Abstract

An examination of stress birefringence around inclusions in 8 garnets during heating to 900 °C, suggests that some changes in birefringence are due to fit-misfit relationships of inclusions in garnet.Some garnets appear to have behaved as natural bombs, which have carefully preserved the misfit relationships since crystallization of the combination of detached or partly detached inclusion in garnet. This combination can be used to determine the temperatures of fit at room temperature for various inclusions in garnet. Using certain approximations the intersection of curves of fit (on a P-T plot) can be employed to determine possible temperatures and pressure of formation of the garnet. In addition the changes in birefringence around inclusions of quartz reveal whether the garnet (or quartz inclusion) crystallized above or below the α-β quartz inversion.This technique is limited chiefly by the lack of P-V-T data on minerals, yet it can be applied to determine possible minimum and maximum temperatures and pressures of formation of garnets or their inclusions.

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