Rb-Sr whole-rock isochron age of the Nissho Toge granite complex, northern Hidaka Mountains, central Hokkaido, Japan

Abstract

We obtained a Rb-Sr whole-rock isochron age of 17.7±0.6 Ma from the Nissho Toge granite complex, which intruded the upper portion of a ∼20-km-thick crustal section exposed in the northern Hidaka Mountains, central Hokkaido, Japan. The initial 87Sr/86Sr ratio is 0.70422±0.00009. This age is similar to U-Pb zircon ages reported previously for the Pankenushi gabbro and Magarisawa tonalite (18.5±0.3 Ma and 18.7±0.5 Ma, respectively), which are both located in the lower portion of the crustal section examined in the present study. Our result suggests that almost all of the magmatic bodies in the crustal section were emplaced contemporaneously, during the Early Miocene.