Nd isotope and detrital zircon U-Pb age constraints on the provenance of the Pyeongan Supergroup (late Paleozoic-Early Triassic) in central eastern Korea

During the late Paleozoic, subduction occurred beneath the both northern and southern margins of the Sino-Korean (North China) Craton (SKC), which led to collision with the Siberian Craton and the South China Craton, respectively. The collision among three cratons resulted in the formation of the Central Asian Orogenic Belt (CAOB) in the northern part of the SKC and the Qinling-Dabie Belt in the southern part. What happened in the east of the SKC during that time is rather unclear, except for the accretion and active arc magmatism recorded in the Japanese Islands. To investigate tectonics of the eastern SKC during the late Paleozoic, sandstone and shale samples taken from the Pyeongan Supergroup in central eastern Korea were analyzed for detrital zircon U-Pb and whole-rock Sm-Nd geochronology. The Pyeongan Supergroup, a Middle Carboniferous-Lower Triassic sedimentary succession in Korea, is largely correlatable to its age-equivalent succession in North China. However, its basinfill is interpreted to have been derived from recycled orogen located to the east-southeast. Detrital zircon age patterns are consistent from the bottom to the top of the succession, with the dominance of 1.7 2.0 Ga zircons (>80%), which suggests in the previous cycle the origination of sediments from Paleoproterozoic basement rocks of the Yeongnam Massif located in the southeast of the studied succession. The presence of some detrital zircon grains of near syn-depositional age suggest contemporaneous magmatic activity in the source terrane. ɛNd(0) varies between -22.7 and -8.7, with an average of -15.5. The lower ɛNd values (<-15.0) match that of the Yeongnam Massif basement rocks, but the higher ɛNd values (>-15.0) suggest significant mixing of juvenile materials, implying the input of the weathered product of late Paleozoic magmatism. Three pulses of relatively high ɛNd values at 315 Ma, 290 Ma, and 265 Ma are observed. The juvenile material with andesitic to basaltic composition is inferred from the poor yielding of detrital zircons of corresponding ages and lack of K-feldspar in sandstone composition. Both detrital zircon U-Pb ages and Nd isotope composition suggest the existence of CAOB-like paleo-orogen to the east of the SKC during the Pyeongan Supergroup deposition.