Abstract
The compositions of sodic pyroxenes from blueschist metabasites in Northwest Turkey were investigated by electronprobe microanalysis. These are compared with sodic pyroxenes from high-grade blueschist terrains and eclogites with special reference to the island of Syros in Greece. Pyroxenes from lawsonite zone metabasites in Northwest Turkey are chloromelanites, aegerine augites and aegerine jadeites with the acmite contents ranging from 65% down to 30%. Epidote-garnet bearing high-grade blueschist metabasites of Syros on the other hand contain omphacite with the acmite content less than 30%. All the analyzed sodic pyroxenes from eclogites and high-grade blueschists in the literature are also omphacites with low acmite contents. It is argued that the acmite content of the sodic pyroxene decreases with rising temperature of metamorphism. This is almost entirely related to the appearance of epidote as an additional ferric ion bearing phase with an increase in temperature.
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