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High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS. Weis, Dominique; Kieffer, Bruno; Barling, Jane; Williams, Gwen A.; Hanano, Diane; Pretorius, Wilma; Scoates, James S.; Goolaerts, Arnaud; Friedman, Richard M. 2006

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Geochemistry Geophysics Geosystems  3  G  AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Published by AGU and the Geochemical Society  Technical Brief Volume 7, Number 8 10 August 2006 Q08006, doi:10.1029/2006GC001283 ISSN: 1525-2027  High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS Dominique Weis and Bruno Kieffer Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4 (dweis@eos.ubc.ca)  Claude Maerschalk Department of Earth and Environmental Sciences, Universite´ Libre de Bruxelles, CP 160/02, Avenue F.D. Roosevelt, 50, B-1050 Brussels, Belgium  Jane Barling Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4  Jeroen de Jong Department of Earth and Environmental Sciences, Universite´ Libre de Bruxelles, CP 160/02, Avenue F.D. Roosevelt, 50, B-1050 Brussels, Belgium  Gwen A. Williams, Diane Hanano, and Wilma Pretorius Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4  Nadine Mattielli Department of Earth and Environmental Sciences, Universite´ Libre de Bruxelles, CP 160/02, Avenue F.D. Roosevelt, 50, B-1050 Brussels, Belgium  James S. Scoates, Arnaud Goolaerts, and Richard M. Friedman Pacific Centre for Isotopic and Geochemical Research, Department of Earth and Ocean Sciences, University of British Columbia, 6339 Stores Road, Vancouver, British Columbia, Canada V6T 1Z4  J. Brian Mahoney Department of Geology, University of Wisconsin-Eau Claire, 105 Garfield Avenue, Eau Claire, Wisconsin 547024004, USA  [1] The Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia has undertaken a systematic analysis of the isotopic (Sr, Nd, and Pb) compositions and concentrations of a broad compositional range of U.S. Geological Survey (USGS) reference materials, including basalt (BCR-1, 2; BHVO-1, 2), andesite (AGV-1, 2), rhyolite (RGM-1, 2), syenite (STM-1, 2), granodiorite (GSP-2), and granite (G-2, 3). USGS rock reference materials are geochemically well characterized, but there is neither a systematic methodology nor a database for radiogenic isotopic compositions, even for the widely used BCR-1. This investigation represents the first comprehensive, systematic analysis of the isotopic composition and concentration of USGS reference materials and provides an important database for the isotopic community. In addition, the range of equipment at the PCIGR, including a Nu Instruments Plasma MC-ICP-MS, a Thermo Finnigan Triton TIMS, and a Thermo  Copyright 2006 by the American Geophysical Union  1 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Finnigan Element2 HR-ICP-MS, permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the TIMS and MC-ICP-MS methods (e.g., Nd isotopic compositions). For each of the reference materials, 5 to 10 complete replicate analyses provide coherent isotopic results, all with external precision below 30 ppm (2 SD) for Sr and Nd isotopic compositions (27 and 24 ppm for TIMS and MC-ICP-MS, respectively). Our results also show that the first- and second-generation USGS reference materials have homogeneous Sr and Nd isotopic compositions. Nd isotopic compositions by MC-ICP-MS and TIMS agree to within 15 ppm for all reference materials. Interlaboratory MC-ICP-MS comparisons show excellent agreement for Pb isotopic compositions; however, the reproducibility is not as good as for Sr and Nd. A careful, sequential leaching experiment of three first- and second-generation reference materials (BCR, BHVO, AGV) indicates that the heterogeneity in Pb isotopic compositions, and concentrations, could be directly related to contamination by the steel (mortar/pestle) used to process the materials. Contamination also accounts for the high concentrations of certain other trace elements (e.g., Li, Mo, Cd, Sn, Sb, W) in various USGS reference materials. Components: 12,951 words, 10 figures, 9 tables. Keywords: MC-ICP-MS; high precision; USGS reference material; Sr-Nd-Pb isotopes; leaching. Index Terms: 1040 Geochemistry: Radiogenic isotope geochemistry; 1094 Geochemistry: Instruments and techniques. Received 22 February 2006; Revised 4 May 2006; Accepted 23 May 2006; Published 10 August 2006. Weis, D., et al. (2006), High-precision isotopic characterization of USGS reference materials by TIMS and MC-ICP-MS, Geochem. Geophys. Geosyst., 7, Q08006, doi:10.1029/2006GC001283.  1. Introduction [2] The recent development of multiple collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) for high-precision isotopic analyses of a large number of elements and the ability of the Ar-ICP source to ionize most elements in the periodic table, has made these instruments critical to the advancement of research in geochemical, environmental and medical fields [Halliday et al., 1998; Albare`de et al., 2004]. The precision achieved on isotopic analyses of Nd, Hf and Pb is significantly better than 100 ppm due to the fact that most of the analyses can be run in static mode. Quality control protocols that monitor accuracy and precision demand well-characterized, homogenous reference materials. In addition, matrix effects can significantly affect the accuracy of the results, contrary to what was initially believed [e.g., Belshaw et al., 1998; Woodhead, 2002]. Therefore the reference material basis must also encompass the entire compositional range of studied samples. Similarly, recent technical improvements in thermo-ionization mass spectrometers (TIMS) have also led to the ability to produce more precise analyses on these instruments [e.g., Caro et al., 2003].  [3] We have carried out a systematic study of some of the most commonly used USGS reference materials: BCR-1, BCR-2, BHVO-1, BHVO-2, AGV-1, AGV-2, STM-1, STM-2, RGM-1, G-2, G-3 and GSP-2. Due to the heterogeneous nature of some of the basaltic samples, both in terms of concentrations and isotopic compositions, leaching experiments were carried out on BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1 and BCR-2 to further extend the study of Weis et al. [2005a]. [4] The availability of both a TIMS (Thermo Electron, Finnigan Triton) and a MC-ICP-MS (Nu Instruments Plasma) in the same laboratory allowed us to carry out a parallel study of Sr and Nd isotopic compositions on the TIMS, and Nd, Hf and Pb isotopic compositions on the MC-ICP-MS. To improve the comparison and reproducibility of the MC-ICP-MS analyses, we also measured Hf and Pb isotopic ratios on two different instruments in two different laboratories (Nu Plasma serial #015 in Brussels and Nu Plasma serial #021 in Vancouver) when possible. [5] The results are presented and discussed for each separate isotopic system, except where it is relevant to combine two systems. This paper focuses on Sr, Nd and Pb isotopes. Hf isotopic results will be presented in a separate paper, because of interesting developments related to the 2 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 1a. Nu Plasma MC-ICP-MS Operating Conditions  RF power Acceleration voltage Mass analyzer pressure Desolvating system Nebulizer Sample uptake rate Spray chamber temperature Membrane temperature Hot gas flow Membrane gas flow  Dry Plasma  Wet Plasma  1350 W $4000 V $2 Â 10À9 mbar DSN-100 ESI mflow 170 – 190 mL/min 110°C 110°C 0.2 L/min 2.5 – 3.5 L/min  1350 W $4000 V $2 Â 10À9 mbar n/a GE Micromist 50 – 100 mL/min 5°C n/a n/a n/a  2.1.1. Felsic Samples  role of labware composition [Weis et al., 2005b] and different separation issues.  [8] Approximately 100 to 150 mg of sample rock powder is loaded into a steel-jacketed acid-washed high-pressure PTFE bomb with 5.0 mL of 48% HF and 1.0 mL of $14 N HNO3, and then dissolved for 5 days at 190°C. Digested samples are dried down on a hotplate overnight at $130°C, reconstituted in 6.0 mL of 6 N HCl and re-bombed for 24 hours at 190°C. Afterward, samples are taken to dryness on a hotplate prior to re-dissolution for ion exchange purification of Pb, Hf, Sr and Nd.  2. Analytical Techniques [6] This study aims to present accurate highprecision isotopic compositions for USGS reference materials. We therefore describe our analytical procedures in some detail to provide the reader with sufficient information to evaluate and apply our methods. Cleaning protocols for high-pressure PTFE bombs and other labware are discussed by Pretorius et al. [2006]. All of the acids used for sample digestion and chemical separation were sub-boiling distilled in Teflon1 bottles, whereas the acids used for cleaning columns were quartzdistilled.  2.1.2. Mafic Samples [9] For mafic samples the rock powders (100 to 250 mg) are placed in 15 mL screw-top Savillex1 beakers with 10.0 mL of 48% HF and 1.0 mL of $14 N HNO3, and then dissolved on a hotplate for 48 hours at 130°C. During this step samples are periodically placed in an ultrasonic bath to ensure complete digestion. After digestion, samples are dried down overnight on a hotplate at $130°C, reconstituted in 6.0 mL of 6 N sub-boiled HCl and re-dissolved for 24 hours at 130°C, before commencing ion exchange chemistry.  2.1. Sample Dissolution Protocol [7] First, a series of tests was carried out to determine the appropriate digestion method for each reference material. This investigation demonstrated that it is critical to use high-pressure PTFE bomb dissolutions to achieve full recovery of trace elements from felsic rocks containing refractory accessory phases [Pretorius et al., 2006]. Full trace element recovery from mafic compositions and volcanic rock types, however, was achieved with a standard hotplate dissolution, in a Savillex1 beaker.  2.2. Ion Exchange Chemistry 2.2.1. Pb Column Chemistry [10] Pb, Hf, Sr and Nd are all purified from the same sample solution. The first stage is the sepa-  Table 1b. Nu Plasma MC-ICP-MS Nd and Pb Collector Configurationsa Element Nd Pb a  H6  H5  H4  H3  H2  H1  Ax  L1  L2  L3  150  148 208  147 207  146 206  145 205  144 204  143 203  142 202  140  L4  L5  Integration Time, s 10 10  Baselines were half-mass zeros and were taken over 30 s, every block.  3 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 2. USGS Reference Materials: Sr Isotopic Analyses (TIMS)a Sample BCR-1  BCR-2  BHVO-1  BHVO-2  AGV-1  AGV-2  Run Number  87  Sr/86Sr  Error (2s)  87  Sr/86Sr Normb  BCR-1 a S6d BCR-1 b S7d BCR-1 b S7d (5 months later) BCR-1 (1) 06/05/03 BCR-1 (2) 06/05/03 BCR-1 (1) 08/08/03 BCR-1 (2) 08/08/03 BCR-1 S10d Mean (2 SD) BCR-2 24/03/03 BCR-2 (1) 19/04/03 BCR-2 04/01/03 BCR-2 (1) 08/08/03 BCR-2 (2) 08/08/03 BCR-2 (3) 08/08/03 BCR-2 (1) 05/12/03 BCR-2 (2) 05/12/03 BCR-2 19/12/03 BCR-2 HA BCR-2 (1) 24/09/03 BCR-2 (2) 24/09/03 BCR-2 9/05/05 Mean (2 SD) BHVO-1 a S1d BHVO-1 a A8d BHVO-1 b S2d BHVO-1 24/03/03 BHVO-1 19/04/03 BHVO-1 08/08/03 BHVO-1 Cad BHVO-1 c S3d Mean (2 SD) BHVO-2 Cbd BHVO-2 24/03/03 BHVO-2 19/04/03 BHVO-2 19/04/03 Dble BHVO-2 (1) 08/08/03 BHVO-2 (1) 08/08/03 (rerun) BHVO-2 HA BHVO-2 (2) 05/12/03 BHVO-2 (1) 05/12/03 BHVO-2 19/12/03 BHVO-2 9/05/05 BHVO-2 9/05/05 Mean (2 SD)  Basalt 0.705024 0.705038 0.705039 0.705023 0.705022 0.705015 0.705013 0.705024 0.705025 0.705018 0.705028 0.705025 0.705030 0.705033 0.705019 0.705017 0.705011 0.705012 0.705012 0.705009 0.705013 0.705020 0.705019 0.703483 0.703502 0.703486 0.703471 0.703470 0.703489 0.703487 0.703487 0.703484 0.703481 0.703484 0.703483 0.703500 0.703494 0.703509 0.703484 0.703485 0.703474 0.703481 0.703482 0.703482 0.703487  6 7 7 9 8 7 7 7 19 6 9 9 7 9 9 9 7 7 7 7 8 7 16 6 6 7 6 10 7 7 6 21 9 6 8 6 8 7 7 6 7 7 7 7 19  0.705014 0.705028 0.705025 0.705017 0.705016 0.705010 0.705011 0.705023 0.705018 0.705014 0.705024 0.705016 0.705016 0.705019 0.705005 0.705017 0.705009 0.705012 0.705008 0.705008 0.705012 0.705009 0.705013 0.703473 0.703488 0.703476 0.703467 0.703464 0.703475 0.703473 0.703486 0.703475 0.703469 0.703480 0.703474 0.703499 0.703480 0.703495 0.703484 0.703483 0.703470 0.703477 0.703471 0.703471 0.703479  AGV-1 a A1d AGV-1 b A2d AGV-1 a S4d AGV-1 b S5d AGV-1 RMFd AGV-1 24/03/03 AGV-1 19/04/03 AGV-1 19/04/03 Dble AGV-1 a S1d AGV-1 D10d Mean (2 SD) AGV-2 b A7d AGV-2 (1) 19/04/03 AGV-2 (2) 19/04/03  Andesite 0.703986 0.704001 0.704006 0.703990 0.703993 0.703992 0.704004 0.704014 0.703987 0.703985 0.703996 0.703988 0.703988 0.703993  13 8 7 7 6 6 8 10 6 7 20 5 8 10  0.703984 0.703989 0.703988 0.703980 0.703983 0.703988 0.703998 0.704008 0.703985 0.703985 0.703989 0.703978 0.703979 0.703984  2 SDc  13  10  17  20  17  4 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 2. (continued) Sample  STM-2  RGM-1  G-2  GSP-2  Run Number  87  Sr/86Sr  Error (2s)  87  Sr/86Sr Normb  2 SDc  AGV-2 a A6d AGV-2 (2) 05/12/03 AGV-2 (1) 05/12/03 AGV-2 19/12/03 AGV-2 (1) 08/08/04 AGV-2 LT9 03/22/05 AGV-2 LT10 03/22/05 Mean (2 SD)  0.703979 0.703984 0.703973 0.703983 0.703986 0.703997 0.703998 0.703987  6 8 7 9 8 7 7 16  0.703977 0.703980 0.703973 0.703983 0.703985 0.703987 0.703988 0.703981  9  STM-2 D10d STM-2 L8d STM-2 L9d STM-2 L10d STM-2 D1d Mean (2 SD)  Syenite 0.703701 0.703704 0.703708 0.703703 0.703707 0.703705  8 7 7 8 9 6  0.703697 0.703703 0.703704 0.703699 0.703703 0.703701  6  RGM-1 A10d RGM-1 (1) 19/04/03 RGM-1 (2) 19/04/03 RGM-1 A5d RGM-1 S2d RGM-1 (2) 19/12/03 RGM-1 (3) 19/12/03 RGM-1 (1) 19/12/03 RGM-1 D9d RGM-1 03/03/05 Mean (2 SD)  Rhyolite 0.704228 0.704219 0.704217 0.704218 0.704220 0.704218 0.704206 0.704208 0.704227 0.704227 0.704219  6 9 8 9 6 7 7 7 9 8 15  0.704214 0.704210 0.704208 0.704203 0.704206 0.704214 0.704202 0.704204 0.704226 0.704215 0.704210  14  G-2 A5d G-2 04/01/04 +HClO4 G-2 04/01/04 No HClO4 G-2 L5d G-2 L6d G-2 D8d G-2 D9d Mean (2 SD)  Granite 0.709783 0.709775 0.709760 0.709766 0.709765 0.709774 0.709766 0.709770  8 6 9 8 7 7 8 16  0.709781 0.709775 0.709760 0.709766 0.709765 0.709774 0.709766 0.709770  14  GSP-2 (1) B5d GSP-2 (2) B6d GSP-2 D2d GSP-2 D3d GSP-2 D5d GSP-2 D5d(rerun) GSP-2 D6d GSP-2 D7d Mean (2 SD)  Granodiorite 0.765112 0.765122 0.765171 0.765175 0.765160 0.765156 0.765202 0.765111 0.765151  4 9 7 7 8 7 8 7 66  0.765096 0.765102 0.765167 0.765171 0.765156 0.765152 0.765198 0.765107 0.765144  75  a  ‘‘Dble’’: same digestion but different columns. Italic: measured after change of one of the Faraday cups. (rerun): sample measured twice with same filament load. The 2s error is the absolute error value of the individual sample analysis (internal error) and reported as times 106. b Measured ratio normalized to SRM 987 87Sr/86Sr = 0.710248. c Here, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. d High-pressure dissolution (the coding corresponds to the pressure-vessel number).  ration of Pb from other elements using an anion exchange column. The discard from this column is then dried down and reconstituted for cation exchange separation of Sr from the rare earth ele-  ments (REE) and Hf. The bulk REE fraction is then processed through exchange column to separate Nd from the remaining REE. The Hf fraction requires two further purification steps [Blichert-Toft et al., 5 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 3. USGS Reference Materials: Nd Isotopic Analyses (TIMS)a Sample BCR-1  BCR-2  BHVO-1  BHVO-2  Run Number BCR-1 Ad BCR-1 Ad (rerun) BCR-1 Bd BCR-1 Bd (rerun) BCR-1 302-6d BCR-1 302-7d BCR-1 (2) 06/05/03 BCR-1 (1) 06/05/03 BCR-1 (1) 08/08/03 BCR-1 a S6d BCR-1 b S7d BCR-1 S10d BCR-1(2) 08/08/03 Mean (2 SD) BCR-2 (1) 19/04/03 BCR-2 24/03/03 BCR-2 04/01/03 BCR-2 (1) 08/08/03 BCR-2 (3) 08/08/03 BCR-2 (2) 08/08/03 BCR-2 HA BCR-2 19/12/03 BCR-2 (1) 05/12/03 BCR-2 (2) 05/12/03 BCR-2 24/09/03 Mean (2 SD) BHVO-1 Aad BHVO-1 Aad (rerun) BHVO-1 Abd BHVO-1 Abd (rerun) BHVO-1 Bad BHVO-1 Bbd BHVO-1 Bbd (rerun) BHVO-1 Cad BHVO-1 Cbd BHVO-1 bd 202-6d BHVO-1 302-8d BHVO-1 24/03/03 BHVO-1 19/04/03 BHVO-1 08/08/03 BHVO-1 a A8d BHVO-1 a S1d BHVO-1 c S3d BHVO-1 b S2d Mean (2 SD) BHVO-2 24/03/03 BHVO-2 19/04/03 Dble BHVO-2 19/04/03 BHVO-2 (1) 08/08/03 BHVO-2 HA BHVO-2 (1) 05/12/03 BHVO-2 (2) 05/12/03 BHVO-2 19/12/03 BHVO-2 19/12/03 (rerun) BHVO-2 Dec04-Jan05 BHVO-2 Dec04-Jan05 BHVO-2 Dec04-Jan05 BHVO-2 Dec04-Jan05 Mean (2 SD)  143  Nd/144Nd  0.512625 0.512626 0.512622 0.512623 0.512621 0.512624 0.512635 0.512643 0.512629 0.512632 0.512639 0.512631 0.512626 0.512629 0.512639 0.512640 0.512639 0.512643 0.512638 0.512631 0.512631 0.512631 0.512627 0.512633 0.512623 0.512634 0.512972 0.512977 0.512969 0.512971 0.512972 0.512972 0.512965 0.512971 0.512967 0.512978 0.512973 0.512967 0.512981 0.512986 0.512977 0.512977 0.512988 0.512985 0.512980 0.512975 0.512983 0.512982 0.512987 0.512982 0.512981 0.512972 0.512977 0.512978 0.512976 0.512981 0.512983 0.512992 0.512979 0.512981  Error (2s) Basalt 8 4 6 6 8 6 4 6 6 5 5 5 5 14 5 5 4 5 6 6 6 5 5 5 7 12 4 4 8 6 8 6 6 8 6 10 2 8 5 6 6 7 5 6 5 13 5 4 6 6 5 7 10 6 5 6 6 6 7 10  145  Nd/144Nd  Error (2s)  0.348395 0.348402 0.348400 0.348401 0.348396 0.348399 0.348410 0.348409 0.348404 0.348411 0.348407 0.348400 0.348408  2 4 3 3 9 9 6 3 3 3 3 3 3  0.348408 0.348410 0.348409 0.348408 0.348407 0.348401 0.348407 0.348403 0.348410 0.348402 0.348407  3 3 3 3 3 3 3 4 4 3 4  0.348395 0.348399 0.348401 0.348401 0.348394 0.348399 0.348398 0.348400 0.348397 0.348394 0.348399 0.348404 0.348410 0.348405 0.348410 0.348408 0.348409 0.348397 0.348406  2 3 3 3 5 3 4 2 3 5 3 3 2 6 3 4 3 4 3  0.348412 0.348408 0.348419 0.348410 0.348405 0.348406 0.348402 0.348408 0.348405 0.348409 0.348406 0.348408 0.348397  3 3 4 3 3 5 5 4 3 3 4 4 4  143  Nd/144Nd Normb 0.512640 0.512641 0.512637 0.512638 0.512636 0.512639 0.512633 0.512641 0.512637 0.512636 0.512643 0.512635 0.512633 0.512638 0.512636 0.512637 0.512636 0.512648 0.512643 0.512639 0.512643 0.512635 0.512631 0.512637 0.512627 0.512637 0.512987 0.512992 0.512984 0.512986 0.512987 0.512987 0.512980 0.512986 0.512982 0.512993 0.512988 0.512982 0.512978 0.512983 0.512982 0.512984 0.512995 0.512992 0.512987 0.512986 0.512981 0.512980 0.512985 0.512987 0.512993 0.512976 0.512981 0.512982 0.512980 0.512985 0.512987 0.512996 0.512983 0.512984  2 SDc  6  12  9  11  6 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 3. (continued) Sample AGV-1  AGV-2  STM-2  RGM-1  G-2  GSP-2  Run Number  143  Nd/144Nd  Error (2s)  145  Nd/144Nd  AGV-1d AGV-1 Ad AGV-1 Ad AGV-1 Bd AGV-1 24/03/03 AGV-1 19/04/03 Dble AGV-1 19/04/03 AGV-1 D10d 11/01/04 AGV-1 a S4d AGV-1 b S5d Mean (2 SD) AGV-2 (2) 19/04/03 AGV-2 (1) 19/04/03 AGV-2 (A) A6d AGV-2 (B) A7d AGV-2 (1) 05/12/03 AGV-2 (2) 05/12/03 AGV-2 08/08/03 AGV-2 19/12/03 Mean (2 SD)  0.512774 0.512773 0.512781 0.512776 0.512787 0.512788 0.512791 0.512789 0.512801 0.512778 0.512784 0.512805 0.512783 0.512798 0.512788 0.512788 0.512783 0.512787 0.512785 0.512790  Andesite 4 8 8 6 5 5 5 5 8 7 18 7 5 5 6 6 6 6 6 16  STM-2 D10d STM-2 L8d STM-2 L9d STM-2 L10d STM-2 D1d Mean (2 SD)  0.512912 0.512902 0.512913 0.512907 0.512914 0.512910  Syenite 5 5 5 5 6 10  0.348406 0.348408 0.348407 0.348405 0.348409  RGM-1 (2) 19/04/03 RGM-1 A10d RGM-1 D9d RGM-1 A5d RGM-1 b A4d RGM-1 (1) 19/12/03 RGM-1 (2) 19/12/03 RGM-1 (3) 19/12/03 RGM-1 05/04/05d Mean (2 SD)  0.512800 0.512797 0.512802 0.512799 0.512798 0.512790 0.512794 0.512797 0.512817 0.512799  Rhyolite 5 7 5 6 5 5 5 5 8 15  0.348407 0.348408 0.348405 0.348404 0.348404 0.348404 0.348403 0.348410 0.348408  G-2d G-2 04/01/04 No HClO4 G-2 04/01/04 + HClO4 G-2 D8d G-2 D9d G-2 L6d G-2 L5d G-2 Dec04-Jan05 G-2 Dec04-Jan05 Mean (2 SD)  0.512218 0.512222 0.512226 0.512222 0.512218 0.512224 0.512227 0.512222 0.512223 0.512222  Granite 6 6 5 6 5 5 6 5 8 6  0.348398 0.348404 0.348408 0.348410 0.348406 0.348409 0.348401 0.348402 0.348412  GSP-2 D2d GSP-2 D3d GSP-2 D5d GSP-2 D6d GSP-2 D7d Mean (2 SD)  0.511368 0.511369 0.511368 0.511369 0.511372 0.511369  Granodiorite 6 6 5 8 6 3  0.348400 0.348403 0.348407 0.348408 0.348405  Error (2s)  0.348391 0.348393 0.348398 0.348395 0.348405 0.348410 0.348406 0.348408 0.348412 0.348400  2 4 3 3 3 3 4 3 6 4  0.348411 0.348406 0.348411 0.348408 0.348407 0.348405 0.348404 0.348403  4 3 4 4 3 4 3 3  3 3 3 4 3  3 3 3 5 3 3 3 3 6  6 4 3 3 3 3 5 6 4  4 4 4 4 4  143  Nd/144Nd Normb 0.512791 0.512790 0.512798 0.512793 0.512785 0.512786 0.512789 0.512793 0.512805 0.512782 0.512791 0.512802 0.512780 0.512798 0.512788 0.512792 0.512787 0.512791 0.512792 0.512791  2 SDc  13  13  0.512917 0.512907 0.512918 0.512912 0.512911 0.512913  9  0.512797 0.512797 0.512806 0.512803 0.512802 0.512794 0.512798 0.512801 0.512820 0.512802  15  0.512233 0.512227 0.512231 0.512227 0.512223 0.512229 0.512232 0.512226 0.512227 0.512228  6  0.511373 0.511374 0.511373 0.511374 0.511377 0.511374  3  7 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  1997]. Elution volumes used for the column procedures are not given as resin properties vary from lot to lot and thus require individual calibration. Exact details are available on request. [11] A standard, low-blank, Pb chemistry is used in which the sample is loaded on a 200 mL column of Biorad AG1-X8 100–200 mesh resin. The column is washed with two cycles of 18 mega ohm water/ 0.5 N HBr/6 N HCl, and conditioned with 18 mega ohm water followed by 0.5 N HBr. The sample is taken up in 0.5 N HBr with complete dissolution ensured by heating (10 min) and ultrasonication (10 min). The solution is then centrifuged at 14500 RPM for 6 min and the supernatant is loaded onto the column. Sr, Hf, and the REE are washed from the column with 0.5 N HBr, after which Pb is eluted in 6 N HCl. The resin is discarded after each Pb chemical separation.  2.2.2. First (Sr+REE) Column Chemistry [12] A standard cation exchange column of Biorad AG50W-X8 resin (100–200 mesh) is used to separate Sr from Hf and the REE. Columns are made of Pyrex or PFA depending on the type of sample and isotopes of interest; samples with Hf and/or Nd concentrations <10 ppm are processed through PFA columns and all others are processed on Pyrex columns [Weis et al., 2005b]. Before use the resin is equilibrated with 1.5 N HCl. The Sr-, Hf- and REE-bearing fraction from the Pb column is dried down and redissolved in 1.5 N HCl by heating at 110°C and ultrasonicating for 10 min. The solution is then centrifuged for 10 min at 3400 RPM and the supernatant carefully loaded onto the column so as to disturb the resin bed as little as possible. The column is then washed with 1.5 N HCl. Hf collection starts immediately after the sample is loaded and continues for the first few mL of 1.5 N HCl. Further washing with 2.5 N HCl removes sample matrix components, including Rb, prior to Sr elution in 2.5 N HCl. Further washing with 4.0 N HCl removes more sample matrix before the REE are eluted. The Sr and REE fractions are dried on a hotplate at $130°C. Columns are cleaned with $100 mL of 6 N HCl prior to re-equilibration with $100 mL of 1.5 N HCl.  10.1029/2006GC001283  2.2.3. Second Column (REE Separation) Chemistry [13] Nd is separated from the other REE on a column using HDEHP (di-2ethylhexyl-orthophosphoric acid)-coated Teflon powder as the ion exchange medium [Richard et al., 1976]. The purification of Nd is especially critical for mass spectrometric analysis due to the presence of isobaric interferences from Sm and Ce on 144Nd and 142Nd, respectively. HDEHP columns cannot separate Ce and Nd efficiently, which is not as critical for the measurement of 143Nd/144Nd as it is for 142Nd/144Nd [Boyet et al., 2003]. The presence of other REE will also reduce the yield of Nd on ionization during TIMS analysis. [14] The column is conditioned with 0.16 N HCl. The dried REE separate from the first cation exchange column is dissolved in 0.16 N HCl and loaded onto the column. The column is then carefully washed with 0.16 N HCl to remove Ba, La and most of the Ce. Nd together with a small fraction of the Ce and Pr is then eluted in 0.16 N HCl. Sm is eluted more than 10 mL after Nd, thereby avoiding any presence of Sm in the Nd cut. All of the heavier REE remain on the column and are subsequently removed with 6 N HCl prior to reuse of the column.  2.3. Mass Spectrometry Analytical Procedure [15] Isotopic composition measurements were performed either on a Thermo Finnigan TIMS (Sr, Nd) or on a Nu Instruments Plasma (Nu 021) MCICP-MS (Nd, Pb) at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the University of British Columbia. In addition, Pb isotopic compositions for some of the USGS reference materials were also measured on the Nu Instruments Plasma MC-ICP-MS (Nu 015) at the Department of Earth and Environmental Sciences of the Universite´ Libre de Bruxelles for interlaboratory comparison. [16] Due to drift in the Sr isotopic ratio of SRM 987 prior to October 2003, which was attributed to a problem with one of the Faraday cups on the TIMS, we have normalized the measured isotopic ratios of the USGS reference materials to SRM 987  Notes to Table 3. a ‘‘Dble’’: same digestion but different columns. Italic: measured after change of one of the Faraday cups. The 2s error is the absolute error value of the individual sample analysis (internal error) and reported as times 106. b Measured ratio normalized to La Jolla 143Nd/144Nd = 0.511858 (based on the mean of the wheel). c Here, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. d High-pressure PTFE digestion bomb (the coding corresponds to the bomb number).  8 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 4. USGS Reference Materials: Nd Isotopic Analyses (MC-ICP-MS)a Sample  Run Number  BCR-1 (A) S6d BCR-1 (A) S6d (rerun) BCR-1 (B) S7d BCR-1 (B) S7d (rerun) BCR-1 (2) 08/08/03 BCR-1 (2) 08/08/03 (rerun) BCR-1 S10d BCR-1 S10d (rerun) Mean (2 SD) BCR-2 BCR-2 HA BCR-2 HA (rerun) BCR-2 (1) 05/12/03 BCR-2 (1) 05/12/03 (rerun) BCR-2 (2) 05/12/03 BCR-2 (2) 05/12/03 (rerun) BCR-2 19/12/03 BCR-2 19/12/03 (rerun) BCR-2 24/09/03 BCR-2 24/09/03 (rerun) Mean (2 SD) BHVO-1 BHVO-1 (A) A8d BHVO-1 (A) A8d (rerun) BHVO-1 (A) S1d BHVO-1 (A) S1d (rerun) BHVO-1 (C) S3d BHVO-1 (C) S3d (rerun) Mean (2 SD) BHVO-2 BHVO-2 HA BHVO-2 HA (rerun) BHVO-2(1) 05/12/03 BHVO-2(1) 05/12/03 (rerun) BHVO-2(2) 05/12/03 BHVO-2(2) 05/12/03 (rerun) BHVO-2 19/12/03 BHVO-2 19/12/03 (rerun) Mean (2 SD) BCR-1  AGV-1  AGV-2  STM-2  AGV-1 (A) S4d AGV-1 (A) S4d (rerun) AGV-1 (B) S5d AGV-1 (B) S5d (rerun) AGV-1 D10d 11/01/04 AGV-1 D10d 11/01/04 (rerun) Mean (2 SD) AGV-2 (1) 05/12/03 AGV-2 (1) 05/12/03 (rerun) AGV-2 (2) 05/12/03 AGV-2 (2) 05/12/03 (rerun) AGV-2 19/12/03 AGV-2 19/12/03 (rerun) AGV-2 (1) 08/08/03 BK13 AGV-2 (1) 08/08/03 BK13 (rerun) Mean (2 SD) STM-2 STM-2 STM-2 STM-2  D10d D10d (rerun) L8d L8d (rerun)  143  144  Nd/  Error Nd (2s)  0.512657 0.512655 0.512641 0.512649 0.512642 0.512641 0.512636 0.512639 0.512645 0.512654 0.512642 0.512635 0.512644 0.512636 0.512635 0.512635 0.512640 0.512632 0.512622 0.512637 0.512988 0.512990 0.512988 0.512977 0.512986 0.512984 0.512986 0.512983 0.512986 0.512982 0.512994 0.512990 0.512983 0.512995 0.512984 0.512987  Basalt 12 13 15 11 11 11 11 12 16 10 11 7 9 11 12 10 10 8 10 17 9 11 12 10 13 11 9 10 9 10 11 11 11 11 9 10  0.512784 0.512804 0.512807 0.512796 0.512801 0.512778 0.512795 0.512780 0.512789 0.512791 0.512767 0.512790 0.512791 0.512787 0.512792 0.512786  Andesite 59 60 14 11 9 10 23 13 12 12 10 11 9 12 11 17  0.512912 0.512915 0.512929 0.512923  Syenite 11 11 9 9  145  144  Nd/  Error Nd (2s)  0.348410 0.348421 0.348414 0.348422 0.348410 0.348418 0.348421 0.348428  6 7 7 8 7 6 6 6  0.348418 0.348419 0.348421 0.348418 0.348416 0.348416 0.348420 0.348417 0.348416 0.348425  5 5 5 5 5 5 7 5 6 6  0.348423 0.348421 0.348418 0.348415 0.348417 0.348421  5 5 7 7 7 7  0.348418 0.348423 0.348420 0.348422 0.348429 0.348411 0.348422 0.348429  6 5 7 7 7 5 8 6  0.348440 0.348438 0.348423 0.348419 0.348424 0.348428  38 32 6 7 6 5  0.348426 0.348414 0.348430 0.348420 0.348421 0.348423 0.348428 0.348415  7 8 8 6 5 7 6 6  0.348420 0.348422 0.348421 0.348427  7 7 5 5  143  Nd/144Nd Normb  0.512659 0.512657 0.512643 0.512650 0.512644 0.512642 0.512637 0.512640 0.512646 0.512652 0.512640 0.512637 0.512646 0.512638 0.512636 0.512637 0.512642 0.512634 0.512623 0.512638 0.512991 0.512992 0.512991 0.512980 0.512987 0.512985 0.512988 0.512989 0.512992 0.512983 0.512995 0.512992 0.512985 0.512996 0.512985 0.512990 0.512789 0.512808 0.512812 0.512801 0.512806 0.512783 0.512800 0.512785 0.512794 0.512795 0.512772 0.512795 0.512796 0.512788 0.512793 0.512790 0.512909 0.512912 0.512926 0.512920  145  2 SD  c  Nd/144Nd Normb  0.348398 0.348409 0.348403 0.348410 0.348398 0.348406 0.348409 0.348416 16 0.348412 0.348413 0.348409 0.348406 0.348404 0.348404 0.348409 0.348405 0.348403 0.348412 15 0.348413 0.348411 0.348408 0.348404 0.348405 0.348408 10 0.348410 0.348414 0.348407 0.348409 0.348416 0.348398 0.348410 0.348417 10 0.348422 0.348420 0.348405 0.348401 0.348406 0.348410 23 0.348408 0.348397 0.348412 0.348402 0.348403 0.348405 0.348415 0.348402 17 0.348409 0.348411 0.348410 0.348416 9 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 4. (continued) Sample  RGM-1  G-2  GSP-2  a  143  Run Number  Nd/144Nd  Error (2s)  145  Nd/144Nd  STM-2 L9d STM-2 L9d (rerun) STM-2 L10d STM-2 L10d (rerun) STM-2 D1d STM-2 D1d (rerun) Mean (2 SD)  0.512928 0.512916 0.512911 0.512912 0.512914 0.512905 0.512917  RGM-1 (2) 19/12/03 RGM-1 (2) 19/12/03 (rerun) RGM-1 (3) 19/12/03 RGM-1 (3) 19/12/03 (rerun) RGM-1 (1) 19/12/03 RGM-1 (1) 19/12/03 (rerun) RGM-1 D9d RGM-1 D9 (rerun) RGM-1 b A4d DSN RGM-1 b A4d DSN (rerun) RGM-1 A5d DSN RGM-1 A5d DSN (rerun) Mean (2 SD)  0.512813 0.512809 0.512798 0.512810 0.512796 0.512804 0.512780 0.512787 0.512795 0.512803 0.512791 0.512795 0.512799  Rhyolite 10 9 9 11 13 12 12 14 5 7 5 9 19  0.348426 0.348427 0.348425 0.348436 0.348431 0.348424 0.348423 0.348409 0.348418 0.348423 0.348410 0.348413  G-2 04/01/04 G-2 04/01/04 (rerun) G-2 D8d G-2 D8d (rerun) G-2 D9d G-2 D9d (rerun) G-2 L5d G-2 L6d G-2 L6d (rerun) G-2 HClO4 G-2 HClO4 (rerun) G-2 D9d 3rd analysis Mean (2 SD)  0.512242 0.512235 0.512233 0.512241 0.512236 0.512232 0.512235 0.512250 0.512245 0.512226 0.512225 0.512235 0.512236  Granite 10 10 9 8 10 14 10 12 11 10 10 10 15  0.348423 0.348415 0.348426 0.348424 0.348425 0.348423 0.348426 0.348433 0.348424 0.348422 0.348425 0.348422  GSP-2 D2d GSP-2 D2d (rerun) GSP-2 D3d GSP-2 D3d (rerun) GSP-2 D5d GSP-2 D5d (rerun) GSP-2 D6d GSP-2 D6d (rerun) GSP-2 D7d GSP-2 D7d (rerun) GSP-2 B5d GSP-2 B5d (rerun) GSP-2 B6d GSP-2 B6d (rerun) Mean (2 SD)  Granodiorite 0.511360 10 0.511366 9 0.511375 9 0.511373 11 0.511362 9 0.511367 8 0.511366 7 0.511376 9 0.511370 9 0.511370 8 0.511375 10 0.511368 11 0.511364 8 0.511360 8 0.511368 11 145  9 8 8 8 11 8 16  0.348423 0.348425 0.348417 0.348419 0.348426 0.348424  0.348415 0.348415 0.348415 0.348414 0.348422 0.348419 0.348418 0.348423 0.348419 0.348425 0.348417 0.348420 0.348415 0.348417  Error (2s) 6 5 4 5 6 6  5 5 7 6 7 7 8 7 4 4 3 4  7 7 6 4 5 7 7 6 7 8 8 5  4 4 5 5 5 5 4 5 5 5 5 6 5 7  143  Nd/144Nd Normb  0.512925 0.512913 0.512907 0.512908 0.512910 0.512902 0.512913 0.512815 0.512812 0.512801 0.512812 0.512798 0.512807 0.512783 0.512789 0.512805 0.512813 0.512801 0.512805 0.512804 0.512241 0.512234 0.512232 0.512239 0.512234 0.512230 0.512233 0.512249 0.512243 0.512225 0.512223 0.512233 0.512235 0.511366 0.511372 0.511380 0.511378 0.511368 0.511373 0.511372 0.511381 0.511376 0.511376 0.511381 0.511374 0.511369 0.511366 0.511374  145  2 SDc  Nd/144Nd Normb  0.348412 0.348415 0.348406 0.348408 0.348416 0.348414 16 0.348415 0.348417 0.348415 0.348425 0.348420 0.348414 0.348413 0.348399 0.348418 0.348423 0.348410 0.348413 20 0.348417 0.348409 0.348420 0.348418 0.348418 0.348417 0.348420 0.348427 0.348418 0.348416 0.348419 0.348416 15 0.348407 0.348407 0.348407 0.348405 0.348414 0.348410 0.348410 0.348415 0.348411 0.348416 0.348409 0.348412 0.348407 0.348408 11  144  (Rerun): ran back-to-back with the 1st analysis. Nd/ Nd = 0.348403 (based on the daily mean of the La Jolla or Rennes analyses). DSN: Nu desolvator, i.e., dry plasma (all other analyses are wet plasma). The 2s error is the absolute error value of the individual sample analysis (internal error) and reported as times 106. b Measured ratio normalized to La Jolla 143Nd/144Nd = 0.511858 or to Rennes 143Nd/144Nd = 0.511973 and 145Nd/144Nd = 0.348403 (based on the daily mean of the La Jolla or Rennes analyses). c Here, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. d High-pressure PTFE digestion bomb (the coding corresponds to the bomb number).  10 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 5. USGS Reference Materials: Pb Isotopic Analyses (MC-ICP-MS)a Sample  Run Number  AGV-2  STM-1  STM-2  Pb/204Pbb  Error (2s)  207  Pb/204Pbb  Error (2s)  208  Pb/204Pbb  Error (2s)  Nu Wet/Dry Plasma  18.8215 18.8247 18.8213 18.8223 18.8225 18.7487 18.7468 18.7623 18.7575 18.7511 18.7657 18.7629 18.7553 18.7364 18.7570 18.7379 18.7529 18.6889 18.6965 18.7123 18.6963 18.6985 18.6299 18.6411 18.6609 18.6541 18.6509 18.6474  Basalt 0.0011 15.6379 0.0011 15.6375 0.0008 15.6345 0.0009 15.6352 0.0031 15.6363 0.0006 15.6252 0.0020 15.6233 0.0009 15.6298 0.0009 15.6247 0.0031 15.6218 0.0026 15.6240 0.0013 15.6240 0.0009 15.6247 0.0009 15.6257 0.0006 15.6249 0.0008 15.6258 0.0195 15.6249 0.0012 15.5707 0.0013 15.5748 0.0044 15.5767 0.0006 15.5719 0.0197 15.5735 0.0015 15.5362 0.0017 15.5387 0.0010 15.5333 0.0017 15.5262 0.0007 15.5328 0.0242 15.5334  0.0010 0.0011 0.0008 0.0008 0.0033 0.0007 0.0018 0.0010 0.0010 0.0024 0.0015 0.0011 0.0009 0.0008 0.0005 0.0008 0.0040 0.0012 0.0012 0.0041 0.0005 0.0055 0.0012 0.0015 0.0009 0.0014 0.0006 0.0094  38.7340 38.7355 38.7315 38.7272 38.7321 38.7136 38.7090 38.7467 38.7326 38.7211 38.7514 38.7350 38.7334 38.6912 38.7343 38.6918 38.7237 38.3514 38.3721 38.3600 38.3597 38.3608 38.2320 38.2293 38.2492 38.2294 38.2435 38.2367  0.0029 0.0032 0.0024 0.0022 0.0073 0.0023 0.0042 0.0031 0.0028 0.0055 0.0049 0.0039 0.0024 0.0023 0.0016 0.0022 0.0405 0.0031 0.0032 0.0098 0.0013 0.0171 0.0035 0.0040 0.0025 0.0034 0.0016 0.0182  W W W W  015 015 015 021  W W W W W W W D D W W  015 015 015 015 021 021 021 021 021 015 015  W W W D  015 015 021 021  W W D W D  015 015 021 015 021  AGV-1 AGV-1 AGV-1 AGV-1 AGV-1 D10c Mean (2 SD) AGV-2 AGV-2 AGV-2 AGV-2a AGV-2b AVG-2a AVG-2b Mean (2 SD)  18.9433 18.9398 18.9415 18.9398 18.9349 18.9399 18.8714 18.8629 18.8671 18.8684 18.8718 18.8713 18.8685 18.8688  Andesite 0.0008 15.6552 0.0008 15.6512 0.0007 15.6549 0.0006 15.6530 0.0007 15.6512 0.0063 15.6531 0.0006 15.6182 0.0016 15.6114 0.0011 15.6230 0.0009 15.6166 0.0008 15.6187 0.0009 15.6182 0.0011 15.6151 0.0063 15.6173  0.0007 0.0008 0.0006 0.0007 0.0008 0.0038 0.0006 0.0014 0.0009 0.0008 0.0008 0.0007 0.0009 0.0071  38.5668 38.5575 38.5623 38.5584 38.5544 38.5599 38.5476 38.5318 38.5509 38.5420 38.5501 38.5472 38.5405 38.5443  0.0022 0.0024 0.0018 0.0018 0.0042 0.0096 0.0023 0.0036 0.0026 0.0028 0.0020 0.0019 0.0026 0.0135  W W W W W  015 015 015 015 021  W W W D D W W  015 015 015 021 021 015 015  STM-1 STM-1 STM-1 STM-1 Mean (2 SD) STM-2 STM-2 replicate STM-2 STM-2 D1c STM-2 L10c STM-2 D10c STM-2 L9c STM-2a STM-2b  19.5163 19.5234 19.5228 19.4956 19.5145 19.7240 19.7192 19.7220 19.7224 19.7154 19.7105 19.7060 19.7135 19.7302  Syenite 0.0006 15.6304 0.0013 15.6312 0.0008 15.6296 0.0006 15.6356 0.0260 15.6317 0.0009 15.6174 0.0019 15.6135 0.0011 15.6163 0.0010 15.6150 0.0015 15.6139 0.0012 15.6138 0.0009 15.6118 0.0013 15.6148 0.0010 15.6189  0.0006 0.0011 0.0007 0.0005 0.0053 0.0008 0.0015 0.0011 0.0016 0.0011 0.0011 0.0010 0.0011 0.0008  39.1886 39.1964 39.1954 39.1693 39.1874 39.4226 39.4132 39.4199 39.4150 39.4087 39.4019 39.3912 39.4105 39.4295  0.0017 0.0034 0.0021 0.0014 0.0252 0.0021 0.0042 0.0032 0.0049 0.0032 0.0024 0.0036 0.0028 0.0023  W W W D  015 015 015 021  W W W W W W W D D  015 015 015 021 021 021 021 021 021  BCR-1 BCR-1 BCR-1 BCR-1 S10c Mean (2 SD) BCR-2 BCR-2 BCR-2 BCR-2 BCR-2 BCR-2/1 $100 ppb BCR-2/2 $120 ppb BCR-2/3 $100 ppb BCR-2a BCR-2b BCR-2a BCR-2b Mean (2 SD) BHVO-1 BHVO-1 BHVO-1 BHVO-1 BHVO-1 Mean (2 SD) BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 Mean (2 SD)  BCR-1  AGV-1  206  11 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 5. (continued) Sample  Run Number  206  Pb/204Pbb  Error (2s)  207  Pb/204Pbb  Error (2s)  208  Pb/204Pbb  Error (2s)  Nu Wet/Dry Plasma  STM-2 L8c STM-2a STM-2b Mean (2 SD) Mean bomb digestion Mean Savillex1 digestion  19.7051 19.7107 19.7255 19.7170 19.7136 19.7207  0.0008 0.0009 0.0009 0.0161 0.0140 0.0136  15.6051 15.6125 15.6144 15.6140 15.6136 15.6154  0.0007 0.0008 0.0006 0.0068 0.0026 0.0045  39.3815 39.4050 39.4164 39.4096 39.4042 39.4167  0.0018 0.0025 0.0022 0.0268 0.0204 0.0162  D W W  021 015 015  RGM-1  RGM-1 RGM-1 RGM-1 RGM-1 D9c RGM-1 Mean (2 SD)  19.0036 18.9962 18.9949 19.0042 19.0027 19.0003  Rhyolite 0.0007 15.6315 0.0007 15.6457 0.0007 15.6430 0.0009 15.6293 0.0006 15.6310 0.0089 15.6361  0.0007 0.0008 0.0008 0.0008 0.0005 0.0153  38.6925 38.6550 38.6487 38.6969 38.6971 38.6780  0.0022 0.0025 0.0025 0.0023 0.0013 0.0481  W W W W D  015 015 015 021 021  G-2  G-2 G-2 G-2 G-2 D8c G-2 D9c G-2 D9/2c G-2 HClO4 G-2a G-2b G-2 L5c G-2 L6c G-2a G-2b Mean (2 SD) Mean bomb digestion Mean Savillex1 digestion G-3 G-3 G-3 G-3a G-3 Bc G-3b G-3a Mean (2 SD)  18.3783 18.4049 18.4026 18.4156 18.3991 18.3987 18.4089 18.3851 18.3953 18.4094 18.4101 18.3873 18.3942 18.3992 18.4019 18.3960 18.4379 18.3444 18.3398 18.3816 18.4242 18.4218 18.3776 18.3896  Granite 0.0008 15.6341 0.0007 15.6394 0.0007 15.6359 0.0010 15.6374 0.0011 15.6342 0.0012 15.6345 0.0008 15.6388 0.0008 15.6337 0.0006 15.6362 0.0008 15.6354 0.0010 15.6354 0.0009 15.6346 0.0006 15.6338 0.0219 15.6357 0.0209 15.6353 0.0233 15.6361 0.0006 15.6401 0.0009 15.6342 0.0007 15.6293 0.0009 15.6354 0.0010 15.6368 0.0009 15.6339 0.0009 15.6307 0.0787 15.6343  0.0008 0.0009 0.0008 0.0010 0.0010 0.0010 0.0007 0.0009 0.0006 0.0007 0.0009 0.0008 0.0007 0.0038 0.0025 0.0049 0.0006 0.0009 0.0007 0.0009 0.0009 0.0008 0.0009 0.0073  38.9144 38.8987 38.8892 38.9133 38.8951 38.8966 38.9085 38.8946 38.9020 38.9025 38.9031 38.8958 38.8940 38.9006 38.9010 38.9001 38.9185 38.8316 38.8200 38.8558 38.8686 38.8587 38.8426 38.8565  0.0027 0.0024 0.0023 0.0026 0.0029 0.0026 0.0020 0.0020 0.0015 0.0020 0.0026 0.0020 0.0017 0.0154 0.0130 0.0190 0.0019 0.0028 0.0022 0.0024 0.0019 0.0022 0.0022 0.0640  W W W W W W W D D D D W W  015 015 015 021 021 021 021 021 021 021 021 015 015  W W W D D W W  015 015 015 021 021 015 015  GSP-2 D2c GSP-2 D2c (rerun) GSP-2 D6c GSP-2 D5c GSP-2 D3c GSP-2 D7c GSP-2a GSP-2b GSP-2a GSP-2b Mean (2 SD) Mean bomb digestion Mean Savillex1 digestion  17.6092 17.6108 17.6224 17.6113 17.6270 17.6096 17.5246 17.5281 17.5244 17.5301 17.5797 17.6151 17.5268  Granodiorite 0.0018 15.5109 0.0023 15.5103 0.0015 15.5126 0.0011 15.5125 0.0017 15.5147 0.0014 15.5114 0.0011 15.5050 0.0010 15.5064 0.0008 15.5048 0.0013 15.5078 0.0919 15.5096 0.0153 15.5121 0.0056 15.5060  0.0017 0.0023 0.0014 0.0010 0.0016 0.0013 0.0011 0.0009 0.0007 0.0011 0.0069 0.0031 0.0028  50.8849 50.8886 50.9599 50.9308 50.7956 50.5748 51.0666 51.1354 51.0736 51.1419 50.9452 50.8391 51.1044  0.0061 0.0074 0.0048 0.0035 0.0053 0.0044 0.0037 0.0037 0.0026 0.0037 0.3483 0.2818 0.0795  W W W W W W D D W W  021 021 021 021 021 021 021 021 015 015  G-3  GSP-2  a (Rerun): same sample, duplicate analysis. a and b: same chemistry series, separate dissolutions. W/D: W: analyses with wet plasma, D: analyses with dry plasma (DSN: Nu desolvator). b All Pb isotopic ratios have been normalized to the SRM 981 triple spike values of Abouchami et al. [2000]; see Table 6 for SRM 981 values. c Bomb digestion (the coding corresponds to the bomb number).  12 of 30  Date of Analysis  b  a  W W W W W W W D W W W W D D D D W D D  0.0094 0.0083 0.0118 0.0084 0.0075 0.0034 0.0041 0.0079 0.0078 0.0062 0.0080 0.0070 0.0072 0.0046 0.0059 0.0100 0.0060 0.0074 0.0111 0.0121 0.0088  255 226 321 229 203 93 111 215 212 168 217 189 197 126 126 272 162 200 303 328 240  Pb/204Pb 2 SDa ppmb  36.7191 36.7184 36.7136 36.7190 36.7195 36.7137 36.7165 36.7129 36.7181 36.7145 36.7161 36.7170 36.7183 36.7177 36.7114 36.7131 36.7138 36.7108 36.7115 36.7163 36.7145  206  0.0040 0.0034 0.0043 0.0029 0.0036 0.0012 0.0014 0.0033 0.0027 0.0024 0.0032 0.0027 0.0030 0.0019 0.0021 0.0034 0.0016 0.0025 0.0036 0.0047 0.0029  260 219 280 190 230 76 87 210 173 156 204 174 192 124 124 219 102 158 235 303 188  Pb/204Pb 2 SDa ppmb  15.4977 15.4976 15.4963 15.4978 15.4979 15.4965 15.4976 15.4958 15.4974 15.4965 15.4968 15.4971 15.4975 15.4969 15.4958 15.4961 15.4965 15.4955 15.4956 15.4968 15.4964  207  0.0046 0.0031 0.0044 0.0037 0.0037 0.0016 0.0012 0.0036 0.0030 0.0026 0.0033 0.0034 0.0030 0.0021 0.0021 0.0026 0.0025 0.0023 0.0031 0.0049 0.0036  269 180 261 216 218 96 73 212 176 155 193 203 176 124 124 155 145 138 184 287 215  Pb/204Pb 2 SDa ppmb  16.9403 16.9410 16.9398 16.9410 16.9413 16.9400 16.9408 16.9400 16.9421 16.9418 16.9410 16.9415 16.9433 16.9423 16.9392 16.9398 16.9398 16.9392 16.9398 16.9400 16.9407  208  The 2 standard deviation on the mean of the SRM 981 analyses on a given day (n varies between 12 and 20). The ppm error.  Nu 015  Wet/Dry 0.00013 0.00019 0.00021 0.00014 0.00013 0.00009 0.00005 0.00013 0.00013 0.00013 0.00017 0.00008 0.00010 0.00009 0.00014 0.00030 0.00007 0.00016 0.00021 0.00025 0.00019  59 89 96 67 62 43 24 59 58 61 79 37 46 44 44 138 31 74 97 114 86  Pb/206Pb 2 SDa ppmb  2.16756 2.16744 2.16729 2.16745 2.16747 2.16730 2.16733 2.16721 2.16726 2.16712 2.16730 2.16729 2.16716 2.16723 2.16725 2.16726 2.16734 2.16722 2.16721 2.16744 2.16724  208  0.00003 0.00005 0.00006 0.00004 0.00002 0.00003 0.00001 0.00005 0.00003 0.00003 0.00006 0.00003 0.00004 0.00003 0.00004 0.00006 0.00006 0.00004 0.00005 0.00005 0.00009  33 53 71 44 25 28 15 53 33 33 67 30 43 33 33 67 63 41 56 56 97  Pb/206Pb 2 SDa ppmb 0.91483 0.91480 0.91479 0.91481 0.91480 0.91480 0.91480 0.91474 0.91472 0.91470 0.91475 0.91474 0.91467 0.91469 0.91479 0.91477 0.91481 0.91477 0.91476 0.91481 0.91475  207  G  3  September 30, 2003 November 10, 2003 December 19, 2003 February 16, 2004 August 9, 2004 Nu 021 September 12, 2003 September 19, 2003 March 24, 2004 July 1, 2004 July 2, 2004 July 7, 2004 July 9, 2004 July 27, 2004 July 28, 2004 August 6, 2004 September 15, 2004 September 22, 2004 September 24, 2004 September 28, 2004 Average Nu 015 n = 65 Average Nu 021 n = 167  Instrument  Table 6. SRM 981 Pb Isotopic Analyses (MC-ICP-MS): Averages for Individual Days  Geochemistry Geophysics Geosystems weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  13 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 7. Leaching Experiment: Pb Isotopic Analyses (MC-ICP-MS) and Sr and Nd Isotopic Analyses (TIMS) for BHVO, BCR, and AGV USGS Reference Materialsa Sample BHVO-1 BHVO-1 BHVO-1 BHVO-2 BHVO-2 BHVO-2 BHVO-1 BHVO-1 BHVO-2 BHVO-2  (1) (2) (3) (1) (2) (3) (1) (3) (2) (3)  residue residue residue residue residue residue leachate leachate leachate leachate  206  Error Pb/204Pbb (2s)  207  Error Pb/204Pbb (2s)  208  Error Pb/204Pbb (2s)  87  Sr/86Src  Error (2s)  143  Nd/144Ndc  Error (2s)  18.6460 18.6435 18.6150 18.6455 18.6378 18.6387 18.7061 18.7311 18.5649 18.5628  0.0007 0.0010 0.0013 0.0009 0.0008 0.0006 0.0007 0.0006 0.0008 0.0010  15.4852 15.4786 15.4847 15.4892 15.4789 15.4797 15.6291 15.6390 15.5987 15.6015  BHVO 0.0006 38.1954 0.0008 38.1733 0.0007 38.1723 0.0011 38.2055 0.0009 38.1881 0.0007 38.1767 0.0008 38.4393 0.0005 38.4721 0.0007 38.2213 0.0008 38.2307  0.0017 0.0025 0.0018 0.0034 0.0027 0.0021 0.0021 0.0015 0.0022 0.0020  0.703464 0.703467 0.703476 0.703484 0.703467 0.703462 0.703493 0.703494 0.703508 0.703496  0.000008 0.000006 0.000007 0.000007 0.000007 0.000007 0.000007 0.000007 0.000007 0.000007  0.512989 0.512981 0.512989 0.512987 0.512987 0.512985 0.512983 0.512981 0.512992 0.512994  0.000006 0.000007 0.000006 0.000005 0.000005 0.000006 0.000008 0.000006 0.000006 0.000006  BCR-1 BCR-1 BCR-2 BCR-2 BCR-2 BCR-1 BCR-1 BCR-2 BCR-2  (1) (2) (1) (2) (3) (1) (2) (1) (3)  residue residue residue residue residue leachate leachate leachate leachate  18.7995 18.8013 18.8007 18.7993 18.6646 18.8232 18.8390 18.6473 18.7951  0.0009 0.0006 0.0007 0.0010 0.0010 0.0006 0.0009 0.0009 0.0006  15.6234 15.6230 15.6241 15.6230 15.6265 15.6302 15.6469 15.6209 15.6146  BCR 0.0008 38.8219 0.0006 38.8228 0.0006 38.8256 0.0009 38.8232 0.0009 38.5279 0.0005 38.6047 0.0008 38.6518 0.0007 38.4955 0.0007 38.7996  0.0022 0.0018 0.0019 0.0029 0.0025 0.0014 0.0020 0.0020 0.0024  0.704981 0.704982 0.704992 0.705012 0.705019 0.705118 0.705095 0.705085  0.000007 0.000008 0.000007 0.000008 0.000013 0.000007 0.000009 0.000008  0.512644 0.512645 0.512641 0.512644 0.512639 0.512647 0.512641 0.512643  0.000005 0.000007 0.000004 0.000007 0.000005 0.000006 0.000008 0.000007  AGV-1 AGV-1 AGV-1 AGV-2 AGV-2 AGV-1 AGV-1 AGV-2 AGV-2  (1) (2) (3) (1) (2) (1) (3) (1) (2)  residue residue residue residue residue leachate leachate leachate leachate  18.9060 18.9047 18.8894 18.9067 18.9078 18.9443 18.9525 18.8126 18.8055  0.0006 0.0007 0.0010 0.0005 0.0005 0.0006 0.0005 0.0007 0.0006  15.6164 15.6165 15.5984 15.6137 15.6157 15.6584 15.6670 15.6251 15.6232  AGV 0.0005 38.5985 0.0006 38.5765 0.0011 38.5181 0.0005 38.5692 0.0004 38.5764 0.0005 38.5480 0.0004 38.5587 0.0012 38.5089 0.0006 38.4951  0.0015 0.0015 0.0037 0.0014 0.0013 0.0015 0.0011 0.0018 0.0017  0.703957 0.703948 0.703946 0.703948 0.703966 0.704025 0.704084 0.704060 0.704054  0.000007 0.000008 0.000008 0.000007 0.000008 0.000008 0.000007 0.000008 0.000008  0.512753 0.512808 0.512800  0.000006 0.000006 0.000006  0.512794 0.512800 0.512795 0.512798 0.512797  0.000005 0.000005 0.000005 0.000005 0.000006  a All isotopic measurements of the leaching experiment were carried out over four days in September 2004. The 2s error is the absolute error value of the individual sample analysis (internal error). b All Pb isotopic ratios have been normalized to the SRM 981 triple-spike values of Abouchami et al. [2000]; see Table 6 for SRM 981 values. c Measured ratio normalized to SRM 987 87Sr/86Sr = 0.710248 and to La Jolla 143Nd/144Nd = 0.511858 (based on the mean of the wheel).  87  Sr/86Sr = 0.710248 relative to the barrel average. For each barrel of 21 filaments, 4 or 5 positions were occupied by a reference material (SRM 987 for Sr and La Jolla or Rennes for Nd). The average of these 4 or 5 analyses corresponds to the barrel average. The normalization procedure has been applied to the Nd isotopic ratios for the La Jolla and Rennes reference materials, with a normalization value of 143Nd/144Nd = 0.511858 [Lugmair et al., 1983] and 0.511973 [Chauvel and BlichertToft, 2001], respectively. [17] Sr and Nd isotopic compositions were measured in static mode with relay matrix rotation (the ‘‘virtual amplifier’’ of Finnigan) on a single Ta and double Re-Ta filament, respectively. The data were corrected for mass fractionation by normalizing to  86  Sr/88Sr = 0.1194 and 146Nd/144Nd = 0.7219, using an exponential law. Replicate analyses of the La Jolla Nd reference material on the Triton TIMS gave 0.511850 ± 15 (n = 73, where n corresponds to the number of analyses) and then 0.511853 ± 12 (n = 118) after one of the Faraday cups was changed. We also analyzed the Rennes Nd reference material [Chauvel and Blichert-Toft, 2001] and obtained 143Nd/144Nd = 0.511970 ± 10 (n = 10). Replicate analyses of the Sr reference material SRM 987 yielded 87Sr/86Sr values of 0.710256 ± 16 (n = 145) and then 0.710252 ± 13 (n = 88) after one of the Faraday cups was changed. Usually, a single analysis consisted of minimum of 135 ratios (9 blocks of 15 cycles) to allow for a full rotation of the virtual amplifier. 14 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Table 8. Pb Concentrations by Isotope Dilution for USGS Reference Materialsa Sample  Pb, ppm  2s  BCR-1 BCR-1 BCR-1 BCR-1 BCR-1 Mean  A B C D  13.16 13.36 13.07 13.79 13.34  0.22 0.16 0.15 0.14 0.64  AGV-1 AGV-1 AGV-1 AGV-1 AGV-1 AGV-1 AGV-1 Mean  A B C D E F  33.01 37.79 40.52 40.46 37.11 35.26 37.36  1.47 1.18 0.81 0.76 0.68 0.60 5.88  2.46 1.98 2.02 1.99 2.04 2.05 2.09  0.01 0.01 0.01 0.01 0.01 0.02 0.37  BHVO-1 BHVO-1 BHVO-1 BHVO-1 BHVO-1 BHVO-1 BHVO-1 Mean a  A B C D E F  Sample  Pb, ppm  2s  BCR-2 BCR-2 BCR-2 BCR-2 BCR-2 BCR-2 Mean  A B C C (rerun) D  10.31 12.35 10.11 10.14 12.21 11.02  0.15 0.15 0.08 0.08 0.13 2.30  AGV-2 AGV-2 AGV-2 AGV-2 AGV-2 Mean  A B C D  13.39 12.53 13.59 13.07 13.15  0.20 0.20 0.13 0.13 0.93  1.62 1.54 1.32 1.48 1.42 1.62 1.63 1.52  0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.24  BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 BHVO-2 Mean  A B C D E F F (rerun)  (Rerun): same filament.  Note that with the new version of the Finnigan software (version 3.0 and higher), the number of blocks must match the number of collectors used, i.e., 5 for Sr and 8 for Nd. Four or five standards are loaded per 21 sample barrel. [18] Nd isotopic compositions were also measured on the Nu Plasma, by static multicollection with Faraday cups on aliquots of the same sample solutions used for TIMS analyses and on separate dissolutions. Instrument parameters and collector configurations are summarized in Tables 1a, 1b, and 2. Each analysis consisted of 60 ratios (3 blocks of 20 cycles), resulting in a 12–13 minute duration of data collection for each individual analysis. Wash-out time and time for standard replicates after every second sample resulted in an average instrument time of 30 min per sample. All Nd isotopes (150, 148, 146, 145, 144, 143, 142) were measured, while simultaneously monitoring masses 147 (Sm) and 140 (Ce) (Table 1b), allowing for interference corrections on masses 144, 148 and 150 (Sm) and 142 (Ce). Except for Ce, all other interference corrections were entirely negligible (e.g., fraction of a mV on 147Sm). Nd isotope measurements were normalized internally to the values reported above for the Triton TIMS measurements, on the basis of the daily mean of  the La Jolla or Rennes reference material analyses. The 144Sm, 148Sm, 150Sm and 142Ce corrections were made using natural isotopic abundances (144Sm = 0.030734, 147Sm = 0.149934, 148Sm = 0.112406, 150Sm = 0.073796, 140Ce = 0.88449, 142 Ce = 0.11114 [Rosman and Taylor, 1998]) corrected for instrumental mass discrimination using an exponential law as monitored by the 146 Nd/144Nd ratio. [19] During the period of data collection, the average value measured for the La Jolla reference material on the Nu Plasma was 0.511856 ± 15 (n = 59) for 143Nd/144Nd and the average for the Rennes Nd reference material was 0.511969 ± 13 (n = 45). This demonstrates the excellent agreement between the MC-ICP-MS and the TIMS instruments. To achieve comparable precision, the amount of material needed for Nd isotopic analyses on the MC-ICP-MS is about double (200–400 ng) for a wet plasma analysis than that for a TIMS or dry plasma analysis (100–150 ng). [20] Pb isotopic compositions were analyzed by static multicollection. The collector array on the Nu Plasma is fixed and a zoom lens is employed to position the masses in the collectors. For Pb, the central collectors (H4-L2) are 1 amu apart and the outer collectors (H6, H5, L3, L4 and L5) are 2 amu 15 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 1. Individual 87Sr/86Sr analyses by TIMS of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, BCR-2, STM-2, RGM-1, G-2, and GSP-2. Note the much larger variations for GSP-2 (see text for discussion). On this page, the lefthand panels report results for the first-generation USGS reference materials (BHVO-1, AGV-1, and BCR-1), and the right-hand panels report results for the second-generation materials (BHVO-2, AGV-2, and BCR-2). Red symbols indicate high-pressure digestion PTFE in a bomb. All blue symbols indicate hotplate Savillex1 digestion. For comparison, on the far right side of each figure, open symbols represent the mean and 2 standard deviations of replicate analyses for both generations (dark blue for first generation, light blue for second generation). For individual analyses, the error bar corresponds to the 2 sigma error on the measured isotopic ratio.  apart. Therefore masses 208 to 202 are measured in collectors H4 to L2 (Table 1b). The configuration for Pb isotopic analyses enables simultaneous collection of Pb (208, 207, 206 and 204) together with Tl (205 and 203) and Hg (202). Tl is used to monitor and correct for instrumental mass discrimination and Hg is used to correct for the isobaric overlap of 204Hg on 204Pb. The 204Hg correction was made using natural abundances (202Hg = 0.29863 and 204Hg = 0.06865) adjusted for instrumental mass fractionation as monitored by the 205 Tl/203Tl ratio. Ion beam intensities for 202Hg  were always below 0.3 mV for all runs (except two), corresponding to a correction of less than 0.2 (0.07) mV on the 204 mass (always >53 mV). [21] To improve the reproducibility of the analytical conditions for the Pb isotopic compositions, and thus the precision and the accuracy (i.e., better precision on 205Tl/203Tl and less interference on 204 Pb), all sample solutions were analyzed with the same [Pb]/[Tl] ratio ($4) as the NIST SRM 981 reference material. To accomplish this, a small aliquot of each sample was analyzed using the Thermo Finnigan Element2 HR-ICP-MS to deter16 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 1. (continued)  mine the exact amount of Pb available for isotopic analysis. During the course of this investigation, 65 analyses of the NIST SRM 981 Pb reference material performed in wet plasma mode on the Nu 015 gave mean values of 208 Pb/ 204 Pb = 36.7163 ± 121 (2 SD), 207Pb/204Pb = 15.4968 ± 47 (2 SD), and 206Pb/204Pb = 16.9400 ± 49 (2 SD), while 167 analyses on the Nu 021 gave mean values of 36.7145 ± 88, 15.4964 ± 29 and 16.9407 ± 36, respectively (Table 6, Figure 4). No significant difference was observed in the values of the SRM 981 reference material measured in the two laboratories. These values are in agreement with previously reported TIMS triplespike values [Galer and Abouchami, 1998], but with slightly lower 208Pb/204Pb ratios ($60 ppm lower). This difference in 208Pb/204Pb is comparable, albeit smaller, to other MC-ICP-MS analyses of SRM 981 [Vance and van Calsteren, 1999]. In light of the reproducibility and accuracy of the Pb isotopic compositions determined on the two Nu Plasma instruments in this study, there was no need to adjust the 205Tl/203Tl ratio from day-to-day; a value of 2.3885 was used for all runs as it yields SRM 981 Pb isotopic compositions within error of the triple-spike values. Depending on the amount of Pb available in each sample, the samples were analyzed in either wet or dry (using a Nu Instruments DSN-100 desolvator) plasma mode,  corresponding to a NIST SRM 981 reference material concentration of 200 ppb (wet) or 40 ppb (dry). Except where the amount of sample material was insufficient, all samples were run with a 208Pb ion beam of >2 V. The reference material was run every two samples. Even though the NIST SRM 981 results were within error of the triple-spike values after online correction for instrumental mass bias by Tl addition, the USGS reference results were further corrected by the sample-standard bracketing method or the ln-ln correction method as described by White et al. [2000] and BlichertToft et al. [2003]. [22] As $100 nanograms of Pb are needed for the analysis of Pb concentrations (load sizes vary between 72 and 140 ng) by isotope dilution using a 205Pb spike ($5 ppb 205Pb), 3.0 to 65.0 mg of sample rock powder was weighed. The Pb column separation is comparable to that outlined in section 2.2 above, except that it was carried out twice to ensure clean separations. Samples, as well as procedural blanks and SRM 981 Pb reference materials, were loaded on degassed, 99.995% 4-pass zone-refined H. Cross Re filaments using the SiGel (SiCl4) – H3PO4 technique and were analyzed with a VG54R single collector TIMS instrument in peak-switching mode at 1450°C. A mass fractionation correction of 17 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 2. Individual 143Nd/144Nd analyses by TIMS of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, BCR-2, STM-2, RGM-1, G-2, and GSP-2. Symbols and color coding as in Figure 1.  0.12%/amu was applied on the basis of repeated SRM 981 analyses conducted throughout the course of the study. An average procedural blank of 75 pg is based on 5 determinations during the course of the study, negligible in comparison to the sample Pb concentration. Individual blanks ranged from 56 – 84 pg, with 208 Pb/ 204 Pb = 37.73, 207Pb/204Pb = 15.59 and 206Pb/204Pb = 18.33, all ±3% (1 SD). Reported concentrations are spike- and blank-corrected (0.06–0.12% of the total) (Table 8).  2.4. Leaching Experiment [23] A preliminary study of BHVO-1 and BHVO-2 [Weis et al., 2005a] showed clear differences in Pb isotopic composition and trace metal concentrations between the two generations of USGS reference materials, confirming the earlier findings of Woodhead and Hergt [2000]. The differences could be ascribed to contamination of the rock powders during processing (crushing, pulverization). We repeated these careful experiments here, on 18 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 2. (continued)  BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1 and BCR-2. The leaching procedure of Weis and Frey [1991, 1996] was used, as this method, which was developed to remove secondary alteration phases from old oceanic basalts, has been shown to be more efficient in obtaining reproducible ratios than that of McDonough and Chauvel [1991] [Weis et al., 2005a].  3. Results and Discussion [24] Sr isotopic results are reported in Table 2, Nd isotopic results in Table 3 (TIMS) and Table 4 (MC-ICP-MS), and Pb isotopic results in Tables 5 and 6. The leaching experiment results are reported in Table 7 and the Pb isotope dilution concentrations in Table 8.  3.1. Sr Isotopic Compositions [25] The Sr isotopic compositions for all analyzed USGS reference materials were obtained with a precision better than 30 ppm (2 SD [n = 5 to 13]), a precision barely larger than the in-run errors (2 SE), which were generally better than ±0.000010  absolute on the measured value (average = 0.000007 ± 3 [n = 91]). This reflects the homogeneity of all these materials. The precision of Sr isotopic ratios of GSP-2, however, was close to 100 ppm, despite careful digestion in high-pressure PTFE digestion bombs (Table 2, Figure 1). This large range of variation for GSP-2 has previously been documented by Raczek et al. [2003], who indicated heterogeneity of GSP-2 with respect to Sr isotopic ratios for aliquots in the 100 mg size range. The precision for Sr concentrations determined on an equivalent sample size (100 mg) and sample matrix (e.g., G-2) was much better (4% RSD) than that found for GSP-2 (8% RSD) using the HR-ICP-MS instrument in the Pretorius et al. [2006] study. GSP-2 has also been found to be inhomogeneous with respect to Li contents, likely related to a nugget effect [Pretorius et al., 2006]. The nugget effect for Li and relatively poor reproducibility of Sr concentrations in GSP-2 compared to G-2 suggests that the Sr isotopic heterogeneity for GSP-2 found in this study may also be partly related to the inhomogeneous distribution of an accessory phase in GSP-2, in addition to incom19 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 3. Individual 143Nd/144Nd analyses by MC-ICP-MS of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, BCR-2, STM-2, RGM-1, G-2, and GSP-2 (orange symbols) compared to the TIMS analyses (dark blue symbols; see Figure 2). In each panel the mean and 2 standard deviations of the replicate analyses are indicated for both MC-ICP-MS (orangefilled purple diamond) and TIMS (blue empty diamond) analyses for comparison.  plete recovery of Sr. Thus GSP-2 is a somewhat poor choice for a reference material for Sr.  results agree entirely with those of Raczek et al. [2003].  [26] The largest difference for Sr isotopic ratios is 11 ppm between AGV-1 and AGV-2, whereas it is 7 ppm between BCR-1 and BCR-2 and 6 ppm between BHVO-1 and BHVO-2 (Figure 1). Taking into account the difference in NIST SRM 987 standard values (e.g., 0.710203 ± 34 (n = 24) for Raczek et al. [2003] versus 0.710256 ± 16 (n = 145) and 0.710252 ± 13 (n = 88) after the change of one of the Faraday cups in this study), our  3.2. Nd Isotopic Compositions [27] For Nd isotopic compositions analyzed by TIMS (Table 3, Figure 2), the in-run errors (2 SE) are more comparable (average = 0.000006 ± 3 [n = 103]) than for Sr. For 143Nd/144Nd, the 2 standard deviations are all below 30 ppm. Nd isotopic ratios of GSP-2 are as reproducible as those of the other USGS reference materials. We 20 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 3. (continued)  have detected no difference between generations 1 and 2 of the analyzed reference materials for BHVO, AGV and BCR (relative difference <3 ppm; Figure 2). The agreement with the results of Raczek et al. [2003] is excellent after normalization of both data sets to the accepted La Jolla 143Nd/144Nd values (0.511839 ± 38 [n = 38] versus 0.511850 ± 15 [n = 73] and 0.511853 ± 12 [n = 118] for this study). [28] The Nd isotopic compositions measured by MC-ICP-MS (Table 4, Figure 3) agree very well with the TIMS values for all USGS reference materials analyzed (relative differences up to 17 ppm). However, sample analysis time by MCICP-MS is about 4–6 times less than by TIMS [Luais et al., 1997], bearing in mind that most of the time and effort lie in the chemistry in both cases. The in-run errors are slightly higher than for the TIMS analyses with an average of ±0.000011 ± 15 (n = 94), which has been reduced during the course of this study by using the desolvator (i.e., increase in sensitivity and decrease in sample size). Replicate analyses of the 143Nd/144Nd ratio are better than 45 ppm (2 SD [n = 6 to 14]). The precision and the accuracy of Nd isotopic analyses by MC-ICP-  MS are also documented by the long-term reproducibility of La Jolla and Rennes Nd reference materials, which have a precision on the 143Nd/144Nd ratio of 29 and 25 ppm, respectively, comparable to the TIMS results. The accuracy of both reference values is better than 10 ppm relative to the accepted value. This indicates that for the Nu Plasma MC-ICP-MS there is no need either to adjust the normalization ratio, as documented earlier for other instruments [Vance and Thirlwall, 2002], or to carry out multidynamic analysis [Thirlwall and Anczkiewicz, 2004] to achieve accurate and precise Nd isotopic analyses. The 145Nd/144Nd average for all the USGS reference materials is 0.348421 ± 12 [n = 94], in agreement with the values recently published by Pearson and Nowell [2005] for data acquired using a Thermo Finnigan Neptune MC-ICP-MS and within error of the multidynamic MC-ICP-MS analysis [see Thirlwall and Anczkiewicz, 2004, Table 9]. Our results support the recent conclusion of Pearson and Nowell [2005] that deviations from exponential mass bias behavior during isotope measurements by MC-ICP-MS might be instrument specific.  21 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  compositions measured by the double-spike technique [Woodhead and Hergt, 2000; Baker et al., 2004]. The only exception is AGV-1 measured by TIMS by Woodhead and Hergt [2000], which appears to be from a different batch (Table 5, Figures 5a). Comparison between the first and second generations of BHVO, BCR and AGV shows significant differences in Pb isotope ratios (Figures 5a and 5b) and concentrations (Table 8 and W. Pretorius et al. (Complete trace elemental characterization of volcanic rock (USGS BHVO-1, BHVO-2, BCR-1, BCR-2, AGV-1, AGV-2, RGM-1, STM-2) reference materials by high resolution inductively coupled plasma-mass spectrometry, manuscript in preparation, 2006); hereinafter referred to as Pretorius et al., manuscript in preparation, 2006), well outside of analytical errors. The reproducibility of repeated analyses of the volcanic USGS reference materials documented in this study varies between 164 to 1298 ppm. Heterogeneous Pb isotope compositions, and significantly higher Pb concentrations (Pretorius et al., manuscript in preparation, 2006), in first-generation reference materials confirm earlier studies [Woodhead and Hergt, 2000; Baker et al., 2004] and indicate that these reference materials are heterogeneous, at least for Pb. This is probably a result of contamination during processing, as documented by the analysis of mortar and pestle material and leaching of some of the reference materials (see Weis et al. [2005a] for discussion). Figure 4. Comparison of the daily averages of SRM 981 for the Nu 015 (blue diamonds) and Nu 021 (red diamonds), with 2 standard deviation bars during the course of this study. The overall average of each instrument is indicated by the square symbols. For comparison, three published values of the SRM 981 measured by the triple-spike method are also indicated as solid black squares in the far left of each diagram [Galer and Abouchami, 1998; Eisele et al., 2003; Regelous et al., 2003].  3.3. Pb Isotopic Compositions [29] Pb isotopic compositions measured on the two different MC-ICP-MS instruments are in good agreement (Figure 4) and both within error of  [30] For felsic compositions (STM-1, STM-2, RGM-1, GSP-2, G-2 and G-3), the reproducibility of the Pb isotopic compositions (Table 5, Figure 5c) is strongly related to whether or not the rock powder was completely and properly digested. This is reflected by the difference in isotopic composition between the samples dissolved by hotplate digestion in Savillex1 beakers versus those dissolved in high-pressure PTFE digestion bombs. In the case of GSP-2 and G-2, Pb isotopic compositions for hotplate-dissolved samples are less radiogenic than for samples digested in high-pressure bombs. The opposite is observed for STM-2. The average Pb isotopic compositions of hotplate and high-pressure bomb digestions nevertheless overlap within 2 standard  Figure 5a. Comparison of Pb isotopic analyses of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, and BCR-2 by MC-ICP-MS (this study, blue diamonds), by TIMS double-spike [Woodhead and Hergt, 2000] (pale pink triangles) and by MC-ICP-MS double-spike [Baker et al., 2004] (dark pink triangles). For each group of analyses, the average and 2 standard deviation error bars are also plotted. Also shown for BCR-1 are the values obtained by the slightly modified Tl-normalization method of Woodhead [2002] (brown circles). All data have been normalized to the SRM 981 triple-spike values of Abouchami et al. [2000]. 22 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 5a 23 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 5b. Overall comparison of Pb isotopic analyses of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, and BCR-2 by MC-ICP-MS (this study, light blue diamonds) and by TIMS double-spike [Woodhead and Hergt, 2000] (light pink triangles). In each case the individual data points are plotted as well as their means and 2 standard deviation error bars. For BHVO-2, there were two different powder splits, 2a and 2b. DS, double spike.  deviations for both G-2 and STM-2, but not for GSP-2. The Pb concentrations for GSP-2 digested in bombs are also significantly higher (13%) than those obtained when digestions are performed on a hotplate [Pretorius et al., 2006] and there is clearly a nugget effect involved. Felsic compositions should always be dissolved under high-pressure conditions. [31] There are also large differences between firstand second-generation reference materials, as STM-2 is distinctly more radiogenic in all Pb isotopic ratios than STM-1, whereas G-2 is more radiogenic than G-3 (Table 5). We interpret this to be likely due to the chemical composition of these rocks and the presence of accessory minerals whose proportion can vary from one sample to another. The significantly higher Pb concentrations in the first-generation reference materials (STM-1 (18 ppm), G-2 (44 ppm) and GSP-1 (55 ppm)) compared to the same second-generation reference materials (STM-2 (10.2 ppm), G-3  (29 ppm) and GSP-2 (42 ppm) [Pretorius et al., 2006]) seem to indicate that contamination during sample processing also affected the felsic compositions.  3.4. Leaching Experiments [32] To investigate the issue of contamination for the mafic volcanic USGS reference materials further, we undertook leaching experiments on BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1 and BCR-2. The results are reported in Table 7. In each case, the leachates, the residues and the unleached powders were analyzed (Figures 6 and 7). For BHVO-1 and BHVO-2, the residues have less radiogenic Pb isotopic compositions than the unleached rock powders, whereas the leachates are distinctly more radiogenic (Figure 6). The same observation is valid for AGV-1 and BCR-1 (except for 208Pb/204Pb), although the opposite is true for AGV-2 and BCR-2 (the residues are more radiogenic than the unleached rock powders). Corre-  Figure 5c. Comparison of Pb isotopic compositions of felsic compositions (STM-2, RGM-1, G-2, G-3, and GSP-2 by MC-ICP-MS). The left-hand panels show 207Pb/204Pb versus 206Pb/204Pb, and the right-hand panels show 208 Pb/204Pb versus 206Pb/204Pb. Red symbols indicate high-pressure digestion in PTFE bombs, and blue symbols indicate hotplate Savillex1 digestion. 24 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 5c 25 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 6. Pb isotopic results of the leaching experiments of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, and BCR-2 analyzed by MC-ICP-MS. For a detailed discussion of this experiment, see Weis et al. [2005a]. Blue symbols indicate the first-generation USGS reference materials (BHVO-1, AGV-1, and BCR-1), whereas results from the second generation (BHVO-2, AGV-2 and BCR-2) are reported in red. The errors on individual runs are smaller than symbol sizes, unless otherwise indicated. Whole rock powder data are represented by circles. Residues after leaching are represented by square symbols, and diamonds indicate the corresponding leachates. Data from Weis et al. [2005a] for BHVO-1 and BHVO-2 (yellow color) and data from Woodhead and Hergt [2000] for double-spike TIMS analyses (triangles) are shown for comparison. In all cases, smaller symbols are for individual analyses of the unleached whole rock powders, and the larger symbols are used for their means and 2 standard deviations.  spondingly, the leachates of AGV-2 and BCR-2 have distinctly less radiogenic Pb isotopic compositions than the unleached powders. In Figure 8, the trace element concentrations of the first- and second-generation reference materials for BHVO, AGV and BCR, as well as for BHVO-1/BHVO-2G  (the USGS reference glass), are compared (Pretorius et al., manuscript in preparation, 2006). The only significant differences between the trace element compositions of the two generations of reference materials are for the elements Li, Mo, Cd, Sn, Sb, Cs, W and Pb. The magnitude, the 26 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 7. 87Sr/86Sr and 143Nd/144Nd of the leaching experiments on BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, and BCR-2 by TIMS. Blue symbols represent first-generation USGS reference materials (BHVO-1, AGV-1, and BCR-1), and the second-generation materials (BHVO-2, AGV-2 and BCR-2) are reported in red. The in-run 2 sigma errors are indicated. Individual analyses of residues after leaching are represented by the square symbols and by diamonds for the leachates. Whole rock unleached powder data (circles) is plotted as the mean of duplicates with their 2 standard deviations (see Tables 2 and 3). 27 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  10.1029/2006GC001283  Figure 8. Ratio of the trace element concentration of generation 1 compared to generation 2 USGS reference materials for BHVO (powder and glass), AGV, and BCR. See text for discussion of important deviations.  relative enrichment of the first-generation versus the second-generation reference materials, and their individual patterns are not consistent among the BHVO, BCR and AGV series materials, supporting the notion of different sources of contamination. For example, BHVO-2 and BCR-2 are clearly contaminated in Mo, whereas AGV-1 is clearly contaminated in Sn, Sb and Pb. All reference materials show differences in Pb concentrations by a factor of 2 to 5, as also documented here by the isotope dilution concentration measurements (Table 8). This has important implications for laser-ablation studies that use fused (i.e., glass) versions of these reference materials prepared from the original powders. The homogeneity of the glasses relative to the size of the typical laser-ablation spot may thus be questionable and should be thoroughly assessed in future studies. [33] The residues after leaching show much more homogeneous Pb isotopic compositions than the unleached whole rocks (Figure 6). Additionally, the differences in Pb isotopic compositions between the first and second generations are significantly reduced after leaching, indicating that this is indeed contamination rather than sample heterogeneity or a leaching issue as observed in some Hawaiian basalts [Abouchami et al., 2000]. The presence of outliers (Figure 6, AGV-1 and BCR-2) among the residues indicates that leaching is not always successful at entirely eliminating contamination from the powders. We have  recently carried out systematic leaching experiments (up to 17 steps) on basalts from Hawaii and Kerguelen to assess the reproducibility of Pb analyses by MC-ICP-MS [Nobre Silva et al., 2005] and achieved external reproducibility lower than 200 ppm. This indicates that sample preparation plays a crucial role in obtaining highprecision Pb isotopic ratios and that MC-ICP-MS can achieve comparable levels of reproducibility as double- or triple-spike TIMS analyses [Eisele et al., 2003; Albare`de et al., 2005; Baker et al., 2005]. [34] There are also slight differences in 87Sr/86Sr between the residues and the unleached powders of BHVO, AGV and BCR (Table 7, Figure 7). The unleached powders are slightly more radiogenic, although only by about twice the external error. The largest differences between residues and unleached powders for 87Sr/86Sr are for AGV-1 and BCR-1 (54 and 51 ppm, respectively). This most probably reflects the presence of minor alteration in these volcanic rocks. The leaching has no effect on 143Nd/144Nd ratios.  4. Conclusions [35] Our study of a broad compositional range of USGS reference materials provides the first complete Sr-Nd-Pb isotopic characterization of 13 of these samples. We highlight the importance of an integrated analytical approach, which allows for a better understanding of the potential issues that 28 of 30  Geochemistry Geophysics Geosystems  3  G  weis et al.: isotopic study of usgs reference materials  arise during sample processing and analysis, from crushing and pulverization, to trace element and isotopic analysis. There is no difference in Sr and Nd isotopic compositions between first- and second-generation USGS reference materials analyzed in this study. The isotopic ratios in Tables 2, 3, and 4 can then be used as recommended 87Sr/86Sr and 143 Nd/144Nd values. Nd isotopic compositions can be measured, with comparable accuracy and precision, either by TIMS or MC-ICP-MS. The situation is somewhat more delicate for Pb isotopic ratios where leaching appears to be necessary to remove any potential contamination introduced during the original preparation of the samples. This compromises the use of the materials as glass reference materials for laser-ablation studies involving Pb concentrations or compositions.  Acknowledgments [36] Funding for this study is from an NSERC Discovery Grant to Weis and an NSERC Major Facility Access Grant to the PCIGR labs. Our thanks go to J. K. Mortensen for initiating the creation of the PCIGR facility at UBC. Andy Burrows from Nu Instruments and Peter Stow from Isomass (for Thermo Finnigan) are thanked for their advice and their support in setting up our instruments at the University of British Columbia and also in ensuring a safe move from the Chemistry Building to the Earth and Ocean Sciences Main Building in late 2004. We are very grateful to the USGS and to Stephen A. Wilson for making their reference materials available. K. P. Jochum, W. I. Ridley, and the G-Cubed editor, V. J. M. Salters, are thanked for their supportive and constructive reviews.  References Abouchami, W., S. J. G. Galer, and A. W. Hofmann (2000), High precision lead isotope systematics of lavas from the Hawaiian Scientific Drilling Project, Chem. Geol., 169, 187 – 209. Albare`de, F., P. Telouk, J. Blichert-Toft, M. Boyet, A. Agranier, and B. K. Nelson (2004), Precise and accurate isotopic measurements using multiple-collector MC-ICP-MS, Geochim. Cosmochim. Acta, 68(12), 2725 – 2744. Albare`de, F., A. Stracke, V. J. 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