10:45 〜 11:00
[SMP25-01] Paleozoic tectonic evolution of the Guryong Group located in the Odesan area, eastern Gyeonggi Massif, Korean Peninsula
キーワード：Eastern Gyeonggi Massif, Paleozoic, Guryong Group, Permo-Triassic collision, Zircon U–Pb age dating
The Qinling–Dabie–Sulu collision belt between the North China and South China Cratons is suggested to be connected to the Hongseong area of the western Gyeonggi Massif (GM), Korean Peninsula based on the report of the eclogite facies metamorphism (Oh et al., 2005). In contrast, the further eastern extension of the Qinling-Dabie-Sulu collision belt within the Korean Peninsula is still under debate, and the Odesan area, eastern GM is one possible candidate for its eastern extension based mainly on the reports of the UHT metamorphism (Oh et al., 2006; Lee et al., 2016). The Hongseong-Odesan belt model which separates the GM into northern and southern GM is further supported by the character of Neoproterozoic magmatism (Lee et al., 2020), a trend of metamorphic grade (Jeong and Oh, 2021), and spatial-temporal distribution of the Triassic magmatic rocks (Kawaguchi et al., 2023), however, further evidence especially from the Odesan area are crucial to evaluate this collision model. The Odesan metamorphic complex is mainly composed of the Paleoproterozoic paragneisses, with subordinate Mesoproterozoic–Paleozoic rock units and Triassic gabbro and mangerite (Yi, 2016). The Paleoproterozoic collision related metamorphism in the Odesan metamorphic complex is strong, which was later superimposed by another strong metamorphism during the Permo–Triassic period due to the collision. Therefore, the evaluation of the metamorphism in the Odesan area is quite difficult to separate metamorphic conditions from each other. However, the Guryong Group (GG), located within the Odesan metamorphic complex is reported to have formed during the Paleozoic (Cho et al., 2014), indicating that the GG has the potential to reveal the Permo–Triassic metamorphism. Moreover, the Paleozoic tectonic evolution of the Korean Peninsula is quite uncertain due to the limited tectono-thermal evidence, and the GG is important for examining the Paleozoic tectono-thermal history of the Korean Peninsula and its implication in Northeast Asia. In this study, LA–ICP–MS zircon U–Pb age dating was performed on six metamorphic rock samples collected from the GG. Metagranite yields weighted mean age of 230.2 ± 4.6 Ma (n = 20; MSWD = 1.6) with 289 ± 8 Ma were obtained from the inherited core. Biotite granitic gneiss shows lower intercept age of 217.2 ± 5.0 Ma (n = 7; MSWD = 7.3) with two inherited cores dated at 2246 ± 24 and 1802 ± 25 Ma were obtained from the inherited core. These two late Triassic ages can be interpreted as the timing of metamorphism as evidenced by low Th/U ratios (0.007–0.001) and zircon micro-texture under the CL images. Most of the dates from the amphibolite show a discordant value, however, the lower intercept age is defined at 261.7 ± 9.4 Ma (n = 4; MSWD = 5.1). Major peak ages and their populations (%) of detrital zircons from the biotite gneiss are ~1840 Ma (population; 8%), ~1510 Ma (8%), ~1170 Ma (11%), and ~774 Ma (11%), while those of other biotite gneiss are ~2623 Ma (8%), ~2380 Ma (13%), and ~1878 Ma (13%). In contrast, the garnet-biotite gneiss shows a markedly different detrital zircon age pattern ranging between 937 and 255 Ma, with the main peaks of ~330 Ma (14%), ~280 Ma (25%), and ~265 Ma (16%), without any Paleoproterozoic to Archaean concordant detrital zircons. Our age dating results suggest that parts of the GG are found to have formed during the Paleoproterozoic similar to the Odesan metamorphic complex, however, the Permian sedimentary rock has been newly identified from the GG. The Permian arc magmatism was initiated at ~283 Ma in the Korean Peninsula (Choi et al., 2021), however, the Carboniferous magmatism has not been reported yet, indicating that the source provenance is unclear. Permian sedimentation along with the Carboniferous detrital zircons identified in this study hold an important key to unraveling the Paleozoic tectono-thermal evolution and Permo–Triassic continental collision in the Korean Peninsula.