Extensive hydrothermal rock alteration in a low pH, steam-heated environment: Hot Springs Basin, Yellowstone National Park

摘要

We present water chemistry data for hot bubbling pools in Hot Springs Basin (HSB), one of the most thermally active basins in Yellowstone National Park, as well as chemistry and water discharge data for Shallow Creek, which drains HSB. The waters are characterized by a low pH and high sulfate and low chloride concentrations. In the bubbling pools, the molar ratios of Na/K and Mg/Ca are ＜ 1, but in Shallow Creek Na/K is ＞ 1, suggesting widespread deposition of alunite. Equilibrium calculations with SOLMINEQ88 indicate that the bubbling pools are undersaturated with respect to primary igneous minerals, supersaturated with respect to alunite, and near saturation with amorphous silica. Two of the pools are also supersaturated with kaolinite, and one is supersaturated with gibbsite and smectite. Based on the mass flux in Shallow Creek and the composition of Lava Creek tuff, we calculate a minimum erosion rate of 0.5 mm/yr in HSB, which is 1-2 orders of magnitude lower than deformation rates measured with geodetic techniques.