抄録
In the Kitakami-massif of north-eastern Japan, there develope many granitic masses, and they have been grouped into two types from their geological relation, i.e. older type of pre-Cretaceous and younger type of Cretaceous age. From these 23 rock masses, 52 samples were collected for K-A dating experiment. As a result, it is ascertained that the granitic rocks of older type would have emplaced more than 222×106 years ago at least, though the value does not show the true age, because of the thermal effect of younger granitic intrusion. On the other hand, it is clarified that most of the younger granitic rocks intruded 120×106 years ago, though some of them show the ages of 128×106 years and 106×106 years.
In conclusion, the underground structure of the Kitakami-massif is considered to be composed of one granitic batholith.
