関東・中部地方に分布する第四紀テフラのフィッション・トラック年代 Fission Track Ages of Several Quaternary Tephras in Kanto and Chubu Regions, Central Japan
Many Quaternary tephra layers are well preserved in the Kanto and Chubu regions of central Japan. In the last 30 years, radiometric ages for some of these tephra layers were determined by various methods. However, previous fission track ages have been shown to be inaccurate by recent work. In this study, 19 Quaternary tephra layers were newly dated by fission track method with zircon crystals based on zeta calibration, as the I.U.G.S. recommended. The ages determined in the southwest area of the Kanto region, in ascending order of stratigraphy, are as follows : GoP<SUB>2</SUB> : 0.27±0.12 Ma, GoP<SUB>1</SUB> : 0.36±0.16 Ma, HBP : 0.43±0.09 Ma, HcP-1 : 0.64±0.23 Ma, HdP-2 0.40±0.17 Ma, Sa Bi : 0.64±0.06 Ma (error is1σ). Ages determined in the Boso Peninsula are as follows : Ks 5 : 0.39±0.20 Ma, Ku 1 : 0.70±0.25 Ma, Kd 10 : 1.20±0.30 Ma. In the Shinshu area of the Chubu region, eight Quaternary tephra layers were dated as follows : Iz-NY : 0.18±0.08 Ma, A<SUB>5</SUB>Pm : 0.31 ± 0.06 Ma, A<SUB>4</SUB>Pm : 0.41±0.07 Ma, A<SUB>3</SUB>Pm 0.39±0.07 Ma, A<SUB>2</SUB>Pm : 0.42±0.08 Ma, A<SUB>1</SUB>Pm : 0.47±0.08 Ma, Nashinoki Cl : 0.74 ±0.09 Ma, Misawa Cl : 0.66±0.09 Ma. The ages determined in the Takayama area of Chubu region are as follows Takayama Pumice : 0.43±0.07 Ma, Kamitakara pfl. : 0.55±0.07 Ma.