Detrital Zircon U-Pb Geochronology and Hf Isotope Geochemistry of the Hayang Group, SE Korea and the Himenoura and Goshoura Groups, SW Japan: Signs of Subduction-Related Magmatism after a Long Resting Period

摘要

There was a hiatus in magmatism in Korea and Japan, located on the eastern continental margin of Asia, during a period of about 40 Ma from 160 Ma to 120 Ma. The cause of the resumption of magmatism since then is not yet well understood. In this study, we analyzed the Hf isotope composition of detrital zircons in the Cretaceous sediments of Korea (Hayang Group) and Japan (Goshoura and Himenoura groups) to investigate the tectonic evolution of eastern Asia in the Early Cretaceous period. εHf(t) in Cretaceous zircons from Japanese samples values from +8.2 to +0.1, suggesting that magmatism was sourced from the depleted juvenile materials, which is compatible with ridge subduction and subsequent melting of the young oceanic crust. εHf(t) values from Cretaceous zircons in the Hayang Group are negative, except for the Jindong Formation, which had a sediment supply from Japan, indicating that the old continental crust material of the Korean Peninsula was included in the magma generation. The detrital zircons of this study exhibit a depleted isotopic character at the beginning of subduction-related magmatism in Permian and Early Cretaceous, and then gradually change to a more enriched composition. This trend may be a typical example of the Pacific-type orogenic cycle.