SHRIMP U-Pb age of zircon from the migmatite zone, Aoyama area, Ryoke metamorphic belt, Japan

Abstract

U-Pb dating and determination of REE pattern of zircon extracted from pelitic migmatite from the Aoyama area, Ryoke metamorphic belt have been done by SHRIMP. The result was 92.5 ± 0.5 Ma and 92.5 ± 0.7 Ma. Zircon includes several-μm-sized possibly melt inclusions between core and rim, and this part is dark in CL images. The REE pattern of zircon rim showed HREE-enriched pattern, suggesting non-equilibrium between garnet. The zircon rim also showed low Th/U ratio (<0.1) and LREE concentration, suggesting coexistence with monazite. This observation is consistent with the CHIME monazite age older than the zircon rim age.