Japan Geoscience Union Meeting 2023

Presentation information

[J] Online Poster

S (Solid Earth Sciences ) » S-CG Complex & General

[S-CG58] New Developments in fluid-rock Interactions: From Surface to Deep Subduction Zone

Sun. May 21, 2023 10:45 AM - 12:15 PM Online Poster Zoom Room (3) (Online Poster)

convener:Atsushi Okamoto(Graduate School of Environmental Studies), Jun Muto(Department of Earth Sciences, Tohoku University), Ikuo Katayama(Department of Earth and Planetary Systems Science, Hiroshima University), Junichi Nakajima(Department of Earth and Planetary Sciences, Tokyo Institute of Technology)

On-site poster schedule(2023/5/21 17:15-18:45)

10:45 AM - 12:15 PM

[SCG58-P22] Abiotic methane synthesis within olivine-hosted fluid inclusions in dolomitic marble

*Hironobu Harada1, Tatsuki Tsujimori1 (1.Tohoku Univesity)


Keywords:olivine, fluid inclusion, serpentinization, methane, dolomitic marble

Abiotic synthesis of hydrocarbon-bearing fluids during geological processes has a significant impact on the evolution of both the Earth's biosphere and the solid Earth. Aqueous alteration of ultramafic rocks, i.e., serpentinization, which forms serpentinite, is one of the geological processes generating abiotic methane (CH4). Experimental efforts have shown the abiotic CH4 generation associated with serpentinization at various temperature1,2. However, it has been pointed out that there are substantial kinetic barriers inhibiting abiotic CH4 synthesis from the reduction of CO2 unless certain catalysts3,4. In the natural environment, although it has been known that shallow low-temperature serpentinizations generate reduced fluids, including H2, the deep high-temperature and high-temperature serpentinization forming antigorite would not generate H2-bearing reduced fluids5. However, recent studies reported that the high-temperature serpentinizations could generate reduced fluids based on the observation of natural antigorite serpentine samples6,7. In any case, the nature and mechanism of abiotic CH4 synthesis during serpentinization have been unclear. In this contribution, we address the olivine-bearing dolomitic marbles as a key lithology to enable the generation of abiotic CH4.

Dolomitic marble is a magnesium-rich metacarbonate rock that contains both calcite and dolomite as carbonate minerals.Metamorphic recrystallization of the dolomitic marble produces various olivine-bearing mineral assemblages. The amphibolite-facies dolomitic marbles collected from the Hida Belt, Japan, consist mainly of calcite, dolomite, and olivine; most olivine crystals have partially serpentinized along the rims and cracks. The C–O isotope compositions of carbonate minerals in the dolomitic marble are δ13C = –3.3 to +2.8‰ and δ18O = +8.6 to +17.3‰ for calcite and δ13C = +0.2 and +0.8‰ and δ18O = +17.9 and +20.0‰ for dolomite. Raman spectroscopic analyses found that the olivine commonly contains CH4-rich fluid inclusions. The fluid inclusions also contain hydrous minerals, such as serpentine (lizardite and/or chrysotile) and brucite. These observations indicate micrometer-scale serpentinization among H2O-rich fluid inclusions and the host olivine after the fluid infiltration. The serpentinization of host olivine generated H2-bearing fluids, and consequently the fluids reduced inorganic carbon, including CO2, HCO3, and CO32, and formed CH4. Such abiotic CH4synthesis in olivine-hosted fluid inclusions has been reported from abyssal and orogenic peridotites8–10. We postulate that abiotic CH4 synthesis in dolomitic marble is a common process. To further our understanding of the contributions to the impact of abiotic CH4 storage in the solid Earth, quantitative estimation of CH4 production is still required.



Reference
1 Berndt et al., 1996. Geology 24, 351–354. https://doi.org/10.1130/0091-7613(1996)024<0351:ROCDSO>2.3.CO;2
2 Okland et al., 2014. Chem. Geol. 387, 22–34. https://doi.org/10.1016/j.chemgeo.2014.08.003
3 McCollom, 2016. Proc. Natl. Acad. Sci. 113, 13965–13970. https://doi.org/10.1073/pnas.1611843113
4 McCollom and Seewald, 2001. Geochim. Cosmochim. Acta 67, 3625–3644. https://doi.org/10.1016/S0016-7037(03)00136-4
5 Evans, 2010. Geology 38, 879–882. https://doi.org/10.1130/G31158.1
6 Boutier et al., 2021. Lithos 396-397, 106190. https://doi.org/10.1016/j.lithos.2021.106190
7 Vitale Brovarone et al., 2020. Nat. Commun. 11, 3880. https://doi.org/10.1038/s41467-020-17342-x
8 Klein et al., 2019. Proc. Natl. Acad. Sci. 116, 17666–17672. https://doi.org/10.1073/pnas.1907871116
9 Grozeva et al., 2020. Phil. Trans. R. Soc. A 378, 20180431. https://doi.org/10.1098/rsta.2018.0431
10 Zhang et al., 2021. Geochim. Cosmochim. Acta 296, 1–17. https://doi.org/10.1016/j.gca.2020.12.016