TY - CHAP
T1 - Predicted Speciation of Carbon in Subduction Zone Fluids
AU - Guild, Meghan
AU - Shock, Everett L.
N1 - Funding Information:
We thank James Leong, Tucker Ely, and Dimitri Sverjensky for their help with coding, databases, and interpretation of the results generated in this study. Thank you to Christy Till, EPIC, and GEOPIG for helpful discussions during every iteration of this work. This work was supported in part with funds from the Sloan Foundation through grants in support of the Extreme Physics and Chemistry community of the Deep Carbon Observatory.
Publisher Copyright:
© 2020 The Authors. Co-published 2020 by the American Geophysical Union and John Wiley and Sons, Inc.
PY - 2020
Y1 - 2020
N2 - High pressure‐temperature aqueous fluids are essential to melt generation, element cycling, and fluid‐melt‐rock reactions occurring in subduction zones. Recent advances in theoretical thermodynamic modeling help facilitate calculations at a range of pressure conditions relevant to subduction zones. Here we explore stable and metastable equilibrium speciation of C1 and C2 aqueous carbon species along a theoretical slab surface pressure‐temperature path. These calculations reveal a thermodynamic drive to stabilize small organic compounds at elevated pressures and temperatures, with pH buffered by the diopside‐antigorite‐forsterite mineral assemblage. At stable equilibrium, oxidized forms of aqueous carbon dominate the speciation at and above oxidation conditions set by the fayalite-magnetite‐quartz (FMQ) assemblage. Under conditions more reduced than FMQ, a larger variety of aqueous carbon species are stabilized. If metastability were to persist along the path targeted by this study, it is predicted that a plethora of C1 and C2 aqueous species would be stabilized, especially under reduced conditions. These results point the way for theoretical geochemical modeling in the pressure‐temperature‐composition space of sub-duction zone fluids and provide new constraints on forms of deep carbon.
AB - High pressure‐temperature aqueous fluids are essential to melt generation, element cycling, and fluid‐melt‐rock reactions occurring in subduction zones. Recent advances in theoretical thermodynamic modeling help facilitate calculations at a range of pressure conditions relevant to subduction zones. Here we explore stable and metastable equilibrium speciation of C1 and C2 aqueous carbon species along a theoretical slab surface pressure‐temperature path. These calculations reveal a thermodynamic drive to stabilize small organic compounds at elevated pressures and temperatures, with pH buffered by the diopside‐antigorite‐forsterite mineral assemblage. At stable equilibrium, oxidized forms of aqueous carbon dominate the speciation at and above oxidation conditions set by the fayalite-magnetite‐quartz (FMQ) assemblage. Under conditions more reduced than FMQ, a larger variety of aqueous carbon species are stabilized. If metastability were to persist along the path targeted by this study, it is predicted that a plethora of C1 and C2 aqueous species would be stabilized, especially under reduced conditions. These results point the way for theoretical geochemical modeling in the pressure‐temperature‐composition space of sub-duction zone fluids and provide new constraints on forms of deep carbon.
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U2 - 10.1002/9781119508229.ch24
DO - 10.1002/9781119508229.ch24
M3 - Chapter
AN - SCOPUS:85101874854
T3 - Geophysical Monograph Series
SP - 285
EP - 302
BT - Geophysical Monograph Series
PB - John Wiley and Sons Inc.
ER -