Thermodynamic analysis of pyroxene-olivine-quartz equilibria in the system CaO-MgO-FeO-SiO sub 2

Journal Article · · American Mineralogist; (USA)

OSTI ID:6842119

Davidson, P M; Lindsley, D H ^[1]

---

1. State Univ. of New York, Stony Brook (USA)

An internally consistent set of thermodynamic models for pyroxenes, olivine, and quartz in the CMFS system has been calibrated simultaneously with orthopyroxene cation distributions, orthopyroxene solution enthalpies, and phase equilibria for coexisting pyroxenes and coexisting pyroxene + olivine + quartz. New experiments on pyroxene + olivine + quartz equilibria constrain the models. Preferred values of model parameters are used to generate component activities that are consistent with the authors' choice of apparent standard-state energies. These values are modified from the compilation of Helgeson et al. to fit newer experimental data and to incorporate coefficients of compressibility and thermal expansion. Calculated geothermometers include those based on equilibria involving one, two, or three pyroxenes. Isothermal, isobaric augite solvus limbs are displaced to higher Ca contents relative to Lindsley's graphs. Calculated geobarometers include those based on assemblages of olivine + quartz + one, two, or three pyroxenes. The calculated temperature for coexisting olivine + quartz + orthopyroxene + augite + pigeonite is 818 {plus minus} 20C, in agreement with previous experiments; the pressure for this assemblage is given by P (in kbar) = 9.15 {minus} 33.8X{sup Pig}{sub Mg}. Silica activity as determined from olivine-pyroxene exchange equilibria is shown to be a function not only of P, T, and Fe/(Fe + Mg) ratio of the assemblage, but also of the olivine (and pyroxene) Ca content, particularly for the olivine-augite exchange.

• OSTI ID: 6842119
• Journal Information: American Mineralogist; (USA), Journal Name: American Mineralogist; (USA) Vol. 74:1-2; ISSN AMMIA; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

15 GEOTHERMAL ENERGY
152002* -- Geothermal Data & Theory-- Properties of Minerals & Rocks
ALKALINE EARTH METAL COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM OXIDES
CHALCOGENIDES
ENTHALPY
EQUILIBRIUM
GEOBAROMETRY
IRON COMPOUNDS
IRON OXIDES
IRON SILICATES
MAGNESIUM COMPOUNDS
MAGNESIUM OXIDES
MAGNESIUM SILICATES
MATHEMATICAL MODELS
MINERALS
OLIVINE
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PARTICLE MODELS
PHASE STUDIES
PHYSICAL PROPERTIES
PYROXENES
QUARTZ
RESERVOIR PRESSURE
RESERVOIR TEMPERATURE
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES
STATISTICAL MODELS
THERMODYNAMIC MODEL
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS