Chemical composition and CHIME dating of monazite from Shiraishiyama, Kobe, Kyotango, Kyoto Prefecture, Japan

Monazite crystals from a pegmatite within the Miyazu Granite, located at Shiraishiyama, Kobe, Kyotango, Kyoto Prefecture, Japan, were analyzed for U, Th, Pb, and rare earth element (REE) concentrations using electron microprobe analysis. Back-scattered electron imaging revealed both oscillatory and sector zoning within the monazite. The crystals exhibit a solid solution between monazite and huttonite components, with a maximum ThO2 content of 30.81 wt%. The empirical formula of the Th-richest composition is (Ce0.336La0.151Nd0.098Y0.041Pr0.033Sm0.016Gd0.008Dy0.004Er0.002Th0.309U0.009Ca0.003)Σ1.010 (P0.660Si0.338)Σ0.998O4. The observed compositional variations suggest that the (Th + U) content is primarily controlled by the coupled substitution (Th, U) + Si = REE + P. The CHIME age of the monazite grains is 61 ± 7 Ma (2σ), which is consistent with previously reported radiometric ages of the Miyazu Granite.