industry scientists and support international research and training opportunities for undergraduate and graduate students.The project will address an emerging debate for the Andes regarding the role of extension during what has been long regarded as uninterrupted shortening, thickening, and uplift along an extensive subduction margin. An orogenic system that fluctuates between compressional and extensional stresses may govern the structural and stratigraphic evolution of Andean-type convergent systems, due to both margin-wide changes in mechanical coupling driven by plate kinematics (rollback/retreating vs. advancing margin) and more-regional changes in subducting-slab dynamics (slab shallowing vs. steepening). This project will focus on an understudied segment of the Andean fold-thrust belt and broken foreland region of northern Patagonia, which contains evidence of not only Cretaceous-Cenozoic shortening and foreland basin evolution but also extensional basin development and drainage reorganization during irregular advance and retreat of the Andean magmatic arc. The research team will conduct a sedimentary/structural basin analysis and restoration of a regional east-west transect in southern Argentina, that will include an enhanced depositional and deformational record, dating of basin-bounding structures, new U-Pb chronostratigraphic and provenance constraints, and revised subsidence and magmatic histories. The results will enable integration across several basin systems in order to identify the patterns of basin genesis, unconformity development, sediment routing, and drainage reorganization during contrasting phases of shortening, extension, and stasis in the southern Andes.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.