Methane, Hydrogen and Helium in Hydrothermal Fluids at 21°N on the East Pacific Rise

  • J. A. Welhan
  • H. Craig
Part of the NATO Conference Series book series (NATOCS, volume 12)


Methane in 350°C hydrothermal fluids at 21°N on the East Pacific Rise occurs in concentrations greater than 1.1 cc (STP)/kg. Hydrogen concentrations vary from 8 to 38 cc(STP)/kg, showing a considerable range between different vent fields. Helium concentrations exceed 0.021 cc(STP)/kg. The injection rates of methane and hydrogen into the deep ocean indicate replacement times of the order of 30 years, implying that consumption of methane and hydrogen in the water column must be very rapid. Variations of end-member concentrations of methane, hydrogen and possibly helium, as well as δ13C(CH4), among vent fields suggests either chemical control of reactive gas abundances and/or variations in gas contents of ridge crest basalts. Measurements of methane and helium in basalt glass from the EPR show CH4/3He ratios of 2.5 × 106, compared to 3.5 × 106 in hydrothermal fluid from the same area. Carbon isotope evidence, CO2 CH4 isotope geothermometry, the lack of suitable thermocatalytic sources of organic carbon, and the similarity between CH4/3He ratios in these hydrothermal fluids and mid-ocean ridge basalts, point to an abiogenic origin of hydrothermal methane, extracted directly from basalt by circulating seawater.


Carbon Isotope Hydrogen Concentration Hydrothermal Fluid Methane Concentration Ambient Seawater 
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Copyright information

© Springer Science+Business Media New York 1983

Authors and Affiliations

  • J. A. Welhan
    • 1
  • H. Craig
    • 1
  1. 1.Isotope Laboratory, Scripps Institution of OceanographyUniversity of California at San DiegoLa JollaUSA

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