Europium isotope fractionation in highly fractionated igneous rocks with large Eu negative anomaly

摘要

One of peculiar geochemical characteristics in the chondrite-normalized REE patterns from highly fractionated granites and high silica rhyolite is extremely large negative Eu anomaly (Eu/Eu* < 0.10) due to very low concentration of Eu. Particularly, Eu provides a valuable information for evolution processes of the earth and planetary materials. Eu has only two isotopes, Eu-151 and Eu-153. In this study, Eu isotope ratios from highly fractionated igneous rocks curated GSJ and USGS and some highly fractionated granites with extremely large Eu negative anomaly were determined by MC-ICP-MS using Sm internal standardization methods. The degree of Eu isotope fractionation (delta Eu-153/151) was calculated on the basis of NIST3117a Eu standard. All of highly fractionated igneous rocks in this study showed that their Eu-153/Eu-151 values are higher than NIST3117a Eu standard, indicating that Eu-151 isotope was enriched in the felsic magma. Our results suggest that a study for Eu isotope fractionation from highly fractionated granites and high silica rhyolite will provide a valuable key for understanding geochemical processes related with magmatic differentiation processes.