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Institut für Wasserbau - IWS

Selected Topics and International Network Lectures

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Dienstag
22.11.2005
16:00 Uhr
Dr. Sebastian Geiger, ETH Zürich, Institute of Isotope Geochemistry and Mineral Resources

Hydrodynamic and thermodynamic modelling of NaCl-H2O fluids: Groundwater flow below volcanoes

Abstract: Many important geological processes in the shallow Earth's crust are related to the simultaneous, often buoyancy driven, movement of heat and dissolved salt (NaCl) in water-rich fluids. These processes encompass the formation of large metallic ore deposits below volcanoes, the cooling of new-formed oceanic crust along mid-ocean ridges, convection in sedimentary basins, or heat transported by fluid flow in geothermal systems. The hydrodynamic and thermodynamic behavior of NaCl-H2O fluids in permeable rocks is fundamentally different from that of pure H2O. During thermohaline convection, so-called double-diffusive and double-convective flow patterns can evolve, because heat diffuses at a higher rate than salt while salt is advected at a faster rate than heat. NaCl-H2O fluids can also separate into two fluid phases, a high-density, high-salinity brine and low-density, low-salinity vapor, at pressures and temperatures well above the critical point of pure H2O (374oC, 221 bar), which is likely a key driver for the formation of the world's major ore deposits of Cu, Mo, Au and other important metals. Previous numerical studies of thermohaline convection have either assumed that the fluid is incompressible and the Boussinesq approximation applies or, in the case of phase separation, that the fluid is pure water. This, however, does not account for the full complexity of thermohaline convection including phase separation at high-temperature and high-pressure. This talk will discuss new numerical approaches for modelling the hydrodynamics and thermodynamics of NaCl-H2O fluid flow and present results related to the formation of economic ore deposits.