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汪双双, 韩延兵, 李艳广, 魏小燕, 靳梦琪, 程秀花. 利用LA-ICP-MS在16 μm和10 μm激光束斑条件下测定独居石U-Th-Pb年龄[J]. 岩矿测试, 2016, 35(4): 349-357. DOI: 10.15898/j.cnki.11-2131/td.2016.04.003
引用本文: 汪双双, 韩延兵, 李艳广, 魏小燕, 靳梦琪, 程秀花. 利用LA-ICP-MS在16 μm和10 μm激光束斑条件下测定独居石U-Th-Pb年龄[J]. 岩矿测试, 2016, 35(4): 349-357. DOI: 10.15898/j.cnki.11-2131/td.2016.04.003
Shuang-shuang WANG, Yan-bing HAN, Yan-guang LI, Xiao-yan WEI, Meng-qi JIN, Xiu-hua CHENG. U-Th-Pb Dating of Monazite by LA-ICP-MS Using Ablation Spot Sizes of 16 μm and 10 μm[J]. Rock and Mineral Analysis, 2016, 35(4): 349-357. DOI: 10.15898/j.cnki.11-2131/td.2016.04.003
Citation: Shuang-shuang WANG, Yan-bing HAN, Yan-guang LI, Xiao-yan WEI, Meng-qi JIN, Xiu-hua CHENG. U-Th-Pb Dating of Monazite by LA-ICP-MS Using Ablation Spot Sizes of 16 μm and 10 μm[J]. Rock and Mineral Analysis, 2016, 35(4): 349-357. DOI: 10.15898/j.cnki.11-2131/td.2016.04.003

利用LA-ICP-MS在16 μm和10 μm激光束斑条件下测定独居石U-Th-Pb年龄

U-Th-Pb Dating of Monazite by LA-ICP-MS Using Ablation Spot Sizes of 16 μm and 10 μm

  • 摘要: 独居石是一种常用的地质年代计,但其内部结构复杂,常具有不同成分分区,只有足够小的激光束斑才能获得地质意义明确的U-Th-Pb年龄。本文在优化ICP-MS参数、匹配两路载气流量(Ar和He)的基础上,设计了两组激光剥蚀条件实验,获得适用于小束斑独居石U-Th-Pb定年的激光剥蚀参数(16 μm,3 J/cm2,5 Hz)和(10 μm,3 J/cm2,4 Hz)。在此条件下分别测定标准样品44069和未知样品15SLS-01,获得标准样品44069的208Pb/232Th和206Pb/238U值的单点测试精度小于3%,其U-Th-Pb年龄结果与前人测得SHRIMP U-Pb年龄和TIMS U-Pb年龄一致;未知样品15SLS-01的208Pb/232Th值的单点测试精度小于3%,206Pb/238U值的单点测试精度介于3%~8%,多点测试206Pb-238U和208Pb-232Th的加权平均年龄在误差范围内一致,其中208Pb-232Th年龄更具代表性。本研究表明在16 μm和10 μm激光束斑下,利用LA-ICP-MS能够实现独居石U-Th-Pb年龄的测定,极大地提高了独居石此种微区定年方法的空间分辨率。

     

    Abstract: Monazite is a common geological chronometer and has complex textures and different chemical domains. Meaningful U-Th-Pb ages for different domains can be obtained only using a suitably small laser beam spot. Based on optimizing the parameters of Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) and matching two channels of carrier gas flows (Ar and He), two groups of laser ablation parameters, 16 μm-3 J/cm2-5 Hz and 10 μm-3 J/cm2-4 Hz, can be obtained for dating monazite using small ablation spot sizes. A standard sample (44069) and an unknown sample (15SLS-01) were dated using the above laser ablation parameters. For 44069, the single-point precision of 208Pb/232Th and 206Pb/238U ratios were less than 3%, and U-Th-Pb age was found to be consistent with the previous SHRIMP and TIMS U-Pb ages. For 15SLS-01, the single-point precision of 208Pb/232Th is less than 3%, whereas that of 206Pb/238U ratios is 3%-8%. However, the weighted average ages of 208Pb-232Th and 206Pb-238U are consistent within the uncertainties, and the 208Pb-232Th age is more representative. The study demonstrated that monazite U-Th-Pb age can be successfully measured by LA-ICP-MS using laser beam spot sizes of 16 μm and 10 μm, which greatly improve the spatial resolution of this micro-dating method.

     

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