In situ analyses of hydrogen and sulfur isotope ratios in basaltic glass using SIMS

Abstract

We developed in situ analyses of hydrogen and sulfur isotope ratios of basaltic glass using high-resolution, multi-collection secondary ion mass spectrometry (CAMECA IMS-1280HR). Hydrogen and sulfur isotopes of standard basaltic glasses were determined by a high-temperature conversion elemental analyzer/isotope ratio mass spectrometer (IRMS) and IRMS, respectively. For the in situ analysis of sulfur isotopes, a defocused Cs beam (~0.5 nA; ~10 μm diameter) was used, but for hydrogen isotopes, we used a larger defocused beam (~5 nA; ~15 μm diameter) to decrease the hydrogen background. For analyses of D/H (³⁴S/³²S) ratios, ¹⁶OH (³²S) and ¹⁶OD (³⁴S) were measured in multi-detection mode with a Faraday cup and an axial electron multiplier, respectively. Each measurement time was 6–7 minutes. Precisions (2 standard errors) for D/H and ³⁴S/³²S ratios were ~6‰ (H₂O > 1 wt%) and ~0.6‰ (S > 1000 ppm), respectively. Our developed method for rapid and high spatial resolution analysis can determine multiple elements and isotopes of volatiles in a single small melt inclusion of ~30 μm diameter. Using this method, we analyzed hydrogen and sulfur isotope ratios of submarine basaltic glasses from mid-oceanic ridges and oceanic islands of Hawaii and confirmed that their D/H and S isotope ratios were consistent with reported values.