Collaborative Research: Internal and external drivers of orogenic episodicity in the Ecuadorian Andes

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Ecuador contains an important record of subduction-related magmatism and tectonic environments during the building of the Andes Mountains. This research will address the roles of tectonic cycles and the accretion of oceanic crust in regulating episodes of magmatism, crustal thickening, and basin subsidence along ocean-continent subduction margins. The project will integrate results from a regional traverse across several sedimentary basins with the record of magmatism across Ecuador, the narrowest segment of the Andes. A range of analytical techniques will be employed to determine the timing of major shifts in basin development, sediment sources, and past drainages, and to recognize periods of crustal thickening, changes in sources of magmatism, and the influence of accreted oceanic crust. The study will provide insights into the geologic processes and geohazards along ocean-continent subduction plate boundaries, offering information that will benefit society by improving risk assessment and infrastructure planning. The project will also catalyze new academic collaborations within the framework of international learning experiences that will facilitate longer term collaborations between US and Ecuadorian researchers, including development of shared undergraduate and graduate geoscience field-course and field-trip opportunities.Over the past decade, competing perspectives have emerged on the tectonic evolution of Cordilleran ocean-continent plate boundaries, including the geologic history of the Andes, the global archetype for Cordilleran convergent systems. Debate largely originates from contrasting emphases on different regions (forearc vs. retroarc) and different components (basins vs. magmatic arc vs. fold-thrust belt) of Cordilleran systems. This project will incorporate analytical techniques, such as sedimentary basin analysis, isotope geochemistry, petrology, and U-Pb geochronology, to identify potentially coupled episodic phases of basin evolution and arc magmatism that may be linked to internally driven orogenic processes (including underthrusting, high-flux magmatism, and buildup then foundering of crustal/lithospheric roots), or externally driven tectonic processes including fluctuating slab dynamics (cycles of subduction shallowing vs. steepening and associated rapid vs. diminished shortening and subsidence) and oceanic terrane accretion. Ecuador contains an important yet underappreciated record of tectonic quiescence or possible extension during what has been long regarded as uninterrupted Cenozoic shortening, thickening, and uplift along the entire Andean margin. Such a fluctuating pattern of mountain building may govern the structural and stratigraphic evolution of many ocean-continent convergent margins, with implications for the tectonic regimes of subduction and collisional systems.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.