Science, Vol.276, No.5309, 91-93, 1997
An Occurrence of Metastable Cristobalite in High-Pressure Garnet Granulite
High-pressure (0.8 gigapascals) granulite facies garnet from Gore Mountain, New York, hosts multiple solid inclusions containing the low-pressure silica polymorph cristobalite along with albite and minor ilmenite. Identification of cristobalite is based on Raman spectra, electron microprobe analysis, and microthermometric measurements on the alpha/beta phase transformation. The cristobalite plus albite inclusions may have originated as small, trapped samples of hydrous sodium-aluminum-siliceous melt. Diffusive loss of water from these inclusions under isothermal, isochoric conditions may have resulted in a large enough internal pressure decrease to promote the metastable crystallization of cristobalite.
Keywords:PHASE-TRANSITION;FLUID INCLUSIONS;RE-EQUILIBRATION;CENTRAL CHINA;COESITE;QUARTZ;METAMORPHISM;BEHAVIOR;KBAR