The peristerite gap in low-grade metamorphic rocks

S. Maruyama, J. G. Liou, K. Suzuki

    Research output: Contribution to journalArticle

    69 Citations (Scopus)

    Abstract

    Coexisting Na-plagioclases from greenschists both in the thermal aureole of the Kasugamura Granite, Japan, and in the low-P metamorphic zone of Yap Island, western Pacific were analyzed in great detail; the peristerite solvus was determined for each suite. The asymmetric solvus has steep albite-rich and gentle oligoclase-rich limbs that are similar to those for higher pressure series. The present results together with those from Vermont, New Zealand, and the Sanbagawa belt indicate that the peristerite solvus shifts toward the albite component and higher temperature with increasing pressure. With increasing pressure, albite co-existing with oligoclase (An=100 Ca/Ca+ Na=20) varies in composition from An 8-9 (in Kasugamura), through An 3 (in Yap Island and Vermont), to An 1 (in New Zealand) and An less than 0.5 (in the Sanbagawa belt). The consolute temperatures for the peristerite solvus estimated from available geothermometry are 420° C in Kasugamura, 450-550° C in Vermont and 550°-600° C in the Sanbagawa belt. The variation of plagioclase composition in progressive metamorphic zones is explained by intersection of a plagioclase-forming reaction and the peristerite immiscibility gap in an isobaric T-XAn diagram. The greenschist zone is characterized by albite, the transition zone by occurrence of peristerite pairs and the amphibolite zone by plagioclase of An 20-50.

    Original languageEnglish
    Pages (from-to)268-276
    Number of pages9
    JournalContributions to Mineralogy and Petrology
    Volume81
    Issue number4
    DOIs
    Publication statusPublished - Dec 1 1982

    ASJC Scopus subject areas

    • Geophysics
    • Geochemistry and Petrology

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