U-Pb ages and Hf isotopic compositions of detrital zircons from the Seochangni Formation of the northeastern Okcheon Metamorphic Belt: Implications to the crustal evolution of the Sino-Korean craton since Paleoproterozoic

Abstract

The age-unknown Seochangni Formation is distributed in the northeastern part of the Okcheon Metamorphic Belt in central South Korea. It unconformably overlies the Paleoproterozoic Busan gneiss complex exposed as a small dome and is in contact with the Cambrian-Ordovician Joseon Supergroup of the Taebaeksan Basin to the east. We separated detrital zircons from the quartzite units of the Seochangni Formation and used SHRIMP and LA-MC-ICPMS to determine their UPb ages and Hf isotopic compositions. The UPb age distribution of the detrital zircons is divided into two types. In the main type, the ages of Late Paleoproterozoic to Mesoproterozoic are dominant, whereas they have little or no older age components of about 1.87Ga and 2.5Ga, which are characteristic of the Korean peninsula basement rocks. However, the minor type has age components of 0.75 Ga and 1.87 Ga. Age patterns similar to the former type have recently been reported in the western region of the Gyeonggi Massif on the Korean peninsula, as well as in the Sangwon System in North Korea and the southern margin of North China Craton. It suggests a correlation between them and a common crustal evolution within a single craton linked since the Paleoproterozoic. The high positive εHf(t) values of detrital zircons in the Late Paleoproterozoic to Mesoproterozoic period indicate an enhanced input of juvenile materials from the depleted mantle, reflecting the igneous activity associated with the breakup of the supercontinent Columbia.