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摘要
The Lamont-Doherty Earth Observatory radiogenic isotope group has been systematically measuring Sr-Nd-Pb-Hf isotopes of USGS reference material BCR-2 (Columbia River Basalt 2), as a chemical processing and instrumental quality control monitor for isotopic measurements. BCR-2 is now a widely used geochemical inter-laboratory reference material (RM), with its predecessor BCR-1 no longer available. Recognising that precise and accurate data on RMs is important for ensuring analytical quality and for comparing data between different laboratories, we present a compilation of multiple digestions and analyses made on BCR-2 during the first author's dissertation research. The best estimates of Sr, Nd and Hf isotope ratios and measurement reproducibilities, after filtering at the 2s level for outliers, were Sr-87/Sr-86= 0.70500011 (2s, 16ppm, n=21, sixteen digestions, one outlier), Nd-143/Nd-144=0.512637 +/- 13 (2s, 25 ppm, n=27, thirteen digestions, one outlier) and Hf-176/Hf-177= 0.282866 +/- 11 (2s, 39ppm, n=25, thirteen digestions, no outliers). Mean Nd and Hf values were within error of those reported by Weis etal. (2006, 2007) in their studies of RMs; mean Sr values were just outside the 2s uncertainty range of both laboratories. Moreover, a survey of published Sr-Nd-Hf data shows that our results fall within the range of reported values, but with a smaller variability. Our Pb isotope results on acid leached BCR-2 aliquots (n=26, twelve digestions, two outliers) were Pb-206/Pb-204=18.8029 +/- 10 (2s, 55ppm), Pb-207/Pb-204=15.6239 +/- 8 (2s, 52ppm), Pb-208/Pb-204=38.8287 +/- 25 (2s, 63ppm). We confirm that unleached BCR-2 powder is contaminated with Pb, and that sufficient leaching prior to digestion is required to achieve accurate values for the uncontaminated Pb isotopic compositions.
- 出版日期2016-3
