Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems

Bernard J. Wood*, Shohei Banno

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    908 Citations (Scopus)

    Abstract

    Use of simple mixing models of orthopyroxene and garnet solid solutions enables extrapolation of experimentally determined equilibria in the MgSiO3-Al2O3 system to uninvestigated parts of pressure-temperature-composition space. Apparent discrepancies in the experimental data for simple and multicomponent systems may be explained by considering the effect of CaO and FeO on reducing pyrope activity in the garnet solid solutions. Equilibration pressures of natural garnet-orthopyroxene assemblages may be calculated, provided temperatures are known, from a combination of the experimental data on the MgSiO3-Al2O3 system and analyses of coexisting natural phases. Despite the presence of a compositional gap in the system, the solubility of enstatite in diopside coexisting with orthopyroxene can also be approximately treated by an ideal solution model. An empirical approach has been developed to take account of Fe2+ on the orthopyroxene-clinopyroxene miscibility gap in natural systems in order to calculate equilibration temperatures of 2-pyroxene assemblages. The model presented reproduces almost all of the available experimental data for multicomponent systems to within 60° C.

    Original languageEnglish
    Pages (from-to)109-124
    Number of pages16
    JournalContributions to Mineralogy and Petrology
    Volume42
    Issue number2
    DOIs
    Publication statusPublished - Jun 1973

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