Speaker: Dr. Lara Wagner
Title: "Flat Slab Seismicity: Clues to the subduction zone water cycle"
Abstract: Two of Earth’s unique (to our knowledge) attributes are the existence of life and the persistence of plate tectonics. One possible link between these two attributes is the Earth’s deep water cycle. In this cycle, water is conveyed by oceanic plates descending at subduction zones back into the Earth’s interior, only to be returned to the surface as these plates dehydrate through a complicated pathway that leads ultimately to volcanism and/or the hydration of the overriding lithosphere. Along the way, this water aids in the chemical evolution of the continental crust on which we live, and along with other volatiles, ensures the persistence of an atmosphere that allows us to breathe.
Tracking this water is, however, a difficult challenge. One clue about its transit from the down going plates into the surrounding mantle can be gleaned from an investigation of intermediate depth earthquakes thought to be caused dehydration related processes in the descending slab. In normal subduction zones, the water released from these earthquakes is difficult to observe, both in the slab and in the overlying mantle. However, in flat slab subduction regions, we can find unique clues about where water is released, and why. Flat slabs are sub ducting plates that descend normally to ~60 – 100 km depth and then flatten, travelling horizontally for hundreds of kilometers before resuming their descent into the mantle. These horizontal plates are too close to the overriding plate to allow for asthenosphere corner flow, meaning material released from these plates stays put and can accumulate over time. The lack of hot asthenosphere also results in a cooling thermal regime that causes a potential delay in dehydration of some hydrous phases. In this talk, I’ll present results from modern flat slab regions in South America and discuss what we can learn from flat slab seismicity about the Earth’s deep water cycle.
Short Bio: My research uses seismic waves to study how the continents we live on grow and evolve over time. Continents exist because of plate tectonics — the process by which the surface of the Earth is continually created, deformed, modified, and recycled back into the planet's interior. Earth is the only planet we know of that has plate tectonics. Without plate tectonics, we would not have an atmosphere or a magnetic field, both of which are essential for life. Despite its importance, our understanding of how plate tectonic processes work is still very basic.
My interest is in understanding what happens when two tectonic plates collide, both in the short term while the collision is ongoing, but also in the long term to study the permanent scars that remain in the continental crust for billions of years and how these might affect ongoing and future deformation and hazards.