A Study of ITP-FT Dating Using Quaternary Obsidian and Glass Shards from Tephra.

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  • 第四紀の黒曜石・テフラ中水和ガラスを用いたＩＴＰ‐ＦＴ年代測定に関する基礎実験
  • ダイ4キ ノ コクヨウセキ テフラチュウ スイワ ガラス オ モチイタ ITP

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Isothermal Plateau Fission Track (ITP-FT) method was applied to samples of obsidians and glass shards from tephra-layers. This method uses one-step pre-annealing, which is combined with size-correction and plateau-correction techniques. An age is determined at a plateau phase. Plateau phases usually occur when induced and spontaneous mean track diameters are coincident, or when induced and spontaneous track density ratios are constant. In the ITP-FT method, plateau phases are determined based only on the coincidence of induced and spontaneous mean track diameters.<br>To improve on the ITP-FT method, it is necessary to estimate the reliability of plateaus obtained from the track diameter method by examining density ratios. In this study, 165°C annealing was carried out in order to reduce annealing time and categorize the relation between a track size coincidence “plateau” and a spontaneous/induced density ratio's constant “plateau”. The results indicate that the plateau phase determined by the coincidence of induced and spontaneous mean track diameters appears after the plateau phase determined by track density ratios. These co-plateau phases are appear after 5 days of annealing. As the result of this experiment, it is concluded that the coincidence of mean track diameters defines a more prominent and strict plateau phase than the track density ratio.<br>Based on the above results, it is suggested that 5 to 10 days annealing at 165°C is adequate to produce plateau stability and mean track diameter coincidence and is the most suitable condition when the ITP-FT method is applied.

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