K-Ar ages of granitic rocks in the northern marginal area of the Kanto Mountains

K-Ar age determinations were carried out for granitic rocks from the northern marginal areas of the Kanto Mountains; Shimonita, Kanezawa and Hiki Hills areas. The age data can be clearly divided into three groups: 250-290 Ma, 105-112 Ma, and 62-66 Ma. the Permian and Early Cretaceous granitic bodies constitute an isolated klippe (the so-called Atokura klippe) in the above three areas. Although the geologic situation of the Permian and Early Cretaceous granites in the tectonic framework of Japanese Islands cannot be specified, it is inferred that they are correlative to the granitic rocks in the Abukuma and/or southern Kitakami Belts, Northeast Japan. -from English summary