Balancing Budgets: Integrated Broadband Seismology and Shortening Estimation in the Fuegian Andes

The tectonic evolution of the Fuegian Andes is one of the least understood aspects of the South American Cordilleran orogeny. The limited observations of crustal thickness and crustal shortening in the region appear to suggest that this portion of the orogen has a significant mass imbalance. If this mass imbalance is confirmed by the observations and analysis proposed in this project, it would have significant implications for the processes of crustal evolution in orogenesis as well as broad implications for other earth processes. To address this important problem, we propose an integrated experiment that combines broadband seismological analysis and structural, stratigraphic, and low-termperature thermochronometry to place new constraints on both the crustal thickening and crustal shortening in the Fuegian Andes. We will deploy a 15 station IRIS/PASSCAL broadband seismic network that crosses all major terrains of the Fuegian Andes for a period of two years. Receiver function analysis of this deployment will yield detailed variations in the crustal thickness across the orogen necessary for mass balance calculations and kinematic history reconstruction. Shear wave anisotropy analysis and any lateral changes in crustal structure will provide constraints on potential contributions of lateral escape of crustal material. Accurate shortening estimates will be developed through integration of ongoing structural studies in the region with the application of foreland basin migration methods. Inclusion of thermochronometry of key tectonic domains and sediment provenance data in the Magallanes basin will put tight bounds on the derived shortening estimates. If our work establishes that the thickness-shortening imbalance is significant, the required crustal efflux in the Fuegian Andes would have far-reaching implications. Within a purely orogenesis framework, the imbalance would provide insight into the efficacy and magnitude of crustal removal mechanisms, including tectonic erosion via ridge subduction that could prove to be transformative. Lead-PI: Dave Barbeau, University of South Carolina. Collaborators: Dr. Mario Pardo, University of Santiago, Chile; Dr. Eduardo Olivero, CADIC, Ushuaia, Argentina; Dr. Marino Russi, OGS, University of Trieste, Italy; Dr. Keith Klepeis, University of Vermont