Abstracts of Annual Meeting of the Geochemical Society of Japan

For the samples of Chinese juniper (Sabina Przewalskii) and Japanese cedar (Cryptomeria japonica), we compared the carbon isotope, carbon content and chemical composition of crude cellulose prepared by diglyme-HCl method with those of alpha-cellulose Our results suggest that the diglyme-HCl method, which appears to be a simple, fast method and safe method for isolating cellulose from tree-ring samples, is effective for isotope analysis of large-number and small samples.

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Osmium isotope is a sensitive tracer of crust and sediment as its eroding form, because of significant contrast between high Os isotope ratio of .crust and sediments and low ratio of mantle. Therefore, Os isotope provides information on contribution of slab component to the island arc lavas and assimilation of continental crust to the source magma during magma ascent. However, whether the frequently observed high Os isotope ratio of arc basalt is derived from slab component or from the overlying continental crust is highly debated. Here we report significantly high 187Os/188Os of Cr-spinel of Mukoo-jima, Izu-Bonin arc. As Cr-spinel is resistant to later alteration and weathering and is the early stage crystal in the fractional crystallization, it preserves the information of very primitive magma without any contamination of late stage crustal assimilation during magma ascent. Cr-spinel of Yome-shima and Chichi-jima island boninites yield low 187Os/188Os of 0.1232 and 0.1242, the lowest values among those of island arc rocks, whereas that of Mukoo-jima Island has extremely high 187Os/188Os of 0.1429. It strongly suggests contribution of the slab component into source magma of Mukoo-jima island and no possible slab component to the source magma of Chichi-jima and Yome-shima boninites.

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Li isotopic ratios of ocean island volcanic rocks from Logudoro, Sardinia were determined with MC-ICP-MS in order to constrain the Li isotopic composition of the EM1-typed mantle source. The Li isotopic compositions of samples from Logudoro represent slightly lighter (+1.5~3 permil) than that of fresh MORB (ca. +3~4 permil). These lowered Li isotopic ratios may be ascribed to the component of the recycled subducted-slab into the mantle source, which had been dehydrated during subduction process

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Active and dead chimney at Kairei field, and active chimney at Edmond field of Central IndianRidge were examined mineralogically in this study.

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