Solubility of simple pelite and granite mineral assemblages in supercritical aqueous chloride solutions.

摘要

The main focus of this dissertation is an experimental study of the solubility of pelitic and granitic mineral assemblages in supercritical aqueous chloride solutions. The solubility of the assemblage ab+kfs+and+qtz was determined at 2kbar and 600° to 650°C, and the solubility of the ab+mu+and+qtz was measured at 550°C/2kbar. Total chloride concentrations were varied from 0.01 to 4m. The solubility of the granitic assemblage ab + mu + kfs + qtz was measured at 1m total chloride and temperatures between 450° and 600°C at 2kbar. Review of previous work and evaluation of our experimental K/Na ratios of a supercritical fluid phase in equilibrium with alkali feldspars confirm that mineral assemblages must buffer all individual species in a fluid phase, including pH, to provide thermodynamically valid interpretation.; Comparison of the experimental data with thermodynamic and activity-composition models unveil that predictions of entropy of the hydrolysis reactions are incorrect. In addition, the speciation of alkali metal chlorides and the activity-composition relationship for aqueous solutes are still inadequate. Aluminum concentrations in granite and low-temperature pelite assemblages are significantly underestimated.; A direct application of the experimental data to simple mass transport calculations for the alteration of a granitic rocks is promising. However, none of the databases describe the temperature dependence of K/Na ratios adequately. The database of Pokrovskii and Helgeson (1995, 1997) best describes the experimental data for most P-T conditions, and it should be chosen for mass transport calculations. Still, quantitative mass transport calculations for metamorphic and ore-forming systems should be done with great caution.; The final part of this dissertation is a summary of a preliminary study of contact metamorphism of the Little Cottonwood contact aureole, Utah. By reconstructing the tilting of the Little Cottonwood intrusion, and mapping the reactions andalusite $\Rightarrow$ sillimanite and muscovite + quartz $\Rightarrow$ Al₂SiO₅ + K-feldspar + H₂O at the western side of the aureole, a simple thermal model is proposed, which is consistent with the observed metamorphic assemblages from the eastern to the western sides of the contact aureole.