TIME-DEPENDENT SORET TRANSPORT - APPLICATIONS TO BRINE AND MAGMA

We have developed a numerical model which simulates the coupling of a compositional field to a time-dependent temperature field and have applied it to natural salt and magma systems. An implicit central difference numerical approach is used in which the coupling of mass and heat is taken into account by chemical and thermal diffusion mass fluxes and a conductive heat flux. Unique in this analysis is the time dependency of the thermal regime and the role of transient thermal gradients in enhancing mass transport. Zero mass flux at the two end boundaries of a Soret cell is required in modeling certain thermal diffusion experiments for deriving the Soret coefficients of brines. For the case of an evolving temperature field, the numerical analysis predicts a transient period where thermal diffusion creates an unexpected enrichment at the hot end of the Soret cell and a depletion at the cold end. For a fixed linear temperature gradient, all NaCl enrichment normally occurs at the cold end of the cell. In a second application, several initial and boundary conditions are incorporated in the one-dimensional model in order to evaluate a variety of magmatic boundary layer scenarios. The results of the magmatic system model indicate that minimal chemical fractionation will occur as the thermal field propagates through the boundary layer.