The Permo-Triassic collision of the North and South China blocks caused the development of the Dabie-Sulu Orogen in China and Songrim Orogen in the Korean Peninsula. Extension after this collision is known from the Dabie-Sulu Orogen, but post-orogenic extension is not well defined in the Korean Peninsula. Extensional deformation along the southern boundary of the Gyeonggi Massif in Korea is characterized by top-down-to-the-south ductile shearing and subsequent brittle normal faulting, and was predated by regional metamorphism and north-vergent contractional deformation. Extension occurred between ~220 and 185 Ma based on the ages of pre-extensional regional metamorphism and post-extensional pluton emplacement. 40Ar/39Ar dating of syn-extensional muscovite in quartz-mica mylonite yields an age of 187.8 ± 5.6 (2σ) Ma, in agreement with constraints from structural relationships. Together with the extensional deformation identified along the northern boundary of the Gyeonggi Massif (~226 Ma), the extension along the southern boundary is probably related to the exhumation of the massif during late-orogenic or post-orogenic extension associated with the Songrim Orogeny of the Korean Peninsula and forms an important event in the Phanerozoic crustal evolution of East Asia.
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Acknowledgments We thank laura Webb for valuable comments on the earlier version of the manuscript. We also acknowledge the constructive reviews by K. de Jong, M. Cho, and an anonymous reviewer, which significantly improved the manuscript. RH thanks his friends (Y. Kim, J. Yi, and S. Kim) for their great help in field-work. This work was supported by the Basic Research Program and the Block Funding Project of the Korea Institute of Geoscience and Mineral Resources (KIGaM).
- Extensional deformation
- Gyeonggi Massif
- North and South China blocks
- Okcheon Belt
- Permo-Triassic collision
- Songrim Orogeny
- Syn-tectonic muscovite
ASJC Scopus subject areas
- General Earth and Planetary Sciences