Experimental Investigations on the Role of H2O in Magmatic Processes

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Intellectual Merit: Experiments are proposed to develop quantitative models of the effects of H2O on the temperature and pressure of melting in the uppermost mantle and fractional crystallization in the Earth's crust. The cycling of water through the Earth's interior is of fundamental importance for understanding the chemical evolution of the Earth over geologic time. The importance of H2O in igneous processes has been known for a long time, but experimental calibrations of the effects of H2O are few and far between. Such data are necessary for developing quantitative tools for estimating H2O abundances in magmas and understanding the influence of H2O on magmatic processes. To make progress new measurements are required on broad range of experimental projects.Three projects are proposed. 1) A systematic investigation of the influence of H2O on the liquidus of natural basaltic melts. These experiments will determine the effects of variable amounts of H2O on liquidus temperature. The experiments will form the basis for models of melting point lowering and help resolve the considerable uncertainty on the influence of small amounts of H2O on melting. 2) Investigation of the role of H2O, pressure and mantle composition on garnet peridotite melting. These experiments will provide quantitative estimates of the role played by H2O and mantle bulk composition (primarily the alkali elements Na2O and K2O) on the composition and temperature of magmas produced in subduction zone and sub continental mantle environments. 3) Experimental studies of the role of H2O and pressure on fractional crystallization of basaltic melts in the crust. In arc magmatic systems the compositional characteristics of differentiated arc magmas and their mineral assemblages provide evidence of the pre-eruptive H2O content, temperature and depth history of differentiation. Experimental studies of basalt and andesite magmas will be carried out at pressures of 300 to 800 MPa over a range of oxygen fugacities under H2O-saturated conditions. This work is motivated by the high pre-eruptive contents (up to 10 wt. % H2O) that have been inferred in arc magmas from the Cascades and Mexican Volcanic Belt. For all of the preceding studies we will develop thermodynamically based analytic models that allow prediction of conditions of melting/crystallization and compositions of melts generated when H2O is involved.Broader Impacts: The information derived from these studies will be broadly disseminated through publication in profrssional journals. The information on H2O will be of broad interest in the geodynamics and mineral physics community and ultimately has relevance for the origin of the Earth's oceans and life on Earth. The experimental expertise gained from this study will be shared with other members of the experimental community and models for predicting temperature, H2O content and pressure of melting/crystallization will be developed and distributed for petrologic modeling. This project will train graduate and undergraduate students in research methods of experimental petrology/geochemistry. The research will allow them to participate in the design, execution and interpretation of experiments, which often provides motivation and interest that lasts throughout their scientific career.