Contrasting source domains for the Phanerozoic granitoids in South Korea revealed by zircon Hf isotopic signatures

Abstract

In situ zircon Hf isotopic analysis was conducted to investigate the characteristics of source materials responsible for generations of the Phanerozoic granitoids in South Korea. The Hf isotopic data compiled from the literature together with this study revealed two principal types of source materials governing the generation of the Permo-Triassic granitoids. One type corresponds to long-lasting, ancient lithospheric materials having highly negative eHf(t) values of –24.3 to –18.6 and is temporally equivalent to the Paleoproterozoic to Neoarchean basement rocks prevalent in South Korea. This type is a primary source material for the Triassic postorogenic granitoids in the Gyeonggi massif. The other type corresponds to juvenile materials accreted by Late Paleozoic continental arc magmatism. This relatively young crust occurs largely in and around the Gyeongsang basin. Systematic southeastward increase in eHf(t) values of both Permo-Triassic and Jurassic granitoids indicates enhanced contributions of juvenile materials toward the paleo-trench. Such a trend is best explained by the chemical mixing of two principal types of source. Northern limit of chemical interactions between ancient and juvenile components is inferred to lie along the central Okcheon belt during the Permo-Triassic. However, this boundary has shifted southeastward in Jurassic to be defined by the Sunchang–Yecheon shear zone, a part of the Honam Shear Zone. The arc-related juvenile crust was also a principal source for the Cretaceous-Paleogene granitoids in the Gyeongsang basin.