In the article titled "High integrated fluid/rock ratios during metamorphism at Naxos: evidence from carbon isotopes of calcite in schists and fluid inclusions" Rob Kreulen (1988) concluded that the metamorphic complex at Naxos was exchanged with a pervasive, externally derived CO2-rich fluid. This conclusion was based on a fluid composition and 613C study of inclusion fluids, and on a fi 13 C and fi 1 s o isotopic study of calcites in pelitic schists. Kreulen found that: 1) the Xco2 of the captured fluids is 60-90 mol% CO2 in about 70% of the inclusions observed, 2) the g13C values of calcites in schists are significantly lower than the values of calcites from massive marbles, 3) the 61ac values of calcite in pelitic schists decrease with decreasing calcite-concentration, and 4) the & 13C values of CO2 in the fluid inclusions are in apparent isotopic equilibrium with the calcite in pelitic rocks. From simple mass balance considerations, Kreulen calculated an integrated fluid/rock ratio of 0.1 to 2.0 for the complete metamorphic system. For his calculations he used an Xco2 value for the fluids of 0.5, an original fitsc of calcite in the pelites of 0 permil, and a 6 13Cco2 of the fluid of -5%0.
The conclusion that a pervasive externally derived CO2rich fluid flowed through the metamorphic complex at Naxos has enormous implications for the metamorphic processes and must be evaluated critically. Kreulen's conclusions depend on the assumptions that: 1) the optical fluid inclusion measurements represent the composition of the metamorphic fluid, 2) the carbonates in the pelitic schists had the same premetamorphic isotopic composition as the marbles, and 3) that there was no isotopic exchange between carbonates and graphite (or hydrocarbons).
We will demonstrate that some of these assumptions are not valid and that the results as well as the conclusions reported by Kreulen (1988) are inconsistent with several geologic and petrologic observations.
In the first part of his argument, Kreulen reported the results of over 1000 optical fluid inclusion measurements in quartz and found that 70% of the inclusions have a composition of 60%-90% CO2 (Kreulen 1977(Kreulen , 1980(Kreulen , 1988)).