Collaborative Research: Experimental Study of H, S, Cl, and F Partitioning Between Apatite, Fluid(s), and Melts: Applications to Magma Evolution and Volatile Component Exsolution

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Intellectual merit. The volatile components water, carbon, sulfur, chlorine, and fluorine affect magma rheology and differentiation, control processes of volcanic degassing and eruption, and influence the dissolution and transport of magmatic components in fluids that cause metasomatism and hydrothermal mineralization. The degassing of magmatic volatiles from volcanoes also fundamentally affects the geochemistry of the atmosphere and oceans - thus influencing Earth's climate. The efficacy of these processes varies directly with the abundances of volatiles. Despite extensive study of magmatic volatile components via analyses of trapped silicate melt inclusions and hydrous minerals in volcanic and plutonic rocks, and complementary experimental and theoretical research, current knowledge of the behavior and abundances of volatiles is insufficient for accurate modeling of fluid processes during magma evolution. In particular, we must better understand when volatile-rich magmatic fluids first exsolve, how their compositions change during magma evolution, and how these fluids accumulate in the apices of magma chambers to control magmatic processes and volcanic activities. The ubiquitous mineral apatite [Ca5(PO4)3(OH,F,Cl)] contains fluorine, chlorine, and hydroxyl ions as essential constituents and may also contain trace- to major-element levels of sulfur. If we have quantitative knowledge of element partitioning, apatite potentially can be used to monitor volatile contents in the magmas from which it forms. The proposed investigation aims to provide that essential calibration information via controlled experiments and detailed analysis of run products formed at known pressure, temperature, and melt composition. The ultimate goal is to develop apatite as a geochemical tool for: (1) estimating magmatic volatile contents at various stages of melt evolution (not always represented by presence of primary melt inclusions), (2) tracking the behavior of volatile components during progressive magma evolution, (3) elucidating the role of magmatic fluids in processes of degassing and volcanic eruption, and (4) improving thermodynamic models that can predict these exchange processes and apply to natural systems.Broader Impacts. This project will likely result in development of powerful alternative methods for assessing magmatic volatile contents. The scientific results and their relevance to society will be conveyed to summer interns participating in an NSF-supported Research Experiences for Undergraduate students (REU) program at the American Museum of Natural History, and to teachers and the generall public via a lecture program (focused on volatiles and geologic processes) at the museum. The museum offers numerous other opportunities to share the results of scientific research with the public through electronic media in exhibition halls. The results will also be shared by training undergraduate students at the University of Maryland and by educating the public through an open-house event on Earth science at the University of Maryland.