Hf isotope compositions of U.S. Geological Survey reference materials

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 176 Hf/ 177 Hf 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 176 Hf/ 177 Hf 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 176 Hf/ 177 Hf. Trace element and isotopic characterization of the borosilicate glass column, borosilicate frits, and quartz columns reveals extremely variable levels of trace elements. The 176 Hf/ 177 Hf 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 176 Hf/ 177 Hf 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 176 Hf/ 177 Hf data can only be acquired if samples are processed using all PTFE Teflon® labware, or quartz and polypropylene.