POST-METAMORPHIC LOW DELTA-C-13 CALCITE IN THE CYCLADIC COMPLEX (GREECE) AND THEIR IMPLICATIONS FOR MODELING FLUID INFILTRATION PROCESSES USING CARBON-ISOTOPE COMPOSITIONS

Calcite veins and overgrowths with deltaC-13 values of -12 parts per t housand to -8 parts per thousand and deltaO-18 values of 24 parts per thousand to 27 parts per thousand are shown to be characteristic featu res of the Cyclades metamorphic complex of Greece. Field and petrograp hic characteristics and the marked carbon and oxygen isotope disequili brium that the veins and overgrowths show with host metamorphic rocks indicate that they developed during post-metamorphic evolution of the complex. The low deltaC-13 values are interpreted to be either the res ult of the oxidation of organic carbon or solution of soil CO2 by surf ace waters moving downwards along extensional fractures generated duri ng the late stages of exhumation. Carbon and oxygen isotopic compositi ons reported for the carbonate fraction of many pelitic schists on Nax os overlap with the range of these late carbonates and may in part ref lect a contribution of this late calcite. Uncertainties regarding the origin of low deltaC-13 values in the carbonates of metamorphic rocks shows that they must be used with caution as tracers of fluid-rock exc hange.