Plagioclase relations in pelites, central Menderes Massif, Turkey. I. The peristerite gap with coexisting kyanite |
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Authors: | J R ASHWORTH M M EVIRGEN |
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Institution: | Department of Geological Sciences, University of Aston in Birmingham, Gosta Green, Birmingham B4 7ET, UK; Jeoloji Mühendislii Bölümü, Mühendislik Fakültesi, Hacettepe Üniversitesi, Beytepe Kampüsü, Ankara, Turkey |
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Abstract: | Abstract In pelites of the central Menderes Massif, albite and oligoclase with only slight chemical zoning coexist in apparent textural equilibrium in the garnet zone, staurolite zone, and staurolite + kyanite transition zone. The metamorphic temperature range is estimated as approximately 440–550°C (from the Hodges-Spear calibration of the garnet-biotite geo-thermometer), or 440–500°C (Ganguly-Saxena calibration). While oligoclase composition at the peristerite gap changes from An22 to An14, albite also becomes more sodic (An1,5–An0.6). The slope of the albite limb is thus the reverse of that reported in other areas, and may not be a true equilibrium feature. Occurrence of kyanite, at temperatures below the crest of the gap, is due to low water activity in the presence of graphite: a H2o is estimated at approximately 0.1–0.2 from the Na content of muscovite coexisting with albite + kyanite + quartz. |
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Keywords: | Key-words: Garnet geothermometry kyanite Menderes Massif Turkey peristerite gap |
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