Assessment of the garnet–clinopyroxene Fe–Mg exchange thermometer using new experimental data

T. H. Green*, J. Adam

*Corresponding author for this work

    Research output: Contribution to journalArticle

    35 Citations (Scopus)

    Abstract

    A detailed high‐pressure experimental study of two mafic xenoliths, in which coexisting garnet and clinopyroxene (± plagioclase, spinel and olivine) were crystallized over a P–T range of 10–30 kbar and 950–1200°C, has revealed significant differences in temperatures from those estimated for coexisting garnets and clinopyroxenes using the Ellis & Green Fe–Mg exchange thermometer. The results show perfect matching at 30 kbar, 1150–1200°C, but increasing deviation at lower pressure and lower temperature, with the Ellis & Green calibration reaching a ΔT (overestimate) of c. 145°C at 10–12 kbar and 950°C. The grossular content of the garnet increases from c. 21 mol.% at 10 kbar to 26–31 mol.% at 30 kbar. These results confirm other recent experimental studies that show that the pressure correction, and possibly to a lesser extent the correction for grossular content, applied by Ellis & Green, are not appropriate for lower pressure conditions, and give estimated temperatures that are significantly high when applied to granulitic terranes formed at c. 10 kbar. The new reconnaissance results allow a graphical interpolation of a garnet–clinopyroxene geothermometer based on the Fe–Mg exchange reaction which should be applicable to assemblages formed under lower crustal conditions.

    Original languageEnglish
    Pages (from-to)341-347
    Number of pages7
    JournalJournal of Metamorphic Geology
    Volume9
    Issue number3
    DOIs
    Publication statusPublished - 1991

    Keywords

    • eclogite
    • geothermometer
    • granulite
    • high‐pressure experimental
    • lower crust

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