NSF Award
1347604
The modern-day topography of western South America results from the convergence and collision of two tectonic plates wherein the Nazca Plate is being shoved at a shallow angle beneath the South American plate in a process called subduction. This project will address the effects of flat-slab subduction in producing the continental deformation that has resulted in the dramatic uplift of the Andes along the western margin of South America. The PIs seek to provide better understanding of the geologic and geodynamic processes that have resulted in the growth of the Argentine Andes, and their results will have important implications for the understanding of ancient mountain building processes, such as the tectonic processes that formed the Rocky Mountains of the western United States during the Sevier and Laramide orogenies. The project involves a significant scientific collaboration with Argentinian geoscientists from the Argentina National Council of Scientific and Technical Research (CONICET) and their students, who will be involved in all facets of the project. The project will contribute to the training of undergraduate students through involvement of students in high-impact research projects and participation in cross-cultural international experiences; it will also contribute to the broadening of participation of underrepresented groups in STEM. Results of the research will be incorporated into research curricula and will be widely disseminated through presentations at meetings and publications. The project also has the potential to improve understanding of seismic risks in the study region that has experienced multiple devastating historic earthquakes. <br/><br/>First-order questions persist regarding fundamental controls of continental deformation along convergent plate margins, including causes and interactions of thin-skin upper crustal to thick-skin lower crustal deformation, influences of pre-existing crustal weaknesses, and relations to subduction dynamics. This project will integrate a variety of structural and rock magnetic techniques in order to better understand the spatial and temporal changes in deformation that have resulted from flat slab subduction of the Naza plate and its interaction with the overriding South American plate. The project will involve the measurement and analysis of faults, folds, and fracture systems; measurements of the anisotropy of magnetic susceptibility to characterize deformation fabrics; will utilize paleomagnetic analysis to understand how crustal blocks have rotated due to deformation; and will use construction of geological cross-sections utilizing geophysical data. The work will focus on five transects that span the effects of normal to flat-slab subduction, and which cross the thick-skin Sierras Pampeanas, thin-skin Precordillera, and mixed mode Principal Cordillera belts of northwest Argentina. The project will: quantify both vertical-axis rotations and spatial-temporal changes in stress/strain fields across a complex mountain system (thick-skin foreland, thin-skin fold-thrust belt, mixed mode belt); provide a new model for the 3-dimensional kinematic evolution of the region; test geodynamic models that predict different along-strike variations in structural style, stress patterns, rotations, and intraplate shortening rates related to a transition from normal to flat-slab subduction; evaluate effects of crustal rheology, basement weaknesses, and basin inversion on patterns of structural trend, stress refraction, and deformation partitioning; and statistically compare stress/strain directions estimated from fault data, magnetic fabric analysis, earthquake focal mechanisms, and available global positioning satellite data.<br/><br/>Funds to support the international activities associated with this project are being provided by the NSF Office of International Science and Engineering.
