1:30 PM - 1:45 PM
[T1-O-18] The igneous and metamorphic evolution from Neoproterozoic to Triassic in Jangbong Island in the northwestern coastal Gyeonggi Massif on the Korean Peninsula
Keywords:Korean Peninsula, Northwestern Gyeonggi Massif, Jangbong Island, Neoproterozoic Amphibolites, Triassic Metamorphism
The geological correlation between the Korean Peninsula and China Cratons is important for the interpretation of the tectonic evolution of Northeast Asia. Jangbong Island is located in the northwestern coastal area of the Gyeonggi Massif on the Korean Peninsula. Combining with previous studies, this study interprets the tectonic evolution of the northern Gyeonggi Massif by analyzing the age of intrusion and metamorphism of the mafic igneous rocks in Jangbong Island. The basement of Jangbong Island consists of Paleoproterozoic gneiss and is covered by Neoproterozoic metasedimentary rocks. These rocks were intruded by mafic dikes that were metamorphosed into amphibolite. All rocks in Jangbong Island were intruded by Triassic gabbro and granite, and Jurassic granites. The U-Pb dating analysis on zircon analysis using LA-ICP-MS gives the intrusion ages of 917-873 Ma for amphibolites. The whole-rock geochemical analysis indicates that amphibolites are all alkaline and tholeiitic basalts formed in a within-plate tectonic setting. Two metamorphic ages of 254.4±2.8 Ma and 231.5±1.9 Ma were obtained from amphibolite with an intrusion age of 873 Ma. On the other hand, one metamorphic age was obtained for two amphibolites which give metamorphic ages of 255±12 Ma and 229.8±1.4 Ma, respectively. Zircons with metamorphic ages of 255-254 Ma have lower trace element contents and Th/U values than zircons with metamorphic ages of 231-229 Ma. During the Permo-Triassic continental collision between the North China Craton and South China Craton, Jangbong Island experienced intermediate-P/T peak metamorphism (680-630 °C/8.6-7.3 kbar) at ca. 255 Ma and then underwent low-P/T retrograde metamorphism (600-560 °C/5.7-3.1 kbar) at ca. 230 Ma. The Triassic gabbro gives an intrusion age of 229.1±0.57 Ma and formed in a post-collisional tectonic setting with Triassic granite. Together with previous data, this study supports the tectonic correlation between the northern Gyeonggi Massif and the North China Craton and the Permo-Triassic collision within the Gyeonggi Massif.