Synthesis of a new olivine reference material by a novel method for in situ iron and magnesium isotope analyses using laser ablation MC-ICP-MS†

Abstract

Olivine is an important rock-forming mineral, and its stable Fe and Mg isotopes provide important indications for identifying important geological processes. In situ Fe and Mg isotopic analyses using laser ablation multiple-collector inductively coupled plasma-mass spectrometry (LA-MC-ICP-MS) have proven to be a powerful strategy for examining isotopic variations in olivine growth zoning. However, the advancement of this technology has been limited by the lack of matrix-matched reference materials. In this study, we developed an efficient protocol for preparing olivine reference materials by combining ultrafine powder preparation and solid-phase sintering techniques, specifically designed for Fe–Mg isotope analyses. The synthesized olivine sample, CUG-OL-Ar, retained the initial chemical properties and showed good laser ablation behavior and a stable signal profile. The ANOVA assessment demonstrated the excellent homogeneity of Fe and Mg isotope compositions in CUG-OL-Ar in different batches. The solution-MC-ICP-MS methods were used to determine the Fe and Mg isotope ratios in CUG-OL-Ar, while the uncertainties of Fe and Mg isotope ratios were calculated based on the ISO GUIDE. The assigned values of δ⁵⁶Fe_IRMM-014 and δ²⁵Mg_SC isotopes in CUG-OL-Ar were 0.00 ± 0.06‰ (2SD, n = 350) and 0.00 ± 0.05‰ (2SD, n = 350), respectively. The good results obtained through measuring Fe and Mg isotopes in different types of reference materials using LA-MC-ICP-MS with CUG-OL-Ar as the external standard proved the practicability and reliability of CUG-OL-Ar.