Experimental Investigation of H2O, Cl, CO2 and SO2 Solubilities in Rhyolite and Andesite Melts at Shallow Crustal Conditions

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AbstractTo better understand how magmatic degassing influences explosive volcanic eruptions and the generation of many of Earth's metallic mineral deposits, the solubilities of the volatiles water, carbon dioxide, sulfur, and chlorine in silicate magmas will be determined experimentally. Volatiles like these are fundamentally important to the evolution of the Earth's mantle, crust, atmosphere, and ocean reservoirs; chemical mobility, via fluids and magmas, within and between these reservoirs; and magmatic degassing processes related to volcanic eruption and the generation of mineral deposits. The capacity of magmas to transport volatiles is a direct function of volatile solubilities in silicate melts, and once these volatile solubilities are exceeded one or more fluid phases exsolve from melts. Current understanding of magmatic fluid exsolution is limited to systems containing just one or two of these volatiles, thus the proposed study will investigate systematically: (1) the solubilities of (water, carbon dioxide, and chlorine) and (water, sulfur dioxide, and chlorine) in rhyolite and andesite melts, and (2) how chlorine is distributed between these geologically important melts and fluids containing these volatiles. The extent to which chlorine is distributed between silicate melt and fluids is of particular interest, because this volatile is a common component of magmas, it is important to mineralizing processes, its behavior provides key constraints on processes of magmatic degassing, and because chlorine in the atmosphere destabilizes ozone and affects other atmospheric processes.The solubility data will be generated through hydrothermal experiments conducted at pressure and temperature conditions that are representative of magmas that degas in the shallow crust, and the products of the experiments will be analyzed by well-established methodologies. The intellectual merit of the proposed investigation springs from the experimental data which are relevant to: (1) the interpretation of volatile solubility mechanisms in silicate melts, (2) models that allow computation of volatile solubilities and predict processes of magmatic degassing, and (3) ongoing geochemical investigations of magmatic degassing behavior based on studies of silicate melt inclusions (which are microscopic samples of silicate glass that are representative of trapped silicate melt). These data will also be useful for models addressing the impact of chlorine on Earth's atmosphere and climate.The proposed investigation also has broader significance because the data, their relevance to science, and their relevance to society will be shared through exhibits and public programs at the American Museum of Natural History. The results and importance of scientific research are presented to the general public through specimens, electronic media, and other media in the museum's permanent exhibition halls; lecture series focused on geologic processes; and through interactions with summer interns participating in an NSF-supported Research Experiences for Undergraduate Students program.