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Hf isotope compositions of U.S. Geological Survey reference materials. Weis, Dominique; Kieffer, Bruno; Hanano, Diane; Nobre Silva, Ines G.; Barling, Jane; Pretorius, Wilma 2007-11-16

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Hf isotope compositions of U.S. Geological Survey reference materials Dominique Weis, Bruno Kieffer, Diane Hanano, Ineˆs Nobre Silva, Jane Barling, 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 (dweis@eos.ubc.ca) Claude Maerschalk and Nadine Mattielli Department of Earth and Environmental Sciences, Universite´ Libre de Bruxelles, CP 160/02, Avenue F.D. Roosevelt, 50, B-1050 Brussels, Belgium [1] A systematic multi-isotopic and trace element characterization of U.S. Geological Survey reference materials has been carried out at the Pacific Centre for Isotopic and Geochemical Research, University of British Columbia. Values of 176Hf/177Hf are recommended for the following reference materials (mean ±2 SD): G-2: 0.282523 ± 6; G-3: 0.282518 ± 1; GSP-2: 0.281949 ± 8; RGM-1: 0.283017 ± 13; STM-1: 0.283019 ± 12; STM-2: 0.283021 ± 5; BCR-1: 0.282875 ± 8; BCR-2: 0.282870 ± 8; BHVO-1: 0.283106 ± 12; BHVO-2: 0.283105 ± 11; AGV-1: 0.282979 ± 6; and AGV-2: 0.282984 ± 9. Reproducibility is better than 50 ppm for the granitoid compositions and better than 40 ppm for the basaltic/andesitic compositions. For the isotopic analyses acquired early in this project on glass columns, Hf isotopic analyses from several of the reference materials were significantly less reproducible than Nd and Sr isotopic analyses determined from the same sample dissolution. The 176Hf/177Hf ratios for relatively radiogenic compositions (BCR-1, 2; BHVO-1, 2; RGM-1) were shifted systematically toward lower values by 100–150 ppm when a borosilicate primary column was used. Although systematic, the shift for felsic compositions was generally within analytical error, except for GSP-2, which has a very low Hf isotopic ratio, where the shift was to higher 176Hf/177Hf. Trace element and isotopic characterization of the borosilicate glass column, borosilicate frits, and quartz columns reveals extremely variable levels of trace elements. The 176Hf/177Hf ratios for these materials are very unradiogenic (borosilicate glass <0.28220; frit = 0.28193 ± 4). The borosilicate frit material appears to be the most variable in elemental concentration and isotopic composition. The quartz material has very low levels (<ppm) of all trace elements. Low 176Hf/177Hf and high Hf concentrations of the borosilicate glass column (16 ppm) and frit material (22 ppm) indicate that only small amounts of such unradiogenic material could cause significant contamination of small samples. For the basaltic (BCR-1, 2; BHVO-1, 2) and rhyolitic (RGM-1) samples, approximately 3 ng of Hf from the column or frit would be enough to produce the observed 100–150 ppm shift. Accurate, high-precision 176Hf/177Hf data can only be acquired if samples are processed using all PTFE Teflon1 labware, or quartz and polypropylene. Components: 7380 words, 5 figures, 4 tables. Keywords: MC-ICP-MS; high precision; USGS reference material; Hf isotopes; labware contamination. Index Terms: 1040 Geochemistry: Radiogenic isotope geochemistry; 1094 Geochemistry: Instruments and techniques. Received 7 September 2006; Revised 19 February 2007; Accepted 27 February 2007; Published 12 June 2007. G3GeochemistryGeophysicsGeosystems Published by AGU and the Geochemical Society AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES Technical Brief Volume 8, Number 6 12 June 2007 Q06006, doi:10.1029/2006GC001473 ISSN: 1525-2027 Copyright 2007 by the American Geophysical Union 1 of 15Weis, D., B. Kieffer, D. Hanano, I. Nobre Silva, J. Barling, W. Pretorius, C. Maerschalk, and N. Mattielli (2007), Hf isotope compositions of U.S. Geological Survey reference materials, Geochem. Geophys. Geosyst., 8, Q06006, doi:10.1029/2006GC001473. 1. Introduction [2] The development of the multiple collector inductively coupled plasma mass spectrometer (MC-ICP-MS) for high-precision isotopic analyses of numerous elements and the ability of the ICP source to ionize nearly all elements in the periodic table has made these instruments very popular [Halliday et al., 1998; Albare`de et al., 2004]. The shift from TIMS to MC-ICP-MS analysis of Hf isotopic compositions has resulted in a major reduction in the sample size of geologic materials (from microgram to nanogram) and a significant improvement in internal and external precision [Blichert-Toft et al., 1997; Vervoort and Blichert- Toft, 1999; Chu et al., 2002]. Thus prior to the late 1990s, Hf isotopic analyses would have been much less vulnerable to contamination during processing than nowadays. In contrast, sample sizes for Nd and Pb isotopic analysis by MC-ICP-MS are similar to or larger than sample sizes required for TIMS analysis. The advantages of MC-ICP-MS for these isotopic systems are more rapid sample throughput, and in the case of Pb, significantly improved precision [e.g., White et al., 2000; Albare`de et al., 2005; Weis et al., 2006]. [3] In addition to the potential for detectable con- tamination in the case of Hf, the plasma source produces more complex interferences than the TIMS source and is also susceptible to matrix effects, as has long been known from ICP-MS [e.g., Beauchemin et al., 1987]. Furthermore, the intrinsic instability of the plasma source means that most MC-ICP-MS analyses are run in static mode. Although these factors were initially neglected, recent studies have shown that mass bias correc- tions are strongly dependent on the cleanliness of the sample [Albare`de and Beard, 2004]. It is now recognized that for accurate, high-precision data it is necessary to analyze matrix-matched reference materials as well as pure standard solutions. This in turn means that it is critical to have a broad compositional range of isotopic reference materials available so that appropriate matrix-matched stand- ards can be selected for analyzing with suites of samples with unknown isotopic compositions. [4] For this reason the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at the Uni- versity of British Columbia undertook a systematic analysis of the concentrations and isotopic compo- sitions of Nd, Sr, Hf and Pb in a broad composi- tional range of United States Geological Survey (USGS) reference materials, including basalt (BCR-1, 2; BHVO-1, 2), andesite (AGV-1, 2), rhyolite (RGM-1), syenite (STM-1, 2), granodiorite (GSP-2), and granite (G-2, 3). These reference materials were already well-characterized geo- chemically (major elements and most trace ele- ments), but lacked isotopic data except for a few single element isotopic investigations of selected materials (e.g., Pb) [Woodhead and Hergt, 2000; Baker et al., 2004; Weis et al., 2005]. [5] Pioneering papers clearly indicated the suscep- tibility of Hf chemistry to high blanks if hydro- fluoric acid is not used in the cleaning operations [Patchett and Tatsumoto, 1980] or from leaching of organic material out of PFA material by perchloric acid [Salters, 1994]. Polypropylene and TFE shrinkable Teflon1 tubes were also recommended to limit the procedural blank for Nd separation chemistry [e.g., Richard et al., 1976]. During the course of this investigation we observed that the reproducibility of Hf isotopic data was somewhat lower than that achieved for Nd and Pb isotopic data (96 ppm versus 30 ppm) when the samples had been processed on glassware. This paper presents the identification and resolution of this problem. Hf isotopic ratios, when PTFE-type Teflon1 or quartz material is used throughout the entire chemistry, have a reproducibility that is comparable to that of MC-ICP-MS Nd or Pb isotopic data (i.e., 30–50 ppm). 2. Analytical Techniques [6] Our study presents accurate high-precision Hf isotopic compositions for USGS reference materi- als. The reader is referred to critical literature papers for the development of Hf and Lu chemical separation and the various issues that appear depending on the instrument used for the isotopic analysis (TIMS, SIMS and MC-ICP-MS) [e.g., Patchett and Tatsumoto, 1980; Salters, 1994; Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 2 of 15Blichert-Toft et al., 1997; Blichert-Toft, 2001]. Cleaning protocols for high-pressure PTFE bombs and other labware in this study are discussed by Pretorius et al. [2006], and dissolution techniques are discussed by Weis 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. All the acids have concentrations of the relevant elements in or below the pg/mL level. 2.1. Hafnium Separation Chemistry [7] The Hf isotope analyses were carried out fol- lowing a modified analytical procedure from Patchett and Tatsumoto [1980] and Blichert-Toft et al. [1997]. Typically, 100–150 mg of rock powderwas dissolved in high-pressure PTFE bombs for felsic samples and in screw-top Savillex1 beakers for mafic samples. For the USGS reference materials processed during this study, estimates of Hf recovered after the dissolution stage are close to 100%. The situation is clearly different for some specific mineral phases, such as rutile and ilmenite (C. E. Morisset, personal communication, 2007). Elution volumes used for the column procedures in this study are not given as resin properties vary from lot to lot and thus require individual calibration. Exact details are available on request. 2.1.1. First Column [8] Several tests were previously performed to compare the Hf separation ability (from Zr, etc.) of different resins (AG50W-X8, AG50W-X12), differ- ent reagents (1.5 N HCl; 1.5 N HCl: 0.1 N HF) and acid volumes. The following methodology has been chosen for the primary Hf column: Pyrex1 or Teflon1 columns are loaded with Bio-Rad AG50W-X8 100–200 mesh cation exchange resin and equilibrated with 1.5 N HCl. (The Pyrex1 columns were available in-house and were initially used to speed up the process of lab installation; the Teflon1 columns were custom-made by Savillex, with a reservoir of 100 mL.) The bed of resin of this column is 20 cm in height for a diameter of 1 cm. Dried sample chlorides are reconstituted in 2.0 mL of 1.5 N HCl. Samples are put on the hotplate at 120–130C for 10 min and ultra- sonicated to ensure complete dissolution and are pipetted onto columns taking care not to disturb the resin. The sample solution is carefully washed with 1 mL of 1.5 N HCl. The Hf aliquot is collected in 10 mL of 2.5 N HCl and dried on a hotplate at 100C. The columns are stripped with 6 N HCl and with 10 mL of 4 N HF prior to re-equilibration with 1.5 N HCl for another sepa- ration if only Hf needs to be isolated. If Sr and/or the REE are collected after the Hf fraction, the procedure is identical to the one described by Weis et al. [2006]. 2.1.2. Second Column [9] Polypropylene columns (Poly Prep1 Bio-Rad Laboratories) are loaded with 2 mL of Bio-Rad AG1-X8 100–200 mesh anionic exchange resin. New resin is used for each batch of chemistry. The function of this second column is to remove P [Patchett and Tatsumoto, 1980], more matrix (i.e., resulting in less ‘‘sticky’’ samples on the MC-ICP- MS) and more specifically, transition metals (elim- inating more Fe, Cu, Zn, Nb and Ta, Cr). The columns are washed with 3 cycles, each consisting of 10 mL of 6 N HCl and 10 mL of 18 megaohm H2O, then with 10 mL of 24 N HF followed by 3 times 10 mL of H2O. The columns are equili- brated with 10 mL of 0.1 N HF/0.5 N HCl. The samples (collected from the first Hf columns) are redissolved in 1.0 mL of 0.1 N HF/0.5 N HCl; they are put on the hotplate for 10 min and ultra- sonicated, and then carefully pipetted onto the resin bed. The sample is washed 2 times with 1.0 mL of 0.1 N HF/0.5 N HCl followed by 8.0 mL of 0.1 N HF/0.5 N HCl. Following this, 0.75 mL of 2.5 N Q HCl, where Q is quartz-distilled acid, is added to the columns. The Hf fraction, also con- taining Ti and Zr, is collected in 5.0 mL of 2.5 N Q HCl (into a Teflon1 beaker). 2.1.3. ‘‘HClO4 Step’’ [10] 250 mL of 70% suprapur1 HClO4 (Seastar Chemicals Inc.) are added to the sample. The sample is placed on a hotplate (190–200C) until white smoke evolves. Heating is maintained until only ‘‘a large drop’’ (200 mL) remains in the beaker. This procedure is repeated 3 more times to eliminate HF, which would impair the third chem- istry step. It is mandatory not to reach dryness because the sample will not redissolve in HCl. If total dryness occurs, the only way to redissolve the residue is by adding concentrated HF to it and starting over the HClO4 step from the beginning. 2.1.4. Third Column [11] Teflon1 columns (0.5 cm diameter and 12 cm long) are loaded with Bio-Rad AG50W-X8 200- 400 mesh cation exchange resin, cleaned with 6 mL Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 3 of 15of 4 N HF followed by 2 times 6 mL of 6 N HCl, then 2 times 6 mL of 2.5 N HCl with a backwash of the resin during the second pass for equilibration. Following this, 0.3 mL of 2.5 N HCl and 30 mL of 30% H2O2 are added to the drop of sample remaining after the HClO4 evaporation step to check if Ti, and therefore Hf, are still present before processing the sample on columns. The sample color becomes yellow to brown due to the formation of a cationic complex of H2O2 with Ti. The sample is carefully pipetted onto the top of the column. The sample is washed with 0.4 mL of 2.5 N HCl followed by 5.0 mL of 2.5 N HCl. The solution containing Hf (and Zr) is collected in 1.0 mL of a mixture of 2.5 N HCl/0.3 N HF followed by 5.0 mL of 2.5 N HCl/0.3 N HF. 2.1.5. Blanks [12] Reagent and total procedural blanks were measured during the course of this study. Reagent blanks are all in the ppt level for all elements of interest (Rb, Sr, Sm, Nd, Lu, Hf and U). For Pb, reagent blanks give 3 pg/mL, except for HF (12 pg). Column blanks averaged 20–70 pg Nd and 8–58 pg Hf during the course of analysis of the USGS reference materials. Interestingly, an acid wash of Teflon1 and glass columns does not yield signifi- cantly different quantities of Hf or Nd (<50 pg). 2.2. Mass Spectrometry Analytical Procedure [13] Hf isotopic compositions were analyzed by static multicollection using a MC-ICP-MS. The collector array on the Nu Plasma is fixed and a zoom lens is employed to position the masses in the collectors. For Hf analyses, the collectors H4 to L3 are used. The configuration used enables si- multaneous collection of Hf (masses 180, 179, 178, 177, 176 and 174) together with monitoring of Lu at mass 175 and Yb at mass 172. The latter two measurements allow interference corrections to be applied to masses 174 and 176. Hf isotope measurements were normalized internally to a 179Hf/177Hf ratio of 0.7325 using an exponential correction. [14] The 176Lu, 176Yb and 174Yb corrections were made using natural abundances (175Lu = 0.97416, 176Lu = 0.02584, 172Yb = 0.2183, 174Yb = 0.3138, 176Yb = 0.1276) corrected for instrumental mass discrimination as monitored by 179Hf/177Hf. The average 175Lu/177Hf is 0.000004 ± 9 and 172Yb/177Hf is 0.000005 ± 14 for 118 analyses of USGS reference materials. This corresponds to a contribution of 11 (±31) ppm and of 0 ppm of Yb and Lu on 176Hf, respectively. For the JMC-475 Hf standard, the corresponding ratios are: 175Lu/177Hf = 0.000003 ± 8 and 172Yb/177Hf = 0.000002 ± 4 (n = 676). The configuration used does not permit correction of mass 180 for the presence of 180Ta, because 181Ta is too small to be monitored for a meaningful correction for Ta on mass 180. Al- though a 180W correction could be applied through monitoring of 182W or 184W, this was not done because in the absence of a 180Ta correction only a partial correction can be made. The presence of 180Ta and 180W can be assessed by comparing 180Hf/177Hf values of samples to the mean (±2 SD) values measured on the standards. None of the USGS reference materials were affected by signif- icant Ta and W interferences (USGS reference material analyses: 180Hf/177Hf = 1.886925 ± 167, n = 118; JMC-475 analyses: 180Hf/177Hf = 1.886878 ± 137, n = 616). [15] Samples were run using a modified sample- standard bracketing approach with JMC-475 Hf standard solution analyzed after every second sam- ple to monitor systematic in-run drift in the stan- dard value. (JMC-475 Hf standard solution available on request to J. Patchett at the University of Arizona. Note that this is the only Hf isotopic composition reference solution. JMC-475, as cur- rently available at Johnson-Matthey, is an ICP-MS standard solution with guaranteed concentration but with a variable isotopic composition.) No systematic drift was observed and the results in Table 1 have been normalized to a 176Hf/177Hf value for JMC-475 of 0.282160, based on the mean of each individual day of analysis (typically 10– 15 runs of JMC-475). During the period of data collection (July 2004 to January 2007) and for runs corresponding to the USGS reference material analyses, the JMC-475 Hf standard gave an un- weighted mean for 176Hf/177Hf of 0.282163 ± 21 (2 SD; n = 676). [16] The stable Hf isotopic compositions and the slopes for the ln-ln trends are reported in Table 2, with a comparison between the JMC-475 standard solutions and the samples. Mafic samples (BCR-1, 2; AGV-1, 2 and BHVO-1, 2) show very similar mass fractionation behavior to the JMC-475 stan- dard solution in ln-ln plots (not shown). However, the felsic samples (G-2, 3; RGM-1; STM-1, 2 and GSP-2) show a slightly different mass fractionation behavior as reflected by a slightly lower slope than standard solutions and mafic samples in these ln-ln Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 4 of 15Table 1. USGS Reference Materials: Hf Isotopic Compositions Sample Run Numbera 176Hf/177Hf Error (2s)b 176Hf/177Hf Normc 2 SDd Nu Plasma Wet/Drye Basalt BCR-1 BCR-1 #7 0.282842 4 0.282850 021 D BCR-1 #7 0.282846 4 0.282854 021 D Mean with glass (2 SD) 0.282844 6 0.282852 6 BCR-1 #15 0.282870 4 0.282872 021 D BCR-1 #16 0.282870 4 0.282875 021 D BCR-1 #17 0.282873 4 0.282880 021 D BCR-1 #20 0.282870 4 0.282876 021 D BCR-1 #22 0.282874 5 0.282871 021 D Mean with Teflon1 (2 SD) 0.282871 4 0.282875 8 BCR-2 BCR-2 #1 0.282829 6 0.282841 021 D BCR-2 #4 0.282851 10 0.282850 015 W BCR-2 #1 0.282822 7 0.282834 021 D BCR-2 #4 0.282846 10 0.282845 015 W BCR-2 #7 0.282844 4 0.282852 021 D BCR-2 #8 0.282813 5 0.282832 021 D BCR-2 #8 0.282811 5 0.282830 021 D BCR-2 #12 0.282855 5 0.282846 021 D BCR-2 #12 0.282850 6 0.282841 021 D Mean with glass (2 SD) 0.282835 34 0.282841 16 BCR-2 #8 0.282859 6 0.282875 021 D BCR-2 #8 0.282858 4 0.282874 021 D BCR-2 #12 0.282876 5 0.282867 021 D BCR-2 #15 0.282875 5 0.282871 021 D BCR-2 #15 0.282874 5 0.282870 021 D BCR-2 #15 0.282871 5 0.282867 021 D BCR-2 #26 0.282880 4 0.282871 021 D BCR-2 #27 0.282861 6 0.282862 021 D BCR-2 #28 0.282862 5 0.282874 021 D BCR-2 #29 0.282854 5 0.282866 021 D Mean with Teflon1 (2 SD) 0.282867 18 0.282870 8 BHVO-1 BHVO-1 #1 0.283063 9 0.283075 021 D BHVO-1 #4 0.283068 9 0.283068 015 W BHVO-1 #1 0.283055 11 0.283067 021 D BHVO-1 #4 0.283089 12 0.283088 015 W BHVO-1 #6 0.283067 6 0.283071 021 D Mean with glass (2 SD) 0.283068 25 0.283074 17 BHVO-1 #17 0.283098 4 0.283107 021 D BHVO-1 #17 0.283089 5 0.283095 021 D BHVO-1 #16 0.283101 7 0.283102 021 D BHVO-1 #15 0.283110 5 0.283106 021 D BHVO-1 #17 0.283108 4 0.283111 021 D BHVO-1 #21 0.283105 5 0.283107 021 D BHVO-1 #30 0.283113 6 0.283114 021 D Mean with Teflon1 (2 SD) 0.283104 16 0.283106 12 BHVO-2 BHVO-2 #1 0.283056 5 0.283068 021 D BHVO-2 #4 0.283056 17 0.283055 015 W BHVO-2 #1 0.283047 6 0.283059 021 D BHVO-2 #4 0.283054 8 0.283054 015 W BHVO-2 #7 0.283065 4 0.283073 021 D BHVO-2 #8 0.283041 4 0.283057 021 D BHVO-2 #8 0.283023 4 0.283039 021 D BHVO-2 #13 0.283082 7 0.283078 021 D BHVO-2 #13 0.283068 6 0.283065 021 D Mean with glass (2 SD) 0.283055 34 0.283061 24 BHVO-2 #9 0.283080 5 0.283099 021 D BHVO-2 #9 0.283085 6 0.283104 021 D BHVO-2 #12 0.283109 5 0.283100 021 D BHVO-2 #12 0.283111 5 0.283107 021 D BHVO-2 #13 0.283094 5 0.283102 021 D BHVO-2 #14 0.283096 7 0.283104 021 D Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 5 of 15Table 1. (continued) Sample Run Numbera 176Hf/177Hf Error (2s)b 176Hf/177Hf Normc 2 SDd Nu Plasma Wet/Drye BHVO-2 #15 0.283113 4 0.283109 021 D BHVO-2 #21 0.283115 6 0.283116 021 D BHVO-2 #27 0.283107 4 0.283108 021 D Mean with Teflon1 (2 SD) 0.283101 26 0.283105 11 Andesite AGV-1 AGV-1 #3 0.282944 5 0.282961 021 D AGV-1 #4 0.282943 10 0.282942 015 W AGV-1 #3 0.282944 6 0.282961 021 D AGV-1 #4 0.282965 10 0.282965 015 W AGV-1 #7 0.282954 4 0.282962 021 D AGV-1 #13 0.282963 5 0.282959 021 D AGV-1 #13 0.282959 5 0.282955 021 D Mean with glass (2 SD) 0.282953 19 0.282958 15 AGV-1 #15 0.282979 4 0.282974 021 D AGV-1 #15 0.282985 4 0.282980 021 D AGV-1 #15 0.282979 5 0.282979 021 D AGV-1 #17 0.282979 5 0.282982 021 D AGV-1 #21 0.282980 5 0.282981 021 D Mean with Teflon1 (2 SD) 0.282980 5 0.282979 6 AGV-2 AGV-2 #3 0.282950 6 0.282967 021 D AGV-2 #4 0.282964 12 0.282963 015 W AGV-2 #3 0.282944 5 0.282961 021 D AGV-2 #4 0.282943 10 0.282943 015 W AGV-2 #6 0.282945 6 0.282948 021 D AGV-2 #13 0.282952 6 0.282949 021 D AGV-2 #13 0.282951 4 0.282948 021 D Mean with glass (2 SD) 0.282950 14 0.282954 19 AGV-2 #15 0.282971 4 0.282977 021 D AGV-2 #16 0.282971 4 0.282979 021 D AGV-2 #17 0.282982 5 0.282984 021 D AGV-2 #20 0.282983 5 0.282989 021 D AGV-2 #22 0.282991 5 0.282988 021 D AGV-2 #27 0.282983 5 0.282984 021 D Mean with Teflon1 (2 SD) 0.282980 15 0.282984 9 Syenite STM-1 STM-1 #2 0.282998 4 0.283016 021 D STM-1 #5 0.283011 11 0.283003 015 W STM-1 #2 0.282995 3 0.283013 021 D STM-1 #5 0.283020 9 0.283013 015 W STM-1 #7f 0.283007 3 0.283015 021 D Mean with glass (2 SD) 0.283006 20 0.283012 10 STM-1 #19f 0.283033 3 0.283015 021 D STM-1 #19f 0.283038 4 0.283023 021 D Mean with Teflon1 (2 SD) 0.283035 7 0.283019 12 STM-2 STM-2 #2 0.282995 3 0.283013 021 D STM-2 #5 0.283015 9 0.283008 015 W STM-2 #2 0.282998 4 0.283016 021 D STM-2 #5 0.283033 9 0.283026 015 W STM-2 #7f 0.283009 3 0.283017 021 D STM-2 #13f 0.283017 4 0.283013 021 D STM-2 #13f 0.283020 4 0.283016 021 D Mean with glass (2 SD) 0.283012 27 0.283015 11 STM-2 #19f 0.283037 4 0.283023 021 D STM-2 #19f 0.283040 3 0.283019 021 D Mean with Teflon1 (2 SD) 0.283038 3 0.283021 5 Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 6 of 15Table 1. (continued) Sample Run Numbera 176Hf/177Hf Error (2s)b 176Hf/177Hf Normc 2 SDd Nu Plasma Wet/Drye Rhyolite RGM-1 RGM-1 #3 0.282978 5 0.282994 021 D RGM-1 #4 0.282995 9 0.282995 015 W RGM-1 #3 0.282983 5 0.283000 021 D RGM-1 #4 0.283006 7 0.283006 015 W Mean with glass (2 SD) 0.282991 26 0.282999 11 RGM-1 #19f 0.283038 5 0.283015 021 D RGM-1 #19 0.283029 4 0.283007 021 D RGM-1 #19 0.283037 4 0.283020 021 D RGM-1 #19 0.283036 4 0.283018 021 D RGM-1 #19f 0.283040 5 0.283024 021 D Mean with Teflon1 (2 SD) 0.283036 8 0.283017 13 Granite G-2 G-2 #3 0.282514 14 0.282531 021 D G-2 #4 0.282530 10 0.282523 015 W G-2 #3 0.282505 5 0.282522 021 D G-2 #6f 0.282516 5 0.282520 021 D Mean with glass (2 SD) 0.282516 21 0.282524 9 G-2 #10f 0.282514 5 0.282521 021 D G-2 #18f 0.282536 3 0.282522 021 D G-2 #19f 0.282544 5 0.282528 021 D G-2 #19f 0.282537 5 0.282520 021 D G-2 #26f 0.282530 8 0.282523 021 D G-2 #29f 0.282508 4 0.282520 021 D G-2 #31f 0.282535 6 0.282523 021 D Mean with Teflon1 (2 SD) 0.282529 26 0.282523 6 G-3 G-3 #3 0.282500 6 0.282517 021 D G-3 #4 0.282506 10 0.282498 015 W G-3 #3 0.282488 5 0.282505 021 D G-3 #4 0.282501 9 0.282493 015 W G-3 #6f 0.282509 5 0.282517 021 D G-3 #12f 0.282507 5 0.282498 021 D Mean with glass (2 SD) 0.282502 15 0.282505 20 G-3 #19f 0.282535 4 0.282518 021 D G-3 #19f 0.282538 3 0.282518 021 D Mean with Teflon1 (2 SD) 0.282536 5 0.282518 1 Granodiorite GSP-2 GSP-2 #3 0.282040 8 0.282057 021 D GSP-2 #4 0.282054 15 0.282047 015 W GSP-2 #3 0.282026 5 0.282042 021 D GSP-2 #4 0.282070 47 0.282062 015 W GSP-2 #6f 0.282072 4 0.282076 021 D GSP-2 #6f 0.282068 6 0.282072 021 D Mean with glass (2 SD) 0.282055 38 0.282059 27 GSP-2 #19f 0.281965 4 0.281946 021 D GSP-2 #19f 0.281972 4 0.281954 021 D GSP-2 #31f 0.281960 4 0.281948 021 D Mean with Teflon1 (2 SD) 0.281966 12 0.281949 8 aThe number corresponds to a day of analysis of USGS reference material on the MC-ICP-MS in a sequence (#1–31), ranging from 21 July 2004 to 18 January 2007. bThe 2s error is the absolute error value of the individual sample analysis (internal error) and reported as times 106. cMeasured ratio normalized to JMC475 176Hf/177Hf = 0.282160 (based on the mean of the day of analysis). dThe 2SD is the 2 standard deviation on the average of the replicate analyses (external error), also reported as times 106. eD, dry plasma analysis, with DSN Nu desolvator; W, wet plasma. fHigh-pressure PTFE digestion bomb. Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 7 of 15plots. We would emphasize that these differences are extremely subtle and within analytical error. 2.3. Trace Element Concentrations and Sr, Nd, and Hf Isotopic Compositions of the Labware Material [17] The labware material, including borosilicate glass, glass frit material and quartz from the columns (0.19 g, 0.035 g and 0.26–0.52 g, respectively) was dissolved in 1 mL of concentrated HNO3 and 10 mL of concentrated HF, both puri- fied by sub-boiling distillation. After evaporation, 3 mL of 6 N HCl, also purified by sub-boiling distillation, were added, from which a small ali- quant (10%) was taken to measure the trace ele- ment concentrations by ICP-MS following the procedure described by Pretorius et al. [2006]. Sr and Nd isotopic compositions were measured according to the PCIGR standard procedure as described by Weis et al. [2006]. 3. Results and Discussion [18] Hf isotopic results for the USGS reference materials are reported in Table 1, trace element concentrations of labware material in Table 3, and Sr, Nd and Hf isotopic compositions of labware material in Table 4. [19] Early in the study, Hf isotopic compositions for USGS reference materials were obtained with a precision better than 96 ppm (2 SD [n = 2 to 9]). The chemical separation of Hf from these samples involved a primary column made of Pyrex1 (i.e., borosilicate glass), used in the past because of its resistance to chemical attack and to its reduced thermal expansion, and because it can be worked at lower temperatures (1300C) than quartz (2300C). These were available in-house. Al- though acceptable, this precision was significantly worse than what we achieved for the other isotopic systems (30 ppm for 87Sr/86Sr and 143Nd/144Nd [Weis et al., 2006]) and the associated errors were significantly larger by a factor 5 or 6 than the in- run errors (2 SE) (Table 1 and Figures 1 and 2). [20] We then repeated the chemical separations on new custom-made Teflon1 columns for the first Hf column. The reproducibility of the Hf isotopic compositions for all USGS reference materials was significantly better with a standard deviation reduced to <46 ppm (2 SD [n = 2 to 10]) (Table 1 and Figures 1 and 2). The Teflon1-processed reference materials have systematically higher Hf isotopic compositions than the glass-processedTa bl e 2. H fM as s Fr ac tio na tio n B eh av io ro fJ M C- 47 5 St an da rd So lu tio n an d U SG S Sa m pl es 17 4 H f/1 77 H fa 17 6 H f/1 77 H fa 17 8 H f/1 77 H fa 18 0 H f/1 77 H fa N um be ro f A na ly se s Ln -L n Sl op es 17 8 H f/1 77 H fV er su s 17 9 H f/1 77 H fb In te rc ep t Co rre la tio n Co ef fic ie nt Ln -L n Sl op es 18 0 H f/1 77 H fV er su s 17 9 H f/1 77 H fb In te rc ep t Co rre la tio n Co ef fic ie nt JM C 47 5 0. 00 86 53 0. 28 21 63 1. 46 73 17 1. 88 68 78 61 6 1. 94 61 1. 05 70 0. 99 85 2. 93 42 0. 48 96 0. 99 89 0. 00 00 08 0. 00 00 21 0. 00 00 96 0. 00 01 37 90 9 75 65 72 A ll U SG S 0. 00 86 54 1. 46 73 59 1. 88 69 25 11 8 1. 94 19 1. 05 54 0. 99 74 2. 91 85 0. 48 35 0. 99 86 0. 00 00 09 0. 00 00 85 0. 00 01 67 10 96 58 88 M af ic co m po sit io ns 0. 00 86 54 1. 46 73 51 1. 88 68 95 74 1. 95 99 1. 06 25 0. 99 84 2. 93 06 0. 48 83 0. 99 88 0. 00 00 09 0. 00 00 74 0. 00 01 27 10 62 50 68 Fe lsi c co m po sit io ns 0. 00 86 55 1. 46 73 72 1. 88 69 77 44 1. 86 53 1. 02 52 0. 99 43 2. 84 83 0. 45 59 0. 99 81 0. 00 00 10 0. 00 00 97 0. 00 01 76 11 44 66 93 a Th e fir st n u m be r co rr es po nd s to th e av er ag e o ft he ra tio s; th e se co n d n u m be r co rr es po nd s to 2 st an da rd de vi at io ns ;a n d th e th ird n u m be r co rr es po nd s to th e re la tiv e st an da rd de vi ati on in pp m . b Ex po ne nt ia lm as s fra ct io na tio n la w fo r1 78 H f/1 77 H f-1 79 H f/1 77 H fc o rr es po nd s to 1. 99 60 an d fo r1 80 H f/1 77 H f-1 79 H f/1 77 H fc o rr es po nd s to 2. 98 51 ,w hi le th e po w er la w co rr es po nd s to 2. 00 16 an d 3. 00 19 , re sp ec tiv el y. Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 8 of 15Table 3. Trace Element Concentrations of Labware Material Determined by HR-ICP-MSa Element Borosilicate A (Short) Borosilicate A (Long) Quartz (Small) Quartz (Large) Fritb (Small) Fritb (Large) Li 2.54 3.03 0.97 2.62 9.72 12.88 V 0.577 0.615 0.013 0.010 1.51 1.67 Co 0.147 0.164 0.011 0.050 1.57 1.10 Ni 1.00 1.07 0.047 0.122 28.57 13.26 Cu 0.89 1.03 0.016 0.057 16.15 4.83 Zn 2.21 2.75 0.36 1.13 96.74 52.78 Ga 2.74 2.82 0.002 0.006 2.32 3.28 Rb 2.39 2.51 0.022 0.083 1.42 6.09 Nb 0.44 0.28 <lodc 0.013 1.21 1.14 Mo <lod <lod 2.89 2.58 <lod <lod Cd 0.040 0.036 0.001 0.006 0.64 0.77 Sn 0.170 0.105 <lod 0.034 15.34 7.40 Sb 0.89 0.86 <lod <lod 1.91 11.66 Cs 0.093 0.081 0.002 0.006 0.29 1.32 Hf 16.33 16.78 0.097 0.28 9.59 22.60 Ta 0.36 0.12 <lod <lod 0.086 0.108 W <lod <lod 1.11 2.45 <lod 0.043 Bi 0.065 0.005 <lod 0.014 0.44 0.033 Th 0.66 0.63 0.45 1.06 1.37 0.86 Sr 8.04 8.03 0.03 0.077 6.17 15.97 Zr 604.39 609.54 1.96 4.62 361.43 912.30 Ba 22.48 22.59 0.05 0.13 33.70 145.47 Pb 1.38 1.44 0.48 0.44 12.04 14.41 U 1.22 1.25 0.67 0.58 1.05 1.46 Sc 0.17 0.16 <lod 0.001 0.41 0.58 Y 1.53 1.50 1.26 0.60 3.83 3.73 La 1.11 1.09 0.10 0.06 3.60 2.17 Ce 2.00 2.01 0.20 0.11 23.01 5.10 Pr 0.24 0.24 0.03 0.014 0.76 0.46 Nd 0.82 0.82 0.12 0.069 2.88 22.78 Sm 0.14 0.13 0.064 0.03 0.46 0.27 Eu 0.025 0.030 0.004 0.001 0.056 0.066 Gd 0.12 0.13 0.16 0.08 0.44 0.28 Tb 0.025 0.022 0.037 0.02 0.074 0.06 Dy 0.18 0.20 0.22 0.10 0.51 0.43 Ho 0.052 0.049 0.034 0.017 0.12 0.13 Er 0.20 0.20 0.075 0.033 0.50 23.24 Tm 0.038 0.036 0.008 0.003 0.069 0.09 Yb 0.29 0.30 0.043 0.022 0.52 0.63 Lu 0.059 0.063 0.006 0.003 0.09 0.13 aTrace element concentrations are in ppm. bFrit also made of borosilicate. c <lod, below limit of detection. Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 9 of 15Table 4. Isotopic Compositions of Labware Material Material 176Hf/177Hfa 2sb 143Nd/144Ndc 2sb 87Sr/86Srd 2sb Borosilicate A (short) 0.282196 5 0.511364 9 0.722688 12 Borosilicate A (long) 0.282199 4 0.511381 9 0.722808 9 Quartz (small) 0.512606 72e Quartz (large) 0.512646 14 0.713162 36 Frit borosilicate (small) 0.512099 14 Frit borosilicate (large) 0.281935 43 0.512250 7 0.715203 12 aMeasured ratio normalized to JMC475 176Hf/177Hf = 0.282160 (based on the mean of the day of analysis on the MC-ICP-MS). bThe 2s error is the absolute error value of the individual sample analysis (internal error) and reported as times 106. cMeasured ratio normalized to La Jolla 143Nd/144Nd = 0.511858 (based on the mean of the day of analysis on the MC-ICP-MS). dMeasured ratio normalized to SRM 987 87Sr/86Sr = 0.710248 (based on the mean of the wheel on the TIMS). eThis value is only given for information; it is not reported in the figures because of its large error. w Figure 1. Individual 176Hf/177Hf analyses of BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1, and BCR-2. The dark blue symbols represent the first-generation USGS reference materials (BHVO-1, AGV-1, and BCR-1), and the light blue symbols represent the second-generation materials (BHVO-2, AGV-2, and BCR-2). The diamond symbols indicate samples processed through glass columns (left part of each individual diagram), and the square symbols are for those processed through Teflon1 columns (right part of each diagram). The mean and 2 standard deviations of replicate analyses for both generations of reference materials are shown to the right of each respective series (yellow- filled diamonds for samples processed through glass and yellow-filled squares for those processed through Teflon1 columns). For individual analyses, the error bar corresponds to the 2 sigma error on the measured isotopic ratio. Literature data are reported for comparison (see references in figure). Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 10 of 15reference materials, except for GSP-2. The absolute difference varies between 0.000021 and 0.000045 for the volcanic mafic-intermediate materials (BHVO-1, BHVO-2, AGV-1, AGV-2, BCR-1 and BCR-2) and for RGM-1. All of these reference materials have 176Hf/177Hf above 0.282870. Only GSP-2, the granodiorite reference material, with a distinctly lower 176Hf/177Hf value of 0.281950, shows a difference in the opposite direction, which is also significantly larger (D = 0.000110). For felsic compositions, i.e., for rocks that have dis- tinctly higher Hf concentrations such as G-2, G-3, STM-1 and STM-2, the difference is within ana- lytical error. [21] The significantly improved precision of the Hf isotopic compositions of the USGS reference mate- rials processed through Teflon1 primary columns reflects the inert nature of this material and brings the reproducibility of Hf isotopic measurements to a similar level to that achieved for Sr and Nd isotopic compositions [Weis et al., 2006]. The homogeneity of these materials in Hf is confirmed, in agreement with the observations made for Sr and Nd isotopic compositions. First- and second-gen- eration powders of reference materials of BHVO, AGV and BCR (relative difference <15 ppm, Figure 1), and of G-2 and G-3 and STM-1 and STM-2 (relative difference <17 ppm, Figure 2) show no difference in Hf isotopic compositions. [22] To document the process of Hf contamination by the glassware and to understand how it can happen, we analyzed the trace element concentra- tions (Table 3) and the isotopic composition (Table 4) of various labware when possible. The borosilicate glass is the most enriched in Hf (16 ppm) and Zr (600 ppm) and is relatively homogeneous (very little variation between the analyses of two differ- ent glasses). The column frits, also made of boro- silicate glass but from another source, show higher trace element concentrations and much larger var- iations (Zr: 361–912 ppm; Hf: 9.6–22.6 ppm; Ce: 23.0–5.1 ppm; Nd: 2.9–22.8 ppm; Pb: 12.0– Figure 2. Individual 176Hf/177Hf analyses of G-2, G-3, RGM-1, GSP-2, STM-1, and STM-2. Literature data and symbols as indicated for Figure 1. Note the much larger variations for GSP-2 (see text for discussion). Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 11 of 15Figure 3. 176Hf/177Hf versus 143Nd/144Nd for USGS reference materials (Nd isotopic ratios from Weis et al. [2006]) compared to the values obtained for some of the borosilicate glassware. The inset in the upper left shows an enlargement of the radiogenic part of the diagram to highlight the differences between glass- and Teflon1-processed samples. Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 12 of 1514.4 ppm, etc.) that are not always correlated (e.g., Ce and Nd, Table 2). Finally, the quartz columns show very low trace element concentrations, all below 1 ppm, except for Li, Zn, Mo, W and Zr (maximum is 4.6 ppm). Only HCl (1.5 N and 2.5 N) is used to collect Hf on the first column and this cannot explain the dissolution of the column lead- ing to sample contamination, especially as the column blanks do not appear to be affected by this process. Although difficult to prove, the only explanation we have is a very subtle dissolution of the column by remnant HF present in the sample itself after its digestion. The reactive surface area of the frit is so important that a very small amount of HF is sufficient to dissolve enough of this material that has the highest Hf concentration. [23] Comparison of the Hf and Nd isotopic com- positions for USGS reference materials and the labware materials is reported in Figure 3. The larger scale inset shows the more radiogenic mate- rials to illustrate the Hf isotopic differences be- tween Teflon1- and glass-processed reference materials. There is no significant difference in Nd isotopic compositions. Both the borosilicate col- umn materials and the frit have significantly less radiogenic Hf (and Nd) isotopic compositions than the USGS reference materials (except GSP-2). [24] Comparison of the trace element concentra- tions of USGS reference materials [Pretorius et al., 2006; 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, 2007 (hereinafter re- ferred to as Pretorius et al., manuscript in prepara- tion, 2007)] with those of the glassware (Figure 4) shows that the amount of Nd present in the glassware is significantly lower than in the samples (Nd concentration ratio varying between 8 to >100), whereas for Hf the borosilicate glasses and the frits have distinctly higher concentrations than all USGS reference materials, except STM-2 (Figure 5). This easily accounts for the fact that there is no difference in Nd isotopic compositions between the USGS reference materials processed through glass columns or through Teflon1 col- umns. Among the REE, only Lu is more enriched in the frit materials than in some reference materi- als. For other elements, such as Ni, Cu and Cd, the frits show the highest concentrations. [25] Nd will be much less sensitive to contamina- tion from the glassware than Hf, taking into account the relative Hf and Nd elemental concen- trations between sample and glassware and the isotopic compositions and amount (100–150 mg) of USGS reference material processed through the column. It is also clear that for Hf isotopic analy- ses, GSP-2, G-2 and G-3 will be much less sensitive to this source of contamination than the volcanic reference materials that have much higher 176Hf/177Hf. For the mafic volcanic reference mate- rials, the difference in isotopic composition between glass and Teflon1 processed samples corresponds to the release of only 3 ng of Hf from the glassware into the sample solution. 4. Conclusions [26] Our study provides the first systematic Hf isotopic characterization of a broad compositional range of USGS reference materials (n = 12). Reproducibility for 176Hf/177Hf is around 30 ppm for the mafic compositions and consistently better than 50 ppm. Our study confirms that with the increased sensitivity of MC-ICP-MS analyses and with the ability to analyze samples with lower Hf concentrations, contamination by labware material can become a potential issue and the use of PTFE- Teflon1 (or quartz) is clearly necessary to avoid this problem. There is no difference in Hf isotopic Figure 4. Rare earth element concentrations (normal- ized to C1 chondrite) for labware material and for four USGS reference materials: BCR-1, RGM-1, G-2, and STM-2 [Pretorius et al., 2006; Pretorius et al., manu- script in preparation, 2007]. The comparison shows that the rare earth element concentrations are at least 10 to >250 times higher in the USGS reference materials than in the labware, except for the heavy rare earth elements in G-2. C1 chondrite-normalizing values fromMcDonough and Sun [1995]. Geochemistry Geophysics Geosystems G3 weis et al.: usgs reference materials 10.1029/2006GC001473 13 of 15compositions between the first and second gener- ations of USGS reference materials analyzed in this study. The isotopic ratios in Table 1 for the samples processed on Teflon1 columns can be used as recommended 176Hf/177Hf reference values. Acknowledgments [27] Funding for this study is from an NSERC Discovery Grant to Weis. Our thanks go to Brian Mahoney for initiating the study of the USGS reference materials and to John Patchett for making his JMC-475 Hf standard solution available. 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. Many thanks to James Scoates for his careful reviews of the manuscript. TheG-Cubed editor, Vincent Salters, and John Patchett and Graham Pearson are thanked for their careful and constructive reviews of the manuscript. References Albare`de, F., and B. Beard (2004), Analytical methods for non-traditional isotopes, Rev. Mineral. Geochem., 55, 113– 152. 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, Geo- chim. Cosmochim. Acta, 68, 2725–2744. Figure 5. Generalized trace element concentration plot (normalized to primitive mantle [McDonough and Sun, 1995]) for labware material and comparison with four USGS reference materials [Pretorius et al., 2006; Pretorius et al., manuscript in preparation, 2007]. 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