The calcite-graphite isotope thermometer; data on graphite bearing marbles from Naxos, Greece

Abstract

Graphite bearing marbles occur in the regional metamorphic complex of Naxos over a continuous temperature range of 380 to 670°C. The graphite is of biogenic origin and changed its original isotopic composition towards values in equilibrium with the calcite. Partial isotope exchange took place at temperatures as low as 380°C, but near equilibrium values were generally not reached below 550°C. The data agree better with the theoretically derived fractionation curve of Bottinga (1969) than with the empirical curve proposed by Valley and O'Neil (1981). We believe that the system will not provide a good thermometer.