Oxygen isotope measurements of terrestrial silicates using a CO2-laser BrF5 fluorination technique and the slope of terrestrial fractionation line

摘要

Here we report oxygen isotopic compositions (both δ18O and δ17O) of San Carlos olivine, Juan de Fuca basalt glass, garnet standard at University of Wisconsin (UWG-2 garnet), National Bureau of standard #28 quartz (NBS-28 quartz), a hydrothermal quartz from China (CQ4 quartz), chert flint standard and a serpentine measured with a CO2-laser BrF5 fluorination system installed at Korea Polar Research Institute. In addition we measured VSMOW (Vienna standard mean ocean water) and SLAP (standard light Antarctic precipitation) with the same line; a scaling factor of 1.056 was obtained to fit the measured SLAP data to the recommended value of δ18OSMOW = −55.5‰. All the other data were corrected using the VSMOW-SLAP scaling factor. Majority of the samples in this work have been measured by several laboratories; our data in general agree very well with previous data. We report data using the delta prime notation, since linearity of a mass-dependent fractionation line holds in δ′17O vs. δ′18O diagram for wide range of oxygen isotopic compositions. Average δ′18O values and 2σ standard error of means are 5.27 ± 0.04‰ for San Carlos olivine, 5.49 ± 0.02‰ for Juan de Fuca basalt glass, 5.73 ± 0.05‰ for UWG-2 garnet, 9.18 ± 0.08‰ for NBS-28 quartz, 23.14 ± 0.36‰ for CQ4 quartz, 33.97 ± 0.16‰ for chert flint standard and 0.78 ± 0.07‰ for the serpentine. Slope of terrestrial fractionation was obtained using these data, which is 0.5248 ± 0.0003 (R2 = 0.99992).