茨城県桜川市山ノ尾ペグマタイト産モナズ石の化学組成とU-Th-Pb化学的年代
論文ID: 230516
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論文ID: 230516
Monazite in a granite pegmatite from Yamanoo, Sakuragawa, Ibaraki Prefecture, Japan has been examined in terms of U, Th, Pb, and rare earth element (REE) chemistry by electron microprobe analysis. This pegmatite occurs as a lenticular vein in the Kabasan granitic body. Oscillatory and sector zoning were observed by back-scattered electron images. An averaged empirical formula was (Ce0.286Nd0.180Sm0.104La0.077Y0.069Pr0.041Gd0.069Dy0.020Er0.004Th0.069U0.011Ca0.052)Σ0.982 (P0.983Si0.027)Σ1.010O4. Compositional variations suggest that the (Th + U) contents are controlled mainly by the coupled substitution (Th, U) + Ca = 2REE. Calculated U-Th-Pb chemical ages based on the assumption that the initial Pb is negligible are 61 ± 11–69 ± 10 Ma (2σ) and consistent with previously reported radiometric ages for the Kabasan granitic body.
