Post-metamorphic low δ13 C calcite in the Cycladic complex (Greece) and their implications for modeling fluid infiltration processes using carbon isotope compositions

Abstract

Calcite veins and overgrowths with δ 13 C values of -12 ‰ to -8 ‰ and δ 18 O values of 24 ‰ to 27 ‰ are shown to be characteristic features of the Cyclades metamorphic complex of Greece. Field and petrographic characteristics and the marked carbon and oxygen isotope disequilibrium that the veins and overgrowths show with host metamorphic rocks indicate that they developed during post-metamorphic evolution of the complex. The low δ 13 C values are interpreted to be either the result of the oxidation of organic carbon or solution of soil CO 2 by surface waters moving downwards along extensional fractures generated during the late stages of exhumation. Carbon and oxygen 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 of this late calcite. Uncertainties regarding the origin of low δ 13 C values in the carbonates of metamorphic rocks shows that they must be used with caution as tracers of fluid-rock exchange