Publication Date:
2021-02-08
Description:
Highlights
• Gases collected from dry seepages and bubbling or dissolved in springs of the ophiolitic body of Kizildag (Turkey).
• Large compositional variation (H2- CH4 or N2-dominated)
• Hydrogen derives from low temperature serpentinization processes
• Methane mainly derives from abiotic processes
• Large isotopic fractionation of methane at one site due to biological oxidation
Abstract
We investigated the geochemical features of the gases released from the Kizildag ophiolitic complex (Hatay, Turkey). Twenty-three samples both dissolved in hyperalkaline waters and free gases (bubbling gases and dry seeps) were collected. Samples were analysed for their chemical (He, H2, O2, N2, CH4 and CO2) and isotopic (He, δ13C-CH4, δ2H-CH4, δ2H-H2) composition including the content and C-isotopic composition of C2 to C5 alkanes in free gases. Analytical results evidence H2 production through low-temperature (〈80 °C) serpentinization processes and subsequent abiogenic CH4 production through Fischer-Tropsch-type reactions. In some sample small additions of methane either of microbial or of thermogenic origin can be hypothesized. At one of the sites (Kisecik) a clear fractionation pattern due to microbial methane oxidation leading to strongly enriched isotopic values (δ13C +15‰ and δ2H −68‰) and depletion in methane concentrations has been evidenced. At the dry gas seep of Kurtbagi methane flux measurements have been made and a preliminary output estimation of about 1000 kg per year has been obtained.
Type:
Article
,
PeerReviewed
Format:
text
DOI:
10.1016/j.marpetgeo.2016.12.017
