Improvements of precision and accuracy in in situ Hf isotope microanalysis of zircon using the laser ablation-MC-ICPMS technique
Improvements of precision and accuracy in in situ Hf isotope microanalysis of zircon using the laser ablation-MC-ICPMS technique
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DOI：
10.1016/j.chemgeo.2005.03.010
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发表时间：
2005-07
期刊：
影响因子：
3.9
通讯作者：
T. Iizuka;T. Hirata
中科院分区：
文献类型：
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作者：
T. Iizuka;T. Hirata
我们开发了一种新的分析技术，通过激光烧蚀-多收集器-电感耦合等离子体质谱 (LA-MC-ICPMS) 精确、准确地原位测量锆石的 Hf 同位素比。新设计的样品池和 N2 混合技术提供了更高的元素灵敏度和更平滑的信号强度分布。为了提高Hf同位素比值分析的准确性，对先前报道的176Yb和176Lu对176Hf同量异位素干扰的校正方法进行了严格评估，发现在同量异位素干扰校正中使用Hf和Yb的独立质量偏差因子可以得到更可靠的Hf同位素数据。为了测试直径小于大多数锆石颗粒典型尺寸的~35 μm 烧蚀坑的 Hf 同位素数据的可靠性，测量了三种锆石（Harvard 91500、南极锆石 PMA7 和 Acasta 锆石 AY199）的 Lu-Hf 同位素。对于锆石标准91500，获得了0.282321±46(2S.D.)的当前176Hf/177Hf同位素比和0.282315±47(2S.D.)的初始176Hf/177Hf同位素比。所得的当前176Hf/177Hf同位素比与之前报道的数据非常一致。我们的原位同位素数据显示，91500颗粒内的Lu/Hf比值变化显着（176Lu/177Hf=0.000130–0.000345），表明当前176Hf/177Hf（大约15 ppm）存在轻微的同位素异质性。对于南极锆石 PMA7，尽管单晶尺寸较小（宽 50–100 μm，长 80–300 μm）并且存在各种矿物包裹体，但初始 176Hf/177Hf 比值的分析精度为 128 ppm [0.281208±36 (2 S.D.)]。对于 Acasta 锆石 AY199，尽管在太古宙早期结晶年龄（3.74 Ga）中 Yb/Hf (∼0.05) 和 Lu/Hf (∼0.01) 同位素比较高，但初始 176Hf/177Hf 比值的分析精度为 187 ppm [0.280160±52 (2 S.D.)]。这些结果清楚地表明，这里开发的原位 Hf 同位素比微分析有潜力成为锆石 Lu-Hf 同位素研究的重要工具。
We have developed a new analytical technique for precise and accurate in situ Hf isotope ratio measurements for zircons by means of laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS). Newly designed sample cell and N2mixing technique provided higher elemental sensitivity with smoother signal intensity profiles. In order to improve the accuracy of the Hf isotope ratio analysis, previously reported correction methods for isobaric interferences on176Hf by176Yb and176Lu were rigorously evaluated, and we found that the use of independent mass bias factors for Hf and Yb in the isobaric interference correction resulted in more reliable Hf isotopic data. In order to test the reliability of the Hf isotopic data from ∼35 μm diameter ablation pits that are smaller than the typical size of most zircon grains, Lu–Hf isotopes for three zircons (Harvard 91500, Antarctic zircon PMA7 and Acasta zircon AY199) were measured. The present176Hf/177Hf isotope ratio of 0.282321±46 (2 S.D.) and initial176Hf/177Hf isotope ratio of 0.282315±47 (2 S.D.) were obtained for zircon standard 91500. The resulting present176Hf/177Hf isotope ratio shows an excellent agreement with the previously reported data. Our in situ isotopic data revealed that the Lu/Hf ratio varied significantly within the 91500 grain (176Lu/177Hf=0.000130–0.000345), suggesting the existence of slight isotopic heterogeneity in present176Hf/177Hf (approximately 15 ppm). For Antarctic zircon PMA7, despite the smaller size of the single grain (50–100 μm wide, 80–300 μm long) and the presence of various mineral inclusions, resulting analytical precision for the initial176Hf/177Hf ratio was 128 ppm [0.281208±36 (2 S.D.)]. For Acasta zircon AY199, despite the high Yb/Hf (∼0.05) and Lu/Hf (∼0.01) isotope ratios with the early Archean crystallization age (3.74 Ga), resulting analytical precision for the initial176Hf/177Hf ratio was 187 ppm [0.280160±52 (2 S.D.)]. These results demonstrate clearly that in situ Hf isotope ratio microanalysis developed here has the potential to become a significant tool for zircon Lu–Hf isotopic study.