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

Abstract

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.