Oxygen Isotope Zoning in Garnet

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Science  18 Oct 1991:
Vol. 254, Issue 5030, pp. 403-406
DOI: 10.1126/science.254.5030.403


Oxygen isotope zoning was examined within garnet with the use of the stable isotope laser probe. Four metamorphic garnets from the regional metamorphic terrane in Vermont and the skarn deposit at Carr Fork, Utah, were examined and were found to be concentrically zoned in δ18O values. The largest variations in δ18O values were observed in the regional metamorphic garnets, where δ18O values change by 3 per mil from core to rim. These oxygen isotope zoning profiles reflect the changes in the δ18O values of the rocks during garnet growth, which are caused by infiltration of fluids and by dehydration reactions during metamorphism.