Geochemical Journal, Vol. 53, 2019
Kenji Shimizu1*, Takayuki Ushikubo1, Tomokazu Murai2, Fumihiro Matsu'ura3, and Yuichiro Ueno2, 3
1Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Monobe-otsu 200, Nankoku City, Kochi 783-8502, Japan
2Department of Earth and Planetary Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku Tokyo 162-8551, Japan
3Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku Tokyo 162-8551, Japan
(Received October 22, 2018; Accepted March 22, 2019)
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.
Key words: hydrogen isotope, sulfur isotope, basaltic glass, secondary ion mass spectrometry, in situ analysis