[S-GL22] Geochronology and Isotope Geology

[SGL22-02] Sub-millimeter scale helium measurement for MORB glass

*Hidenori Kumagai¹, Keiko Sato^2,1,3, Ieyoshi Shimizu¹ (1.Japan Agency for Marine-Earth Science and Technology, 2.National Institute of Technology, Fukushima College, 3.Okayama, Univ. of Science)

Keywords:Laser probe, MORB glass, Helium isotope ratio

Regardless of the recent extensive effort to reduce the contamination/interference of the atmospheric component at the noble gas analyses (e.g. Moreira et al., 2018), such contamination/interference of the atmospheric component were still commonly reported in the upper-mantle-derived samples. On the other hand, the authors have reported a preliminary single-grain helium isotope analysis for an olivine taken from an alkaline lava fragment sampled from low 3He/4He super-segment of Southwest Indian Ridge (Kumagai et al., Goldschmidt Conference, 2008). In the experiment, analytical uncertainty was not small mainly due to the more than 10% contribution of blank correction.


We will report in the presentation, our recent trials for MORB glass shards with sub-millimeter spatial resolution using an infrared laser probe; assembled by Marubun Co. using SDL-IFL-15 (JDF uniphase co.) of which wavelength is 1110nm and 0.2 mm of focusing diameter in ×5 optical magnification. In a preliminary trial, the MORB glass shard with thick color was immediately melted within 0.5 seconds with 2W power of the output. The released amount of He was sufficient to be detected by an old-generation noble gas mass spectrometer GVI5400He under 400μA trap current condition; approx. 0.5mV output were recorded. The reduced volume of the extraction volume and mass spectrometer were also contributed to this output. Accumulated data set will be further reported.