Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments
Antigorite dehydration is a process able to release, in comparison with other minerals, the highest amount of H<sub>2</sub>O from a subducting slab. The released fluid delivers critical elements (e.g., S, Cu, and REE) to the overlying subarc mantle, modifying the mantle source of arc mag...
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MDPI AG
2023-04-01
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| Series: | Geosciences |
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| Online Access: | https://www.mdpi.com/2076-3263/13/5/130 |
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| author | Andrea Maffeis Simona Ferrando James Alexander Denis Connolly Maria Luce Frezzotti Daniele Castelli |
| author_facet | Andrea Maffeis Simona Ferrando James Alexander Denis Connolly Maria Luce Frezzotti Daniele Castelli |
| author_sort | Andrea Maffeis |
| collection | DOAJ |
| description | Antigorite dehydration is a process able to release, in comparison with other minerals, the highest amount of H<sub>2</sub>O from a subducting slab. The released fluid delivers critical elements (e.g., S, Cu, and REE) to the overlying subarc mantle, modifying the mantle source of arc magmas and related ore deposits. Whether antigorite breakdown produces oxidising or reducing fluids is debated. Whereas previous studies have investigated antigorite dehydration in serpentinites (i.e., in a (C)AMFS-H<sub>2</sub>O system), this contribution is devoted to the CMFS-COHS carbonate system, which is representative of the metacarbonate sediments (or carbonate-dominated ophicarbonate rocks) that sit atop the slab. Thermodynamic modelling is used to investigate the redox effect of the carbonate-buffered antigorite dehydration reactions (i.e., brucite breakdown and antigorite breakdown) on electrolytic fluid geochemistry as a function of <i>P</i>-<i>T</i>-<i>f</i>O<sub>2</sub>. The influence of <i>P</i>-<i>T</i>-<i>f</i>O<sub>2</sub> conditions on the solubility of C and S, solute-bound H<sub>2</sub> and O<sub>2</sub>, fluid pH, the average valence states of dissolved C and S, and the fluid redox budget indicates that, in metacarbonate sediments, the CaCO<sub>3</sub>+antigorite reaction tends to produce reducing fluids. However, the redox state of such fluids is buffered not only by the redox state of the system but also, most importantly, by concomitantly dissolving redox-sensitive minerals (i.e., carbonates, graphite, pyrite, and anhydrite). A qualitative correlation between the redox state of the system and the possible depth of fluid release into the mantle wedge is also derived. |
| first_indexed | 2024-03-11T03:41:23Z |
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| last_indexed | 2024-03-11T03:41:23Z |
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| series | Geosciences |
| spelling | doaj.art-3edb6ff03d1e43afa240a64f8b4092f92023-11-18T01:30:51ZengMDPI AGGeosciences2076-32632023-04-0113513010.3390/geosciences13050130Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate SedimentsAndrea Maffeis0Simona Ferrando1James Alexander Denis Connolly2Maria Luce Frezzotti3Daniele Castelli4Dipartimento di Scienze della Terra, Università degli Studi di Torino, 10125 Turin, ItalyDipartimento di Scienze della Terra, Università degli Studi di Torino, 10125 Turin, ItalyInstitute for Geochemistry and Petrology, Department of Earth Sciences, ETH Zurich, CH 8092 Zurich, SwitzerlandDipartimento di Scienze dell’Ambiente e della Terra, Università degli Studi di Milano-Bicocca, 20126 Milano, ItalyDipartimento di Scienze della Terra, Università degli Studi di Torino, 10125 Turin, ItalyAntigorite dehydration is a process able to release, in comparison with other minerals, the highest amount of H<sub>2</sub>O from a subducting slab. The released fluid delivers critical elements (e.g., S, Cu, and REE) to the overlying subarc mantle, modifying the mantle source of arc magmas and related ore deposits. Whether antigorite breakdown produces oxidising or reducing fluids is debated. Whereas previous studies have investigated antigorite dehydration in serpentinites (i.e., in a (C)AMFS-H<sub>2</sub>O system), this contribution is devoted to the CMFS-COHS carbonate system, which is representative of the metacarbonate sediments (or carbonate-dominated ophicarbonate rocks) that sit atop the slab. Thermodynamic modelling is used to investigate the redox effect of the carbonate-buffered antigorite dehydration reactions (i.e., brucite breakdown and antigorite breakdown) on electrolytic fluid geochemistry as a function of <i>P</i>-<i>T</i>-<i>f</i>O<sub>2</sub>. The influence of <i>P</i>-<i>T</i>-<i>f</i>O<sub>2</sub> conditions on the solubility of C and S, solute-bound H<sub>2</sub> and O<sub>2</sub>, fluid pH, the average valence states of dissolved C and S, and the fluid redox budget indicates that, in metacarbonate sediments, the CaCO<sub>3</sub>+antigorite reaction tends to produce reducing fluids. However, the redox state of such fluids is buffered not only by the redox state of the system but also, most importantly, by concomitantly dissolving redox-sensitive minerals (i.e., carbonates, graphite, pyrite, and anhydrite). A qualitative correlation between the redox state of the system and the possible depth of fluid release into the mantle wedge is also derived.https://www.mdpi.com/2076-3263/13/5/130antigorite dehydrationredoxthermodynamic modellingelectrolytic fluidredox budgetsubduction |
| spellingShingle | Andrea Maffeis Simona Ferrando James Alexander Denis Connolly Maria Luce Frezzotti Daniele Castelli Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments Geosciences antigorite dehydration redox thermodynamic modelling electrolytic fluid redox budget subduction |
| title | Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments |
| title_full | Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments |
| title_fullStr | Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments |
| title_full_unstemmed | Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments |
| title_short | Fluid Redox Fingerprint of the CaCO<sub>3</sub>+Antigorite Dehydration Reaction in Subducted Metacarbonate Sediments |
| title_sort | fluid redox fingerprint of the caco sub 3 sub antigorite dehydration reaction in subducted metacarbonate sediments |
| topic | antigorite dehydration redox thermodynamic modelling electrolytic fluid redox budget subduction |
| url | https://www.mdpi.com/2076-3263/13/5/130 |
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