In situ Calcite U-Pb Geochronology by High-sensitivity Single-collector LA-SF-ICP-MS
In situ Calcite U-Pb Geochronology by High-sensitivity Single-collector LA-SF-ICP-MS
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采用高灵敏度单接收器 LA-SF-ICP-MS 进行原位方解石 U-Pb 地质年代学
DOI：
10.1007/s11430-021-9907-1
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发表时间：
2022
期刊：
影响因子：
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通讯作者：
Fuyuan Wu
中科院分区：
文献类型：
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作者：
Shitou Wu;Yueheng Yang;Nick M. W. Roberts;Ming Yang;Hao Wang;Zhongwu Lan;Bohang Xie;Tianyi Li;Lei Xu;Chao Huang;Liewen Xie;Jinhui Yang;Fuyuan Wu
激光烧蚀-电感耦合等离子体质谱(LA-−-MS)方解石U-ICPPb年代学是一种新兴的方法，具有广泛的应用前景。由于方解石中铀和铅的含量很低，使用更高灵敏度的仪器，如扇形场(SF)电感耦合等离子体质谱仪(ICPMS)，比更常用的四极(Q)电感耦合等离子体质谱仪(ICPMS)具有优势。利用热元素XR电感耦合等离子体质谱，我们证明了喷气+X锥体与氮气增强技术相结合对铀和铅同位素的测量具有最好的灵敏度。这种更高的灵敏度提高了方解石U−铅同位素测量的精度，并允许在高空间分辨率(<；110µm)下进行测年，以及对238U(<；1微克−1)和/或207Pb含量较低的样品(即年轻样品<；10 Ma)进行测年。使用85微米的光斑尺寸和低通量(∼2.0J cm−2)，激光在NISTSRM614、ARM-3和WC-1标准物质中诱导的206Pb/238U元素分馏微不足道(<；2.2%)。采用优化后的仪器参数，对四种常用的方解石U-−铅标准物质(WC-1、达夫棕槽、JT和ASH-15)进行了分析。结果与已发表的同位素稀释数据吻合良好，证明了我们技术的可靠性。ARM-3是一种安山岩玻璃，由于其适中的U(∼3.75微克−1)和铅(∼12.7微克−1)的含量，被证明是一种合适的207Pb/206Pb定标和仪器优化的参考物质。我们进一步证明，使用LA-ICPMS元素映射的图像引导方法是获得稳健年龄的有效工具。
U−Pb geochronology of calcite using laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is an emerging method, with potential applications to a vast array of geological problems. Due to the low levels of U and Pb in calcite, measurement using higher-sensitivity instruments, such as sector field (SF) ICP-MS, have advantages over more commonly used quadrupole (Q) ICP-MS instruments. Using a Thermo Element XR ICP-MS, we demonstrate that the Jet+X cone combination with the N2enhancement technique provides the best sensitivity for measuring U and Pb isotopes. This higher sensitivity improves the precision of calcite U−Pb isotope measurements, and permits dating at high spatial resolutions (<110 µm) and for samples containing low contents of238U (<1 µg g−1) and/or207Pb (i.e., young samples <10 Ma). Using a spot size of 85 µm with a low fluence (∼2.0 J cm−2), the laser-induced elemental fractionation of206Pb/238U in the NIST SRM 614, ARM-3 and WC-1 reference materials are insignificant (<2.2%). Adopting the optimized instrument parameters, we analysed four commonly-used calcite U−Pb reference materials (WC-1, Duff Brown Tank, JT, and ASH-15). The results match well with published isotope dilution data, demonstrating the reliability of our technique. ARM-3, an andesitic glass, is shown to be an appropriate reference material for both207Pb/206Pb calibration and instrument optimization because of its moderate contents of U (∼3.75 µg g−1) and Pb (∼12.7 µg g−1). We further demonstrate that the image-guided approach using LA-ICP-MS elemental mapping is an efficient tool in obtaining robust ages.