The behaviour of components in complex fluid mixtures under high T-P conditions

Abstract

The chemical behaviour of salts in complex hydrothermal fluids is not well understood over most of the P-T conditions of geochemical interest. This study of the behaviour of electrolyte components in complex fluid mixtures over a range of pressures and temperatures is designed to help to decipher the physico-chemical conditions of natural hydrothermal processes. The information is also necessary to test and develop new equations of state for hydrothermal fluids.Specifically, we have explored the variation in the concentration of dissolved components with the composition of the host solution, at fixed component activity. In this context, highly soluble substances such as chloride salts present experimental problems. Investigations of the relative behaviour of pairs of components whose activity ratio can be fixed, prove the simplest experimentally. An example of this is exchange equilibria of the type:

Geochemical and stable isotope resetting in shear zones from Täschalp: constraints on fluid flow during exhumation in the Western Alps

“…Solubilities of Na and Ca calculated using the computer program Geochemists Workbench (Bethke, 1994) are predicted to increase as temperature decreases (at c. 10 −4 −10 −7 moles °C −1 ) with more minor depletions in Mg ( c. 10 −7 −10 −10 moles °C −1 ). These results do not change markedly when X CO2 values are varied within the limits of those recorded in the shear zones (up to 0.1: Cartwright & Barnicoat, 2002), as is also predicted by Korzhinskiy (1995). Calculations by Dipple & Ferry (1992) for a wide variety of rock types at higher temperatures yield similar results and also show that the pressure dependency of the solubility of those elements is generally far lower than the temperature dependency.…”