科研之友
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摘要
In this study, we developed a method for measuring Sm-Nd isotopic ratios in samples with low Nd contents (<100 mu g 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 (similar to 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 mu g 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 Sm-147/Nd-144 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 Nd-143/Nd-144 internal precision is <120 ppm (2s) for a Nd-146 signal >0.15 V, whereas the Nd-143/Nd-144 internal precision is <80 ppm (2s) for a Nd-146 signal >0.3 V. The addition of water vapour did not suppress the matrix effects for Sm-147/Nd-144 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.
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单位桂林理工大学; 中国科学院
