New natural and fused quartz reference materials for oxygen isotope microanalysis

Abstract

Silicon dioxide (SiO2) occurs as both crystallized quartz and amorphous quartz, and their oxygen isotope is widely used to trace the source of hydrothermal fluids, to reconstruct paleotemperature of oceans and to provide genetic constraints on petrogenetic studies. Precise and accurate oxygen isotope analysis, therefore, is fundamental for the application of oxygen isotope study. Secondary Ion Mass Spectrometry (SIMS) is capable of obtaining oxygen isotope information at micron levels, but precise and accurate SIMS isotopic microanalysis requires high quality reference materials to correct instrumental mass fractionation and to monitor data quality. In this study, we report two reference materials, a natural crystallized quartz (Qinghu-Qtz) from Qinghu quartz monzonite (Guangdong, P.R. China) and a fused amorphous quartz (Glass-Qtz). Multiple SIMS analyses suggest that both Qinghu-Qtz and Glass-Qtz are homogeneous in terms of oxygen isotope composition at ca. 20 µm level, with a two-standard deviation of 0.50 ‰ (N = 1083) and 0.22 ‰ (N = 283), respectively. In comparison, the widely utilized NBS-28 quartz reference material, designed for bulk analysis, is less homogeneous at micro levels. The δ18OVSMOW values of the two reference materials were obtained by conventional fluorination isotope ratio mass spectrometry (IRMS) and the recommended δ18OVSMOW values were 8.49 ± 0.20 ‰ (Qinghu-Qtz, 2 SD, N = 12) and 1.68 ± 0.08 ‰ (Glass-Qtz, 2 SD, N = 10).