K-Ar dating on the metamorphic rocks in Japan II

The Hitachi metamorphic rocks in southern Abukuma plateau

Abstract

K-Ar dating on micas from twelve metamorphic rocks and one granitic rock in the Hitachi district, southern Abukuma plateau, were carried out. Measured ages of metamorphic rocks including so-called Tamadare and Nishidohira gneisses have a range from 101×10⁶ years to 120×10⁶ years. These obtained ages by K-Ar method are roughly correlated to the Middle Cretaceous. On the basis of K-Ar age determinations on metamorphic and granitic rocks, some considerations on the relation between them in the Abukuma plateau are briefly noted.