Late Permian CHIME ages of the Hida Gneiss and early Triassic age of the Mizunashi Granite in the Amo area of the Hida terrane, central Japan

Abstract

The CHIME (chemical Th-U-total Pb isochron method) dating of the Hida Gneiss, the Mizunashi Granite and a pegmatite vein have been carried out by precise microprobe analyses of monazite. The CHIME ages are 249±5 and 251±7 Ma for the Hida Gneiss, 237±6 Ma for the Mizunashi Granite and 180±3 Ma for the Pegmatite vein. There is no age signature older than ca. 250 Ma even in the center of monazite grains; monazite ages date the first attainment of Hida metamorphism to the grade of monazite formation, the amphibolite facies. The emplacement of the Mizunashi Granite at 237 Ma may correspond to the peak metamorphism of the Hida Gneiss. The pegmatite vein in the Mizunashi Granite can be correlated in age with the Jurassic Funatsu granitic rocks.