Oxygen-Isotope Geochemistry of Quaternary Rhyolite From the Mineral Mountains, Utah, U.S.A.
Oxygen isotope analyses were made of phenocryst and glass separates from four Quarternary rhyolite flows and domes in the Mineral Mountains, southwest Utah. With the exception of biotite in all samples and alkali feldspar in the rhyolite domes, all minerals appear to be in close oxygen isotope exchange equilibrium. The geothermometry equations proposed by Bottinga and Javoy (1973) and Javoy (1977) for quartz, alkali feldspar and magnetite produce the best agreement with temperature results from two-feldspar and iron-titanium oxide geothermometry for these rhyolites. If the rhyolites were generated by partial melting in the crust, their whole-rock (glass) 6180 values (6.3 to 6.9 permil) are consistent with generation from I-type (Chappell and White, 1974, O'Neil and Chappell, 1977; O-Neil et al., 1977) sources.