Stable isotope analysis of small amount of carbon dioxide and its application to the microscale isotopic zoning of graphite crystals in metamorphic rocks.

Abstract

A conventional dynamic mass spectrometer with an inlet system specially modified for microscale samples was used to measure carbon isotopic ratio of subsamples within individual graphite crystals collected from Hida metamorphic belt, central Japan. The graphite crystals with three different occurrences i.e., in pelitic gneiss, skarn deposit, and crystalline limestone were examined for their isotopic zonation. Single graphite crystals collected from pelitic gneiss and hedenbergite skarn deposit has homogeneous isotopic distribution, whereas composite graphites of marble show complicated zonation which may imply the evolution of the metamorphic fluid during metamorphism.