Lithium isotope composition of basalt glass reference material

We present data on the lithium isotope compositions of glass reference materials from the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) determined by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). Our data on the USGS basaltic glass standards agree within 2 parts per thousand, independent of the sample matrix or Li concentration. For SIMS analysis, we propose use of the USGS glasses GSD-1G (delta Li-7 31.14 +/- 0.8 parts per thousand, 2 sigma) and BCR-2G (delta Li-7 4.08 +/- 1.0 parts per thousand, 2 sigma) as suitable standards that cover a wide range of 11 isotope compositions. lithium isotope measurements on the silica-rich NIST 600 glass series by MC-ICPMS and TIMS agree within 0.8 parts per thousand, but SIMS analyses show systematic isotopic differences. Our results suggest that SIMS U isotope analyses have a significant matrix bias in high-silica materials. Our data are intended to serve as a reference for both microanalytical and bulk analytical techniques and to improve comparisons between U isotope data produced by different methodologies.