Paleozoic tectonics of the southwestern Gyeonggi massif, South Korea: Insights from geochemistry, chromian-spinel chemistry and SHRIMP U-Pb geochronology

Arc magmas, metavolcanics and hydrated mantle peridotite from the Hongseong area in western Gyeonggi massif provide evidence for Paleozoic subduction tectonics in the Korean Peninsula. Zircons in a tonalitic orthogneiss from the Wolhyeonri complex dated in this study through SHRIMP U-Pb technique yield ages of ca. 437. Ma and ca. 414. Ma. In addition, SHRIMP U-Pb zircon dating of a garnet-bearing paragneiss in the Wolhyeonri complex records evidence for Middle Paleozoic (ca. 427. Ma) thermal metamorphism. Petrological and geochemical data from the Paleozoic suite provide robust evidence for mid Paleozoic arc-related magmatism.Petrological and geochemical data from the Paleozoic suite, including the composition of chromian spinel from the serpentinite bodies enclosing high-pressure mafic and felsic blocks also suggest rifted arc/forearc tectonic setting in a supra-subduction zone environment. The serpentinite bodies preserve the imprints of forearc magmas derived through significant mantle/melt interaction during the opening and subsequent evolution of the forearc. These results indicate that the Paleozoic Hongseong area might have been located in an arc-forearc tectonic environment coeval with the plutonism and volcanism preserved in the Wolhyeonri complex. The Hongseong area thus preserves important clues to the Paleozoic subduction prior to the subsequent Triassic "Alpine-type" collision, suggesting a common tectonic linkage among Paleozoic to Triassic East Asian continents before the final assembly of the Pangaea supercontinent.