Geochemically diverse hydrothermal vents in Yellowstone Lake, Wyoming.
Abstract
Two geochemically and mineralogically distinct classes of sublacustrine hydrothermal fluids and associated deposits have been recognized in Yellowstone Lake. The hydrothermal endmembers are represented by the Deep Hole east of Stevenson Island (SI Deep Hole) and the SE West Thumb Deep Vent field (SE WT Field), which were investigated using a remotely operated submersible vehicle (ROV) from 2016 to 2018. The SI Deep Hole is the deepest part of Yellowstone Lake (120 m), with up to 174°C fluids heated by steam that condenses on mixing with cold lake water within a clay alteration cap largely comprised of kaolinite and boehmite. The SI Deep Hole hydrothermal vents are analogous to steam-heated hot springs elsewhere in Yellowstone, such as the Mud Volcano that are typified by fumaroles and acid-sulfate fluids. The sublacustrine counterpart is more aptly termed "carbonic-acid-sulfide", owing to acidity controlled largely by dissolved CO2 and a relative lack of sulfate from H2S oxidation due to limited dissolved oxygen supply in lake waters relative to air.
The 53 m deep SE WT Field achieve fluids have temperatures of up to 141°C, and are neutral-chloride fluids broadly similar to those that produce siliceous deposits in many subaerial YNP geyser basins such as at Old Faithful. Geothermometry calculations and conservative indicator (Cl, enthalpy, and ẟD) relationships indicate the SE WT Field fluids equilibrated at ~215°C following mixing between oxygenated dilute cold groundwater and a hydrothermal parent fluid with T = 345 to 364°C, Cl = 400 ppm, and ẟD = -149‰. The ẟD values of SE WT Field fluids cannot be derived from lake water, implying km-scale lateral hydrothermal fluid flow from outside the boundary of Yellowstone Lake. The fluid compositions and hydrothermal processes operating in the two sublacustrine vent systems are broadly comparable to those that affect their subaerial counterparts, however, the hydrostatic pressures that permit more elevated temperatures than the subaerial counterparts provide a window into deeper-seated fluid boiling, mixing, redox and water-rock reactions to better understand the evolution and hazards associated with sublacustrine hydrothermal activity in volcanic-hydrothermal terrain elsewhere.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.V23A..06F
- Keywords:
-
- 4302 Geological;
- NATURAL HAZARDS;
- 7280 Volcano seismology;
- SEISMOLOGY;
- 8424 Hydrothermal systems;
- VOLCANOLOGY;
- 8488 Volcanic hazards and risks;
- VOLCANOLOGY