フィッショントラック法による黒曜石の噴出年代とウラン濃度の測定-2-本州中部,伊豆諸島産出の黒曜石について

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Obsidian specimens from seven geologic localities among nine (Fig. 1) in Central Honshu and Izu Islands were submitted to dating assay. While the non-flake quality obsidian contains many bubbles, second phase particles, and string-like microlites that make the counting of spontaneous fission tracks difficult, the compact flake quality obsidian is easy to determine the time of its eruption.Wada-pass, Kirigamine, Hakone (Hatajuku, Ashinoyu), and Horaiji yield the flake quality obsidian. The time of eruption and the uranium content of obsidian specimens from these localities were measured as follows (Table 1):Fission Track Dates Uranium Contents(106yrs) (ppm by weight)Wada-pass 0.85 6.8Kirigamine Hakone 1.30 3.2Hatajuku Ashinoyu 0.12 0.6Horaiji 15.9 3.3These results show, when the system errors are taken into consideration, that four fission track dates and three uranium contents differ from each other. Accordingly, when obsidian materials from archaeological sites are measured of the time of eruption and the uranium content, it is likely that the geologic sources of these materials may be identified by comparing the results of materials with those of the geologic sources obtained so far.
日本第四紀学会の論文