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王家松, 许雅雯, 彭丽娜, 李国占. 应用激光拉曼光谱研究锆石LA-ICP-MS U-Pb定年中的α通量基体效应[J]. 岩矿测试, 2016, 35(5): 458-467. DOI: 10.15898/j.cnki.11-2131/td.2016.05.003
引用本文: 王家松, 许雅雯, 彭丽娜, 李国占. 应用激光拉曼光谱研究锆石LA-ICP-MS U-Pb定年中的α通量基体效应[J]. 岩矿测试, 2016, 35(5): 458-467. DOI: 10.15898/j.cnki.11-2131/td.2016.05.003
Jia-song WANG, Ya-wen XU, Li-na PENG, Guo-zhan LI. Laser Raman Spectroscopic Study and LA-ICP-MS U-Pb Dating of Zircons from the Badaling Granitic Complex[J]. Rock and Mineral Analysis, 2016, 35(5): 458-467. DOI: 10.15898/j.cnki.11-2131/td.2016.05.003
Citation: Jia-song WANG, Ya-wen XU, Li-na PENG, Guo-zhan LI. Laser Raman Spectroscopic Study and LA-ICP-MS U-Pb Dating of Zircons from the Badaling Granitic Complex[J]. Rock and Mineral Analysis, 2016, 35(5): 458-467. DOI: 10.15898/j.cnki.11-2131/td.2016.05.003

应用激光拉曼光谱研究锆石LA-ICP-MS U-Pb定年中的α通量基体效应

Laser Raman Spectroscopic Study and LA-ICP-MS U-Pb Dating of Zircons from the Badaling Granitic Complex

  • 摘要: α通量基体效应是由标准锆石与样品锆石之间的晶体损伤(以α通量表示)不同引起的激光剥蚀速率和坑下分馏行为的差异,已被证实是导致锆石LA-ICP-MS U-Pb定年结果存在系统偏倚的重要原因。α通量越高,剥蚀速率越快,坑下分馏越明显,然而α通量基体效应的校正尚未引起足够的重视。本文采用激光拉曼光谱和LA-ICP-MS对八达岭花岗杂岩样品进行研究,结果表明:实际α通量(DαP)≤0.75×1018 g-1的锆石样品,蜕晶化程度较弱,其定年结果存在的α通量基体效应可以忽略;DαP>0.75×1018 g-1的锆石样品,蜕晶化程度较高,其定年结果受α通量基体效应的影响明显,依据年龄差-DαP经验方程如y=347.8×exp(0.260×10-15x)进行校正可获得准确的年龄结果。本研究认为:采用激光拉曼光谱和半高宽(FWHM)-DαP校准曲线获得目标锆石DαP,利用年龄差-DαP经验方程估计LA-ICP-MS系统偏倚,是校正α通量基体效应的可行途径。

     

    Abstract: Alpha dose matrix effect is the discrepancy of ablation rate and down-hole fractionation induced by the difference of crystal damage degree (alpha dose) between standard zircons and sample zircons. It has been proved to be the cause of systematic bias of zircon U-Pb dating by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS). Alpha dose is closely related to ablation rate and down-hole fractionation behaviour of zircon. The higher the alpha dose, the faster the ablation rate and more obvious is the down-hole fractionation. However, the correction of alpha dose matrix effect has received little attention thus far. In this study, Laser Raman Spectroscopy and LA-ICP-MS were used to analyze zircons from the Badaling Granitic Complex rocks. Results show that the metamictization degree is low when the actual retained alpha dose (DαP) is no more than 0.75×1018 g-1 and the matrix effect is negligible. However, when the actual retained alpha dose (DαP) is larger than 0.75×1018 g-1, metamictization degree is high and the dating results are obviously affected byalpha dose matrix effect. For this reason, U-Pb data of zircons need to be corrected using the'Age offset-DαP'empirical equation such as y=347.8×exp(0.260×10-15x). In conclusion, it was found that this is a feasible method to correct alpha dose matrix effect by using Laser Raman Spectroscopy and a full width at half maximum (FWHM)-DαP correction curve to obtain DαP values of analyzed zircons by using age deviations-DαP empiric formula to determine the systematic deviations of LA-ICP-MS.

     

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