R6: Plutonic rocks, volcanic rocks and subduction factory

[R6-P-07] Sr–Nd–Hf isotopic systematics for the Habu granodiorite, eastern part of Yamaguchi Prefecture

*Masaaki OWADA¹, Yusaku Akimoto², Mariko Nagashima¹, Keisuke Eshima¹, Atsushi Kamei³, Nobuhisko Nakano⁴, Kenta Kawaguchi⁵, Yasuhito Osanai⁴ (1. Yamaguchi Univ., 2. YON-C, 3. Shimane Uni., 4. Kyushu Univ., 5. Hiroshima Univ.)

Keywords:Habu granodiorite, Magmatic processes, Source materials, Multi-isotopic systematics, Igneous activities Southwest Japan

We performed geological, petrographical, and geochemical investigations including Sr–Nd–Hf isotopic studies for the Habu granodiorite located in the eastern part of Yamaguchi Prefecture, and discussed its magmatic processes and source materials. The laccolithic Habu granodiorite consists mainly of the leucocratic biotite granodiorite (leucocratic facies) surrounded by the thin-skinned hornblende-biotite granodiorite (melanocratic facies). Zircon U–Pb dating gives ages of c. 105 Ma for both lithofacies. Although the whole-rock chemical data of both lithofacies make monotonous trends on some binary plots, the leucocratic facies are slightly affected by crustal contaminations, as evidenced by Sr–Nd isotopic features. Epsilon Hf isotopic model ages revealed that the Habu granodiorite would be derived from the mafic lower crust probably separated from the depleted mantle during the Mesoproterozoic time.