In situ measurement of Re-Os isotopes in mantle sulfides by laser ablation multicollector-inductively coupled plasma mass spectrometry: analytical methods and preliminary results
In situ measurement of Re-Os isotopes in mantle sulfides by laser ablation multicollector-inductively coupled plasma mass spectrometry: analytical methods and preliminary results
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DOI：
10.1016/s0016-7037(01)00823-7
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发表时间：
2002-03
影响因子：
5
通讯作者：
N. Pearson;O. Alard;W. Griffin;S. Jackson;S. O’Reilly
中科院分区：
文献类型：
--
作者：
N. Pearson;O. Alard;W. Griffin;S. Jackson;S. O’Reilly
开发了一种使用连接到多接收器诱导耦合等离子体质谱仪 (MC-ICPMS) 的激光烧蚀微型探针原位测定幔源橄榄岩中硫化物单晶中 Re-Os 同位素的方法。 MC-ICPMS 的高精度锇同位素分析通过实验室间锇标准品的测量得到证实。质量偏差校正程序的评估表明，指数定律提供了对 Os 同位素数据的最佳拟合，并且 Re 和 Os 的质量分馏系数之比在典型仪器操作条件范围内保持恒定。该关系使得能够精确且精确地校正187Re对187Os的同量异位干扰，使187Re/188Os值高达1.6。研究结果显示了西伯利亚和从克拉通金伯利岩橄榄石大晶中的单一硫化物包裹体，以及法国从克拉通和中央高原橄榄岩捕虏体中硅酸盐中和间隙硅酸盐中的硫化物。对于直径大于 50 μm、Os 含量≥40 ppm 的封闭硫化物，187Os/188Os 比值精度为 0.1%（2 SE），相当于 N-TIMS 全岩数据。间隙硫化物通常具有较低的 Os（10 至 30 ppm），分析精度较低（~1 至 2%），但仍提供有关 Os 在岩石圈内运动的有价值的信息。硅酸盐中的硫化物包裹体比间隙硫化物保留了明显更少的放射性锇同位素组成，因此产生了明显更古老和更真实的铼锇年龄信息。全岩Os同位素组成反映了不同代的封闭型和间隙型硫化物的比例；这使人们对许多已发表的“枯竭年龄”的意义产生了质疑。
A method has been developed for the in situ determination of Re-Os isotopes in single grains of sulfides in mantle-derived peridotites using a laser ablation microprobe attached to a multicollector-induced coupled plasma mass spectrometer (MC-ICPMS). High-precision Os isotope analysis by MC-ICPMS is demonstrated by the measurement of interlaboratory Os standards. Evaluation of mass bias correction procedures shows that the exponential law provides the best fit to the Os isotope data and that the ratio of the mass fractionation coefficients for Re and Os remains constant for the range of typical instrument operating conditions. This relationship enables the accurate and precise correction of the isobaric interference of187Re on187Os for187Re/188Os values up to 1.6. Results are presented for single sulfide inclusions in olivine macrocryts from kimberlites in the Siberian and Slave Cratons, and sulfides enclosed in silicates and interstitial to silicates in peridotite xenoliths from the Slave Craton and Massif Central, France. Enclosed sulfides larger than 50 μm in diameter and with Os contents ≥40 ppm give187Os/188Os ratios with a precision of 0.1% (2 SE), which is equivalent to N-TIMS whole-rock data. Interstitial sulfides typically have lower Os (10 to 30 ppm) and give analyses with lower precision (∼1 to 2%) but still provide valuable information on the movement of Os within the lithosphere. The sulfide inclusions in silicates preserve significantly less radiogenic Os isotopic compositions than interstitial sulfides and accordingly produce significantly older and more realistic Re-Os age information. Whole-rock Os isotope compositions reflect the proportions of different generations of enclosed and interstitial sulfides; this calls into question the significance of many published “depletion ages.”