Determination of cosmogenic 36Cl in rocks by isotope dilution:: innovations, validation and error propagation
Determination of cosmogenic 36Cl in rocks by isotope dilution:: innovations, validation and error propagation
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DOI：
10.1016/j.chemgeo.2006.03.001
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发表时间：
2006-10-15
期刊：
影响因子：
3.9
通讯作者：
Elmore, David
中科院分区：
文献类型：
--
作者：
Desilets, Darin;Zreda, Marek;Elmore, David
陆地岩石中宇宙成因Cl-36的测量提供了有关地貌和表面特征暴露年龄的定量信息。用于制备Cl-36样品的同位素稀释法现在被广泛使用，因为它允许在单个加速器质谱靶上同时测量Cl-36和Cl，提高了Cl测定的准确度和精度，并减少了岩石样品的大小和实验室工作。在本文中，我们描述了一种新的实施同位素稀释的Cl-36测年，报告的实验数据验证这种方法的准确性，并显示如何在测量的稳定同位素比的误差传播到错误的曝光age.Successful应用同位素稀释的Cl-36测年要求Cl在消化过程中被保留。我们在密封的酸消化弹中进行提取，以防止Cl损失，并将消化时间减少90%以上。同位素稀释得到的Cl-36/Cl值在8对硅酸盐样品的常规（未加标）值的1 σ内，并得到17个硅酸盐样品中的14个样品的Cl浓度与离子特异性电极法一致。碳酸盐样品的三个加标重复的结果也与未加标Cl-36/Cl一致，但我们发现同位素稀释比离子特异性电极法更准确地估计了天然Cl浓度。我们还准备了五个石灰石样品在开放的容器中存在过量的Ag+，以防止挥发的Cl。这种方法可以处理较大的样品（弹的容量为5克），并将是有用的样品与低浓度的Cl或低Cl-36/Cl时，不溶性氟化物不沉淀在消化容器。在开放和封闭容器中消化的成对样品的结果表明，开放容器消化是制备加标碳酸盐样品的可靠方法。(c)2006 Elsevier B. V.保留所有权利。
Measurements of cosmogenic Cl-36 in terrestrial rocks provide quantitative information about exposure ages of landforms and surface features. The isotope dilution method for preparing Cl-36 samples is now widely used because it allows Cl-36 and Cl to be measured simultaneously on a single accelerator mass spectrometry target, increases the accuracy and precision of Cl determinations, and reduces rock sample size and laboratory work. In this paper we describe a new implementation of isotope dilution to Cl-36 dating, report experimental data verifying the accuracy of this approach, and show how errors in the measured stable isotope ratio propagate to errors in exposure ages.Successful application of isotope dilution to Cl-36 dating requires that Cl be retained during digestion. We performed extractions in a sealed acid-digestion bomb to prevent Cl losses and to reduce digestion times by more than 90%. Isotope dilution gives Cl-36/Cl values within 1 sigma of conventional (unspiked) values for 8 paired silicate samples, and gives Cl concentrations that are consistent with the ion specific electrode method for 14 of 17 silicate samples. Results from three spiked replicates of a carbonate sample are also consistent with the unspiked Cl-36/Cl, but we found that isotope dilution gives a more accurate estimate of native Cl concentration than the ion specific electrode method. We also prepared five limestone samples in open vessels in the presence of excess Ag+ to prevent volatilization of Cl. This method would permit processing of larger samples (the bomb's capacity is 5 g), and would be useful for samples with low concentration of Cl or low Cl-36/Cl when insoluble fluorides do not precipitate in the digestion vessel. Results from paired samples digested in both open and closed vessels suggest that open-vessel digestion is a reliable way of preparing spiked carbonate samples. (c) 2006 Elsevier B.V. All rights reserved.