Hydrothermal alteration and microbial sulfate reduction in peridotite and gabbro exposed by detachment faulting at the Mid-Atlantic Ridge, 15°20′N (ODP Leg 209): A sulfur and oxygen isotope study

Whole rock sulfur and oxygen isotope compositions of altered peridotites and gabbros from near the 15°20′N Fracture Zone on the Mid‐Atlantic Ridge were analyzed to investigate hydrothermal alteration processes and test for a subsurface biosphere in oceanic basement. Three processes are identified. (...

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Bibliographic Details
Published in:Geochemistry, geophysics, geosystems : G3 geophysics, geosystems : G3, 2007-08, Vol.8 (8), p.Q08002-n/a
Main Authors: Alt, Jeffrey C., Shanks III, Wayne C., Bach, Wolfgang, Paulick, Holger, Garrido, Carlos J., Beaudoin, Georges
Format: Article
Language:English
Subjects:
biosphere
Geochemistry
Hydrothermal systems
mid-ocean ridges
Mid-oceanic ridge processes
Stable isotope geochemistry
stable isotopes
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Summary:Whole rock sulfur and oxygen isotope compositions of altered peridotites and gabbros from near the 15°20′N Fracture Zone on the Mid‐Atlantic Ridge were analyzed to investigate hydrothermal alteration processes and test for a subsurface biosphere in oceanic basement. Three processes are identified. (1) High‐temperature hydrothermal alteration (∼250–350°C) at Sites 1268 and 1271 is characterized by 18O depletion (2.6–4.4‰), elevated sulfide‐S, and high δ34S (up to ∼2 wt% and 4.4–10.8‰). Fluids were derived from high‐temperature (>350°C) reaction of seawater with gabbro at depth. These cores contain gabbroic rocks, suggesting that associated heat may influence serpentinization. (2) Low‐temperature (
ISSN:1525-2027
1525-2027
DOI:10.1029/2007GC001617