Theory, laboratory experiments, and empirical observation suggest that many aqueous fluid inclusions in calcite reequilibrate during overheating, and therefore some homogenization temperatures (Th) record a temperature close to the maximum reached by the rock. This characteristic suggests that aqueous fluid inclusions in calcite can be used to establish maximum temperature (Tpeak). To test this hypothesis, we have compiled fluid inclusion Tpeak, mean random vitrinite reflectance (Rm), and present-day Tpeak from 46 diverse geologic systems that have been at Tpeak from 104 to 106 yr. Present Tpeak ranged from 65 to 345 °C, Th modes and means ranged from 59 to 350 °C, and Rm data ranged from 0.4% to 4.6%, spanning the temperature and thermal maturity range associated with burial diagenesis, hydrothermal alteration, and low-grade metamorphism.
Plots of Th and Tpeak data for systems thought to be currently at maximum temperature demonstrate close agreement between Th and present Tpeak in sedimentary basins. Although caution should be applied, the relation suggests that Th of aqueous fluid inclusions in calcite may be a useful measure of maximum temperature. This study also compares Th to mean random vitrinite reflectance (Rm) to offer further support for the use of Th as a measure of Tpeak, and to provide a better understanding of Rm. Th correlates well with Rm and results in a curve similar to Rm vs. Tpeak calibrations determined by other workers. The strong correlation (correlation coefficient r = 0.93) between Tpeak and Rm in these systems suggests that maximum temperature is the major control on thermal maturation.