Subduction of crustal C governs the long-term global C cycling. The role of carbonates recycling in subduction zones and the related dissolution of C at various depths have been the subject of a large body of literature over the last decades. Much less is known about the contribution of carbonaceous material (CM) to the deep C cycling in subduction zones. This paper presents natural evidence for intense fluid-mediated leaching of CM in pelitic schists at high-pressure/low-temperature conditions relevant to the forearc region of subducting slabs. Manifestations of such process were identified along fluid pathways at various scales in the blueschist-facies subduction complexes of both Alpine Corsica and the Western Alps. Microstructural, whole-rock and Raman analyses across a selected metasomatic aureole were used to quantify the amount and mechanisms of C loss during fluid-rock interaction. In samples affected by intense fluid infiltration, > 90% of the initial CM was removed from the rock. Microstructural and micro-Raman data indicate selective leaching of disordered CM relative to nearly crystalline graphite. The collected data allowed constraining the magnitude of fluid fluxes required to bleach the studied CM-bearing lithologies at different P-T-fO2 conditions, which corresponds to rather high time-integrated fluid fluxes in the order of ~106 m3/m2. In settings of large-scale fluid channeli- zation, such as along regional-scale, lithological/tectonic boundaries or at the top of the subducted sedimentary pile, intense dissolution of subducted CM is expected. This process may thus exert a negative feedback on the sink of C phases into the deep mantle over the geological timescales and contribute to the release of isotopically light C from subducting slabs in forearc regions.

Vitale Brovarone A., Tumiati S., Piccoli F., Ague J.J., Connolly J.A.D., Beyssac O. (2020). Fluid-mediated selective dissolution of subducting carbonaceous material: Implications for carbon recycling and fluid fluxes at forearc depths. CHEMICAL GEOLOGY, 549, 1-19 [10.1016/j.chemgeo.2020.119682].

Fluid-mediated selective dissolution of subducting carbonaceous material: Implications for carbon recycling and fluid fluxes at forearc depths

Vitale Brovarone A.
;
2020

Abstract

Subduction of crustal C governs the long-term global C cycling. The role of carbonates recycling in subduction zones and the related dissolution of C at various depths have been the subject of a large body of literature over the last decades. Much less is known about the contribution of carbonaceous material (CM) to the deep C cycling in subduction zones. This paper presents natural evidence for intense fluid-mediated leaching of CM in pelitic schists at high-pressure/low-temperature conditions relevant to the forearc region of subducting slabs. Manifestations of such process were identified along fluid pathways at various scales in the blueschist-facies subduction complexes of both Alpine Corsica and the Western Alps. Microstructural, whole-rock and Raman analyses across a selected metasomatic aureole were used to quantify the amount and mechanisms of C loss during fluid-rock interaction. In samples affected by intense fluid infiltration, > 90% of the initial CM was removed from the rock. Microstructural and micro-Raman data indicate selective leaching of disordered CM relative to nearly crystalline graphite. The collected data allowed constraining the magnitude of fluid fluxes required to bleach the studied CM-bearing lithologies at different P-T-fO2 conditions, which corresponds to rather high time-integrated fluid fluxes in the order of ~106 m3/m2. In settings of large-scale fluid channeli- zation, such as along regional-scale, lithological/tectonic boundaries or at the top of the subducted sedimentary pile, intense dissolution of subducted CM is expected. This process may thus exert a negative feedback on the sink of C phases into the deep mantle over the geological timescales and contribute to the release of isotopically light C from subducting slabs in forearc regions.
2020
Vitale Brovarone A., Tumiati S., Piccoli F., Ague J.J., Connolly J.A.D., Beyssac O. (2020). Fluid-mediated selective dissolution of subducting carbonaceous material: Implications for carbon recycling and fluid fluxes at forearc depths. CHEMICAL GEOLOGY, 549, 1-19 [10.1016/j.chemgeo.2020.119682].
Vitale Brovarone A.; Tumiati S.; Piccoli F.; Ague J.J.; Connolly J.A.D.; Beyssac O.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11585/827256
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