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利用飞秒激光剥蚀电感耦合等离子体质谱(fs-LA-ICP-MS)对锆石和铀矿之间的Pb/U分馏行为,以及纳米比亚白岗岩中晶质铀矿进行了详细的原位微区U-Pb年代学研究.结果表明,fs-LA-ICP-MS分析过程中铀矿和锆石之间表现出显著不同的Pb/U分馏行为,利用锆石标准物质M257校正铀矿U-Pb定年标准物质GBW04420得到的年龄偏大17%.因此,精确的铀矿LA-ICP-MS原位微区U-Pb定年需要基体匹配的标准物质进行校正.以GBW04420为外标,利用fs-LA-ICP-MS在10?m,1 Hz激光条件,同时配备信号匀化装置(SSD)的前提下,对两个来自纳米比亚罗辛(Rossing)铀矿床东南侧欢乐谷(Gaudeanmus)地区的白岗岩岩石薄片中晶质铀矿进行了分析.其中一个样品给出的U-Pb谐和年龄为(507±1)Ma(2?,n=21),两个样品206Pb/238U加权平均年龄分别为(504±3)Ma(2?,n=21)和(503±3)Ma(2?,n=22).分析结果与前人的热电离质谱为基础的同位素稀释法(ID-TIMS)结果一致((509±1)和(508±12)Ma).同时与铀矿共生锆石给出的U-Pb上交点年龄结果 ((506±33)Ma(2?,n=29)和(501±51)Ma(2?,n=29))在误差范围内相同.由于共生高U锆石严重的Pb丢失,所以铀矿定年相对于共生锆石定年结果更为精确可靠.GBW04420是一个可以用于铀矿原位微区U-Pb同位素准确定年的标准物质.
The Pb / U fractionation behavior between zircon and uranium deposits by femtosecond laser ablation inductively coupled plasma mass spectrometry (fs-LA-ICP-MS) and the in-situ microscopic U-Pb geochronology was used to study the U-Pb geochronology of the uranium deposit. The results show that the Pb-U fractionation behavior between uranium deposits and zircons during the fs-LA-ICP- Pb dating standard material GBW04420 get 17% longer than the age, so accurate uranium ore LA-ICP-MS in-situ micro-U-Pb dating need matrix matching standard material to be corrected.With GBW04420 as external standard, the use of fs- LA-ICP-MS was performed on two white samples from the Gaudeanmus area to the southeast of the Rossing uranium deposit, Namibia, at 10 μm and 1 Hz laser conditions with a signal homogenization device (SSD) Analysis of the crystalline uranium deposits from granite and rock samples shows that the U-Pb harmonic age of one of the samples is (507 ± 1) Ma (2Å, n = 21), and the weighted average 206Pb / 238U (504 ± 3) Ma (2 ?, n = 21) and (503 ± 3) Ma (2 ?, n = 22) .The results of the analysis were consistent with those of the previous ID- TIMS) Results one (509 ± 1) and (508 ± 12) Ma, respectively.At the same time, the results of U-Pb dating on the U-Pb uranium deposit were (506 ± 33) Ma ± 51) Ma (2?, N = 29) are within the error range. The uranium dating is more accurate and reliable relative to the dating of symbiotic zircons due to the severe Pb loss from the symbiotic high U zircon.GBW04420 is a Reference material for U-Pb isotopic dating of uranium deposits in situ.