Abstract
CO2 laser-heating in a fluorinating atmosphere was used to obtain O-18/O-16 analyses of coexisting garnet, staurolite, muscovite, chlorite, and quartz from a sample of the Gassetts schist, southeastern Vermont, USA. Garnet and quartz deltaO-18V-SMOW values vary on a millimeter scale while values for other minerals are uniform within analytical uncertainties. Garnets exhibit O-18/O-16 zoning with core deltaO-18 values of 10.9 +/- 0.3 parts per thousand and rim values of 10.1 +/- 0.2. The depletion of O-18 in garnet rims correlates with reversals in cation zonation and intracrystalline textural unconformities. Quartz plucked from a garnet core yields a deltaO-18 of 14.8 parts per thousand while vein quartz deltaO-18 values vary from 14.3 +/- 0.2 in centers to 13.8 +/- 0.1 at margins. Staurolite, muscovite, and chlorite have mean deltaO-18 values of 10.8, 11.9, and 10.3, respectively.