Analysis of trace elements in zircon at high mass resolving power using forward-geometry secondary ion mass spectrometry
Analysis of trace elements in zircon at high mass resolving power using forward-geometry secondary ion mass spectrometry
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使用正向几何二次离子质谱法以高质量分辨率分析锆石中的痕量元素
DOI：
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发表时间：
2023
期刊：
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通讯作者：
John Valley
中科院分区：
文献类型：
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作者：
Tyler Blum;Kouki Kitajima;Noriko Kita;John Valley
锆石中的微量元素是估算岩浆压力、温度和分异作用的基础，为了解地球历史上的岩浆演化提供了工具。最近，经验关系导致有人提出，包括钪 - 钇 - 铌 - 铈 - 镱 - 铪 - 铀在内的特定微量元素是现代地球不同构造环境的特征[1]。这些关系的更广泛应用在一定程度上受到了与钪和铌的准确且可重复测量相关的挑战的限制；它们各自只有一种天然同位素，并且分别需要m/Δm>12000和m/Δm>14000来解决与⁹⁰Zr⁺⁺和⁹²ZrH⁺的干扰。我们介绍了在大半径、正向几何结构的IMS - 1280上，在质量分辨率 = 12500（m/Δm，10%峰高全宽）的情况下，维持数天至数周的准确磁场校准的分析方法。在磁场循环过程中，要在峰上保持准确定位，需要±15ppm的精度（Δm/m，95%峰高全宽），同时要考虑漂移和扰动。为此，我们监测特定主量元素和金属氧化物峰的大约半峰高处的计数率；每次分析后，相对计数率用于对这些以及其他26个插值微量元素质量的磁场设置进行微小（ppm级）调整。对参考物质进行超过10天的定期分析表明，大多数测量的微量元素，包括钪和铌，相对分析不确定度在10%或以下。非均相和/或低浓度元素的变异性与已发表文献中引用的范围相当。检测限和精度得益于（1）具有更高束流密度（5.5nA）的射频等离子体源
Trace elements in zircon form the basis for estimates of magmatic pressures, temperatures, and differentiation, providing tools to understand magma evolution throughout Earth history. Recently, empirical relations have led to the proposal that specific trace elements, including Sc-Y-Nb-Ce-Yb-Hf-U, are distinctive of different tectonic settings on the modern Earth [1]. Broader application of these relations has been tempered, in part, by the challenges associated with accurate and reproducible measurement of Sc and Nb; each has a single naturally occurring isotope, and require m /Δ m >12000 and m /Δ m >14000 to resolve interferences with 90 Zr ++ and 92 ZrH + , respectively. We present analytical methods for maintaining accurate magnetic field calibration for days-to-weeks at a mass resolving power=12500 ( m /Δ m, full width at 10% peak height) on the large-radius, forward-geometry IMS-1280. Maintaining accurate positioning on peaks during magnetic field cycling requires ±15ppm precision (Δ m / m, full width at 95% peak height) while accounting for drift and perturbations. To achieve this, we monitor count rates at the approximate half-height-width of specific major element and metal-oxide peaks; relative count rates are used to make small (ppm-level) adjustments to the magnetic field settings for these and 26 other interpolated trace element masses after each analysis. Regular analysis of reference materials over >10 days shows the majority of measured trace elements, including Sc and Nb, have relative analytical uncertainties at or below 10%. Heterogeneous and/or low concentration elements show variability comparable to the ranges cited in published literature. Detection limits and precision benefit from (1) an RF-plasma source with higher beam density (5.5nA