Precise elemental and isotope ratio determination by simultaneous solution nebulization and laser ablation-ICP-MS: application to U-Pb geochronology
Precise elemental and isotope ratio determination by simultaneous solution nebulization and laser ablation-ICP-MS: application to U-Pb geochronology
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DOI：
10.1016/s0009-2541(99)00168-0
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发表时间：
2000-03-27
期刊：
影响因子：
3.9
通讯作者：
McDonough, WF
中科院分区：
文献类型：
--
作者：
Horn, I;Rudnick, RL;McDonough, WF
我们已经开发了一种通过同时溶液雾化和激光烧蚀电感耦合等离子体质谱法进行精确原位元素和同位素比测量的程序，其可以应用于同位素和元素比测定（例如，Li-6/Li-7、B-10/B-11、Ca/Sr等）。使用四极质谱仪，我们的程序产生的精度小于或等于2.0%（所有误差是2 σ的标准误差）的Pb-206/U-238和Pb-207/Pb-206和小于或等于3%的Pb-207/U-235在新元古代或更老的锆石和斜锆石与U含量大于或等于65 - 270 ppm。重要的是，这是在不使用外部校准标准的情况下完成的。我们雾化含有已知量的天然Tl和U-235 Spike的溶液，同时消融未知的辅助相。这允许烧蚀信号中的Pb/Pb以及Pb/U的精确质量区分校正。激光诱导元素分馏铅从U观察到的激光脉冲的数量（弹坑深度）的近函数，并呈指数反比与光斑大小。这些系统学使我们能够校正元素分馏。直径大于或等于150 μ m的斑点显示没有明显的Pb/U分馏，而35 μ m的斑点U变得逐渐耗尽相对于Ph，在2分钟的烧蚀期内Pb/U增加了四倍。对于哈佛标准锆石91500，我们获得Pb-206/U-238年龄为1061 +/-4Ma，Pb-207/Pb-206年龄为1074 +/-8Ma（TIMS年龄：Pb-206/U-238为1065Ma，[Wiedenbeck，M.，Alle，P.，Corfu，F.，格里芬，W. L.，Meier，M.，Ober，F.，von Quant，A.，罗迪克，J.C.，Spiegel，J.，1995.三种天然锆石标准，用于U-Th-Pb、Lu-Hf、微量元素和稀土元素分析。地质支架。新闻19，1 - 23]）;对于SHRIMP锆石标准，SL 13，我们获得Pb-206/U-238年龄为578 +/-10 Ma，Pb-207/Pb-206年龄为595 +/-13 Ma（TIMS年龄：572 Ma，[Claoue-Long，J.C.，Compston，W.，Roberts，J.，范宁，C.M.，1995.两个石炭纪年龄：锆石SHRIMP定年与常规锆石年龄及40Ar/39Ar分析的比较地质年代学时间尺度和全球地层对比。SEPM Special Publication，pp. 3 - 21]，SHRIMP的Pb-206/U-238年龄：580 - 565 Ma，[Compston，W.，1999.仪器分析的地质年代：第29届哈尔蒙讲座。Mineralogical杂志63，297 - 311]）。Phalaborwa斜锆石呈强烈的反向不整合，上截距年龄为2057 +/-8 Ma（TIMS年龄：1 Ma，[Reischmann，T.，1995.南非Phalaborwa火成杂岩中斜锆石（ZrO2）的精确U/Pb年龄测定S. Afr.J.Geol.98，98]; 2059.8 Ma，[Heaman，L.M.，LeCheminant，A.N.，斜锆石（ZrO_2）的共生和U-Pb系统ChemicalGeology 110，95 - 126]）和类似于0 Ma的较低截距。这些结果表明，LA-ICP-MS是能够定年的精度和准确度相媲美SHRIMP的副相。(C)2000 Elsevier Science B.V.保留所有权利。
We have developed a procedure for precise in situ elemental and isotope ratio measurements by simultaneous solution nebulization and laser ablation inductively coupled plasma mass spectrometry, which can be applied to isotope and element ratio determinations (e.g., Li-6/Li-7, B-10/B-11, Ca/Sr and others) covering the entire mass range. Using a quadrupole mass spectrometer, our procedure yields precision of less than or equal to 2.0% (all errors are 2 sigma of the standard error) for Pb-206/U-238 and Pb-207/Pb-206 and less than or equal to 3% for Pb-207/U-235 in neo-Proterozoic or older zircons and baddeleyite with U contents greater than or equal to 65-270 ppm. Importantly, this is accomplished without the use of an external calibration standard. We nebulize a solution containing known amounts of natural Tl and a U-235 Spike simultaneously with ablation of an unknown accessory phase. This allows precise mass discrimination correction of Pb/Pb as well as Pb/U in the ablated signal. Laser-induced elemental fractionation of Pb from U is observed to be a near function of the number of laser pulses (crater depth) and is inversely exponentially correlated with spot size. These systematics allow us to correct for elemental fractionation. Spots with diameters greater than or equal to 150 mu m show no appreciable Pb/U fractionation, whereas for 35 mu m spots U becomes progressively depleted relative to Ph, with a factor of four increase in Pb/U over a 2-min ablation period. For the Harvard standard zircon, 91 500, we obtain a Pb-206/U-238 age of 1061 +/- 4 Ma and a Pb-207/Pb-206 age of 1074 +/- 8 Ma (TIMS age: 1065 Ma for Pb-206/U-238, [Wiedenbeck, M., Alle, P., Corfu, F., Griffin, W.L., Meier, M., Ober, F., von Quant, A., Roddick, J.C., Spiegel, J., 1995. Three natural zircon standards for U-Th-Pb, Lu-Hf, trace element and REE analyses. Geostand. Newsl. 19, 1-23]); for the SHRIMP zircon standard, SL13, we obtain a Pb-206/U-238 age of 578 +/- 10 Ma and a Pb-207/Pb-206 age of 595 +/- 13 Ma (TIMS age: 572 Ma, [Claoue-Long, J.C., Compston, W., Roberts, J., Fanning, C.M., 1995. Two carboniferous ages: A comparison of SHRIMP zircon dating with conventional zircon ages and 40Ar/39Ar analysis. In: Geochronology Time Scales and Global Stratigraphic Correlation. SEPM Special Publication, pp. 3-21], Pb-206/U-238 age from SHRIMP: 580-565 Ma, [Compston, W., 1999. Geological age by instrumental analysis: The 29th Halmond Lecture. Mineralogical Magazine 63, 297-311]). The Phalaborwa baddeleyite is strongly reverse discordant yielding an upper intercept age of 2057 +/- 8 Ma (TIMS age: 1 Ma, [Reischmann, T., 1995. Precise U/Pb age determination with baddeleyite (ZrO2), a case study from the Phalaborwa igneous complex, South Africa. S. Afr. J. Geol. 98, 98]; 2059.8 Ma, [Heaman, L.M., LeCheminant, A.N., Paragenesis and U-Pb systematics of baddeleyite (ZrO2). Chemical Geology 110, 95-126]) and a lower intercept at similar to 0 Ma. These results demonstrate that LA-ICP-MS is capable of dating accessory phases with precision and accuracy comparable to SHRIMP. (C) 2000 Elsevier Science B.V. All rights reserved.