The Imjingang Belt in the middle-western Korean Peninsula has tectonically been correlated with the Permo-Triassic Qinling-Dabie-Sulu collisional belt between the North and South China cratons in terms of collisional tectonics.Within the belt, crustal-scale extensional ductile shear zones that were interpreted to be formed during collapsing stage with thrusts and folds were reported as evidence of collisional events by previous studies.In this study, we tried to understand the nature of deformation along the southern boundary of the belt in the Munsan area based on the interpretations of recently conducted structural analyses.To figure out the realistic geometry of the study area, the down-plunge projection was carried out based on the geometric relationships between structural elements from the detailed field investigation.We also conducted kinematic interpretations based on the observed shear sense indicators from the outcrops and the oriented thin-sections made from the mylonite samples.The prominent structures of the Munsan area are the regional-scale ENE-WSW striking thrust and the N-S trending map-scale folds, both in its hanging wall and footwall areas.Shear sense indicators suggest both eastward and westward vergence, showing opposite directions on each limb of the map-scale folds in the Munsan area.In addition, observed deformed microstructures from the biotite gneiss and the metasyenite of the Munsan area suggest that their deformation conditions are corresponding to the typical mid-crustal plastic deformation of the quartzofeldspathic metamorphic rocks.These microstructural results combined with the macro-scale structural interpretations suggest that the shear zones preserved in the Munsan area is mostly related to the development of the N-S trending map-scale folds that might be formed by flexural folding rather than the previously reported E-W trending crustal-scale extensional ductile shear zone by Permo-Triassic collision.These detailed examinations of the structures preserved in the Imjingang Belt can further contribute to solving the tectonic enigma of the Korean collisional orogen.
Permo-Triassic high-pressure (HP) mafic granulites, together with the Bibong retrogressed eclogite, preserved along the central western Korean Peninsula provide important insights into the Late Permian to Triassic collisional orogeny in northeast Asia. The metamorphic pressure–temperature–time (P–T–t) paths of these rocks, however, remain poorly constrained and even overestimated, owing to outdated geothermobarometers and inaccurate isopleth techniques. Here we evaluate the metamorphic P–T conditions of Triassic HP mafic granulites including those in Baekdong, Sinri and Daepan and the Bibong Triassic retrogressed eclogite in the Hongseong area, and the Permo-Triassic Samgot mafic granulite in the Imjingang Belt of the central western Korean Peninsula through the application of modern phase equilibria techniques. The Baekdong and Samgot mafic granulites and the Bibong retrogressed eclogite yield a range of 12.0–16.0 kbar and 800–900 °C, representing HP granulite facies conditions. The Sinri and Daepan granulites from the Hongseong area show relatively lower grade metamorphic conditions between HP granulite and normal granulite facies, and are characterized by sub-isothermal decompression during exhumation. The similarities in the metamorphic ages and the post-collisional igneous activity from the central western Korean Peninsula indicate that the Triassic ages represent the retrograde stage of the metamorphic P–T paths. In contrast, the Late Permian metamorphic ages, which are older than protolith ages of the post-collisional igneous rocks, correspond to the possible prograde stage of metamorphism. The P–T–t paths presented in this paper, together with the metamorphic ages and post-orogenic igneous events reported from these areas suggest trace of the subduction, accretion and exhumation history, and indicate a tectonic linkage among the northeast Asian continents during the Paleo-Tethyan Ocean closure.
 The South Sea of Korea has three offshore concession blocks, including a Joint Development Zone(JDZ) that is set up by the license agreement between Korea and Japan. The geological research of the offshore South Sea of Korea is insufficient to define the evolution history and its significance for petroleum accumulation. In this study, evolution of the Xihu Sag within the JDZ area at the South Sea of Korea is tackled based on re-interpretation of the seismic and well data, and are correlated tectonically with that of the ECSSB(East China Sea Shelf Basin). The ECSSB has been initially developed as a back-arc basin over the over-riding Paleo-Pacific plate, and experienced complex tectonic history by successive subduction of the tectonic plates including the Paleo-Pacific (Izanagi) Plate, the Pacific plate, and the Philippine plate since Late Cretaceous in age. The results indicate that the study area can be subdivided into three tectonic domains: Western Slope Belt, Central Uplift Belt, and East Slope Belt. The structural similarity with those of the ECSSB, although the details of structural characteristics are different in different localities, under regional influence of successive subductions of the same tectonic plates, resulting in the conclusion that the area can be assigned into the northeastern ends of the Xihu Sag of the northeastern ECSSB. This might be a common feature of oil–gas accumulation in the eastern ECSSB, and highlights the potential for petroleum exploration at the study area, although further studies on the play concept and complex petroleum system of the area are required.
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