ABSTRACT

The rare earth element (REE) europium (Eu) exists in Eu²⁺ and Eu³⁺ states. The Eu²⁺ can be substituted for Ca²⁺ during plagioclase feldspar crystallization in reducing magmas to create an observable Eu anomaly in REE distribution patterns. Europium has two stable isotopes, ¹⁵¹Eu and ¹⁵³Eu. Recent reports for Eu isotope ratios in igneous rocks indicate that Eu anomalies and isotope fractionation show good correlation, suggesting that Eu isotope fractionation appears due to feldspar crystallization during magma differentiation. Here, we report Eu isotope ratio and REE concentrations for five feldspar standard reference materials (SRMs) such as JF-1, JF-2, SRM 70a, SRM 70b, and SRM 99a prepared by the Geological Survey of Japan (GSJ) and National Institute of Standards and Technology (NIST) of USA. This study is the first investigation of the Eu isotope variation in feldspars to test several hypotheses for the origin of Eu isotope fractionation in igneous rocks. The chemical compositions of four feldspar SRMs except SRM 99a indicate that they are close to the KAlSi₃O₈ end-member within the feldspar series.