Preliminary data for volcanic aerosols from Vulcan Masaya, Nicaragua, indicate that platinum group element (PGE) concentrations are significantly higher than PGE concentrations in urban air. Urban air is generally considered contaminated with PGE released from automotive catalytic converters. Such aerosol particles regionally contaminate urban areas with Pt, Pd and Rh. Long range transport of such particles is the suspected cause of increasing PGE concentrations in the environment, as recorded in Greenland snow and ice since the mid 1970s. If PGE concentrations measured in volcanic aerosols from Vulcan Masaya are typical of volcanic aerosols in general, volatile PGE emissions are globally significant and merit detailed study. Magmatic fractionation of Re-Os-Ir-Rh-Ru-Pt-Pd is governed by the volatility of relevant PGE-containing complexes (e.g., oxides, hydrogen halides, sulfides) and the physicochemical properties of the magma (temperature, fugacities of relevant chemical species). Preliminary data for volcanic aerosols from Vulcan Masaya, Nicaragua, indicate that PGE abundance patterns are strongly and uniquely fractionated (i.e., high Pd/Pt, Os/Ir, Ru/Rh) compared to other important sources of PGE. These unique patterns, in conjunction with 187Os/188Os, may serve as a unique fingerprint for volcanic sources of PGEs, provided they are typical for volcanic exhalations in general. If PGE abundance patterns are a unique geochemical indicator of PGE sources in the geologic record, they may have potential applications ranging from the identification of disputed impact layers to assessing origins of PGE concentrations in the environment.
We propose to investigate volatility of Re, Os and complementary PGE at magmatic conditions by analyzing aerosol filters (gaseous and particle-bound PGE) from three well-monitored volcanic systems - Pu'u O'o vent of the Kilauea volcano, Hawaii; Vulcan Masaya, Nicaragua; Etna volcano, Italy. These sites encompass a wide spectrum of volcanic systems, i.e., archetypical mantle-plume, intraplate and subduction related volcanoes with significant SO2 fluxes. Our preliminary data from Vulcan Masaya seem to support the hypothesis that volatile PGE abundance patterns, in combination with Os isotope analyses, can be used to distinguish magmatic from anthropogenic and extraterrestrial PGE sources. We propose to analyze a suite of 60-100 samples for Re/Os/PGE and Os isotopic composition. Complementary major and trace element analyses will be carried out to place the Re/Os/PGE data in a broader geochemical context. Broader Impacts: In addition to advancing basic understanding of interaction between the extraterrestrial environment, the ocean, crust and mantle, this study will provide research and educational opportunities (REU) for two undergraduate Summer Student Fellows at WHOI. The project will also foster international collaborations with scientists in England and France. Peucker-Ehrenbrink and Sims will continue to participate in a variety of outreach efforts to share our scientific results with graduate students in the MIT/WHOI Joint Program and the general public.
