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Stable isotope studies of vent fluids and chimney minerals, southern Juan de Fuca Ridge: Sodium metasomatism and seawater sulfate reduction

Journal Article · · J. Geophys. Res.; (United States)
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Sulfur isotope values (delta/sup 34/S) or H/sub 2/S in vent fluids from the southern Juan de Fuca Ridge hydrothermal sites range from 4.0 to 7.4% and are variably /sup 34/S-enriched with respect to coexisting inner wall chimney sulfides. Chimney sulfides range from 1.6 to 5.7%. The chimneys consist of Fe-sphalerite zoned to inner zinc sulfide and chalcopyrite ( +- isocubanite)-pyrrhotite lining channels. Sulfide from inner walls of type A chimneys have the lightest delta/sup 34/S values. Type B chimneys (porous, unzoned, low-Fe-sphalerite) have the isotopically heaviest chimney sulfides and occur at vent sites distal to the along-axis shallow point of the ridge crest, hence distal to the magma chamber. These variations are largely ascribed to sulfate reduction by ferrous iron in the hydrothermal fluid in chimneys of substrate mounds, probably due to transitory entrainment of ambient sulfate-bearing seawater. The delta/sup 18/O values of end-member hydrothermal fluids range from 0.6 to 0.8%, significantly lower than the delta/sup 18/O values at 21 /sup 0/N vent fluids. The deltaD values of the fluid samples range from -2.5 to 0.5%. Isotopic differences from the 21 /sup 0/N fluids may be due to slightly higher water/rock ratios, approximately 1.0, in the southern Juan de Fuca Ridge hydrothermal system. Admixture of a small amount of residual brine from an earlier phase separation even may have contributed water with low deltaD values.
Research Organization:
U.S. Geological Survey, Reston, Virginia
OSTI ID:
5537010
Journal Information:
J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 92:B11; ISSN JGREA
Country of Publication:
United States
Language:
English

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Related Subjects

15 GEOTHERMAL ENERGY
152004* -- Geothermal Data & Theory-- Isotope & Trace Element Studies
CHALCOGENIDES
CHEMICAL REACTIONS
DEUTERIUM
EVEN-EVEN NUCLEI
FLUIDS
FRACTIONATION
GEOTHERMAL FLUIDS
HYDROGEN COMPOUNDS
HYDROGEN ISOTOPES
HYDROGEN SULFIDES
HYDROTHERMAL ALTERATION
ISOTOPE RATIO
ISOTOPES
LIGHT NUCLEI
NUCLEI
ODD-ODD NUCLEI
OXYGEN 18
OXYGEN COMPOUNDS
OXYGEN ISOTOPES
PACIFIC OCEAN
REDUCTION
SEA-FLOOR SPREADING
SEAS
SEAWATER
SEPARATION PROCESSES
STABLE ISOTOPES
SULFIDES
SULFUR 34
SULFUR COMPOUNDS
SULFUR ISOTOPES
SURFACE WATERS
VENTS
WATER