This project will expand our understanding of how a specific tectonic setting, flat slab subduction, affects the continents on which we live. Flat slab subduction occurs when an oceanic plate that normally descends into the Earth`s mantle at a constant angle of dip changes its geometry and instead sinks only to ~50 miles depth and then travels horizontally for hundreds of miles beneath the continent before returning to the deep Earth`s interior. An episode of flat slab subduction beneath the western United States is believed to be responsible not only for the formation of the Rocky Mountains and the extensive ore deposits of the Colorado Mineral Belt, but also for wide spread explosive volcanism that erupted ~500,000 km3 of silicic magma across the western United States between 36 and 18 million years ago (Mt. St. Helens erupted ~1 km3 for comparison). This volcanism is believed to be due to the effects of the removal of the flat slab and the resumption of a normal subduction geometry, but it has been difficult to study because of the amount of time that has passed since this occurred in the western United States, and because of uncertainty about the geometry of the flat slab that existed before that. In Colombia, there is a unique setting where a once extensive flat slab has split into two parts, one of which remains flat, and one that has comparatively recently foundered and returned to a normal subduction geometry. While this flat slab is much smaller than the one that affected the western United States, the researchers will study the processes responsible for the mountain building, ore deposits, and volcanic hazards in Colombia to gain a better understanding about how continents evolve over time and how these types of volcanic events are related to this specific tectonic environment. This project includes an embedded teacher training initiative led by the Carnegie Academy for Science Education (CASE) which will involve six teachers, two from each PI city (DC, Austin, and Phoenix). Teachers will participate in training, fieldwork, and all-hands meetings throughout the project, and will develop bilingual lesson plans that can be shared through STEM teacher networks. PIs will work closely with the teachers and with CASE in the development of these lesson plans, and will visit teacher classrooms to interact directly with students and to provide feedback. In addition, this project brings together a diverse team that includes two female PIs, and four international collaborators.

This research seeks to take advantage of Colombia`s unique tectonic setting to evaluate the effects of flat slab subduction and subsequent foundering on the geochemical, structural, and dynamic evolution of continental lithosphere. Flat slab subduction has been identified along most ocean-continent convergent margins, and has been invoked to explain major tectonic events including the Laramide Orogeny, the evolution of the Altiplano Plateau, and intraplate deformation and volcanism in China. The northern Andes of Colombia provide an ideal location to assess flat slab effects as the retroarc region in central Colombia directly juxtaposes a modern flat slab with a segment that re-steepened over ~4 Ma. The investigators will compare and contrast flat slab and normal subduction, allowing for both across-strike and along-strike comparison of the records of magmatism, crustal structure, lithospheric metasomatism, basin subsidence, and orogenic uplift. To accomplish these objectives, the research team will include multiple disciplines like geochronology, geochemistry, seismology, basin analysis, structure, tectonics, thermochronology, and geodynamics. Project PIs and collaborators will 1) seismically image both the flat and normally dipping slab regions, and the transition between the two, to obtain evidence of the developing and persistent effects of flat slab subduction on the overriding lithosphere; 2) study the magmatic and geochemical effects of flat subduction on the overriding lithosphere through time by analyzing the resulting igneous products, both above the flat slab and along the region of flat slab foundering; 3) investigate the spatial and temporal patterns of subsidence and uplift associated with flat slabs and their foundering through sedimentary and thermochronologic analyses of the Magdalena and Llanos basins and flanking Central and Eastern Cordilleras in both settings, and 4) integrate these constraints into geodynamic models that will improve our understanding of the conditions and parameters that control the dynamics of flat slabs and subduction in general.

This award is cofunded by the Prediction of and Resilience against Extreme Events (PREEVENTS) program.

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.

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Dennis Geist
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University of Texas Austin
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