Zircon U–Pb ages on plutonic rocks in the eastern area of 1:200,000 quadrangle, Toyama, central Japan

Abstract

With the revision of the Geological Map of Japan 1: 200,000 “Toyama”, zircon ²³⁸U–²⁰⁶Pb ages of pre-Paleogene plutonic rocks in the area were measured, and the igneous history in the Hida Belt was discussed. Of the Hida Older Granites, the intrusion age of the Hayatsukigawa Granite in the western area is 224.8 ± 1.7 Ma, and that of the Unazuki Granite and Funakawa Granite in the eastern area is 236.5 ± 3.1 Ma and 240.7 ± 4.1 Ma, respectively. The Hayatsukigawa Granite is an independent body from the adjacent augen mylonite, because its intrusion age is different from that (250–240 Ma) of the protolith of the augen mylonite. On the other hand, parts of the Otodani Gabbro and Unazuki Granite in the Geological Map of Japan 1:50,000 “Tomari” area show 195.6 ± 2.0 Ma and 192.0 ± 2.4 Ma, respectively, indicating the intrusion of Early Jurassic time. It was found that these should be classified as the Hida Younger Granites.