Submicron spatial resolution Pb–Pb and U–Pb dating by using a NanoSIMS equipped with the new radio-frequency ion source,Journal of Analytical Atomic Spectrometry

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Submicron spatial resolution Pb–Pb and U–Pb dating by using a NanoSIMS equipped with the new radio-frequency ion source
Journal of Analytical Atomic Spectrometry ( IF 3.1 ) Pub Date : 2021-05-22 , DOI: 10.1039/d1ja00085c
Jia-Long Hao _{1,

2,

3,

4,

5} , Wei Yang _{1,

2,

3,

4,

5} , Sen Hu _{1,

2,

3,

4,

5} , Rui-ying Li _{1,

2,

3,

4,

5} , Jiang-Long Ji _{1,

2,

3,

4,

5} , Hitesh G. Changela _{1,

2,

3,

4,

5} , Yang-Ting Lin _{1,

2,

3,

4,

5}

Affiliation

This paper is the first to report a Pb–Pb and U–Pb analytical method at a sub-micron scale using a NanoSIMS equipped with the new radio-frequency (RF) ion source. The RF ion source can generate a high-density primary beam to improve spatial resolution. A focused Gaussian beam of ∼450 pA with a diameter of ∼480 nm was utilized, significantly smaller in size than the 1.7 μm beam with the same current generated by the conventional duoplasmatron source. However, the high-density primary beam causes a more significant depth effect. Thus, a larger raster area (10 × 10 μm²) is selected to eliminate the mass fractionation caused by the depth effect. Other settings and data processing were similar to previous methods with a Duo source. Zircon standard M257 and baddeleyite standard Phalaborwa yielded ²⁰⁷Pb/²⁰⁶Pb ages of 547 ± 30 Ma and 2058 ± 13.8 Ma, respectively. These results agree well with the reference age values within analytical uncertainties. Using zircon Qinghu as a standard, zircon M257 and 91500 yielded U–Pb ages of 567.7 ± 6.8 Ma and 1056 ± 15 Ma, respectively, consistent with the recommended values within the analytical uncertainties. Three 4–5 μm zirconolite grains from the lunar meteorite Northwest Africa 8127 (NWA 8127) gave Pb–Pb ages of 3201 ± 25 Ma, 3174 ± 6 Ma and 3170 ± 14 Ma. One grain shows a variation of Pb/Pb age corresponding to the sub-micron scale distribution of U and Pb, probably due to the heavy impact on the moon. This technique is the first reported submicron Pb–Pb and U–Pb dating, which can be widely applied for sub-micron Pb–Pb and U–Pb dating for the tiny Zr-rich minerals from extraterrestrial samples.

中文翻译：

使用配备新型射频离子源的 NanoSIMS 进行亚微米空间分辨率 Pb-Pb 和 U-Pb 测年

本文首次报道了使用配备新型射频 (RF) 离子源的 NanoSIMS 在亚微米尺度上的 Pb-Pb 和 U-Pb 分析方法。RF 离子源可以产生高密度的初级束以提高空间分辨率。使用直径为 480 nm 的约 450 pA 聚焦高斯光束，其尺寸明显小于具有相同电流的 1.7 μm 光束，该光束由常规双等离子体源产生。然而，高密度主光束会导致更显着的深度效应。因此，选择更大的栅格区域（10 × 10 μm ²）来消除深度效应引起的质量分馏。其他设置和数据处理类似于以前使用 Duo 源的方法。锆石标准品 M257 和斜锆石标准品 Phalaborwa 产量为²⁰⁷铅/ ²⁰⁶铅年龄分别为 547 ± 30 Ma 和 2058 ± 13.8 Ma。这些结果与分析不确定度内的参考年龄值非常吻合。以清湖锆石为标准，锆石 M257 和 91500 的 U-Pb 年龄分别为 567.7 ± 6.8 Ma 和 1056 ± 15 Ma，与分析不确定度内的推荐值一致。来自月球陨石西北非洲 8127 (NWA 8127) 的三个 4-5 μm 锆石颗粒给出了 3201 ± 25 Ma、3174 ± 6 Ma 和 3170 ± 14 Ma 的 Pb-Pb 年龄。一颗颗粒显示出与 U 和 Pb 的亚微米级分布相对应的 Pb/Pb 年龄变化，可能是由于对月球的严重影响。该技术是首次报道的亚微米Pb-Pb和U-Pb定年，可广泛应用于地外样品中微小富Zr矿物的亚微米Pb-Pb和U-Pb定年。

更新日期：2021-07-07

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