A profile of multiple sulfur isotopes through the Oman ophiolite

Oeser, M., Strauss, H., Wolff, P. E., Koepke, J., Peters, M., Garbe-Schönberg, Dieter and Dietrich, M. (2012) A profile of multiple sulfur isotopes through the Oman ophiolite Chemical Geology, 312 . pp. 27-46.

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Abstract

The mineralogy, sulfur contents, and multiple sulfur isotopic compositions were determined for a complete section through the Oman ophiolite at the Wadi Gideah area located in the Wadi Tayin Massif (southern domain of the ophiolite complex) in order to characterize the various processes of sulfur cycling in the Oman ophiolite which is regarded as representing the best example of fast-spreading oceanic lithosphere on land. Upper crustal rocks (lavas and sheeted dikes) exhibit pervasive alteration due to intense circulation of seawater. Sulfate is the dominant sulfur phase, and sulfur (delta S-34) and oxygen isotopic compositions of sulfate suggest that sulfate is mainly derived from late Cretaceous seawater. S-34 enrichments in sulfides (with respect to mantle sulfur) and low sulfide-S contents (<10 ppm) reflect precipitation of hydrothermal sulfides followed by oxidation of sulfides during seafloor weathering. Clearly negative delta S-34 values of CRS (Cr-reducible sulfur) in one pillow basalt sample indicate that microbial reduction of seawater sulfate occurred within the lavas during low-temperature alteration. Rocks of the gabbro/sheeted dike transition zone display variable delta S-34(CRS) values (between 0.5 parts per thousand and 5.5 parts per thousand) paired with a wide range in sulfide-S contents (<1 to 489 ppm). This reflects the dynamic nature of this interface between the hydrothermal circulation system of the upper crust and the magmatic system dominating the lower crust. Low delta S-34(sulfate-S) values indicate that sulfate in those rocks mainly results from oxidation of igneous sulfides. Although lower crustal rocks of the Oman ophiolite are affected by high-temperature alteration resulting in leaching and redistribution of sulfide-S, delta S-34 values of monosulfide and disulfide minerals scatter around the value for mantle sulfur (0 parts per thousand). Delta S-33* values of CRS between -0.020 parts per thousand and -0.038 parts per thousand clearly differ from those of upper crustal rocks. Either this documents leaching processes operating in the lower crust, or lower crustal rocks have preserved a primary multiple sulfur isotopic composition that deviates from the postulated mantle value (Delta S-33* = 0.0 parts per thousand). Rocks from the mantle sequence of the Oman ophiolite are affected by serpentinization under highly reducing conditions at low water-rock ratios followed by a further stage of serpentinization under oxidizing conditions at high water-rock ratios. The first stage of alteration results in loss of sulfur (sulfide-S contents <60 ppm) paired with delta S-34(sulfide) values around 0 parts per thousand. The second stage leads to S-34-enriched sulfide phases and also low sulfide-S contents. Sulfate-S contents vary from 5 ppm to 213 ppm and are generally higher than in the lower crust. Sulfur and oxygen isotopic compositions of sulfate suggest that sulfate is mainly derived from late Cretaceous seawater. (C) 2012 Elsevier B.V. All rights reserved.

Document Type: Article
Additional Information: Oeser, M Leibniz Univ Hannover, Inst Mineral, Callinstr 3, D-30167 Hannover, Germany Leibniz Univ Hannover, Inst Mineral, Callinstr 3, D-30167 Hannover, Germany Univ Munster, Inst Geol & Palaontol, D-48149 Munster, Germany Leibniz Univ Hannover, Inst Mineral, D-30167 Hannover, Germany Univ Kiel, Inst Geowissensch, D-24118 Kiel, Germany
Keywords: multiple sulfur isotopes oman ophiolite fast-spreading oceanic crust sulfur cycling microbial sulfate reduction u-pb geochronology temperature hydrothermal circulation altered oceanic basalts mid-atlantic ridge fore-arc mantle semail-ophiolite geologic history samail ophiolite phanerozoic seawater
Research affiliation: OceanRep > The Future Ocean - Cluster of Excellence > FO-R07
Kiel University
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
ISSN: 0009-2541
Projects: Future Ocean
Date Deposited: 14 May 2014 10:10
Last Modified: 25 Feb 2017 10:47
URI: http://eprints.uni-kiel.de/id/eprint/24135

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