Estimates of dissolved CO2 in subduction-zone fluids are based on thermodynamic models, relying on a very sparse experimental data base. Here, we present experimental data at 1-3 GPa, 800 °C, and ∆FMQ ≈ -0.5 for the volatiles and solute contents of graphite-saturated fluids in the systems COH, SiO2-COH ( + quartz/coesite) and MgO-SiO2-COH ( + forsterite and enstatite). The CO2 content of fluids interacting with silicates exceeds the amounts measured in the pure COH system by up to 30 mol%, as a consequence of a decrease in water activity probably associated with the formation of organic complexes containing Si-O-C and Si-O-Mg bonds. The interaction of deep aqueous fluids with silicates is a novel mechanism for controlling the composition of subduction COH fluids, promoting the deep CO2 transfer from the slab-mantle interface to the overlying mantle wedge, in particular where fluids are stable over melts.Current estimates of dissolved CO2 in subduction-zone fluids based on thermodynamic models rely on a very sparse experimental data base. Here, the authors show that experimental graphite-saturated COH fluids interacting with silicates at 1-3 GPa and 800 °C display unpredictably high CO2 contents.

Silicate dissolution boosts the CO2 concentrations in subduction fluids / S. Tumiati, C. Tiraboschi, D.A. Sverjensky, T. Pettke, S. Recchia, P. Ulmer, F. Miozzi, S. Poli. - In: NATURE COMMUNICATIONS. - ISSN 2041-1723. - 8:1(2017 Sep 20), pp. 616.1-616.10. [10.1038/s41467-017-00562-z]

Silicate dissolution boosts the CO2 concentrations in subduction fluids

S. Tumiati
Primo
;
S. Poli
Ultimo
2017

Abstract

Estimates of dissolved CO2 in subduction-zone fluids are based on thermodynamic models, relying on a very sparse experimental data base. Here, we present experimental data at 1-3 GPa, 800 °C, and ∆FMQ ≈ -0.5 for the volatiles and solute contents of graphite-saturated fluids in the systems COH, SiO2-COH ( + quartz/coesite) and MgO-SiO2-COH ( + forsterite and enstatite). The CO2 content of fluids interacting with silicates exceeds the amounts measured in the pure COH system by up to 30 mol%, as a consequence of a decrease in water activity probably associated with the formation of organic complexes containing Si-O-C and Si-O-Mg bonds. The interaction of deep aqueous fluids with silicates is a novel mechanism for controlling the composition of subduction COH fluids, promoting the deep CO2 transfer from the slab-mantle interface to the overlying mantle wedge, in particular where fluids are stable over melts.Current estimates of dissolved CO2 in subduction-zone fluids based on thermodynamic models rely on a very sparse experimental data base. Here, the authors show that experimental graphite-saturated COH fluids interacting with silicates at 1-3 GPa and 800 °C display unpredictably high CO2 contents.
subduction; COH fluids; experimental petrology
Settore GEO/07 - Petrologia e Petrografia
   Trasferimento di elementi volatili ai margini di placca convergenti: relazioni tra eterogeneità dei fluidi/fusi COH e anomalie tettoniche nelle zone di subduzione
   MINISTERO DELL'ISTRUZIONE E DEL MERITO
   2012R33ECR_001
20-set-2017
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2434/524644
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