Origin of methane-rich natural gas at the West Pacific convergent plate boundary.

Sano, Yuji, Kinoshita, Naoya, Kagoshima, Takanori, Takahata, Naoto, Sakata, Susumu, Toki, Tomohiro, Kawagucci, Shinsuke, Waseda, Amane, Lan, Tefang, Wen, Hsinyi, Chen, Ai-Ti, Lee, Hsiaofen, Yang, Tsanyao F., Zheng, Guodong, Tomonaga, Yama, Roulleau, Emilie and Pinti, Daniele L. (2017) Origin of methane-rich natural gas at the West Pacific convergent plate boundary. Open Access Scientific Reports, 7 (Article number: 15646). DOI 10.1038/s41598-017-15959-5.

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Abstract

Methane emission from the geosphere is generally characterized by a radiocarbon-free signature and might preserve information on the deep carbon cycle on Earth. Here we report a clear relationship between the origin of methane-rich natural gases and the geodynamic setting of the West Pacific convergent plate boundary. Natural gases in the frontal arc basin (South Kanto gas fields, Northeast Japan) show a typical microbial signature with light carbon isotopes, high CH4/C2H6 and CH4/³He ratios. In the Akita-Niigata region – which corresponds to the slope stretching from the volcanic-arc to the back-arc –a thermogenic signature characterize the gases, with prevalence of heavy carbon isotopes, low CH4/C2H6 and CH4/³He ratios. Natural gases from mud volcanoes in South Taiwan at the collision zone show heavy carbon isotopes, middle CH4/C2H6 ratios and low CH4/³He ratios. On the other hand, those from the Tokara Islands situated on the volcanic front of Southwest Japan show the heaviest carbon isotopes, middle CH4/C2H6 ratios and the lowest CH4/³He ratios. The observed geochemical signatures of natural gases are clearly explained by a mixing of microbial, thermogenic and abiotic methane. An increasing contribution of abiotic methane towards more tectonically active regions of the plate boundary is suggested.

Document Type: Article
Keywords: Origin, Methane-rich natural gas, West Pacific convergent plate boundary
Refereed: Yes
Open Access Journal?: Yes
DOI etc.: 10.1038/s41598-017-15959-5
ISSN: 2045-2322
Projects: FLOWS
Date Deposited: 27 Apr 2018 12:38
Last Modified: 01 Feb 2019 15:04
URI: http://oceanrep.geomar.de/id/eprint/42880

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