YELLOWSTONE RESEARCH

The Grand Canyon of the Yellowstone River, Yellowstone Park, has incised about 300 vertical meters of post-caldera rhyolites that were altered by hydrothermal fluids related to older hot spring activity. The rocks provide a unique opportunity to investigate water/rock interaction in hot spring vents and feeder systems. They have been largely ignored by past researchers, who have focused on the spectacular active hot springs in the Park that serve as modern analogues to the older Canyon hydrothermal systems. One preliminary Ar-Ar age on alunite has shown that the alteration is at least 143,000 years old (from Dr. Mike Cosca’s lab, University of Lausanne, Switzerland). More analyses are planned.

This research has been funded recently by the National Science Foundation. Opportunities are available for graduate student research. Please contact me for more information (plarson@wsu.edu).

Grand Canyon of the Yellowstone River:

Older Hydrothermal Alteration

Pervasive hydrothermal alteration in the Grand Canyon of the Yellowstone River below Inspiration Point.

The temperature of boiling (pure water), the mole fraction of liquid and vapor in a closed system boiling model, and oxygen isotope fractionations between liquid-steam and quartz-water (l) for a hydrothermal fluid rising along the hydrostatic boiling curve for 300 meters below the surface. These curves provide one set of parameters for interpreting the hydrothermal environment in the canyon walls. Preliminary oxygen isotope ratios for hydrothermal quartz within 10 meters of the paleosurface range from about -2 to 2 per mil.

Graduate student Akinori Takeuchi and myself on the edge of the canyon on Sulfur Creek, near Seven Mile Hole in the Grand Canyon. The rocks below us are altered Tuff of Sulfur Creek (470 ka), one of the rhyolites of the Upper Basin Member of the postcollapse rhyolites. Hydrothermal minerals near this area yield an Ar-Ar age of 138 ka.

Preliminary research results are being presented at the Fall, 2006, AGU meeting in San Francisco. The poster title is “Older shallow hydrothermal activity along the north edge of the Yellowstone caldera” (Larson, Cosca, Takeuchi, and Yano). Two figures from the poster are shown here.

Ar-Ar plateau age for hydrothermal alunite from the Seven Mile Hole area, Grand Canyon of the Yellowstone River. The analysis was conducted in the laboratory of Dr. Mike Cosca, University of Lausanne, Switzerland.

Chemical gains and losses due to rock-hydrothermal fluid interaction. The green pattern represents unaltered Tuff of Sulfur Creek and Canyon Flow, the canyon wall protoliths. Red lines are kaolinite-alunite altered rocks, black lines are illite-silica altered rocks.