Episodes 2021; 44(4): 385-399
Published online December 1, 2021
Copyright © International Union of Geological Sciences.
by Chul Lim1, Chang Whan Oh1*, Duck K. Choi2, Youn-Joong Jeong3, and Amitava Chatterjee4
1Department of Earth and Environmental Sciences, Jeonbuk National University, South Korea
2School of Earth and Environmental Sciences, Seoul National University, South Korea
3Scientific instrumentation & management, Korea Basic Science Institute, South Korea
4Department of Earth Sciences, Indian Institute of Technology Bombay (IITB), India
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One of critical boundaries in Korea is the boundary between the Taebaeksan Basin and the Ogcheon metamorphic belt. We performed field mapping and geochronological/ geochemical analyses in the Jecheon-Maepo areas. In the Bonghwajae section, the “Yamisan unit” (761 ± 3 Ma) belonging to the Ogcheon Supergroup occurs eastward beyond previous limit of Ogcheon metamorphic belt. Farther east, the post-Cambrian “Soyari unit” of uncertain affinity occurs. The Soyari unit borders a typical sequence of Taebaeksan Basin to the east in Maepo. We suggest that the boundary between the Ogcheon metamorphic belt and the Taebaeksan Basin is more than 20 km wide zone. Occurrence of the “Danri window” shows that the Ogcheon Supergroup sequence overlies the Joseon Supergroup unit along a decollement in the Jecheon-Maepo areas. The decollements and NW- to NNW-trending structures resulted from NE- or ENE-directed shortening probably during the Songrim Orogeny (Indosinian). We consider two alternative models for the origin/structural relationship between the Taebaeksan Basin and the Ogcheon metamorphic belt. In one plate model, the Taebaeksan Basin had formed close to the Ogcheon metamorphic belt. In two plate model, the Taebaeksan Basin had formed in the North China Block, and was transported hundreds kilometers southward along a continental transform fault.