1966 Volume 56 Issue 2 Pages 41-55
K-A dating on about 60 granitic samples from the area between Osima Peninsula in Hokkaido to Fossa Magna in Middle Honshu, (dating ages of the Kitakami and Abukuma Massif were already reported), were carried out. As a result, the granitic activities of these districts were classified into the following five periods:
1) Later stage of the lower Cretaceous
2) Early stage of the upper Cretaceous
3) Later Cretaceous_??_early Tertiary
4) Miocene of the Tertiary
5) Later Miocene to the Pliocene
Former three periods' granitic rocks of the Cretaceous to the older Tertiary ages, intrude in echelon form of NNW direction from east to west, i.e. 120×106 years' granites invade in outer side, 90×106 years' in middle and 60×106 years' emplaced inner side as seen in Figure 1.