Geochemistry of Hydrothermally Altered Sediments, Pore Fluids, and Hydrothermal Explosion Deposits from Yellowstone Lake
Abstract
Yellowstone Lake is one of the most active hydrothermal areas in Yellowstone with several large hydrothermal explosion craters and hundreds of active and currently inactive sublacustrine hydrothermal vents. As part of the Hydrothermal Dynamics of Yellowstone Lake (HD-YLAKE) project, we studied hydrothermal alteration in piston and gravity cores from sites such as the Deep Hole vent field southeast of Stevenson Island, a now-inactive hydrothermal dome, and Elliott's Hydrothermal Crater.
Hydrothermally altered muds in gravity cores related to low-Cl fluids (less than average lake water at 5.5 mg/kg) in both the Deep Hole vent field and in a piston core from the inactive hydrothermal dome contain smectite, kaolinite, chlorite, pyrite, anhydrite, and quartz; an assemblage typical of vapor-dominated alteration in subaerial thermal basins. Dissolved SiO2 in pore fluids increases with depth to 100-150 mg/kg in most cores due to near-complete diatom dissolution during alteration. Stable isotope (δD and δ18O) values of pore fluids in the Deep Hole vent field are consistent with hot vapor-dominated (H2O, CO2, and H2S) fluids from depth mixing with lake water trapped during sedimentation. Piston cores into Elliott's Crater penetrated a thick (>3 m) sequence of explosion-derived sediment that contains quartz, albite, smectite, chlorite, pyrite, and anhydrite and lacks kaolinite; δ18O values of bulk sediment allow temperature estimates of ~170oC. This core has low-Cl (<5.5 mg/kg) pore fluids above the explosion deposits and higher Cl fluids in the explosion deposits, with a sharp increase in Cl values near the bottom of the core (to 9.5 mg/kg), indicating a transition from vapor-rich to alkaline-chloride fluids with depth. Sediments from the older Mary Bay hydrothermal explosion deposit in other cores contain quartz, albite, chlorite, pyrite, anhydrite, and smectite, consistent with alkaline-chloride fluid alteration; δ18O values suggest a temperature of 200oC. Explosion deposits in Yellowstone Lake show enrichment in most elements and depletion in As, Cu, Ta, and W relative to normal lake sediments, due mainly to alteration prior to explosion. Pore water and hydrothermal alteration studies indicate low- and high-Cl fluids produce distinctly different mineral assemblages and chemical signatures.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V33D0207S
- Keywords:
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- 4302 Geological;
- NATURAL HAZARDS;
- 7280 Volcano seismology;
- SEISMOLOGY;
- 8424 Hydrothermal systems;
- VOLCANOLOGY;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY