Post-metamorphic low delta (super 13) C calcite in the Cycladic Complex (Greece) and their implications for modeling fluid infiltration processes using carbon isotope compositions

Calcite veins and overgrowths with delta (super 13) C values of -12 to -8 per mille and delta (super 18) O values of +24 to +27 per mille are shown to be characteristic features of this metamorphic complex on the islands of Sifnos and Tinos. Field and petrographic characteristics and the marked C and O isotope disequilibrium that the veins and overgrowths show with the host metamorphic rocks indicate that they developed during post-metamorphic evolution of the complex. The low delta (super 13) C values are interpreted as being either the result of the oxidation of C (sub org) or solution of soil CO (sub 2) by surface waters moving downwards along extensional fractures generated during the late stages of exhumation. C and O isotopic compositions reported for the carbonate fraction of many pelitic schists on Naxos overlap with the range of these late carbonates and may in part reflect a contribution from this late calcite. Uncertainties about the origin of the low delta (super 13) C values in the carbonates of metamorphic rocks show that they must be used with caution as tracers of fluid-rock exchange.