High-precision in situ analysis of Pb isotopes in melt inclusions by LA-ICP-MS and application of Independent Component Analysis

Abstract

We report a high-precision ²⁰⁶Pb-based lead isotope composition of olivine-hosted melt inclusions in basaltic rocks from Rarotonga Island, Polynesia, in the southern Pacific, using femtosecond laser ablation (FsLA)-multiple Faraday collector-inductively coupled plasma-mass spectrometry (MFC-ICP-MS). This improved method enables high-precision analysis of Pb isotopes from low-Pb (≤10 ppm) melt inclusions with a crater size of ~30 μm in diameter and depth. The small crater size allows for further analysis of major and trace elements from the same melt inclusions using FsLA-sector field (SF)-ICP-MS. Using Pb isotope ratios of two olivine-hosted melt inclusions, we suggest that the mantle source beneath Rarotonga Island is heterogeneous. Such identification becomes possible owing to high-precision in situ analysis of Pb isotopes in melt inclusions and application of statistical approaches such as Independent Component Analysis to the analytical data.