Characteristics of Crataceous-Paleogene granitoids from northern part of Northeast Honshu

Abstract

There are many Cretaceous-Paleogene granitoid masses distribute in the Shirakami and Taiheizan. Each emplasement ages are 86-92 Ma with the Shirakami granitoids and 85-97 Ma Taihei granitoids by Rb-Sr whole rock isochron and K-Ar mineral method. The Kitakami granitoids indicate same radiometric ages 100-135 Ma by each method, but the Abukuma granitoids show 125-100 Ma Rb-Sr to 120-110, 105-95 Ma hornblende K-Ar and 95-90 Ma biotite K-Ar ages. On the initial ratio about the Sr, Nd isotopes, the Shirakami and the Taihei granitoids space in the North-zone (Kagami et al., 2000) and correlatable to the Abukuma granitoids.