229 Crustal Petrology (Posters)
This session explores various igneous and metamorphic processes that have shaped Earth’s crust. We welcome contributions from the micro- to macroscale, from the deep to shallow crust, and from field- to laboratory- to modeling-based.
Tuesday, 21 October 2025
8:00 AM - 5:30 PM
HBGCC, Hall 1
Equations-of-State for Fluids in the C-O-H System: A Comparison between Predicted and Measured Values
Paper number: 229-18
Program: Technical Sessions
Time: 8:00 AM – 8:00 AM
Authors
Abstract
Fluids in the Earth’s interior influence rocks properties, including melting temperatures, mineralogies, and rheologies. H2O is the most abundant species in the crust and upper mantle, CO2 is also common and, in the C-O-H system, CH4 is a significant component under reducing conditions. Models that describe the thermodynamic properties of fluids provide insight into fluid related processes, and this study compares equations-of-state (EOS) with experimentally determined properties to determine which EOS, if any, best reproduces these data. This comparison is restricted to EOS that, at a minimum, include H2O, CO2, and CH4, at temperatures (T) and pressures (P) from 400 to 1600˚C and 0.2 to 6 GPa. Four equations-of-state are included: Belonoshko & Saxena (1992) Geochim Cosmochim Acta, v. 56, p 361, (BeSa(92)); Holland & Powell (1991) Contrib Min Pet, v. 109, p. 265, (HP(91)); Churakov & Gottschalk, M. (2003a) Geochim Cosmochim Acta, v. 67, p. 2397 (CG(03)); and Zhang & Duan, (2009) Geochim Cosmochim Acta, v.73, p. 2089 (ZD(09)).
H2O: All EOS yield values of VH2O (V - molar volume) consistent with measured values to 900˚C and 0.6 GPa. At P > 1.5 GPa CG(03) and ZD(09) yield values of VH2O that, on average, provide the best agreement at T from 1000 to 1600˚C. CO2: At P < 1 GPa and T from 400˚C to 1400˚C no EOS is clearly most consistent with measured values of VCO2. At T > 1000˚C and P between 0.8 and 2.0 GPa, BeSa(92) yields the most accurate values of ƒCO2 (ƒ - fugacity), while at higher pressures ZD(09) yield better agreement at T from 925˚C to 1650˚C. CH4: Measured values of CH4 are available to 1 GPa at T < 400˚C and, therefore, choice of EOS is difficult at elevated T and P > 1 GPa.
No single EOS best describes the measured values of V or ƒ over the entire range of P-T and, therefore, choice of EOS depends on the P-T conditions. However, at P > 1.5 GPa CG(03) and ZD(09) yield values of H2O most consistent with the measurements. ZD(09) yields the most accurate values of ƒCO2 at P > 1.5 GPa, although CG(03) also agrees with the measured values within uncertainty. Extrapolation of any EOS beyond the P and T range included in experimental studies may involve significant uncertainties.
Geological Society of America Abstracts with Programs. Vol. 57, No. 6
doi: 10.1130/abs/2025AM-414204
© Copyright 2025 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.