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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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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 54702- 4004, 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 G3GeochemistryGeophysicsGeosystems Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Technical Brief Volume 7, Number 8 10 August 2006 Q08006, doi:10.1029/2006GC001283 ISSN: 1525-2027 Copyright 2006 by the American Geophysical Union 1 of 30Finnigan 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 analy- ses 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 geo- chemical, 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 ppmdue to the fact that most of the analyses can be run in static mode. Quality control protocols that monitor ac- curacy 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 spec- trometers (TIMS) have also led to the ability to produce more precise analyses on these instru- ments [e.g., Caro et al., 2003]. [3] We have carried out a systematic study of some of the most commonly used USGS reference materi- als: 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 concen- trations and isotopic compositions, leaching experi- ments were carried out on BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1 and BCR-2 to further ex- tend 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 andNu Plasma serial #021 inVancouver) 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 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 2 of 30role of labware composition [Weis et al., 2005b] and different separation issues. 2. Analytical Techniques [6] This study aims to present accurate high- precision isotopic compositions for USGS refer- ence 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 quartz- distilled. 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 demon- strated 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. 2.1.1. Felsic Samples [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 190C. Digested samples are dried down on a hotplate overnight at 130C, recon- stituted in 6.0 mL of 6 N HCl and re-bombed for 24 hours at 190C. Afterward, samples are taken to dryness on a hotplate prior to re-dissolution for ion exchange purification of Pb, Hf, Sr and Nd. 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 130C. 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 130C, reconstituted in 6.0 mL of 6 N sub-boiled HCl and re-dissolved for 24 hours at 130C, before com- mencing ion exchange chemistry. 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 1a. Nu Plasma MC-ICP-MS Operating Conditions Dry Plasma Wet Plasma RF power 1350 W 1350 W Acceleration voltage 4000 V 4000 V Mass analyzer pressure 2  109 mbar 2  109 mbar Desolvating system DSN-100 n/a Nebulizer ESI mflow GE Micromist Sample uptake rate 170–190 mL/min 50–100 mL/min Spray chamber temperature 110C 5C Membrane temperature 110C n/a Hot gas flow 0.2 L/min n/a Membrane gas flow 2.5–3.5 L/min n/a Table 1b. Nu Plasma MC-ICP-MS Nd and Pb Collector Configurationsa Element H6 H5 H4 H3 H2 H1 Ax L1 L2 L3 L4 L5 Integration Time, s Nd 150 148 147 146 145 144 143 142 140 10 Pb 208 207 206 205 204 203 202 10 aBaselines were half-mass zeros and were taken over 30 s, every block. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 3 of 30Table 2. USGS Reference Materials: Sr Isotopic Analyses (TIMS)a Sample Run Number 87Sr/86Sr Error (2s) 87Sr/86Sr Normb 2 SDc Basalt BCR-1 BCR-1 a S6d 0.705024 6 0.705014 BCR-1 b S7d 0.705038 7 0.705028 BCR-1 b S7d (5 months later) 0.705039 7 0.705025 BCR-1 (1) 06/05/03 0.705023 9 0.705017 BCR-1 (2) 06/05/03 0.705022 8 0.705016 BCR-1 (1) 08/08/03 0.705015 7 0.705010 BCR-1 (2) 08/08/03 0.705013 7 0.705011 BCR-1 S10d 0.705024 7 0.705023 Mean (2 SD) 0.705025 19 0.705018 13 BCR-2 BCR-2 24/03/03 0.705018 6 0.705014 BCR-2 (1) 19/04/03 0.705028 9 0.705024 BCR-2 04/01/03 0.705025 9 0.705016 BCR-2 (1) 08/08/03 0.705030 7 0.705016 BCR-2 (2) 08/08/03 0.705033 9 0.705019 BCR-2 (3) 08/08/03 0.705019 9 0.705005 BCR-2 (1) 05/12/03 0.705017 9 0.705017 BCR-2 (2) 05/12/03 0.705011 7 0.705009 BCR-2 19/12/03 0.705012 7 0.705012 BCR-2 HA 0.705012 7 0.705008 BCR-2 (1) 24/09/03 0.705009 7 0.705008 BCR-2 (2) 24/09/03 0.705013 8 0.705012 BCR-2 9/05/05 0.705020 7 0.705009 Mean (2 SD) 0.705019 16 0.705013 10 BHVO-1 BHVO-1 a S1d 0.703483 6 0.703473 BHVO-1 a A8d 0.703502 6 0.703488 BHVO-1 b S2d 0.703486 7 0.703476 BHVO-1 24/03/03 0.703471 6 0.703467 BHVO-1 19/04/03 0.703470 10 0.703464 BHVO-1 08/08/03 0.703489 7 0.703475 BHVO-1 Cad 0.703487 7 0.703473 BHVO-1 c S3d 0.703487 6 0.703486 Mean (2 SD) 0.703484 21 0.703475 17 BHVO-2 BHVO-2 Cbd 0.703481 9 0.703469 BHVO-2 24/03/03 0.703484 6 0.703480 BHVO-2 19/04/03 0.703483 8 0.703474 BHVO-2 19/04/03 Dble 0.703500 6 0.703499 BHVO-2 (1) 08/08/03 0.703494 8 0.703480 BHVO-2 (1) 08/08/03 (rerun) 0.703509 7 0.703495 BHVO-2 HA 0.703484 7 0.703484 BHVO-2 (2) 05/12/03 0.703485 6 0.703483 BHVO-2 (1) 05/12/03 0.703474 7 0.703470 BHVO-2 19/12/03 0.703481 7 0.703477 BHVO-2 9/05/05 0.703482 7 0.703471 BHVO-2 9/05/05 0.703482 7 0.703471 Mean (2 SD) 0.703487 19 0.703479 20 Andesite AGV-1 AGV-1 a A1d 0.703986 13 0.703984 AGV-1 b A2d 0.704001 8 0.703989 AGV-1 a S4d 0.704006 7 0.703988 AGV-1 b S5d 0.703990 7 0.703980 AGV-1 RMFd 0.703993 6 0.703983 AGV-1 24/03/03 0.703992 6 0.703988 AGV-1 19/04/03 0.704004 8 0.703998 AGV-1 19/04/03 Dble 0.704014 10 0.704008 AGV-1 a S1d 0.703987 6 0.703985 AGV-1 D10d 0.703985 7 0.703985 Mean (2 SD) 0.703996 20 0.703989 17 AGV-2 AGV-2 b A7d 0.703988 5 0.703978 AGV-2 (1) 19/04/03 0.703988 8 0.703979 AGV-2 (2) 19/04/03 0.703993 10 0.703984 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 4 of 30ration of Pb from other elements using an anion exchange column. The discard from this column is then dried down and reconstituted for cation ex- change 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., Table 2. (continued) Sample Run Number 87Sr/86Sr Error (2s) 87Sr/86Sr Normb 2 SDc AGV-2 a A6d 0.703979 6 0.703977 AGV-2 (2) 05/12/03 0.703984 8 0.703980 AGV-2 (1) 05/12/03 0.703973 7 0.703973 AGV-2 19/12/03 0.703983 9 0.703983 AGV-2 (1) 08/08/04 0.703986 8 0.703985 AGV-2 LT9 03/22/05 0.703997 7 0.703987 AGV-2 LT10 03/22/05 0.703998 7 0.703988 Mean (2 SD) 0.703987 16 0.703981 9 Syenite STM-2 STM-2 D10d 0.703701 8 0.703697 STM-2 L8d 0.703704 7 0.703703 STM-2 L9d 0.703708 7 0.703704 STM-2 L10d 0.703703 8 0.703699 STM-2 D1d 0.703707 9 0.703703 Mean (2 SD) 0.703705 6 0.703701 6 Rhyolite RGM-1 RGM-1 A10d 0.704228 6 0.704214 RGM-1 (1) 19/04/03 0.704219 9 0.704210 RGM-1 (2) 19/04/03 0.704217 8 0.704208 RGM-1 A5d 0.704218 9 0.704203 RGM-1 S2d 0.704220 6 0.704206 RGM-1 (2) 19/12/03 0.704218 7 0.704214 RGM-1 (3) 19/12/03 0.704206 7 0.704202 RGM-1 (1) 19/12/03 0.704208 7 0.704204 RGM-1 D9d 0.704227 9 0.704226 RGM-1 03/03/05 0.704227 8 0.704215 Mean (2 SD) 0.704219 15 0.704210 14 Granite G-2 G-2 A5d 0.709783 8 0.709781 G-2 04/01/04 +HClO4 0.709775 6 0.709775 G-2 04/01/04 No HClO4 0.709760 9 0.709760 G-2 L5d 0.709766 8 0.709766 G-2 L6d 0.709765 7 0.709765 G-2 D8d 0.709774 7 0.709774 G-2 D9d 0.709766 8 0.709766 Mean (2 SD) 0.709770 16 0.709770 14 Granodiorite GSP-2 GSP-2 (1) B5d 0.765112 4 0.765096 GSP-2 (2) B6d 0.765122 9 0.765102 GSP-2 D2d 0.765171 7 0.765167 GSP-2 D3d 0.765175 7 0.765171 GSP-2 D5d 0.765160 8 0.765156 GSP-2 D5d(rerun) 0.765156 7 0.765152 GSP-2 D6d 0.765202 8 0.765198 GSP-2 D7d 0.765111 7 0.765107 Mean (2 SD) 0.765151 66 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. bMeasured ratio normalized to SRM 987 87Sr/86Sr = 0.710248. cHere, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. dHigh-pressure dissolution (the coding corresponds to the pressure-vessel number). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 5 of 30Table 3. USGS Reference Materials: Nd Isotopic Analyses (TIMS)a Sample Run Number 143Nd/144Nd Error (2s) 145Nd/144Nd Error (2s) 143Nd/144Nd Normb 2 SDc Basalt BCR-1 BCR-1 Ad 0.512625 8 0.348395 2 0.512640 BCR-1 Ad (rerun) 0.512626 4 0.348402 4 0.512641 BCR-1 Bd 0.512622 6 0.348400 3 0.512637 BCR-1 Bd (rerun) 0.512623 6 0.348401 3 0.512638 BCR-1 302-6d 0.512621 8 0.348396 9 0.512636 BCR-1 302-7d 0.512624 6 0.348399 9 0.512639 BCR-1 (2) 06/05/03 0.512635 4 0.348410 6 0.512633 BCR-1 (1) 06/05/03 0.512643 6 0.348409 3 0.512641 BCR-1 (1) 08/08/03 0.512629 6 0.348404 3 0.512637 BCR-1 a S6d 0.512632 5 0.348411 3 0.512636 BCR-1 b S7d 0.512639 5 0.348407 3 0.512643 BCR-1 S10d 0.512631 5 0.348400 3 0.512635 BCR-1(2) 08/08/03 0.512626 5 0.348408 3 0.512633 Mean (2 SD) 0.512629 14 0.512638 6 BCR-2 BCR-2 (1) 19/04/03 0.512639 5 0.348408 3 0.512636 BCR-2 24/03/03 0.512640 5 0.348410 3 0.512637 BCR-2 04/01/03 0.512639 4 0.348409 3 0.512636 BCR-2 (1) 08/08/03 0.512643 5 0.348408 3 0.512648 BCR-2 (3) 08/08/03 0.512638 6 0.348407 3 0.512643 BCR-2 (2) 08/08/03 0.512631 6 0.348401 3 0.512639 BCR-2 HA 0.512631 6 0.348407 3 0.512643 BCR-2 19/12/03 0.512631 5 0.348403 4 0.512635 BCR-2 (1) 05/12/03 0.512627 5 0.348410 4 0.512631 BCR-2 (2) 05/12/03 0.512633 5 0.348402 3 0.512637 BCR-2 24/09/03 0.512623 7 0.348407 4 0.512627 Mean (2 SD) 0.512634 12 0.512637 12 BHVO-1 BHVO-1 Aad 0.512972 4 0.348395 2 0.512987 BHVO-1 Aad (rerun) 0.512977 4 0.348399 3 0.512992 BHVO-1 Abd 0.512969 8 0.348401 3 0.512984 BHVO-1 Abd (rerun) 0.512971 6 0.348401 3 0.512986 BHVO-1 Bad 0.512972 8 0.348394 5 0.512987 BHVO-1 Bbd 0.512972 6 0.348399 3 0.512987 BHVO-1 Bbd (rerun) 0.512965 6 0.348398 4 0.512980 BHVO-1 Cad 0.512971 8 0.348400 2 0.512986 BHVO-1 Cbd 0.512967 6 0.348397 3 0.512982 BHVO-1 bd 0.512978 10 0.348394 5 0.512993 202-6d 0.512973 2 0.348399 3 0.512988 BHVO-1 302-8d 0.512967 8 0.348404 3 0.512982 BHVO-1 24/03/03 0.512981 5 0.348410 2 0.512978 BHVO-1 19/04/03 0.512986 6 0.348405 6 0.512983 BHVO-1 08/08/03 0.512977 6 0.348410 3 0.512982 BHVO-1 a A8d 0.512977 7 0.348408 4 0.512984 BHVO-1 a S1d 0.512988 5 0.348409 3 0.512995 BHVO-1 c S3d 0.512985 6 0.348397 4 0.512992 BHVO-1 b S2d 0.512980 5 0.348406 3 0.512987 Mean (2 SD) 0.512975 13 0.512986 9 BHVO-2 BHVO-2 24/03/03 0.512983 5 0.348412 3 0.512981 BHVO-2 19/04/03 Dble 0.512982 4 0.348408 3 0.512980 BHVO-2 19/04/03 0.512987 6 0.348419 4 0.512985 BHVO-2 (1) 08/08/03 0.512982 6 0.348410 3 0.512987 BHVO-2 HA 0.512981 5 0.348405 3 0.512993 BHVO-2 (1) 05/12/03 0.512972 7 0.348406 5 0.512976 BHVO-2 (2) 05/12/03 0.512977 10 0.348402 5 0.512981 BHVO-2 19/12/03 0.512978 6 0.348408 4 0.512982 BHVO-2 19/12/03 (rerun) 0.512976 5 0.348405 3 0.512980 BHVO-2 Dec04-Jan05 0.512981 6 0.348409 3 0.512985 BHVO-2 Dec04-Jan05 0.512983 6 0.348406 4 0.512987 BHVO-2 Dec04-Jan05 0.512992 6 0.348408 4 0.512996 BHVO-2 Dec04-Jan05 0.512979 7 0.348397 4 0.512983 Mean (2 SD) 0.512981 10 0.512984 11 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 6 of 30Table 3. (continued) Sample Run Number 143Nd/144Nd Error (2s) 145Nd/144Nd Error (2s) 143Nd/144Nd Normb 2 SDc Andesite AGV-1 AGV-1d 0.512774 4 0.348391 2 0.512791 AGV-1 Ad 0.512773 8 0.348393 4 0.512790 AGV-1 Ad 0.512781 8 0.348398 3 0.512798 AGV-1 Bd 0.512776 6 0.348395 3 0.512793 AGV-1 24/03/03 0.512787 5 0.348405 3 0.512785 AGV-1 19/04/03 Dble 0.512788 5 0.348410 3 0.512786 AGV-1 19/04/03 0.512791 5 0.348406 4 0.512789 AGV-1 D10d 11/01/04 0.512789 5 0.348408 3 0.512793 AGV-1 a S4d 0.512801 8 0.348412 6 0.512805 AGV-1 b S5d 0.512778 7 0.348400 4 0.512782 Mean (2 SD) 0.512784 18 0.512791 13 AGV-2 AGV-2 (2) 19/04/03 0.512805 7 0.348411 4 0.512802 AGV-2 (1) 19/04/03 0.512783 5 0.348406 3 0.512780 AGV-2 (A) A6d 0.512798 5 0.348411 4 0.512798 AGV-2 (B) A7d 0.512788 6 0.348408 4 0.512788 AGV-2 (1) 05/12/03 0.512788 6 0.348407 3 0.512792 AGV-2 (2) 05/12/03 0.512783 6 0.348405 4 0.512787 AGV-2 08/08/03 0.512787 6 0.348404 3 0.512791 AGV-2 19/12/03 0.512785 6 0.348403 3 0.512792 Mean (2 SD) 0.512790 16 0.512791 13 Syenite STM-2 STM-2 D10d 0.512912 5 0.348406 3 0.512917 STM-2 L8d 0.512902 5 0.348408 3 0.512907 STM-2 L9d 0.512913 5 0.348407 3 0.512918 STM-2 L10d 0.512907 5 0.348405 4 0.512912 STM-2 D1d 0.512914 6 0.348409 3 0.512911 Mean (2 SD) 0.512910 10 0.512913 9 Rhyolite RGM-1 RGM-1 (2) 19/04/03 0.512800 5 0.348407 3 0.512797 RGM-1 A10d 0.512797 7 0.348408 3 0.512797 RGM-1 D9d 0.512802 5 0.348405 3 0.512806 RGM-1 A5d 0.512799 6 0.348404 5 0.512803 RGM-1 b A4d 0.512798 5 0.348404 3 0.512802 RGM-1 (1) 19/12/03 0.512790 5 0.348404 3 0.512794 RGM-1 (2) 19/12/03 0.512794 5 0.348403 3 0.512798 RGM-1 (3) 19/12/03 0.512797 5 0.348410 3 0.512801 RGM-1 05/04/05d 0.512817 8 0.348408 6 0.512820 Mean (2 SD) 0.512799 15 0.512802 15 Granite G-2 G-2d 0.512218 6 0.348398 6 0.512233 G-2 04/01/04 No HClO4 0.512222 6 0.348404 4 0.512227 G-2 04/01/04 + HClO4 0.512226 5 0.348408 3 0.512231 G-2 D8d 0.512222 6 0.348410 3 0.512227 G-2 D9d 0.512218 5 0.348406 3 0.512223 G-2 L6d 0.512224 5 0.348409 3 0.512229 G-2 L5d 0.512227 6 0.348401 5 0.512232 G-2 Dec04-Jan05 0.512222 5 0.348402 6 0.512226 G-2 Dec04-Jan05 0.512223 8 0.348412 4 0.512227 Mean (2 SD) 0.512222 6 0.512228 6 Granodiorite GSP-2 GSP-2 D2d 0.511368 6 0.348400 4 0.511373 GSP-2 D3d 0.511369 6 0.348403 4 0.511374 GSP-2 D5d 0.511368 5 0.348407 4 0.511373 GSP-2 D6d 0.511369 8 0.348408 4 0.511374 GSP-2 D7d 0.511372 6 0.348405 4 0.511377 Mean (2 SD) 0.511369 3 0.511374 3 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 7 of 301997]. Elution volumes used for the column pro- cedures 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 Bio- rad 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 pro- cessed 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 110C and ultrasonicat- ing 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 con- tinues 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 130C. Columns are cleaned with 100 mL of 6 N HCl prior to re-equilibration with 100 mL of 1.5 N HCl. 2.2.3. Second Column (REE Separation) Chemistry [13] Nd is separated from the other REE on a column using HDEHP (di-2ethylhexyl-orthophos- phoric 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 re- use of the column. 2.3. Mass Spectrometry Analytical Procedure [15] Isotopic composition measurements were per- formed either on a Thermo Finnigan TIMS (Sr, Nd) or on a Nu Instruments Plasma (Nu 021) MC- ICP-MS (Nd, Pb) at the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the Uni- versity of British Columbia. In addition, Pb isoto- pic compositions for some of the USGS reference materials were also measured on the Nu Instru- ments Plasma MC-ICP-MS (Nu 015) at the De- partment of Earth and Environmental Sciences of the Universite´ Libre de Bruxelles for interlabora- tory 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. bMeasured ratio normalized to La Jolla 143Nd/144Nd = 0.511858 (based on the mean of the wheel). cHere, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. dHigh-pressure PTFE digestion bomb (the coding corresponds to the bomb number). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 8 of 30Table 4. USGS Reference Materials: Nd Isotopic Analyses (MC-ICP-MS)a Sample Run Number 143Nd/144Nd Error (2s) 145Nd/144Nd Error (2s) 143Nd/144Nd Normb 2 SDc 145Nd/144Nd Normb Basalt BCR-1 BCR-1 (A) S6d 0.512657 12 0.348410 6 0.512659 0.348398 BCR-1 (A) S6d (rerun) 0.512655 13 0.348421 7 0.512657 0.348409 BCR-1 (B) S7d 0.512641 15 0.348414 7 0.512643 0.348403 BCR-1 (B) S7d (rerun) 0.512649 11 0.348422 8 0.512650 0.348410 BCR-1 (2) 08/08/03 0.512642 11 0.348410 7 0.512644 0.348398 BCR-1 (2) 08/08/03 (rerun) 0.512641 11 0.348418 6 0.512642 0.348406 BCR-1 S10d 0.512636 11 0.348421 6 0.512637 0.348409 BCR-1 S10d (rerun) 0.512639 12 0.348428 6 0.512640 0.348416 Mean (2 SD) 0.512645 16 0.512646 16 BCR-2 BCR-2 HA 0.512654 10 0.348418 5 0.512652 0.348412 BCR-2 HA (rerun) 0.512642 11 0.348419 5 0.512640 0.348413 BCR-2 (1) 05/12/03 0.512635 7 0.348421 5 0.512637 0.348409 BCR-2 (1) 05/12/03 (rerun) 0.512644 9 0.348418 5 0.512646 0.348406 BCR-2 (2) 05/12/03 0.512636 11 0.348416 5 0.512638 0.348404 BCR-2 (2) 05/12/03 (rerun) 0.512635 12 0.348416 5 0.512636 0.348404 BCR-2 19/12/03 0.512635 10 0.348420 7 0.512637 0.348409 BCR-2 19/12/03 (rerun) 0.512640 10 0.348417 5 0.512642 0.348405 BCR-2 24/09/03 0.512632 8 0.348416 6 0.512634 0.348403 BCR-2 24/09/03 (rerun) 0.512622 10 0.348425 6 0.512623 0.348412 Mean (2 SD) 0.512637 17 0.512638 15 BHVO-1 BHVO-1 (A) A8d 0.512988 9 0.348423 5 0.512991 0.348413 BHVO-1 (A) A8d (rerun) 0.512990 11 0.348421 5 0.512992 0.348411 BHVO-1 (A) S1d 0.512988 12 0.348418 7 0.512991 0.348408 BHVO-1 (A) S1d (rerun) 0.512977 10 0.348415 7 0.512980 0.348404 BHVO-1 (C) S3d 0.512986 13 0.348417 7 0.512987 0.348405 BHVO-1 (C) S3d (rerun) 0.512984 11 0.348421 7 0.512985 0.348408 Mean (2 SD) 0.512986 9 0.512988 10 BHVO-2 BHVO-2 HA 0.512983 10 0.348418 6 0.512989 0.348410 BHVO-2 HA (rerun) 0.512986 9 0.348423 5 0.512992 0.348414 BHVO-2(1) 05/12/03 0.512982 10 0.348420 7 0.512983 0.348407 BHVO-2(1) 05/12/03 (rerun) 0.512994 11 0.348422 7 0.512995 0.348409 BHVO-2(2) 05/12/03 0.512990 11 0.348429 7 0.512992 0.348416 BHVO-2(2) 05/12/03 (rerun) 0.512983 11 0.348411 5 0.512985 0.348398 BHVO-2 19/12/03 0.512995 11 0.348422 8 0.512996 0.348410 BHVO-2 19/12/03 (rerun) 0.512984 9 0.348429 6 0.512985 0.348417 Mean (2 SD) 0.512987 10 0.512990 10 Andesite AGV-1 AGV-1 (A) S4d 0.512784 59 0.348440 38 0.512789 0.348422 AGV-1 (A) S4d (rerun) 0.512804 60 0.348438 32 0.512808 0.348420 AGV-1 (B) S5d 0.512807 14 0.348423 6 0.512812 0.348405 AGV-1 (B) S5d (rerun) 0.512796 11 0.348419 7 0.512801 0.348401 AGV-1 D10d 11/01/04 0.512801 9 0.348424 6 0.512806 0.348406 AGV-1 D10d 11/01/04 (rerun) 0.512778 10 0.348428 5 0.512783 0.348410 Mean (2 SD) 0.512795 23 0.512800 23 AGV-2 AGV-2 (1) 05/12/03 0.512780 13 0.348426 7 0.512785 0.348408 AGV-2 (1) 05/12/03 (rerun) 0.512789 12 0.348414 8 0.512794 0.348397 AGV-2 (2) 05/12/03 0.512791 12 0.348430 8 0.512795 0.348412 AGV-2 (2) 05/12/03 (rerun) 0.512767 10 0.348420 6 0.512772 0.348402 AGV-2 19/12/03 0.512790 11 0.348421 5 0.512795 0.348403 AGV-2 19/12/03 (rerun) 0.512791 9 0.348423 7 0.512796 0.348405 AGV-2 (1) 08/08/03 BK13 0.512787 12 0.348428 6 0.512788 0.348415 AGV-2 (1) 08/08/03 BK13 (rerun) 0.512792 11 0.348415 6 0.512793 0.348402 Mean (2 SD) 0.512786 17 0.512790 17 Syenite STM-2 STM-2 D10d 0.512912 11 0.348420 7 0.512909 0.348409 STM-2 D10d (rerun) 0.512915 11 0.348422 7 0.512912 0.348411 STM-2 L8d 0.512929 9 0.348421 5 0.512926 0.348410 STM-2 L8d (rerun) 0.512923 9 0.348427 5 0.512920 0.348416 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 9 of 30Table 4. (continued) Sample Run Number 143Nd/144Nd Error (2s) 145Nd/144Nd Error (2s) 143Nd/144Nd Normb 2 SDc 145Nd/144Nd Normb STM-2 L9d 0.512928 9 0.348423 6 0.512925 0.348412 STM-2 L9d (rerun) 0.512916 8 0.348425 5 0.512913 0.348415 STM-2 L10d 0.512911 8 0.348417 4 0.512907 0.348406 STM-2 L10d (rerun) 0.512912 8 0.348419 5 0.512908 0.348408 STM-2 D1d 0.512914 11 0.348426 6 0.512910 0.348416 STM-2 D1d (rerun) 0.512905 8 0.348424 6 0.512902 0.348414 Mean (2 SD) 0.512917 16 0.512913 16 Rhyolite RGM-1 RGM-1 (2) 19/12/03 0.512813 10 0.348426 5 0.512815 0.348415 RGM-1 (2) 19/12/03 (rerun) 0.512809 9 0.348427 5 0.512812 0.348417 RGM-1 (3) 19/12/03 0.512798 9 0.348425 7 0.512801 0.348415 RGM-1 (3) 19/12/03 (rerun) 0.512810 11 0.348436 6 0.512812 0.348425 RGM-1 (1) 19/12/03 0.512796 13 0.348431 7 0.512798 0.348420 RGM-1 (1) 19/12/03 (rerun) 0.512804 12 0.348424 7 0.512807 0.348414 RGM-1 D9d 0.512780 12 0.348423 8 0.512783 0.348413 RGM-1 D9 (rerun) 0.512787 14 0.348409 7 0.512789 0.348399 RGM-1 b A4d DSN 0.512795 5 0.348418 4 0.512805 0.348418 RGM-1 b A4d DSN (rerun) 0.512803 7 0.348423 4 0.512813 0.348423 RGM-1 A5d DSN 0.512791 5 0.348410 3 0.512801 0.348410 RGM-1 A5d DSN (rerun) 0.512795 9 0.348413 4 0.512805 0.348413 Mean (2 SD) 0.512799 19 0.512804 20 Granite G-2 G-2 04/01/04 0.512242 10 0.348423 7 0.512241 0.348417 G-2 04/01/04 (rerun) 0.512235 10 0.348415 7 0.512234 0.348409 G-2 D8d 0.512233 9 0.348426 6 0.512232 0.348420 G-2 D8d (rerun) 0.512241 8 0.348424 4 0.512239 0.348418 G-2 D9d 0.512236 10 0.348425 5 0.512234 0.348418 G-2 D9d (rerun) 0.512232 14 0.348423 7 0.512230 0.348417 G-2 L5d 0.512235 10 0.348426 7 0.512233 0.348420 G-2 L6d 0.512250 12 0.348433 6 0.512249 0.348427 G-2 L6d (rerun) 0.512245 11 0.348424 7 0.512243 0.348418 G-2 HClO4 0.512226 10 0.348422 8 0.512225 0.348416 G-2 HClO4 (rerun) 0.512225 10 0.348425 8 0.512223 0.348419 G-2 D9d 3rd analysis 0.512235 10 0.348422 5 0.512233 0.348416 Mean (2 SD) 0.512236 15 0.512235 15 Granodiorite GSP-2 GSP-2 D2d 0.511360 10 0.348415 4 0.511366 0.348407 GSP-2 D2d (rerun) 0.511366 9 0.348415 4 0.511372 0.348407 GSP-2 D3d 0.511375 9 0.348415 5 0.511380 0.348407 GSP-2 D3d (rerun) 0.511373 11 0.348414 5 0.511378 0.348405 GSP-2 D5d 0.511362 9 0.348422 5 0.511368 0.348414 GSP-2 D5d (rerun) 0.511367 8 0.348419 5 0.511373 0.348410 GSP-2 D6d 0.511366 7 0.348418 4 0.511372 0.348410 GSP-2 D6d (rerun) 0.511376 9 0.348423 5 0.511381 0.348415 GSP-2 D7d 0.511370 9 0.348419 5 0.511376 0.348411 GSP-2 D7d (rerun) 0.511370 8 0.348425 5 0.511376 0.348416 GSP-2 B5d 0.511375 10 0.348417 5 0.511381 0.348409 GSP-2 B5d (rerun) 0.511368 11 0.348420 6 0.511374 0.348412 GSP-2 B6d 0.511364 8 0.348415 5 0.511369 0.348407 GSP-2 B6d (rerun) 0.511360 8 0.348417 7 0.511366 0.348408 Mean (2 SD) 0.511368 11 0.511374 11 a(Rerun): ran back-to-back with the 1st analysis. 145Nd/144Nd = 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. bMeasured 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). cHere, 2 SD is the 2 standard deviation on the mean of the individual reference material analyses. dHigh-pressure PTFE digestion bomb (the coding corresponds to the bomb number). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 10 of 30Table 5. USGS Reference Materials: Pb Isotopic Analyses (MC-ICP-MS)a Sample Run Number 206Pb/204Pbb Error (2s) 207Pb/204Pbb Error (2s) 208Pb/204Pbb Error (2s) Wet/Dry Nu Plasma Basalt BCR-1 BCR-1 18.8215 0.0011 15.6379 0.0010 38.7340 0.0029 W 015 BCR-1 18.8247 0.0011 15.6375 0.0011 38.7355 0.0032 W 015 BCR-1 18.8213 0.0008 15.6345 0.0008 38.7315 0.0024 W 015 BCR-1 S10c 18.8223 0.0009 15.6352 0.0008 38.7272 0.0022 W 021 Mean (2 SD) 18.8225 0.0031 15.6363 0.0033 38.7321 0.0073 BCR-2 BCR-2 18.7487 0.0006 15.6252 0.0007 38.7136 0.0023 W 015 BCR-2 18.7468 0.0020 15.6233 0.0018 38.7090 0.0042 W 015 BCR-2 18.7623 0.0009 15.6298 0.0010 38.7467 0.0031 W 015 BCR-2 18.7575 0.0009 15.6247 0.0010 38.7326 0.0028 W 015 BCR-2/1 100 ppb 18.7511 0.0031 15.6218 0.0024 38.7211 0.0055 W 021 BCR-2/2 120 ppb 18.7657 0.0026 15.6240 0.0015 38.7514 0.0049 W 021 BCR-2/3 100 ppb 18.7629 0.0013 15.6240 0.0011 38.7350 0.0039 W 021 BCR-2a 18.7553 0.0009 15.6247 0.0009 38.7334 0.0024 D 021 BCR-2b 18.7364 0.0009 15.6257 0.0008 38.6912 0.0023 D 021 BCR-2a 18.7570 0.0006 15.6249 0.0005 38.7343 0.0016 W 015 BCR-2b 18.7379 0.0008 15.6258 0.0008 38.6918 0.0022 W 015 Mean (2 SD) 18.7529 0.0195 15.6249 0.0040 38.7237 0.0405 BHVO-1 BHVO-1 18.6889 0.0012 15.5707 0.0012 38.3514 0.0031 W 015 BHVO-1 18.6965 0.0013 15.5748 0.0012 38.3721 0.0032 W 015 BHVO-1 18.7123 0.0044 15.5767 0.0041 38.3600 0.0098 W 021 BHVO-1 18.6963 0.0006 15.5719 0.0005 38.3597 0.0013 D 021 Mean (2 SD) 18.6985 0.0197 15.5735 0.0055 38.3608 0.0171 BHVO-2 BHVO-2 18.6299 0.0015 15.5362 0.0012 38.2320 0.0035 W 015 BHVO-2 18.6411 0.0017 15.5387 0.0015 38.2293 0.0040 W 015 BHVO-2 18.6609 0.0010 15.5333 0.0009 38.2492 0.0025 D 021 BHVO-2 18.6541 0.0017 15.5262 0.0014 38.2294 0.0034 W 015 BHVO-2 18.6509 0.0007 15.5328 0.0006 38.2435 0.0016 D 021 Mean (2 SD) 18.6474 0.0242 15.5334 0.0094 38.2367 0.0182 Andesite AGV-1 AGV-1 18.9433 0.0008 15.6552 0.0007 38.5668 0.0022 W 015 AGV-1 18.9398 0.0008 15.6512 0.0008 38.5575 0.0024 W 015 AGV-1 18.9415 0.0007 15.6549 0.0006 38.5623 0.0018 W 015 AGV-1 18.9398 0.0006 15.6530 0.0007 38.5584 0.0018 W 015 AGV-1 D10c 18.9349 0.0007 15.6512 0.0008 38.5544 0.0042 W 021 Mean (2 SD) 18.9399 0.0063 15.6531 0.0038 38.5599 0.0096 AGV-2 AGV-2 18.8714 0.0006 15.6182 0.0006 38.5476 0.0023 W 015 AGV-2 18.8629 0.0016 15.6114 0.0014 38.5318 0.0036 W 015 AGV-2 18.8671 0.0011 15.6230 0.0009 38.5509 0.0026 W 015 AGV-2a 18.8684 0.0009 15.6166 0.0008 38.5420 0.0028 D 021 AGV-2b 18.8718 0.0008 15.6187 0.0008 38.5501 0.0020 D 021 AVG-2a 18.8713 0.0009 15.6182 0.0007 38.5472 0.0019 W 015 AVG-2b 18.8685 0.0011 15.6151 0.0009 38.5405 0.0026 W 015 Mean (2 SD) 18.8688 0.0063 15.6173 0.0071 38.5443 0.0135 Syenite STM-1 STM-1 19.5163 0.0006 15.6304 0.0006 39.1886 0.0017 W 015 STM-1 19.5234 0.0013 15.6312 0.0011 39.1964 0.0034 W 015 STM-1 19.5228 0.0008 15.6296 0.0007 39.1954 0.0021 W 015 STM-1 19.4956 0.0006 15.6356 0.0005 39.1693 0.0014 D 021 Mean (2 SD) 19.5145 0.0260 15.6317 0.0053 39.1874 0.0252 STM-2 STM-2 19.7240 0.0009 15.6174 0.0008 39.4226 0.0021 W 015 STM-2 replicate 19.7192 0.0019 15.6135 0.0015 39.4132 0.0042 W 015 STM-2 19.7220 0.0011 15.6163 0.0011 39.4199 0.0032 W 015 STM-2 D1c 19.7224 0.0010 15.6150 0.0016 39.4150 0.0049 W 021 STM-2 L10c 19.7154 0.0015 15.6139 0.0011 39.4087 0.0032 W 021 STM-2 D10c 19.7105 0.0012 15.6138 0.0011 39.4019 0.0024 W 021 STM-2 L9c 19.7060 0.0009 15.6118 0.0010 39.3912 0.0036 W 021 STM-2a 19.7135 0.0013 15.6148 0.0011 39.4105 0.0028 D 021 STM-2b 19.7302 0.0010 15.6189 0.0008 39.4295 0.0023 D 021 Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 11 of 30Table 5. (continued) Sample Run Number 206Pb/204Pbb Error (2s) 207Pb/204Pbb Error (2s) 208Pb/204Pbb Error (2s) Wet/Dry Nu Plasma STM-2 L8c 19.7051 0.0008 15.6051 0.0007 39.3815 0.0018 D 021 STM-2a 19.7107 0.0009 15.6125 0.0008 39.4050 0.0025 W 015 STM-2b 19.7255 0.0009 15.6144 0.0006 39.4164 0.0022 W 015 Mean (2 SD) 19.7170 0.0161 15.6140 0.0068 39.4096 0.0268 Mean bomb digestion 19.7136 0.0140 15.6136 0.0026 39.4042 0.0204 Mean Savillex1 digestion 19.7207 0.0136 15.6154 0.0045 39.4167 0.0162 Rhyolite RGM-1 RGM-1 19.0036 0.0007 15.6315 0.0007 38.6925 0.0022 W 015 RGM-1 18.9962 0.0007 15.6457 0.0008 38.6550 0.0025 W 015 RGM-1 18.9949 0.0007 15.6430 0.0008 38.6487 0.0025 W 015 RGM-1 D9c 19.0042 0.0009 15.6293 0.0008 38.6969 0.0023 W 021 RGM-1 19.0027 0.0006 15.6310 0.0005 38.6971 0.0013 D 021 Mean (2 SD) 19.0003 0.0089 15.6361 0.0153 38.6780 0.0481 Granite G-2 G-2 18.3783 0.0008 15.6341 0.0008 38.9144 0.0027 W 015 G-2 18.4049 0.0007 15.6394 0.0009 38.8987 0.0024 W 015 G-2 18.4026 0.0007 15.6359 0.0008 38.8892 0.0023 W 015 G-2 D8c 18.4156 0.0010 15.6374 0.0010 38.9133 0.0026 W 021 G-2 D9c 18.3991 0.0011 15.6342 0.0010 38.8951 0.0029 W 021 G-2 D9/2c 18.3987 0.0012 15.6345 0.0010 38.8966 0.0026 W 021 G-2 HClO4 18.4089 0.0008 15.6388 0.0007 38.9085 0.0020 W 021 G-2a 18.3851 0.0008 15.6337 0.0009 38.8946 0.0020 D 021 G-2b 18.3953 0.0006 15.6362 0.0006 38.9020 0.0015 D 021 G-2 L5c 18.4094 0.0008 15.6354 0.0007 38.9025 0.0020 D 021 G-2 L6c 18.4101 0.0010 15.6354 0.0009 38.9031 0.0026 D 021 G-2a 18.3873 0.0009 15.6346 0.0008 38.8958 0.0020 W 015 G-2b 18.3942 0.0006 15.6338 0.0007 38.8940 0.0017 W 015 Mean (2 SD) 18.3992 0.0219 15.6357 0.0038 38.9006 0.0154 Mean bomb digestion 18.4019 0.0209 15.6353 0.0025 38.9010 0.0130 Mean Savillex1 digestion 18.3960 0.0233 15.6361 0.0049 38.9001 0.0190 G-3 G-3 18.4379 0.0006 15.6401 0.0006 38.9185 0.0019 W 015 G-3 18.3444 0.0009 15.6342 0.0009 38.8316 0.0028 W 015 G-3 18.3398 0.0007 15.6293 0.0007 38.8200 0.0022 W 015 G-3a 18.3816 0.0009 15.6354 0.0009 38.8558 0.0024 D 021 G-3 Bc 18.4242 0.0010 15.6368 0.0009 38.8686 0.0019 D 021 G-3b 18.4218 0.0009 15.6339 0.0008 38.8587 0.0022 W 015 G-3a 18.3776 0.0009 15.6307 0.0009 38.8426 0.0022 W 015 Mean (2 SD) 18.3896 0.0787 15.6343 0.0073 38.8565 0.0640 Granodiorite GSP-2 GSP-2 D2c 17.6092 0.0018 15.5109 0.0017 50.8849 0.0061 W 021 GSP-2 D2c (rerun) 17.6108 0.0023 15.5103 0.0023 50.8886 0.0074 W 021 GSP-2 D6c 17.6224 0.0015 15.5126 0.0014 50.9599 0.0048 W 021 GSP-2 D5c 17.6113 0.0011 15.5125 0.0010 50.9308 0.0035 W 021 GSP-2 D3c 17.6270 0.0017 15.5147 0.0016 50.7956 0.0053 W 021 GSP-2 D7c 17.6096 0.0014 15.5114 0.0013 50.5748 0.0044 W 021 GSP-2a 17.5246 0.0011 15.5050 0.0011 51.0666 0.0037 D 021 GSP-2b 17.5281 0.0010 15.5064 0.0009 51.1354 0.0037 D 021 GSP-2a 17.5244 0.0008 15.5048 0.0007 51.0736 0.0026 W 015 GSP-2b 17.5301 0.0013 15.5078 0.0011 51.1419 0.0037 W 015 Mean (2 SD) 17.5797 0.0919 15.5096 0.0069 50.9452 0.3483 Mean bomb digestion 17.6151 0.0153 15.5121 0.0031 50.8391 0.2818 Mean Savillex1 digestion 17.5268 0.0056 15.5060 0.0028 51.1044 0.0795 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). bAll 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. cBomb digestion (the coding corresponds to the bomb number). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 12 of 30Tabl e 6. SR M 98 1 Pb Isotopi c Analyse s (MC-ICP -MS) :A verage s fo rIndividua lDay s Instrumen t Dat e o fAnalysi s W et/Dr y 20 6 Pb /20 4 P b 2 SD a pp m b 20 7 Pb /20 4 P b 2 SD a pp m b 20 8 Pb /20 4 P b 2 SD a pp m b 20 8 Pb /20 6 P b 2 SD a pp m b 20 7 Pb /20 6 P b 2 SD a pp m b N u 01 5 Septembe r30 ,200 3 W 36.719 1 0.009 4 25 5 15.497 7 0.004 0 26 0 16.940 3 0.004 6 26 9 2.1675 6 0.0001 3 59 0.9148 3 0.0000 3 33 Novembe r10 ,200 3 W 36.718 4 0.008 3 22 6 15.497 6 0.003 4 21 9 16.941 0 0.003 1 18 0 2.1674 4 0.0001 9 89 0.9148 0 0.0000 5 53 Decembe r19 ,200 3 W 36.713 6 0.0 11 8 32 1 15.496 3 0.004 3 28 0 16.939 8 0.004 4 26 1 2.1672 9 0.0002 1 96 0.9147 9 0.0000 6 71 Februar y 16 ,200 4 W 36.719 0 0.008 4 22 9 15.497 8 0.002 9 19 0 16.941 0 0.003 7 21 6 2.1674 5 0.0001 4 67 0.9148 1 0.0000 4 44 Augus t9 ,200 4 W 36.719 5 0.007 5 20 3 15.497 9 0.003 6 23 0 16.941 3 0.003 7 21 8 2.1674 7 0.0001 3 62 0.9148 0 0.0000 2 25 N u 02 1 Septembe r12 ,200 3 W 36.713 7 0.003 4 93 15.496 5 0.001 2 76 16.940 0 0.001 6 96 2.1673 0 0.0000 9 43 0.9148 0 0.0000 3 28 Septembe r19 ,200 3 W 36.716 5 0.004 1 11 1 15.497 6 0.001 4 87 16.940 8 0.001 2 73 2.1673 3 0.0000 5 24 0.9148 0 0.0000 1 15 Marc h 24 ,200 4 D 36.712 9 0.007 9 21 5 15.495 8 0.003 3 21 0 16.940 0 0.003 6 21 2 2.1672 1 0.0001 3 59 0.9147 4 0.0000 5 53 Jul y 1, 200 4 W 36.718 1 0.007 8 21 2 15.497 4 0.002 7 17 3 16.942 1 0.003 0 17 6 2.1672 6 0.0001 3 58 0.9147 2 0.0000 3 33 Jul y 2, 200 4 W 36.714 5 0.006 2 16 8 15.496 5 0.002 4 15 6 16.941 8 0.002 6 15 5 2.1671 2 0.0001 3 61 0.9147 0 0.0000 3 33 Jul y 7, 200 4 W 36.716 1 0.008 0 21 7 15.496 8 0.003 2 20 4 16.941 0 0.003 3 19 3 2.1673 0 0.0001 7 79 0.9147 5 0.0000 6 67 Jul y 9, 200 4 W 36.717 0 0.007 0 18 9 15.497 1 0.002 7 17 4 16.941 5 0.003 4 20 3 2.1672 9 0.0000 8 37 0.9147 4 0.0000 3 30 Jul y 27 ,200 4 D 36.718 3 0.007 2 19 7 15.497 5 0.003 0 19 2 16.943 3 0.003 0 17 6 2.1671 6 0.0001 0 46 0.9146 7 0.0000 4 43 Jul y 28 ,200 4 D 36.717 7 0.004 6 12 6 15.496 9 0.001 9 12 4 16.942 3 0.002 1 12 4 2.1672 3 0.0000 9 44 0.9146 9 0.0000 3 33 Augus t6 ,200 4 D 36.7 11 4 0.005 9 12 6 15.495 8 0.002 1 12 4 16.939 2 0.002 1 12 4 2.1672 5 0.0001 4 44 0.9147 9 0.0000 4 33 Septembe r15 ,200 4 D 36.713 1 0.010 0 27 2 15.496 1 0.003 4 21 9 16.939 8 0.002 6 15 5 2.1672 6 0.0003 0 13 8 0.9147 7 0.0000 6 67 Septembe r22 ,200 4 W 36.713 8 0.006 0 16 2 15.496 5 0.001 6 10 2 16.939 8 0.002 5 14 5 2.1673 4 0.0000 7 31 0.9148 1 0.0000 6 63 Septembe r24 ,200 4 D 36.710 8 0.007 4 20 0 15.495 5 0.002 5 15 8 16.939 2 0.002 3 13 8 2.1672 2 0.0001 6 74 0.9147 7 0.0000 4 41 Septembe r28 ,200 4 D 36.7 11 5 0.0 11 1 30 3 15.495 6 0.003 6 23 5 16.939 8 0.003 1 18 4 2.1672 1 0.0002 1 97 0.9147 6 0.0000 5 56 Averag e N u 01 5 n = 65 36.716 3 0.012 1 32 8 15.496 8 0.004 7 30 3 16.940 0 0.004 9 28 7 2.1674 4 0.0002 5 11 4 0.9148 1 0.0000 5 56 Averag e N u 02 1 n = 16 7 36.714 5 0.008 8 24 0 15.496 4 0.002 9 18 8 16.940 7 0.003 6 21 5 2.1672 4 0.0001 9 86 0.9147 5 0.0000 9 97 a Th e 2 st an da rd de vi at io n o n th e m ea n o ft he SR M 98 1 an al ys es o n a gi ve n da y (n v ar ie s be tw ee n 12 an d 20 ). b Th e pp m erro r. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 13 of 3087Sr/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 normaliza- tion value of 143Nd/144Nd = 0.511858 [Lugmair et al., 1983] and 0.511973 [Chauvel and Blichert- Toft, 2001], respectively. [17] Sr and Nd isotopic compositions were mea- sured 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 86Sr/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. 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 206Pb/204Pbb Error (2s) 207Pb/204Pbb Error (2s) 208Pb/204Pbb Error (2s) 87Sr/86Src Error (2s) 143Nd/144Ndc Error (2s) BHVO BHVO-1 (1) residue 18.6460 0.0007 15.4852 0.0006 38.1954 0.0017 0.703464 0.000008 0.512989 0.000006 BHVO-1 (2) residue 18.6435 0.0010 15.4786 0.0008 38.1733 0.0025 0.703467 0.000006 0.512981 0.000007 BHVO-1 (3) residue 18.6150 0.0013 15.4847 0.0007 38.1723 0.0018 0.703476 0.000007 0.512989 0.000006 BHVO-2 (1) residue 18.6455 0.0009 15.4892 0.0011 38.2055 0.0034 0.703484 0.000007 0.512987 0.000005 BHVO-2 (2) residue 18.6378 0.0008 15.4789 0.0009 38.1881 0.0027 0.703467 0.000007 0.512987 0.000005 BHVO-2 (3) residue 18.6387 0.0006 15.4797 0.0007 38.1767 0.0021 0.703462 0.000007 0.512985 0.000006 BHVO-1 (1) leachate 18.7061 0.0007 15.6291 0.0008 38.4393 0.0021 0.703493 0.000007 0.512983 0.000008 BHVO-1 (3) leachate 18.7311 0.0006 15.6390 0.0005 38.4721 0.0015 0.703494 0.000007 0.512981 0.000006 BHVO-2 (2) leachate 18.5649 0.0008 15.5987 0.0007 38.2213 0.0022 0.703508 0.000007 0.512992 0.000006 BHVO-2 (3) leachate 18.5628 0.0010 15.6015 0.0008 38.2307 0.0020 0.703496 0.000007 0.512994 0.000006 BCR BCR-1 (1) residue 18.7995 0.0009 15.6234 0.0008 38.8219 0.0022 0.704981 0.000007 0.512644 0.000005 BCR-1 (2) residue 18.8013 0.0006 15.6230 0.0006 38.8228 0.0018 0.704982 0.000008 0.512645 0.000007 BCR-2 (1) residue 18.8007 0.0007 15.6241 0.0006 38.8256 0.0019 0.704992 0.000007 0.512641 0.000004 BCR-2 (2) residue 18.7993 0.0010 15.6230 0.0009 38.8232 0.0029 0.705012 0.000008 0.512644 0.000007 BCR-2 (3) residue 18.6646 0.0010 15.6265 0.0009 38.5279 0.0025 0.705019 0.000013 0.512639 0.000005 BCR-1 (1) leachate 18.8232 0.0006 15.6302 0.0005 38.6047 0.0014 0.705118 0.000007 0.512647 0.000006 BCR-1 (2) leachate 18.8390 0.0009 15.6469 0.0008 38.6518 0.0020 0.705095 0.000009 0.512641 0.000008 BCR-2 (1) leachate 18.6473 0.0009 15.6209 0.0007 38.4955 0.0020 0.705085 0.000008 0.512643 0.000007 BCR-2 (3) leachate 18.7951 0.0006 15.6146 0.0007 38.7996 0.0024 AGV AGV-1 (1) residue 18.9060 0.0006 15.6164 0.0005 38.5985 0.0015 0.703957 0.000007 0.512753 0.000006 AGV-1 (2) residue 18.9047 0.0007 15.6165 0.0006 38.5765 0.0015 0.703948 0.000008 0.512808 0.000006 AGV-1 (3) residue 18.8894 0.0010 15.5984 0.0011 38.5181 0.0037 0.703946 0.000008 0.512800 0.000006 AGV-2 (1) residue 18.9067 0.0005 15.6137 0.0005 38.5692 0.0014 0.703948 0.000007 AGV-2 (2) residue 18.9078 0.0005 15.6157 0.0004 38.5764 0.0013 0.703966 0.000008 0.512794 0.000005 AGV-1 (1) leachate 18.9443 0.0006 15.6584 0.0005 38.5480 0.0015 0.704025 0.000008 0.512800 0.000005 AGV-1 (3) leachate 18.9525 0.0005 15.6670 0.0004 38.5587 0.0011 0.704084 0.000007 0.512795 0.000005 AGV-2 (1) leachate 18.8126 0.0007 15.6251 0.0012 38.5089 0.0018 0.704060 0.000008 0.512798 0.000005 AGV-2 (2) leachate 18.8055 0.0006 15.6232 0.0006 38.4951 0.0017 0.704054 0.000008 0.512797 0.000006 aAll 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). bAll 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. cMeasured ratio normalized to SRM 987 87Sr/86Sr = 0.710248 and to La Jolla 143Nd/144Nd = 0.511858 (based on the mean of the wheel). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 14 of 30Note 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 moni- toring 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, 142Ce = 0.11114 [Rosman and Taylor, 1998]) corrected for instrumental mass discrimination us- ing an exponential law as monitored by the 146Nd/144Nd ratio. [19] During the period of data collection, the aver- age 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 agree- ment 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 Table 8. Pb Concentrations by Isotope Dilution for USGS Reference Materialsa Sample Pb, ppm 2s Sample Pb, ppm 2s BCR-1 BCR-2 BCR-1 A 13.16 0.22 BCR-2 A 10.31 0.15 BCR-1 B 13.36 0.16 BCR-2 B 12.35 0.15 BCR-1 C 13.07 0.15 BCR-2 C 10.11 0.08 BCR-1 D 13.79 0.14 BCR-2 C (rerun) 10.14 0.08 Mean 13.34 0.64 BCR-2 D 12.21 0.13 Mean 11.02 2.30 AGV-1 AGV-2 AGV-1 A 33.01 1.47 AGV-2 A 13.39 0.20 AGV-1 B 37.79 1.18 AGV-2 B 12.53 0.20 AGV-1 C 40.52 0.81 AGV-2 C 13.59 0.13 AGV-1 D 40.46 0.76 AGV-2 D 13.07 0.13 AGV-1 E 37.11 0.68 Mean 13.15 0.93 AGV-1 F 35.26 0.60 Mean 37.36 5.88 BHVO-1 BHVO-2 BHVO-1 A 2.46 0.01 BHVO-2 A 1.62 0.01 BHVO-1 B 1.98 0.01 BHVO-2 B 1.54 0.01 BHVO-1 C 2.02 0.01 BHVO-2 C 1.32 0.01 BHVO-1 D 1.99 0.01 BHVO-2 D 1.48 0.01 BHVO-1 E 2.04 0.01 BHVO-2 E 1.42 0.01 BHVO-1 F 2.05 0.02 BHVO-2 F 1.62 0.01 Mean 2.09 0.37 BHVO-2 F (rerun) 1.63 0.01 Mean 1.52 0.24 a(Rerun): same filament. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 15 of 30apart. 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 discrim- ination 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 instru- mental mass fractionation as monitored by the 205Tl/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 analyt- ical conditions for the Pb isotopic compositions, and thus the precision and the accuracy (i.e., better precision on 205Tl/203Tl and less interference on 204Pb), 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 deter- 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 left- hand 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. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 16 of 30mine 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 208Pb/204Pb = 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 mea- sured in the two laboratories. These values are in agreement with previously reported TIMS triple- spike values [Galer and Abouchami, 1998], but with slightly lower 208Pb/204Pb ratios (60 ppm lower). This difference in 208Pb/204Pb is compara- ble, 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 Instru- ments 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 Blichert- Toft 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 sec- tion 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 fila- ments using the SiGel (SiCl4) – H3PO4 technique and were analyzed with a VG54R single collector TIMS instrument in peak-switching mode at 1450C. A mass fractionation correction of Figure 1. (continued) Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 17 of 300.12%/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 208Pb/204Pb = 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 concentra- tions between the two generations of USGS refer- ence 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 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. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 18 of 30BHVO-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 concentra- tions 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 homoge- neity 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 deter- mined 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 repro- ducibility 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 incom- Figure 2. (continued) Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 19 of 30plete recovery of Sr. Thus GSP-2 is a somewhat poor choice for a reference material for Sr. [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 results agree entirely with those of Raczek et al. [2003]. 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 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 (orange- filled purple diamond) and TIMS (blue empty diamond) analyses for comparison. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 20 of 30have detected no difference between generations 1 and 2 of the analyzed reference materials for BHVO, AGVand 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 MC- ICP-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 reproduc- ibility of La Jolla and RennesNd 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 multi- dynamic analysis [Thirlwall and Anczkiewicz, 2004] to achieve accurate and preciseNd 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 exponen- tial mass bias behavior during isotope measure- ments by MC-ICP-MS might be instrument specific. Figure 3. (continued) Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 21 of 303.3. 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 compositions measured by the double-spike tech- nique [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 spec- trometry, manuscript in preparation, 2006); here- inafter 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 docu- mented in this study varies between 164 to 1298 ppm. Heterogeneous Pb isotope compositions, and significantly higher Pb concentrations (Pre- torius 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 prob- ably 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). [30] For felsic compositions (STM-1, STM-2, RGM-1, GSP-2, G-2 and G-3), the reproducibil- ity 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 dis- solved 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 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]. 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]. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 22 of 30Figure 5a Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 23 of 30deviations 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 first- and 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 min- erals whose proportion can vary from one sample to another. The significantly higher Pb concen- trations 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 radio- genic than the unleached rock powders). Corre- 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. 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 208Pb/204Pb versus 206Pb/204Pb. Red symbols indicate high-pressure digestion in PTFE bombs, and blue symbols indicate hotplate Savillex1 digestion. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 24 of 30Figure 5c Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 25 of 30spondingly, the leachates of AGV-2 and BCR-2 have distinctly less radiogenic Pb isotopic com- positions than the unleached powders. In Figure 8, the trace element concentrations of the first- and second-generation reference materials for BHVO, AGVand BCR, as well as for BHVO-1/BHVO-2G (the USGS reference glass), are compared (Pre- torius 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 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 fromWoodhead 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. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 26 of 30Figure 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). Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 27 of 30relative 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 concen- tration measurements (Table 8). This has impor- tant 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 be- tween the first and second generations are sig- nificantly 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 leach- ing is not always successful at entirely eliminat- ing contamination from the powders. We have recently carried out systematic leaching experi- ments (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 prep- aration plays a crucial role in obtaining high- precision 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 alter- ation 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 com- plete 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 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. Geochemistry Geophysics Geosystems G3 weis et al.: isotopic study of usgs reference materials 10.1029/2006GC001283 28 of 30arise 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 sec- ond-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 143Nd/144Nd values. Nd isotopic compositions can be measured, with comparable accuracy and preci- sion, 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 compro- mises 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 construc- tive 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 mea- surements using multiple-collector MC-ICP-MS, Geochim. Cosmochim. Acta, 68(12), 2725–2744. Albare`de, F., A. Stracke, V. J. M. Salters, D. Weis, J. Blichert- Toft, P. Te´louk, and A. Agranier (2005), Comment to ‘‘Pb isotopic analysis of standards and samples using a 207Pb-204Pb double spike and thallium to correct for mass bias with a double-focusing MC-ICP-MS’’ by Baker et al., Chem. Geol., 217, 171–174. Baker, J., D. Peate, T.Waight, andC. 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