An experimental and theoretical study of geochemical processes in active and fossil hydrothermal systems

The effect of temperature on metal mobility in subseafloor hydrothermal systems: Constraints from basalt alteration experiments. Crystalline basalt was reacted with a Na-Ca-K-Cl fluid of seawater chlorinity at 400{dollar}spcirc{dollar}, 350{dollar}spcirc{dollar}, and 300{dollar}spcirc{dollar}C, 400 bars and a fluid/rock mass ratio of 1, to assess the effect of temperature on metal mobility in ridge-crest hydrothermal systems. Basalt alteration at 400{dollar}spcirc{dollar}C yielded a fluid characterized by high Zn, Cu, Fe, and Mn concentrations. Lowering temperature to 350{dollar}spcirc{dollar}C, and then to 300{dollar}spcirc{dollar}C, caused dissolved metal concentrations to decrease drastically. Kinetic trends observed during the cooling phases of the experiment are confirmed by the relative abundances of dissolved metals in hot-spring fluids influenced by heat loss processes. These results help constrain maximum temperatures attained by ridge-crest hydrothermal fluids in subseafloor reaction zones.; Organic-rich sediment alteration: An experimental and theoretical study at elevated temperatures and pressures. Organic-rich sediment was reacted with seawater at 200{dollar}spcirc{dollar} and 300{dollar}spcirc{dollar}C, 500 bars, and an initial fluid/sediment mass ratio of 4 to evaluate the role of organic matter in sediment alteration processes at elevated temperatures and pressures. Fluid chemistry varied systematically in response to organic matter decomposition and aluminosilicate alteration.; Experimental results permit us to evaluate fluid-mineral equilibria in complex fluids containing high dissolved concentrations of organically derived species, and constrain better alteration processes in subseafloor hydrothermal systems at sediment covered spreading centers, such as the Guaymas Basin, Gulf of California.; Experimental determination of calcium hydroxide and calcium acetate complex stability at 100{dollar}spcirc{dollar}-350{dollar}spcirc{dollar}C and 500 bars: Constraints from portlandite solubility in deionized water and acetate solutions. The solubility of portlandite was measured in H{dollar}sb2{dollar}O and acetate solutions of varying concentration (1-10 mmolal) in the temperature range 100-350{dollar}spcirc{dollar}C at 500 bars. Stability constants for calcium acetate and calcium hydroxide complexes were retrieved from the experimental data and indicate increased stability of calcium acetate and calcium hydroxide with increasing temperature. These results allow us to assess the solubility of metal sulfides in organic-rich hydrothermal systems.