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Isotopic composition of gypsum in the Macquarie Island ophiolite: implications for the sulfur cycle and the subsurface biosphere in oceanic crust

Alt, J.C., Davidson, G.J., Teagle, D.A.H. and Karson, J.A. (2003) Isotopic composition of gypsum in the Macquarie Island ophiolite: implications for the sulfur cycle and the subsurface biosphere in oceanic crust Geology, 31, (6), pp. 549-552. (doi:10.1130/0091-7613(2003)031<0549:ICOGIT>2.0.CO;2).

Record type: Article

Abstract

The O, S, and Sr isotope compositions were determined for 17 samples of gypsum that replaced anhydrite in the sheeted-dike complex of the Macquarie Island ophiolite. Elevated ?34S (26.2‰–29.0‰) and ?18O values (12.5‰–14.4‰) of gypsum compared to those of seawater sulfate are the result of microbial sulfate reduction. Low organic carbon contents and little sulfate reduction in sediments, plus a large basaltic Sr component in the gypsum (87Sr/86Sr = 0.70446–0.70524), indicate that the sulfate source was not pore waters in the overlying sediment. Low ?34S values of sulfide in basalt lavas are consistent with microbial reduction of seawater sulfate within the volcanic rocks. Tectonic activity at the slow-spreading ridge allowed evolved formation waters to enter hot sheeted-dike complex basement, resulting in heating and precipitation of anhydrite. Results show that microbes can leave geochemical tracers of their activity in oceanic basement and that anhydrite can be preserved in oceanic crust and may be of significance for the oceanic sulfur budget.

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More information

Published date: 2003
Keywords: sulfates, hydrothermal processes, bacteria, biosphere, mid-ocean ridges.

Identifiers

Local EPrints ID: 2102
URI: http://eprints.soton.ac.uk/id/eprint/2102
ISSN: 0091-7613
PURE UUID: 5b407e6a-6761-4a69-b6ce-17f2f5bc27f1
ORCID for D.A.H. Teagle: ORCID iD orcid.org/0000-0002-4416-8409

Catalogue record

Date deposited: 11 May 2004
Last modified: 17 Jul 2017 17:16

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Contributors

Author: J.C. Alt
Author: G.J. Davidson
Author: D.A.H. Teagle ORCID iD
Author: J.A. Karson

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