Thermodynamic modelling of C-O-H fluids

H2O, CO2, CH2, CO, H-2 and O-2 are the most important species in crustal fl uids. The composition of these C-O-H fluids can be calculated if the pressu re, temperature, carbon activity, and either the oxygen fugacity or the ato mic H/O ratio of the fluid is known. The calculation methods are discussed and calculation results are illustrated with isobaric T-X-i, P-T, and isoba ric-isothermal ternary C-O-H diagrams. Fluid inclusion compositions, in par ticular, the X-CO2/(X-CO2 + X CH4) ratio, can be used for C-O-H model calcu lations. However, care should be taken about possible post-entrapment chang es, which may have modified the chemical composition of the fluid inclusion . (C) 2001 Elsevier Science B.V. All rights reserved.