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

摘要: Whole rock sulfur and oxygen isotope compositions of altered peridotites gabbros from near the 15°20′N Fracture Zone on Mid-Atlantic Ridge were analyzed to investigate hydrothermal alteration processes test for a subsurface biosphere in oceanic basement. Three are identified. (1) High-temperature (∼250–350°C) at Sites 1268 1271 is characterized by 18O depletion (2.6–4.4‰), elevated sulfide-S, high δ34S (up ∼2 wt% 4.4–10.8‰). Fluids derived high-temperature (>350°C) reaction seawater with gabbro depth. These cores contain gabbroic rocks, suggesting that associated heat may influence serpentinization. (2) Low-temperature (<150°C) serpentinization 1272 1274 δ18O 8.1‰), sulfide-S ∼3000 ppm), negative (to −32.1‰) reflect microbial reduction sulfate. holes penetrate faults depth, links between faulting temperatures (3) Late low-temperature oxidation sulfide minerals caused loss rocks close seafloor. Sulfate all sites contains component oxidized minerals. Low sulfate result kinetic fractionation during or indicate readily low-δ34S reduction. Results show peridotite be commonly affected fluids ± mafic intrusions widespread mantle exposed