SHRIMP U-Pb dating of detrital zircons in paragneiss from Oki-Dogo Island, western Japan

抄録

We obtained the radiometric ages of detrital zircons from two samples of paragneiss from Oki-Dogo Island, Japan, from the ²³⁸U/²⁰⁶Pb ratio and isotopic composition of Pb determined using a Sensitive High-Resolution Ion MicroProbe (SHRIMP II). The zircons show two main age clusters around 2200 Ma and 1800 Ma, with some discordant ages. One zircon grain has a rim with a concordant age of 236 ± 3 Ma, which is consistent with the age of peak metamorphism in the Hida Metamorphic Belt. The modal proportions of zircon ages from Oki-Dogo Island are clearly different from those for paragneiss of the Hida Terrane. This indicates that the Oki Gneiss is derived from an Early Proterozoic rock and is different from the Hida Gneiss in terms of provenance and/or the depositional age of the parent sediment.