Helium isotopes: Lower geyser basin, Yellowstone National Park

Journal Article · Tue Nov 10 04:00:00 EST 1987 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JB092iB12p12477· OSTI ID:5563574

Kennedy, B M; Reynolds, J H; Smith, S P; Truesdell, A H

High /sup 3/He//sup 4/He ratios associated with the Yellowstone caldera reflect the presence of a magmatic helium component. This component is ultimately derived from a mantle plume capped by a cooling batholith underlying the caldera. In surface hot springs, fumaroles, etc., the /sup 3/He//sup 4/He ratio varies from approx.1 to 16 tims the air ratio. The variations are produced by varying degrees of dilution of the magmatic component with radiogenic helium. The radiogenic helium is crustal-derived and is thought to be scavenged from aquifers in which the hydrothermal fluids circulate. We determined the helium iosotopic composition in 12 different springs from the Lower Geyser Basin, a large hydrothermal basin with the caldera. The /sup 3/He//sup 4/He ratio was found to vary from approx.2.7 to 7.7 times the air ratio. The variations correlate with variations in water chemistry. Specifically, the /sup 3/He//sup 4/He ratio increased with total bicarbonate concentration. The dissolved bicarbonate is from gas-water-rock interactions involving CO/sub 2/ and Na silicates. The concentration of bicarbonate is a function of the availability of dissolved CO/sub 2/, which, in turn, is a function of deep boiling with phase separation prior to CO/sub 2/-bicarbonate conversion. The correlation of high /sup 3/He//sup 4/He ratios with high bicarbonate is interpreted as the result of deep dilution of a single thermal fluid with cooler water during ascent to the surface. The dilution and cooling deters deep boiling, and therefore both CO/sub 2/ and /sup 3/He are retained in the rising fluid. Fluids that are not diluted with boil to a greater extent, losing a large proportion of /sup 3/He, as well as CO/sub 2/, leaving a helium-poor residual fluid in which the isotopic composition of helium will be strongly affected by the addition of radiogenic helium.

• Research Organization: Department of Physics, University of California, Berkeley, California
• OSTI ID: 5563574
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 92:B12; ISSN JGREA
• Country of Publication: United States
• Language: English

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AGE ESTIMATION
CHEMICAL COMPOSITION
CHEMISTRY
EARTH MANTLE
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOCHEMISTRY
HELIUM 3
HELIUM 4
HELIUM ISOTOPES
HOT SPRINGS
IGNEOUS ROCKS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
MAGMA
NUCLEI
PLUMES
PUBLIC LANDS
ROCK-FLUID INTERACTIONS
ROCKS
STABLE ISOTOPES
THERMAL SPRINGS
VARIATIONS
VOLCANIC ROCKS
WATER CHEMISTRY
WATER SPRINGS
YELLOWSTONE NATIONAL PARK