Structural geometry of the Taean area in the Western Gyeonggi Massif: Implications for the tectonic evolution of the Korean Peninsula and East Asia

The Korean Peninsula, in East Asia alongside China and Japan, is tectonically linked to these neighboring regions. Notably, the Qinling-Dabie-Sulu Belt, located between the North China Craton (NCC) and the South China Craton (SCC), includes intervening microcontinents and has been proposed to extend into the Korean Peninsula. However, robust tectonic correlations were not made due to a lack of understanding of detailed geology for both regions. Within the Korean Peninsula, the Western Gyeonggi Massif has been tectonically linked to this belt, preserving evidence of Permo-Triassic orogeny and a related fold-thrust belt associated with a subduction followed by a collision.

The Taean area of the Western Gyeonggi Massif is a part of this Permo-Triassic fold-thrust belt and retains typical contractional fold-thrust belt structures. The Paleoproterozoic Seosan Group, which forms the basement underlying the Paleozoic Taean Formation, shows systematic NE-SW trending repetitions in map view. To decipher the structural geometry of these repetitions in the Taean area, structural geometric interpretations have been conducted based on detailed field mapping. The results reveal that the overall structural geometry of the study area comprises NE-SW trending overturned folds. These folds plunge to the southwest in the northern, southern, and eastern parts of the area, and the northeast in the central part. This multi-plunging asymmetric fold geometry, displaying northwest vergence, can be interpreted as second-order folds within the hanging wall of the regional-scale fault located in the eastern part of the study area. These fault-related folds suggest basement-involved deformation possibly related to the Permo-Triassic collisional orogeny preserved in central-western Korean Peninsula, based on the newly obtained SHRIMP titanite U-Pb age (ca. 205 Ma) of a deformed mafic intrusion in the study area.

Understanding the spatial and temporal evolution of these structures will provide valuable insights into the tectonic significance of the orogenic belt in the Western Gyeonggi Massif of the Korean Peninsula. This, in turn, will enhance our understanding of the role of the Korean Peninsula in the tectonic evolution of the East Asian continent as a whole.