抄録
Fission-track (FT) analysis of zircon was carried out for sandstones collected from the Otaki Group of the Cretaceous Shimanto accretionary complex in the Mitsumine district of the Kanto Mountains, central Japan. The results show the FT ages to be approximately 54 Ma and 59 Ma. Metamorphic conditions of the Otaki Group indicate temperarures in excess of 300°C, which exceeds the condition of partial annealing zone in zircon. Therefore, the above results suggest that the Otaki Group cooled below 260±50°C at around 54-59 Ma. The cooling age and metamorphism during the latest Cretaceous present a slow-cooling history of the Otaki Group with the cooling rate of ~3.6°C/Myr.
