Oxygen three-isotope ratios of silicate reference materials determined by direct comparison with VSMOW-oxygen

Abstract

The δ17O and δ18O values of some international silicate reference materials such as NBS-28 quartz, NBS-30 biotite, UWG2 garnet, San Carlos olivine and some mineral separates of terrestrial origin were re-evaluated on the VSMOW-SLAP scale using the CO2-laser fluorination technique. To report their δ 18O values on the VSMOW-SLAP scale, the δ 17O and δ18O values of O2 directly derived from VSMOW and SLAP were measured using the same preparation line as used for the silicates. Application of the VSMOW-SLAP scale to the above silicate reference samples resulted in the δ18O values of NBS-28 quartz, NBS-30 biotite, UWG2 garnet and San Carlos olivine that are 9.18, 4.88, 5.59 and 5.289‰, respectively. The data form a straight line in the 103 In(1 + δ167O/103) vs. 103 In(1 + δ18O/103) plot with a slope of 0.526 ± 0.003 (standard error at 95% confidence limit), but the line for the waters (VSMOW, GISP, SLAP and MSA-6) seems to have a slightly steeper slope of 0.528 ± 0.001, although difference of the slopes is not statistically significant. Copyright © 2008 by The Geochemical Society of Japan.