Citation:

98JB00576

Name: Sulfur concentrations and isotopic composition of serpentinized oceanic peridotites
Published: 1998
License: https://creativecommons.org/licenses/by/3.0/

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Abstract:

The mineralogy, contents, and isotopic compositions of sulfur in oceanic serpentinites reflect variations in temperatures and fluid fluxes. Serpentinization of <1 Ma peridotites at Hess Deep occurred at high temperatures (200°-400°C) and low water/rock ratios. Oxidation of ferrous iron to magnetite maintained low ƒO2 and produced a reduced, low-sulfur assemblage including NiFe alloy. Small amounts of sulfate reduction by thermophilic microbes occurred as the system cooled, producing low-delta34S sulfide (1.5‰ to -23.7‰). In contrast, serpentinization of Iberian Margin peridotites occurred at low temperatures(~20°-200°C) and high water/rock ratios. Complete serpentinization and consumption of ferrous iron allowed evolution to higher ƒO2. Microbial reduction of seawater sulfate resulted in addition of low-delta34S sulfide (~15 to ~43‰) and formation of higher-sulfur assemblages that include valleriite and pyrite. The high SO4/total S ratio of Hess Deep serpentinites (0.89) results in an increase of total sulfur and high delta34S of total sulfur (mean ~8‰). In contrast, Iberian Margin serpentinites gained large amounts of 34S-poor sulfide (mean total S = 3800 ppm), and the high sulfide/total S ratio (0.61) results in a net decrease in delta34S of total sulfur (mean ~ -5‰). Thus serpentinization is a net sink for seawater sulfur, but the amount fixed and its isotopic composition vary significantly. Serpentinization may result in uptake of 0.4-14 * 10**12 g S/yr from the oceans, comparable to isotopic exchange in mafic rocks of seafloor hydrothermal systems and approaching global fluxes of riverine sulfate input and sedimentary sulfide output.

Project(s):

Ocean Drilling Program (ODP)

Coverage:

Median Latitude: 21.558513 * Median Longitude: -56.960280 * South-bound Latitude: 2.277200 * West-bound Longitude: -101.446000 * North-bound Latitude: 40.838800 * East-bound Longitude: -12.474000

Date/Time Start: 1992-12-31T08:30:00 * Date/Time End: 1993-04-17T12:00:00

Event(s):

147-895B * Latitude: 2.277300 * Longitude: -101.446000 * Date/Time Start: 1992-12-31T08:30:00 * Date/Time End: 1993-01-01T02:15:00 * Elevation: -3832.0 m * Penetration: 10.3 m * Recovery: 1.02 m * Location: North Pacific Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 1 core; 10.3 m cored; 0 m drilled; 9.9 % recovery

147-895C * Latitude: 2.277200 * Longitude: -101.446000 * Date/Time Start: 1993-01-01T02:15:00 * Date/Time End: 1993-01-03T01:30:00 * Elevation: -3831.0 m * Penetration: 37.9 m * Recovery: 5.73 m * Location: North Pacific Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 4 cores; 37.9 m cored; 0 m drilled; 15.1 % recovery

147-895D * Latitude: 2.277300 * Longitude: -101.446000 * Date/Time Start: 1993-01-03T01:30:00 * Date/Time End: 1993-01-08T08:00:00 * Elevation: -3832.0 m * Penetration: 93.7 m * Recovery: 19.08 m * Location: North Pacific Ocean * Campaign: * Basis: Joides Resolution * Method/Device: Drilling/drill rig (DRILL) * Comment: 9 cores; 93.7 m cored; 0 m drilled; 20.4 % recovery

License:

Creative Commons Attribution 3.0 Unported (CC-BY-3.0)

Size:

2 datasets

Download Data

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Datasets listed in this publication series

Alt, JC; Shanks, WC (1998): (Table 1) Whole rock sulphur concentrations of ODP Site 147-895. https://doi.org/10.1594/PANGAEA.713716
Alt, JC; Shanks, WC (1998): (Table 3) Whole rock sulphur concentrations of ODP Site 149-897. https://doi.org/10.1594/PANGAEA.713717