KINEMATIC INTERPRETATION OF MULTI-OROGENIC EVENTS ALONG MAJOR TECTONIC LINES: A EXAMPLE IN THE CENTRAL PART OF KOREAN PENINSULA

Kinematic interpretation in multi-deformation areas with overprinted deformation structures is challenging. Okcheon Belt is a NE-SW trending a major deformed sedimentary belt, which is lithologically, stratigraphically, and tectonically complex unit. However, it is importance for understanding the tectonic evolution of the Korean Peninsula. Recently, although several hypotheses have been proposed for the Okcheon Belt, there are no agreement with each other. Therefore, it is essential to identify key evidences for the kinematics associated with the major tectonic lines in the Okcheon Belt. In this study, we have conducted a detailed field survey in Danyang area to understand the kinematics of the Okdong fault and the Gakdong thrust, which are the main tectonic lines in the Okcheon Belt. The field data suggests that the two faults have a similar attitude of NE-SW striking and NW dipping. The stratigraphy around the faults also shows similar attitude because it is controlled by these two tectonic lines. Folds in the study area are dominated with Northward plunging folds with some Eastward plunging folds. The northward plunging fold is associated with the gakdong thrust. The lower Paleozoic laminated sedimentary rocks( Dumugol, Hwajeol, and Myobong Formations) show several deformation structures indicating both dextral and sinistral bedding-parallel shears. The dextral shear structure shows an increase in kinematic vorticity number (W_k) closer to the Okdong fault, and the intersection lineation is dominated by northward plunging. This indicates that the laminated sedimentary rocks accommodated the oblique-slip shear deformation along the Okdong fault. The changes of W_k and the similarity between the fold axis and intersection lineation suggest that the Okdong fault and Gokdong thrust may have developed by strain partitioning during the single orogenic event. Additionally, because the sinistral shear is identified as a post-dextral shear event, the sinistral shear may have been caused by the tectonic inversion of the post-orogenic event. However, further studies are needed over a larger area to test this hypothesis.

Acknowledgement: This research was supported by a grant(2022-MOIS62-001(RS-2022-ND640011)) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety(MOIS, Korea).