Paleoproterozoic to Cenozoic zircon U–Pb ages with Hf signatures from metamorphic rocks and granodiorite of Tokunoshima: constraints on the geotectonic subdivision of the Ryukyu island arc, Southwest Japan

A groundbreaking study reveals that the Omo Formation on Tokunoshima Island, part of the Ryukyu island arc in Southwest Japan, shares geological origins with Cathaysia in the South China block. Using LA-ICP-MS U–Pb and Hf isotope analysis on zircons from metamorphic rocks and granodiorite, researchers identified Paleoproterozoic to Cenozoic age ranges, indicating Early Jurassic reworking of older continental crust. The positive εHf(t) values in Paleoproterozoic zircons (+12.7 to +0.8) contrasted with negative values in Jurassic zircons (−19.6 and −22.8), suggesting significant tectonic activity. Additionally, granodiorite zircon ages (61.3 ± 1.0 Ma) with positive εHf(t) values (+12.0 to +12.6) correlate with juvenile magmatic activity in the San-in batholith belt, hinting at a shared geological history across Southwest Japan.

Yamamoto, H., Okamoto, K., Chung, S.-L., Lee, H.-Y., Mita, Y., Ueda, S., & Terabayashi, M. (2020). Paleoproterozoic to Cenozoic zircon U–Pb ages with Hf signatures from metamorphic rocks and granodiorite of Tokunoshima: constraints on the geotectonic subdivision of the Ryukyu island arc, Southwest Japan. International Geology Review, 64(3), 425–440. https://doi.org/10.1080/00206814.2020.1858356