- 著者
- Kenji Shimizu Takayuki Ushikubo Takeshi Kuritani Naoto Hirano Shigeru Yamashita
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- pp.GJ22019, (Released:2022-11-22)
- 被引用文献数
- 1
Analyses of elemental abundances by secondary ion mass spectrometry (SIMS) require matrix-matched standard samples to account for the matrix effect on correction factors. This requirement makes it difficult to obtain accurate results for geological samples of variable chemistry. In this study, we prepared 39 volcanic glasses of foiditic, basaltic, basaltic andesitic, rhyolitic and pure SiO2 compositions, including synthetic samples and natural samples collected from the deep seafloor. The measured H2O contents of these samples were in the range 0.02–4.8 wt%. We showed that calibration curves (H2O content vs. 16OH−/30Si−SIMS ratio) differed according to the composition of the volcanic glasses. Our results demonstrated that for a particular 16OH/30SiSIMS ratio, water content could differ by up to a factor of five, depending on the composition of the volcanic glass. Although the correction factor (the slope of the calibration curve for water [H2O/(16OH−/30Si−)SIMS]) was weakly correlated with SiO2 content, we identified a stronger correlation with the molar weight (g mol−1, on a one-oxygen mole basis) of the silicate glasses. Our results suggest that modification of the correction factor for the matrix effect on SIMS-based H2O content of volcanic glasses according to their molar weights provides more accurate water contents of silicate glasses, regardless of their chemical composition and water content and without the need for a series of standard glasses of known water contents.
- 著者
- NAOTO HIRANO
- 出版者
- GEOCHEMICAL SOCIETY OF JAPAN
- 雑誌
- GEOCHEMICAL JOURNAL (ISSN:00167002)
- 巻号頁・発行日
- vol.45, no.2, pp.157-167, 2011-04-20 (Released:2013-11-01)
- 参考文献数
- 63
- 被引用文献数
- 1 43
One extremely young volcano (0.05–1 Ma) and other young volcanoes (1.8, 4.2, 6.0, and 8.5 Ma) composed of strongly alkaline magma were recently discovered on the abyssal plain of the Early Cretaceous (135 Ma) Pacific Plate. These volcanoes were dubbed “petit-spots”. The petit-spot volcanic province represents more than 8 Myr of activity over a large area (~600 km along the direction of plate motion), but with a relatively small volume of magma production, thus indicating a small supply of heat inconsistent with a hotspot. The low-flux petit-spot volcanoes may be related to the occurrence of a tensional field of lithosphere caused by plate flexure, with the ascending melt derived from a mantle source susceptible to partial melting. Rock samples from the young volcanoes are highly vesicular (up to 60%) despite high hydrostatic pressures at 6000 m water depth, indicating volatile-rich magmas. The depleted heavy rare earth elements and high radiometric isotopic ratios of noble gases indicate the magma was derived from upper mantle. Nevertheless, the low 143Nd/144Nd, high 87Sr/86Sr, low 206Pb/204Pb, and low 207Pb/204Pb ratios are similar to enriched or fertile compositions such as oceanic island basalts. These apparently conflicting data are explained by the extremely small degree of partial melting of recycled materials in the degassing mantle of the asthenosphere, probably with carbonate in the source. The petit-spot volcanoes, therefore, provide a unique window into the nature of the oceanic plate and underlying asthenosphere prior to subduction.