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.
Darling
RS
R. S. Darling, Department of Geology, State University of New York College at Cortland, Cortland, NY 13045, USA. I.-M. Chou, U.S. Geological Survey, 955 National Center, Reston, VA 20192, USA. R. J. Bodnar, Department of Geological Sciences, 4044 Derring Hall, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA.
Chou
IM
Bodnar
RJ