新潟県に分布する7枚の第四紀テフラのLA-ICP-MSによるジルコンU-Pb年代

抄録

Here, we report zircon uranium-lead (U-Pb) dating by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) to better constrain the eruption ages of seven widespread Quaternary tephras distributed across Niigata Prefecture, Japan. Two samples (HK10, Og) are from well-documented tephras in the literature, and the other five samples (Odaira, Yokokura, Kimigaeri, Oguriyama, Shimizu Pass) are from local districts in Niigata Prefecture. We applied three different U-Pb age calculations which yielded ages of 0.4-1.7 Ma for the samples. The U-Pb ages for the >0.5 Ma tephras are similar among the three methods, whereas a small discrepancy exists for the <0.5 Ma tephras. Our U-Pb ages are compared with previous age estimates in the literature, and five tephras (HK10, Og, Yokokura, Kimigaeri, Oguriyama) yield consistent ages between the present and previous studies. The ages of the other two tephras (Odaira, Shimizu Pass) differ from previous estimates, whose reasons are also mentioned.