Chlorine Isotope Geochemistry of Volcanic Systems

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Intellectual merit. To better understand the effects of recycling of surface materials to the mantle at subduction zones, it is proposed to measure the content and isotopic composition of chlorine (Cl) in magmas and aqueous fluids from volcanoes in the Central American and Marianas volcanic arcs. Ideally, the isotopic composition (37Cl/35Cl ratios) potentially can provide critical information regarding the source of the Cl in these types of samples. Earlier work by the PIs shows that different reservoirs in subducting oceanic slabs have distinctive Cl isotopic composition, but also indicate that significant isotopic variation occurs in fumarolic gases due to isotopic fractionation associated with selective outgassing of HCl from aqueous ? thereby complicating interpretation of gas samples. It is proposed to carry out systematic studies of lavas and tephras from well-characterized active volcanoes to better constrain the Cl budget at selected sites. A laboratory study will be conducted to quantify isotopic fractionation between silicate melts and coexisting aqueous vapor, with the aim of improving interpretations of Cl data for volcanic gases. Finally, time-series studies will also be conducted on gases, and perhaps lavas, at the waxing Poas volcano in an attempt to understand how Cl systematics vary in response to increased magmatic inputs over time. Broader impacts include support for an early-career female post-doctoral scientist (Jaime Barnes) and involvement of several undergraduates in data acquisition and interpretation. Results from the proposed research project will be coupled with previous data for subduction zone lavas and ongoing work on oceanic island basalts and integrated into science classes for pre-service teachers to enhance understanding of geologic processes and geochemical recycling in the Earth''s mantle.