In situ measurement of Sm–Nd isotopic ratios in geological materials with Nd < 100 μg g−1 by LA-MC-ICP-MS

Abstract

In this study, we developed a method for measuring Sm–Nd isotopic ratios in samples with low Nd contents (<100 μg g⁻¹) by LA-MC-ICP-MS. The use of jet sample and X skimmer cones, with the addition of a small water vapour flow (∼5 mL min⁻¹) significantly improved the instrumental sensitivity by a factor of 1.9–3.6, and has little effect on Nd instrumental mass bias. The accuracy and precision of our analytical method is demonstrated by analysis of eight geological reference glasses (Nd = 21.4–60.9 μg g⁻¹). The obtained Sm–Nd isotope data are consistent with their recommended values. The measurement of a clinopyroxene megacryst (JLM-1) indicates that matrix effects on ¹⁴⁷Sm/¹⁴⁴Nd calibration between clinopyroxene and the measured geological reference glasses are insignificant. The inverse correlation between the analytical precision and the Nd signal intensity shows that the ¹⁴³Nd/¹⁴⁴Nd internal precision is <120 ppm (2s) for a ¹⁴⁶Nd signal >0.15 V, whereas the ¹⁴³Nd/¹⁴⁴Nd internal precision is <80 ppm (2s) for a ¹⁴⁶Nd signal >0.3 V. The addition of water vapour did not suppress the matrix effects for ¹⁴⁷Sm/¹⁴⁴Nd calibration. The Sm–Nd isotopic compositions of the Panzhihua clinopyroxene measured with our method indicate that the Panzhihua layered intrusion behaved as a closed magmatic system that experienced limited crustal contamination. The method presented in this study is a rapid and accurate technique for in situ analysis of Sm–Nd isotopes of low-Nd samples, such as volcanic glass, clinopyroxene and hornblende.