Geochemical significance of Eu isotope fractionation in anorthosite

Abstract

Recently, Lee and Tanaka [1-2] developed a method to accurately measure the Eu isotope ratio using MC-ICP-MS. Lee and Tanaka [3] also reported an Eu isotope fractionation (¹⁵¹Eu enrichment compared to ¹⁵³Eu) in the highly fractionated igneous rocks with extremely large Eu negative, and proposed that Eu isotope fractionation in the highly fractionated igneous rocks might be related with anorthosite emplacement due to feldspar crystallization. The anorthosite at Sancheong-Hadong area in the southern part of Korean Peninsular is found as long belt. The Sancheong-Hadong anorthosites have a geochemical characteristic of extremely large Eu positive anomaly in the chondrite-normalized REE pattern. Therefore, in this study, we had performed an experiment to determine the Eu isotope ratio of the Korean anorthosite in order to confirm the idea by Lee and Tanaka [3]. Our results clearly showed a geochemical feature that the anorthosite was enriched in ¹⁵³Eu isotope enrichment compared to ¹⁵¹Eu isotope. In addition, the relationship between Eu anomaly in the chondrite-normalized REE pattern and Eu isotope ratio from igneous rock materials indicates that Eu isotope fractionation in igneous rocks should be derived from feldspar crystallization during magmatic differentiation [1] Lee, S-G. and Tanaka, T. (2019) Determination of Europium isotopic ratio by multi-collector inductively coupled plasma mass spectrometry using a Sm internal standard, Spectrochm. Acta Part B, v.156, 42-50.[2] Lee, S-G. and Tanaka, T. (2021) Gd matrix effects on Eu isotope fractionation using MC-ICP-MS: Optimizing Europium isotope ratio measurements in geological rock samples. Int.J.Mass.Spec.116668.[3] Lee, S-G. and Tanaka, T. (2021) Eu isotope fractionation in highly fractionated igneous rocks with large Eu negative anomaly Geochem. J. v.55, No.4, e9-e17.