Provenance of the late Paleozoic Pyeongan Supergroup in the southern Korean Peninsula and its tectonic implications

Abstract

The Pyeongan Supergroup is the Upper Carboniferous–Lower Triassic sedimentary succession in the Korean Peninsula, distributed in the Pyeongnam Basin in North Korea and the Okcheon Belt in South Korea. This thesis aims to provide a better understanding of the East Asian tectonics by adopting multiple methods on the Pyeongan Supergroup sediments at different spatial and temporal scales. Chapter 1 is a case study on the Samcheok coalfield of the Taebaeksan Basin, the type area of the upper Paleozoic succession in the southern Korean Peninsula. Detrital zircon U–Pb age and Sm–Nd isotope composition of the Pyeongan Supergroup in the Samcheok coalfield were analyzed. The 1.8–2.0 Ga-dominated zircon age pattern and the Nd isotope composition (average εNd(0) = -15.5 ± 4.0) of the Pyeongan Supergroup most closely reflect the signature of the Yeongnam Massif basements, and support the previous hypothesis that the Pyeongan Supergroup was mostly derived from a paleo-orogen located to the east–southeast. Relatively higher εNd(0) values and increased occurrence of syn-depositional zircons in the lowermost and the upper parts of the succession indicate considerable mixing of juvenile materials at ca. 320 Ma and 260 Ma. Chapter 2 examines the hypothesis in a larger spatial scale by putting focus on the lowermost part of the upper Paleozoic succession. Detrital zircon U–Pb age of the contemporaneous Upper Carboniferous strata in the entire Sino-Korean Block was compared by literature survey and a new age dating. While the zircon age distributions from different basins in North China reflect mixed contribution from the Inner Mongolia Paleo-uplift in the north and the Central China Orogenic Belt in the south, the upper Carboniferous strata in Korea is uniquely characterized by a dense cluster of 1.84–1.90 Ga-aged zircon grains. In a situation where the sediments were unlikely provided from the north, the age characteristics shown in localities in Korea is best explained by the derivation from the Paleoproterozoic Yeongnam Massif basements. Chapter 3 deals with two levels of questions. First, the basic tectonic framework regarding the correlation of the Korean Peninsula with the neighboring Chinese blocks is revisited by the review on the stratigraphy and detrital zircon age of the Pyeongan Supergroup in the southern Korean Peninsula. The results favor the tectonic view that the entire Okcheon Belt was a single tectonic unit belonging to the Sino-Korean Block. Second, a more detailed tectonic model is proposed based on the comprehensive analysis of the detrital zircon U–Pb age data of the Pyeongan Supergroup sediments in various parts of the Okcheon Belt. Collectively, this study supports the active continental margin setting in the east of the Sino-Korean Block during the late Paleozoic, which may have been a southward continuation of the Paleo-Asian Ocean subduction along the northern margin of the block.