Determination of REE abundances and Eu isotope ratio in GSJ and NIST feldspar reference standards (JF-1, JF-2, SRM 70a, 70b and SRM 99a) using ICP-QMS and MC-ICP-MS

Seung-Gu Lee, Yoshihiro Asahara, Goeun Kim

Rare earth element (REE) concentrations in feldspars provide valuable information for understanding geochemical implications during the evolution of igneous rocks due to magma differentiation. Europium (Eu) is one of the REEs and exists in oxidation states (Eu2+ and Eu3+) states. Eu2+ can be substituted for Ca2+ during plagioclase feldspar crystallization in reducing magmas, which becomes a cause of Eu anomaly in igneous rocks. In addition, Eu has two stable isotopes (151Eu and 153Eu). Recent reports for Eu isotope ratio in igneous rocks indicated that Eu anomaly and Eu isotope fractionation in igneous rocks had a good correlation, suggesting that magmatic differentiation might bring out Eu isotope fractionation due to feldspar crystallization. Here, we first report Eu isotope ratio and REE concentration for various kinds of feldspar standard reference materials (SRMs) prepared by NIST and GSJ in order to confirm whether Eu isotope fraction in igneous rocks should be derived from feldspar crystallization during magma evolution or not. Most feldspar SRMs have chondrite LREE-enriched and HREE depleted or flattened pattern with large Eu positive anomalies except for NIST SRM70b. The potassium feldspar SRMs are enriched in the lighter Eu isotope (i.e., negative values of δ153Eu), whereas the sodium feldspar SRM(NIST SRM 99a) is enriched in the heavier Eu isotope (i.e. positive value of δ153Eu). Our results indicate that crystallization of sodic feldspar potassic feldspar may have different geochemical features in Eu isotope ratio variation in the geological materials.