National Geochemical Survey of Australia: Samarium-Neodymium Isotopes Dataset

Preamble -- The 'National Geochemical Survey of Australia: The Geochemical Atlas of Australia' was published in July 2011 along with a digital copy of the NGSA geochemical dataset (http://dx.doi.org/10.11636/Record.2011.020). The NGSA project is described here: www.ga.gov.au/ngsa. A recent review of the original and ensuing NGSA outputs and impacts can be found in Caritat (2022). The present dataset contains additional geochemical data obtained on NGSA samples: Samarium-Neodymium Isotopes Dataset. Abstract -- Ninety three coarse-fraction (<2 mm) Bottom Outlet Sediment (BOS, on average 60 – 80 cm depth) NGSA samples mostly from three continental-scale cross-sections (one central north-south cross-section, one central east-west, and one southern east-west) were analysed for the samarium (Sm) and neodymium (Nd) isotopes 147Sm, 143Nd, and 144Nd to determine the 143Nd/144Nd and 147Sm/144Nd isotope ratios, initial epsilon Nd (εNd0), and single and two-stage depleted mantle model ages TDM and T2DM (in Ga or billion years). Together these samples represent over 490,000 km2 of catchment area sourcing the sampled fluvial/alluvial sediments. The summary statistics for 143Nd/144Nd and εNd0 results are shown below. Stats 143Nd/144Nd εNd0 Min 0.511014 -31.68 25% 0.511550 -21.22 Median 0.511817 -16.02 MAD 0.000232 4.53 Average 0.511802 -16.31 SD 0.000342 6.67 75% 0.512019 -12.07 Max 0.512623 -0.29 The method is briefly summarised below. Samples were analysed at University of Melbourne (UOM) by Roland Maas and University of Alberta (UOA) by Rob Creaser. At UOM all analyses were by isotope dilution. Samples were dissolved at high pressure, and Sm and Nd extracted using Eichrom TRU- and LN-resin columns. Isotopic analyses were by Multi Collector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS), with Nd mass bias corrected by internal normalisation to 146Nd/145Nd = 2.0719425 (equivalent to 146Nd/144Nd = 0.7219). In-run errors (2se) were ± 0.000010 or lower, external precision (2sd) ± 0.000020. All 143Nd/144Nd results have been adjusted to LaJolla=0.511860. The TIMS reference for JNd-1 is 0.512117, and BCR-2 has a nominal 147Sm/144Nd of 0.1382 and 143Nd/144Nd of 0.512640 ± 20. At UOA rock powders were accurately weighed and totally spiked with a known amount of mixed 150Nd-149Sm tracer solution and dissolved at high pressure for 5 days. Sm and Nd were extracted and separated by conventional cation and HDEHP-based chromatography (Creaser et al., 1997). Chemical processing blanks were < 120 picograms of either Sm or Nd, and are insignificant relative to the amount of Sm or Nd analysed for any rock sample. Isotopic analyses were determined in static mode by MC-ICP-MS (Schmidberger et al., 2007). All isotope ratios were normalized for variable mass fractionation to a value of 146Nd/144Nd = 0.7219. The 143Nd/144Nd ratio of samples are presented here relative to a value of 0.511850 for the La Jolla Nd isotopic standard, monitored by use of an in-house Alfa Nd isotopic standard for each analytical session. Sm isotopic abundances were normalized for variable mass fractionation to a value of 1.17537 for 152Sm/154Sm. The mixed 150Nd-149Sm tracer solution used was calibrated directly against the Caltech mixed Sm/Nd normal described by Wasserburg et al. (1981). Using this mixed tracer, the measured 147Sm/144Nd ratios for the international rock standard BCR-1 ranged from 0.1380 to 0.1382, suggesting a reproducibility for 147Sm/144Nd of ~ ± 0.1 % for real rock powders. The value of 147Sm/144Nd determined for BCR-1 was within the range of reported literature values by isotope dilution methods. A full report on this dataset will be available shortly as a Geoscience Australia Record. REFERENCES CITED Caritat, P. de, 2022. The National Geochemical Survey of Australia: review and impact. Geochemistry: Exploration, Environment, Analysis, 22, geochem2022-032. https://doi.org/10.1144/geochem2022-032 Creaser, R.A., Erdmer, P., Stevens, R.A. and Grant, S.L., 1997. Tectonic affinity of Nisutlin and Anvil assemblage strata from the Teslin tectonic zone, northern Canadian Cordillera: constraints from neodymium isotope and geochemical evidence. Tectonics, 16, 107-121. https://doi.org/10.1029/96TC03317 Schmidberger, S.S., Heaman, L.M., Simonetti, A., Creaser, R.A. and Whiteford, S., 2007. Lu-Hf, in-situ Sr and Pb isotope and trace element systematics for mantle eclogites from the Diavik diamond mine: evidence for Paleoproterozoic subduction beneath the Slave craton, Canada. Earth and Planetary Science Letters, 254, 55-68. https://doi.org/10.1016/j.epsl.2006.11.020 Wasserburg, G.J., Jacobsen, S.B., DePaolo, D.J., McCulloch, M.T. and Wen, T., 1981. Precise determination of Sm/Nd ratio, Sm, Nd isotopic abundances in standard solutions. Geochimica et Cosmochimica Acta, 45, 2311-2323.前言 《澳大利亚国家地球化学调查：澳大利亚地球化学图集》（National Geochemical Survey of Australia: The Geochemical Atlas of Australia）于2011年7月发布，同时附带了澳大利亚国家地球化学调查（National Geochemical Survey of Australia，简称NGSA）地球化学数据集的数字版本（http://dx.doi.org/10.11636/Record.2011.020）。NGSA项目的详细介绍可参见：www.ga.gov.au/ngsa。关于NGSA原始成果及后续产出与影响的最新综述可参考Caritat（2022）。本数据集包含针对NGSA样品获取的额外地球化学数据：钐-钕同位素数据集（Samarium-Neodymium Isotopes Dataset）。 摘要 对93份粗组分（<2 mm）底出口沉积物（Bottom Outlet Sediment，简称BOS，平均深度60~80 cm）的NGSA样品进行了分析，这些样品主要取自3个大陆尺度剖面：1个南北向中部剖面、1个东西向中部剖面以及1个东西向南部剖面。分析对象为钐（Sm）、钕（Nd）同位素147Sm、143Nd与144Nd，旨在测定143Nd/144Nd与147Sm/144Nd同位素比值、初始εNd（εNd0），以及单阶段和两阶段亏损地幔模式年龄TDM与T2DM（单位为Ga，即十亿年）。这些样品对应的汇水区域总面积超过49万平方公里，为所采集的河流/冲积沉积物的物源区。 143Nd/144Nd 和 εNd0 的汇总统计结果如下： | 统计参数 | 143Nd/144Nd | εNd0 | |---------|-------------|------| | 最小值 | 0.511014 | -31.68 | | 25%分位数 | 0.511550 | -21.22 | | 中位数 | 0.511817 | -16.02 | | 绝对中位差 | 0.000232 | 4.53 | | 平均值 | 0.511802 | -16.31 | | 标准差 | 0.000342 | 6.67 | | 75%分位数 | 0.512019 | -12.07 | | 最大值 | 0.512623 | -0.29 | 分析方法简述如下： 样品分别由墨尔本大学（University of Melbourne, UOM）的Roland Maas与阿尔伯塔大学（University of Alberta, UOA）的Rob Creaser完成分析。 在墨尔本大学，所有分析均采用同位素稀释法：样品经高压溶解后，使用Eichrom TRU树脂柱与LN树脂柱分离钐与钕。同位素分析采用多接收电感耦合等离子体质谱仪（Multi Collector Inductively Coupled Plasma Mass Spectrometer，简称MC-ICP-MS）完成，Nd的质量分馏通过内标校正，校正参数为146Nd/145Nd = 2.0719425（等价于146Nd/144Nd = 0.7219）。运行内误差（2se）为±0.000010或更低，外部精度（2sd）为±0.000020。所有143Nd/144Nd结果均已校正至拉霍亚（La Jolla）Nd同位素标准值0.511860。JNd-1的热电离质谱（TIMS）参考值为0.512117，BCR-2的标称147Sm/144Nd为0.1382，143Nd/144Nd为0.512640 ± 20。 在阿尔伯塔大学，首先准确称量岩石粉末，加入已知量的150Nd-149Sm混合稀释剂溶液，经高压溶解5天。采用常规阳离子色谱与基于HDEHP的色谱法分离钐与钕（Creaser等，1997）。化学处理空白的钐或钕含量均小于120皮克，相对于岩石样品中分析的钐或钕量可忽略不计。采用MC-ICP-MS静态模式进行同位素分析（Schmidberger等，2007）。所有同位素比值均以146Nd/144Nd = 0.7219校正质量分馏。样品的143Nd/144Nd比值以拉霍亚（La Jolla）Nd同位素标准0.511850为基准给出，每次分析会使用内部Alfa Nd同位素标准进行监控。Sm同位素丰度以152Sm/154Sm = 1.17537校正质量分馏。所用的150Nd-149Sm混合稀释剂直接根据Wasserburg等（1981）描述的加州理工学院混合Sm/Nd标准进行校准。使用该混合稀释剂时，国际岩石标准BCR-1的实测147Sm/144Nd比值介于0.1380至0.1382之间，表明对实际岩石粉末的147Sm/144Nd测定重现性约为±0.1%。测得的BCR-1的147Sm/144Nd值处于同位素稀释法文献报道值的范围内。 本数据集的完整报告即将作为澳大利亚地球科学局（Geoscience Australia）记录发布。 参考文献 1. Caritat, P. de, 2022. 澳大利亚国家地球化学调查：综述与影响. 《地球化学：勘探、环境与分析》, 22, geochem2022-032. https://doi.org/10.1144/geochem2022-032 2. Creaser, R.A., Erdmer, P., Stevens, R.A. and Grant, S.L., 1997. 加拿大北部科迪勒拉山系Teslin构造带Nisutlin与Anvil组合地层的构造亲缘性：来自钕同位素与地球化学证据的约束. 《构造学》, 16, 107-121. https://doi.org/10.1029/96TC03317 3. Schmidberger, S.S., Heaman, L.M., Simonetti, A., Creaser, R.A. and Whiteford, S., 2007. 加拿大Diavik钻石矿幔源榴辉岩的Lu-Hf、原位Sr与Pb同位素及微量元素体系：加拿大Slave克拉通下方古元古代俯冲作用的证据. 《地球与行星科学通讯》, 254, 55-68. https://doi.org/10.1016/j.epsl.2006.11.020 4. Wasserburg, G.J., Jacobsen, S.B., DePaolo, D.J., McCulloch, M.T. and Wen, T., 1981. 标准溶液中Sm/Nd比值、Sm、Nd同位素丰度的精确测定. 《地球化学与宇宙化学学报》, 45, 2311-2323.