Timings of deposition and metamorphism of the "Sanbagawa Belt" in the Tenryu area, southwest Japan

Abstract

U-Pb ages of detrital zircons and white mica K-Ar ages are obtained from two psammitic schists from the Sanbagawa Belt, Tenryu area. The youngest zircon ages and white mica ages of the sample from Western Unit yield 94 and 70 Ma, respectively. On the othe hand, the ages of the sample from Eastern Unit yield 73 and 55 Ma, respectively. Western Unit had been already at the metamorphism stage when the Eastern Unit, was still at the depositional stage. The present results may induce the development of a model that a metamorphic belt is subdivided into some units formed at different stages. And "120 Ma metamorphic belt" is not identified in the Tenryu area.