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Geochemistry of clumped isotopologues of CH₄ within fluid inclusions in Alpine tectonic quartz fissures

Mangenot, Xavier and Tarantola, Alexandre and Mullis, Josef and Girard, Jean-Pierre and Le, Van-Hoan and Eiler, John M. (2021) Geochemistry of clumped isotopologues of CH₄ within fluid inclusions in Alpine tectonic quartz fissures. Earth and Planetary Science Letters, 561 . Art. No. 116792. ISSN 0012-821X. https://resolver.caltech.edu/CaltechAUTHORS:20210219-130654360

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Abstract

Petroleum-bearing fluid inclusions are small encapsulations of oil and gas that persist in the rock record long after their parent fluids have moved on. The chemical and isotopic compositions of inclusions offer a unique way to investigate hydrocarbon formation pathways in deep Earth environments and in ancient geological times. Here we use stable isotope compositions of methane, including clumped isotopologues ¹³CH₃D and ¹²CH₂D₂, to evaluate the formation conditions of methane within fluid inclusions in Alpine tectonic quartz fissures. We observe that this CH₄ is relatively ¹³C and ²H enriched (δ¹³C = −26 to −39‰; δ²H = −126 to −146‰), consistent with the formation by advanced catagenesis of organic matter, and has clumped isotope compositions indicating intramolecular isotopic equilibrium at catagenetic to low-grade (sub-greenschist) metamorphic temperatures (TΔ¹³CH₃D: 120-300 °C; TΔ¹²CH₂D=120-260 °C). Our findings, combined with an analysis of the geographic distributions of inclusion-bearing fissures and fluid inclusion PVT behaviors, provide direct evidence of reservoirs of thermogenic methane trapped beneath the Alps during Mid-Miocene tectonic nappe emplacement (c.a. 25 to 15 Ma). The gas was sequestered in a concentrated form that likely favored the accumulation of up to 50,000-150,000 Megatons (Mt) of CH₄ across the Helvetic domain in Switzerland. Following the subsequent tectonic uplift during the period 17 to 10 Ma, we suggest that the trapped methane-rich fluids migrated to shallower depths along faults, leading to the release of Alpine metamorphic methane into near-surface aquifers and the atmosphere at rates of 0.01 to 0.03 Mt⋅y⁻¹.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1016/j.epsl.2021.116792DOIArticle
https://www.sciencedirect.com/science/article/pii/S0012821X21000510PublisherArticle
ORCID:
AuthorORCID
Mangenot, Xavier0000-0001-8770-6767
Le, Van-Hoan0000-0002-2692-8718
Alternate Title:Geochemistry of clumped isotopologues of CH4 within fluid inclusions in Alpine tectonic quartz fissures
Additional Information:© 2021 Elsevier B.V. Received 8 November 2020, Revised 20 January 2021, Accepted 29 January 2021, Available online 19 February 2021. We thank Hao Xie for technical assistance in methane clumped isotope analyses and Jonathan Treffkorn for his help on the vacuum extraction of fluid inclusion volatiles. We are also grateful to Thomas Rigaudier for his support in water isotope analysis. This study is supported with funds provided by Total. This paper greatly benefited from constructive comments by Robert, J. Bodnar and one anonymous reviewer. CRediT authorship contribution statement: X.M., A.T., J.M., J.P.G. and J.E. designed research; X.M., A.T., V.H.L. performed research; X.M., A.T., J.M., J.P.G. and J.E. analysed data; and X.M., A.T., J.M., J.P.G., V.H.L. and J.E. wrote the paper. Data availability: Datasets generated by this study are available in the digital data repository. The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Funders:
Funding AgencyGrant Number
TotalUNSPECIFIED
Subject Keywords:methane clumped isotope; fluid inclusions; tectonic veins; Mid-Miocene
Record Number:CaltechAUTHORS:20210219-130654360
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20210219-130654360
Official Citation:Xavier Mangenot, Alexandre Tarantola, Josef Mullis, Jean-Pierre Girard, Van-Hoan Le, John M. Eiler, Geochemistry of clumped isotopologues of CH4 within fluid inclusions in Alpine tectonic quartz fissures, Earth and Planetary Science Letters, Volume 561, 2021, 116792, ISSN 0012-821X, https://doi.org/10.1016/j.epsl.2021.116792.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:108130
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:19 Feb 2021 22:07
Last Modified:19 Feb 2021 22:07

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