Detrital zircon U-Pb ages of the Cretaceous Akaishi Group in the Shimanto Belt, Akaishi Mountains

Abstract

We conducted U-Pb dating of detrital zircons from three sandstones of the central section of the Akaishi Group, which is part of the Shimanto Belt in the Akaishi Mountains. The youngest single-grain ages are 113.6±2.3 Ma (1σ), 114.1±1.6 Ma (1σ), and 100.8±1.2 Ma (1σ) from west to east. The weighted mean ages of the youngest clusters are 115.4±1.4 Ma (1σ), 125.8±1.6 Ma (1σ), and 107.5±1.5 Ma (1σ). These results indicate that the central part of the Akaishi Group was deposited after the Aptian or Albian (Early Cretaceous). The zircon ages are slightly older than the radiolarian ages (Albian to Cenomanian), but the two sets of ages are consistent.