Hydrothermal gases offshore Milos Island, Greece

Botz, Reiner, Stüben, Doris, Winckler, Gisela, Bayer, Reinhold, Schmitt, Manfred and Faber, Eckhard (1996) Hydrothermal gases offshore Milos Island, Greece Chemical Geology, 130 (3-4). pp. 161-173. DOI 10.1016/0009-2541(96)00023-x.

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Hydrothermal fluids emerge from the seafloor of Paleohori Bay on Milos. The gases in these fluids contain mostly CO2 but CH4 concentrations up to 2% are present. The stable carbon isotopic composition of the CO2 (near 0%) indicates an inorganic carbon source (dissociation of underlying marine carbonates). The carbon and hydrogen isotopes of most CH4 samples are enriched in the heavy species ([delta]13C = -9.4 to -17.8[per mille sign]; [delta]D = -102 to -189[per mille sign]) which is believed to be characteristic for an abiogenic production of CH4 by CO2-reduction (Fischer-Tropsch reactions). Depletions in the deuterium content of three CH4 samples (to -377%) are probably caused by unknown subsurface rock alteration processes. Secondary hydrogen isotope exchange processes between methane, hydrogen and water are most likely responsible for calculated unrealistic methane formation temperatures. We show that excess helium, slightly enriched in 3He, is present in the hydrothermal fluids emerging the seafloor of Paleohori Bay. When the isotopic ratio of the excess component is calculated a 3He/4Heexcess of 3.6 · 10-6 is obtained: This indicates that the excess component consists of about one third of mantle helium and two thirds of radiogenic helium. We infer that the mantle-derived component has been strongly diluted by radiogenic helium during the ascent of the fluids to the surface.

Document Type: Article
Research affiliation: Kiel University
Refereed: No
DOI etc.: 10.1016/0009-2541(96)00023-x
ISSN: 0009-2541
Date Deposited: 02 Feb 2012 09:22
Last Modified: 08 Oct 2012 10:42
URI: http://eprints.uni-kiel.de/id/eprint/16386

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