Abstract

Samples of granite from Wollaston and Chandos Lake plutons and of associated paragneiss and granitized paragneiss show, on heating, complex decrepigraphs. Of the several observed stages of decrepitation, believed to be due to misfit of solid inclusions, the highest temperature stage was taken to represent the temperature of formation of the rocks (uncorrected for pressure). The average temperatures of formation are 680 degrees C. (Wollaston granite), 657 degrees C. (biotite paragneiss), and 710 degrees C. (Chandos Lake granite, and syenite). The peak heights of the anomalous stage of decrepitation (410 degrees -480 degrees C.) are suggested as a criterion for distinguishing certain metasomatic granites from magmatic granites.

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