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    标准锆石91500在LA−ICP−MS石榴子石U−Pb定年中的应用

    Application of standard zircon 91500 in LA−ICP−MS garnet U−Pb dating

      摘要
    • 摘要:
      研究目的 激光剥蚀电感耦合等离子体质谱法是当前同位素地质定年的重要手段，其分析准确性高度依赖于使用基体匹配的标准物质进行校准。锆石是目前应用最广泛的U−Pb定年标准矿物，而石榴子石等矿物缺乏相应的高质量年龄标准物质。石榴子石作为常见造岩矿物，近年来在矽卡岩型矿床年代学研究中应用日益增多，其标准物质的缺位制约了该矿物LA−ICP−MS定年技术的应用。针对石榴子石，开展适用于LA−ICP−MS U−Pb定年的标准物质研制与校准方法研究，以支持相关矿床年代学工作的深入开展。
      研究方法 利用LA−ICP−MS对黑龙江老柞山和西藏难爬日2个矽卡岩型矿床中的石榴子石开展了以锆石91500为外标的U−Pb定年研究。
      研究结果 在老柞山矿床中获得了2件石榴子石样品LZS-1和LZS-2的U−Pb年龄，其下交点年龄分别为106.9±4.0 Ma（MSWD=0.057，n=25)和108.9±9 Ma（MSWD=1.4，n=46)，与前人在不同实验室以石榴子石标样TaoChong测得的石榴子石U−Pb年龄（分别为104.4±4.2 Ma和107.4±1.1 Ma）及成矿岩体花岗闪长斑岩锆石U−Pb年龄（104.6±1.8 Ma）在误差范围内一致。在难爬日矿床中获得了1件石榴子石样品NPR-1 U−Pb年龄，其下交点年龄为205.7±3.9 Ma（MSWD=2.4，n=26），与前人在该地区报道的成矿岩体的锆石U−Pb年龄（211.0±1.8 Ma）在误差范围内一致。
      结论 结果表明，锆石与石榴子石之间的基体效应十分微弱，以标准锆石91500标定的石榴子石U−Pb年龄具有较高的准确度和可靠性，因此可以利用标准锆石91500对石榴子石进行U−Pb年龄标定。

       

      Abstract:
      Objective Laser ablation−inductively coupled plasma−mass spectrometry (LA−ICP−MS) is an important method for isotopic geochronology, and its analytical accuracy relies heavily on calibration using matrix−matched reference materials. Zircon is currently the most widely used reference mineral for U−Pb dating, while minerals such as garnet lack corresponding high−quality age reference materials. As a common rock−forming mineral, garnet has seen increasing application in the geochronological study of skarn−type deposits in recent years. However, the absence of suitable reference materials restricts the application of LA−ICP−MS dating for this mineral. This study aims to develop reference materials and calibration methods suitable for LA−ICP−MS U−Pb dating of garnet, thereby supporting further advancements in related deposit geochronology research.
      Methods This study employed LA−ICP−MS to conduct U−Pb dating on garnet samples from the Laozuoshan skarn deposit in Heilongjiang and the Nanpari skarn deposit in Tibet, using zircon 91500 as an external standard.
      Results For the Laozuoshan deposit, two garnet samples, LZS−1 and LZS−2, yielded lower intercept U−Pb ages of 106.9 ± 4.0 Ma (MSWD = 0.057, n = 25) and 108.9 ± 9 Ma (MSWD = 1.4, n = 46), respectively. These ages are consistent within error with previously reported U−Pb ages of garnet (104.4 ± 4.2 Ma and 107.4 ± 1.1 Ma, respectively) obtained using the garnet reference material TaoChong in different laboratories, as well as with the U−Pb age of the ore−forming granodiorite porphyry (104.6 ± 1.8 Ma). For the Nanpari deposit, one garnet sample, NPR−1, yielded a lower intercept U−Pb age of 205.7 ± 3.9 Ma (MSWD = 2.4, n = 26), which is consistent within error with the previously reported zircon U−Pb age of the ore−forming intrusion in this region (211.0 ± 1.8 Ma).
      Conclusions These results indicate that the matrix effects between zircon and garnet are minimal. Using standard zircon 91500 for U−Pb age calibration of garnet demonstrates high accuracy and reliability. Therefore, standard zircon 91500 can be effectively utilized for U−Pb age calibration of garnet.

       

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