Abstract
D/H ratios and amounts of the water extracted from hornblende, biotite, muscovite and volcanic glass by step-wise heating under vacuum were measured and the D/H fractionation factors between released and remaining water in each step were calculated by the Rayleigh distillation model. Most of the dehydration of the hydrous silicates took place at temperatures higher than 700°C, while most of the water in dacitic glasses was released at temperatures lower than 600°C. The fractionation factors for the minerals were much less than unity, i.e., the remaining water is enriched in deuterium. The isotopic fractionation pattern of higher temperature fractions for the hydrous silicates could be represented by a single α value. The values for the glasses were quite close to unity and in the higher temperature fractions they are commonly larger than unity.
