Zircon U-Pb ages of the Ryoke granitoids from the Takanawa Peninsula, northwest Shikoku, southwest Japan

摘要

We carried out zircon U-Pb dating of the Ryoke granitoids exposed in the Takanawa Peninsula to determine their magmatic ages. The granitoids are mainly comprised of tonalite, granodiorite, and granite. The new zircon U-Pb ages are: 93.68 ± 0.79 Ma for a tonalite sample, 88.90 ± 0.61 Ma for a granodiorite sample, and 98.8 ± 1.0 Ma, 96.29 ± 0.98 Ma, 96.0 ± 1.0 Ma, and 93.86 ± 0.93 for granite samples. The new zircon U-Pb ages suggest multiple intrusive episodes with granitoid magmas of variable compositions in the Takanawa Peninsula area during ~ 99-89 Ma. Contrary to previous geological studies that postulated a three-stage intrusive sequence starting with tonalite intrusion, followed by granodiorite, and culminating by granite intrusions, our results indicate that early magmatism in the study area was granitic in composition.