The Fate of Subducted Carbon Dioxide During Metamorphism, Syros and Tinos Islands, Greece

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Earth's subduction zones are marked by the deep ocean trenches where one tectonic plate sinks (subducts) beneath another into Earth's mantle, commonly at speeds of inches per year. Subduction zones are of critical societal importance because they host the world's largest earthquakes - including those that produce deadly tsunamis - and the most destructive volcanoes. Moreover, subduction is a driver of the geological carbon cycle, a prerequisite for Earth's temperate climate and life. Roughly a hundred million tons of carbon stored in rocks are subducted each year across the globe. Yet major disagreements surround how much of this carbon, mostly in the form of carbon dioxide, is actually released from subduction zones to make the journey back to the surface. Is this carbon dioxide largely taken deep into Earth's mantle, or does the bulk of it ascend to ultimately interact with the atmosphere and hydrosphere? The proposed work will shed light on these questions by determining the nature, processes, and amounts of carbon transport recorded by the spectacularly-exposed fossil subduction complexes of Syros and Tinos islands, Greece. This is a necessary step for quantifying natural and anthropogenic (human) contributions to the long-term evolution of climate and climate change. The proposed work is a field-based petrological study of metamorphic decarbonation processes involving serpentinite-chlorite mélange (Syros, Tinos) and metasedimentary mélange (Tinos) intercalated or tectonically juxtaposed with metavolcanic, metaclastic, and metacarbonate rocks. The closed- and open-system behavior of carbonate-bearing lithologies will be quantified to determine the degree of external fluid infiltration and make maps of fluid composition and time-integrated devolatilization fluxes. This has not been done before at a regional scale in subduction complexes. The proposal goals will be achieved via thermodynamic modeling of fluid chemistry based on measured rock and mineral compositions; Raman spectroscopy of fluid inclusions to identify simple (e.g. water-carbon dioxide) or more complex fluids containing dissolved solutes; oxygen and carbon stable isotope work to assess fluid sources and flow pathways; and mineral and bulk-rock chemical analyses to determine metasomatic reactions. Quantitative estimates of carbon dioxide transport will provide important new inputs to models of the geologic carbon cycle. The work will support a Ph.D. student from an under-represented group in science as well as several undergraduates, and produce educational modules about the carbon cycle for both the Yale Peabody Museum of Natural History and the Natural History Museum of Crete, Greece.