Constraints on fluid origins and migration velocities along the Marmara Main Fault (Sea of Marmara, Turkey) using helium isotopes

P. Burnard*, S. Bourlange, P. Henry, L. Geli, M. D. Tryon, B. Natal'in, A. M.C. Sengör, M. S. Özeren, M. N. Çagatay

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

45 Citations (Scopus)

Abstract

Fluids venting from the submarine portion of the Marmara Main Fault (part of the North Anatolian Fault system, Turkey) were sampled in Ti bottles deployed by submersible. The fluids consist of mixtures of fault derived gases, fault related cold seep fluids, and ambient seawater; these components can readily be distinguished using the isotopes of He and the He/Ne ratios. 3He/ 4He ratios range between 0.03±0.1 and 4.9±0.4Ra, indicating that both crustal and mantle derived sources of helium are sampled by the fault. The dominant gas in all the samples analyzed is methane with the abundance of CO 2 below detection (≤2%) in the mantle rich (high 3He/ 4He) fluids. This is in contrast to nearly all mantle derived fluids where the C species are dominated by CO 2. While high CH 4/CO 2 ratios may reflect organic or inorganic reactions within the crust which reduce mantle derived CO 2 to methane, this is not a priori necessary: we show that simple dilution of mantle fluids with methane produced within local sediments could result in the high 3He/ 4He, methane rich gases currently emanating from the fault. This observation is supported by an anticorrelation between 3He/ 4He and C/ 3He, which is consistent with addition of C and 4He simultaneously to the fluids.The highest 3He/ 4He ratios were found in the Tekirdag Basin, at the foot of the escarpment bordering the Western Sea of Marmara, where seismic data are consistent with the presence of a fault network at depth which could provide conduits permitting deep-seated fluids to rise to the surface. The lack of recent volcanism, or any evidence of underlying magmatism in the area, along with low temperature fluids, strongly suggests that the 3He-rich helium in these fluids was derived from the mantle itself with the Marmara Main Fault providing a high permeability conduit from the mantle to the surface. Assuming that the mantle source to the fluids originally had a 3He/ 4He ratio of 6Ra, the minimum fluid velocities (considering only vertical transport and no mixing with parentless 4He) implied by the high 3He/ 4He ratios are of the order of 1-100mmyr -1.

Original languageEnglish
Pages (from-to)68-78
Number of pages11
JournalEarth and Planetary Science Letters
Volume341-344
DOIs
Publication statusPublished - Aug 2012

Funding

The captain and crew of the R/V Atalante and all who made sampling in the Sea of Marmara possible are warmly thanked for their considerable efforts on our behalf. Financial support to M. Tryon was provided by NSF Award no. OCE-0647361. Two anonymous reviewers are thanked for their reviews and Yuri Taran is particularly thanked for discussions and comments during the review process. This is CRPG contribution number 2159.

FundersFunder number
National Science FoundationOCE-0647361
Directorate for Geosciences0647361

    Keywords

    • Fluids
    • Gas emission
    • Helium
    • Marmara Sea
    • North Anatolian Fault

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