Middle Paleozoic metamorphism in the Hongseong area, South Korea, and tectonic significance for Paleozoic orogeny in northeast Asia

The Baekdong and Gwangcheon areas are located within the Hongseong collision belt of South Korea, and the discovery of late Permian-Triassic eclogites has confirmed this belt as an extension of the Qinling-Dabie-Sulu collision belt in China. The Qinling-Dabie-Sulu belt records a middle Paleozoic continental collision in addition to the late Permian-Triassic collision of the North and South China cratons. In this paper, we present evidence for middle Paleozoic igneous and metamorphic events in the Baekdong and Gwangcheon areas. Metabasites and meta-basaltic andesites in the Baekdong area originated in an arc tectonic setting at ca. 470-437. Ma, and underwent an intermediate-P/T metamorphism (6.2-8.2. kbar, 620-700. °C) at ca. 418-405. Ma. The meta-basaltic andesite in the Gwangcheon area underwent a high-pressure granulite facies metamorphism (close to the eclogite facies) at ca. 392-381. Ma. P-T values of 15.7-19.9. kbar and 860-890. °C were obtained for the peak metamorphism using conventional geothermobarometry, and conditions of 16-17. kbar and 870-920. °C were estimated by thermodynamic pseudosection analysis using the Perplex X program. Together with the late Permian-Triassic eclogites previously reported from the Hongseong area, these middle Paleozoic igneous activities that were related to subduction and metamorphism indicate that the Hongseong area underwent collision in the middle Paleozoic (418-381. Ma), in addition to the late Permian-Triassic collision, as recorded in the Qinling-Dabie-Sulu belt in China.