This project will examine volatile abundances (water, CO2, Cl, and S) in olivine-hosted melt inclusions from lavas from the Austral Island chain. Previous study of lavas from these islands indicates the involvement of three distinct mantle components, including a component believed to derive from ancient recycled oceanic crust. Volatile element abundance and speciation data will be combined with major and trace element data as well as in situ Pb-isotope data to evaluate several fundamental questions regarding the genesis of these lavas and the nature of their mantle sources. Specific questions that will be addressed include: (i) do variations in Cl concentrations and Cl/K2O ratios in Austral Islands melt inclusions derive from shallow melt/crust or melt/hydrosphere interaction, or do these variations track volatile element abundances in the different mantle reservoirs involved in basalt genesis? (ii) to what extent do water and chlorine abundances correlate with other isotopic and trace element signatures indicative of the presence of recycled oceanic crust? (iii) how much water or chlorine is retained in subducted oceanic crust and returned to the deep mantle after subduction-induced dehydration?
The abundance and distribution of water and other volatile species in the mantle has a significant effect on mantle convection, melt generation, and other fundamental processes involved in the chemical and physical evolution of the Earth's interior. Interaction of the Earth's interior with the hydrosphere and atmosphere may also alter the Earth's surface environment on geologic timescales. At present, the amount and distribution of water and other volatiles in the mantle are poorly constrained. It is also unclear whether the processes of plate creation and later subduction result in a net gain or a net loss of water and other volatiles at the Earth's surface. This study will provide a better understanding of the abundance and origin of volatile species in different mantle reservoirs and the role that plate tectonics and plate subduction have played in controlling degassing (and possibly re-gassing) of the mantle over time.
