Tectonic Evolution of the Okcheon Fold-Thrust Belt, southern Korean Peninsula: Insights into Paleozoic Tectonics and Orogenic Processes along the East Asian Continental Margin

The Okcheon fold-thrust belt, located in the southern Korean Peninsula, serves as a natural laboratory for understanding the formation and evolution of the orogenic belts along the East Asian continental margin during complex Paleozoic tectonics in East Asia. The belt preserves various sedimentary basins developed at different geological times and tectonic settings, which have experienced various orogenic events forming an area of significant scientific debate. This study integrates biomarker analysis, and U-Pb detrital and igneous zircon geochronology to redefine the stratigraphy of the Okcheon belt. Redefined stratigraphy, cross-section profiled constructions using down-plunge projections, structural interpretations based on detailed field survey, and cross-section balancing were conducted to figure out new insights into the structural evolution of this belt. These together with evidence from previously reported publications, the spatiotemporal scenarios for the evolution of the Okcheon fold-thrust belt could be summarized as follows. (1) The Okcheon Belt was formed during the Neoproterozoic intracontinental rifting resulted in the creation of a rift basin in the Taebaeksan Zone. This is followed by subsequent deposition of miogeoclinal carbonate sediments, known as the Joseon Supergroup. Throughout this time, the Okcheon Zone remained as a basement high without sedimentation. (2) During the Devonian, sporadic magmatic events and contractional deformation in the Gyeonggi Massif supported the higher structural relief of the Gyeonggi Massif than the Okcheon Belt. In addition, the Taebaeksan Zone was higher structural relief relative to the Okcheon Zone in the Okcheon Belt. The differences in basement geometry before deposition of the Carboniferous clastic wedge resulted in differences in depositional environments and lithologic variations in the Okcheon and Pyeongan supergroups. These are supported by previously reported Devonian detrital zircon U-Pb age dates from the meta-sedimentary rocks in the Okcheon Belt, existence of angular unconformity between the Joseon Supergroup and the subsequent supergroups, and distinct lithologic differences between the lower parts of two Supergroups, etc. (3) Finally the Late Permian to Early Triassic marks a significant period in tectonic history of the Okcheon Belt that is characterized by extensive crustal deformation and formation of a complex fold-thrust belt system. Key structural features such as the Bonghwajae Tectonic Window and the Yeongwol connecting-splay duplex support presence of typical fold-thrust features in the central part of the belt. However, other regions like the Gyemyeongsan Thrust and Wachon Klippe display signs of basement-involved deformation, where Proterozoic basement rocks are notably involved in the deformation style. These will provide spatio-temporal evolution of the Okcheon Belt, which will offer significant insight into tectonic processes along the East Asian continental margin during Paleozoic to Early Triassic period.