Silicate dissolution boosts the CO<sub>2</sub> concentrations in subduction fluids.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 28931819.
- Also identified by DOI 10.1038/s41467-017-00562-z and PMC identifier 5606994.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Estimates of dissolved CO<sub>2</sub> 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, SiO<sub>2</sub>-COH ( + quartz/coesite) and MgO-SiO<sub>2</sub>-COH ( + forsterite and enstatite). The CO<sub>2</sub> 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 CO<sub>2</sub> transfer from the slab-mantle interface to the overlying mantle wedge, in particular where fluids are stable over melts.Current estimates of dissolved CO<sub>2</sub> 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 CO<sub>2</sub> contents.