The density of H2O-NaCl-CO2/SiO2 fluids in the crust and upper mantle

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Aqueous fluids are major vector for mass (and heat) transfer in the Earth’s interior and their reactive flow through the crust and mantle controls the mobilization and transport/deposition of elements and solute species. A quantitative understanding of fluid-mediated mass transport processes thus relies on an accurate modeling of fluid-rock interactions that couples the thermochemical description with the integrated fluid flow regimes. Modeling of reactive fluid flow in deep settings is however limited due to sparse constrains on the density of mixed saline-volatile solvents at relevant high pressure-high temperature conditions. The aim of this proposal is thus to develop experimentally constrained density models for mixed complex fluids in the H2O-NaCl-CO2/SiO2 system that is a proxy for deep fluids in a broad range of geological settings, from mid-oceanic ridges to subduction zones. We will apply a combination of synchrotron X-ray absorption and Brillouin scattering spectroscopy coupled with high pressure vessels outfitted for hydrothermal studies to extend the available density data over one order of magnitude in pressure, up to 60 kbar and 800 ⁰C. The gathered experimental datasets will be implemented in continuous predictive density models valid at conditions that pertain to fluid processes in the crust and upper mantle. The new density models will be formulated to ensure compatibility with numerical codes that simulate reactive fluid flow in crustal settings. Ultimately, this will permit the application of the present results to constrain the effect of fluid chemistry on the fluid pathways and time scales and hence, on the formation of large metal deposits.