Helium Isotopes In Geothermal And Volcanic Gases Of The Western United States, I, Regional Variability And Magmatic Origin

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Journal Article: Helium Isotopes In Geothermal And Volcanic Gases Of The Western United States, I, Regional Variability And Magmatic Origin

Abstract
Helium isotope ratios in gases of thirty hot springs and geothermal wells and of five natural gas wells in the western United States show no relationship to regional conductive heat flow, but do show a correlation with magma-based thermal activity and reservoir fluid temperature (or total convective heat discharge). Gases from high-T (> 200°C) reservoirs have 3He/4He > 2 _ the atmospheric value, with high He concentrations due to the input of magmatic helium. Low-T reservoirs generally have 3He/4He less than the atmospheric ratio, with very low H2 contents, which appear to be qualitative criteria for the absence of a magmatic heat source. To first order, He/(CO2 + H2S) ratios are inversely correlated with 3He/4He and are consistent with a two-component mixture of radiogenic (crustal) and magmatic (mantle) helium. The 3He-enriched high-T component has a restricted range of He/(CO2 + H2S) between about 5 and 50 ppmv. On the premise that CO2 and H2S concentrations are T-dependent due to mineral-fluid equilibria, the correlation of reservoir temperature and 3He/4He ratio, together with the restricted range of He/(CO2 + H2S) ratios observed in high-T magmatic systems, suggests that the amount of magmatic He and the amount of CO2 (and H2S) in these geothermal reservoirs are related to fluid temperature via the amount of magmatic heat and volatiles input to a particular geothermal reservoir.

Authors 
J. A. Welhan, R. J. Poredai, W. Rison and H. Craig








Published Journal 
Journal of Volcanology and Geothermal Research, 1988





DOI 
Not Provided
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Citation

J. A. Welhan,R. J. Poredai,W. Rison,H. Craig. 1988. Helium Isotopes In Geothermal And Volcanic Gases Of The Western United States, I, Regional Variability And Magmatic Origin. Journal of Volcanology and Geothermal Research. (!) .


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  1. U.S. West Region
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