摘要
利用热电离质谱(TIMS)和207Pb-204Pb双稀释法测定低含量Pb岩石样品的同位素比值,可以有效校正由质谱分析造成的同位素分馏效应,提高铅同位素比值测定的精度和准确度。本文利用中国科学院广州地球化学研究所Triton TIMS,建立了207Pb-204Pb双稀释剂测试方法,并对Pb含量为5~20 ng的国际标样SRM981进行3个月的TIMS仪器测定,双稀释剂法外部校正后得到的206Pb/204Pb、207Pb/204Pb和208Pb/204Pb外部精度分别为±0.0034、±0.0046和±0.0100(2sd,n=28)。达到或优于其他国际高水平TIMS实验室双稀释剂法测定精度。同时,运用新方法对国际岩石标样AGV-2和BCR-2进行测定,得到的比值分别为:206Pb/204Pb=18.870±0.006、207Pb/204Pb=15.619±0.003、208Pb/204Pb=38.546±0.012和206Pb/204Pb=18.752±0.011、207Pb/204Pb=15.619±0.005、208Pb/204Pb=38.723±0.020,与国际同类实验室测定结果和精度一致,表明该新建方法是可靠的。运用207Pb-204Pb双稀释剂法对岩石样品进行测定,可获得高精度铅同位素比值,尤其对低含量Pb的基性、超基性地质样品测定有很大的优势。
^207Pb-^204Pb double spike method has been developed at Guangzhou Institute of Geochemistry in order to obtain high quality Pb isotope ratio. This method could effectively correct the mass fractionation effects for Pb isotopic analysis of samples with low Pb concentration by thermal ionization mass spectrometry （TIMS）. The minimum amount of Pb per load can be as low as 5×10^-9-20×10^-9 g, and the analysis method could effectively improve precision and accuracy. In this study, we determined Pb isotopic composition of SRM 981 using ^207Pb-^204Pb double spike, the external precisions of ^206Pb/^204Pb, ^207Pb/^204Pb and ^208Pb/^204Pb are ±0.0034, ±0.0046 and ±0.0100 （2×sd, n=28, t=3 months）. Meanwhile we have analyzed standard reference rocks of USGS： AGV-2 and BCR-2 by using the same procedure, the isotopic ratios for AGV-2 and BCR-2 are ^206Pb/^204Pb=18.870±0.006, ^207Pb/^204Pb=15.619±0.003, ^208Pb/^204Pb=38.546±0.012 and ^206Pb/^204Pb=18.752±0.011, ^207Pb/^204Pb=15.619±0.005, ^208Pb/^204Pb=38.723＋0.020, respectively. These values are identical to published data within uncertainty, independent of minor variations in loading and run parameters. Specially, this method is superb for precise and accurate isotope analyses of geological samples such as mafic and ultramafic rocks with low level Pb concentration, and will be a powerful tool in the future.
出处
《地球化学》
CAS
CSCD
2013年第2期103-115,共13页
Geochimica
基金
国家自然科学重点基金(40930316)
中国科学院广州地球化学研究所公共技术资助项目
国家重点基础研究发展计划(2009BC421004)
广西自然科学基金(2012GXNSFCA053007)
