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Geochemical Journal
Geochemical Journal An open access journal for geochemistry
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In situ analyses of hydrogen and sulfur isotope ratios in basaltic glass using SIMS

Kenji Shimizu, Takayuki Ushikubo, Tomokazu Murai, Fumihiro Matsu’ura, Yuichiro Ueno
Geochemical Journal, Vol. 53, No. 3, P. 195-207, 2019

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.

KEYWORDS

hydrogen isotope, sulfur isotope, basaltic glass, secondary ion mass spectrometry, in situ analysis

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