Because many hydrous marine sediments entering subduction zones lack CO2 (i.e., lack carbonate minerals), dehydration would be dominant over decarbonation upon subduction. Under this funding, the PIs will compute subduction zone devolatilization for the major lithologic types of CO2-free hydrous marine sediments: red clays, hydrothermal (ferruginous) clays, turbidites, and mixed lithologies, i.e., radiolaria/diatom oozes mixed with clays or volcanic ash, using a variety of constraints from ODP drill sites off the Izu-Bonin- Marianas and Costa Rica-Nicaragua. Because the carbonate content of altered basalts in the upper oceanic crust increases with age, the PIs will compare metamorphic devolatilization of oceanic metabasalts in subduction zones with Jurassic crust (e.g., Marianas) with those subducting late Cenozoic crust (e.g., Costa Rica), and will quantify the relative contributions of the various volatile-bearing assemblages and assess the depth distribution of volatile release. A primary goal of the proposed research is to quantify metamorphic devolatilization for the lithologies entering these subduction zones and to compare the results with the distribution of earthquake hypocenters and volcanic activity associated with each subduction zone.
