Tectonic evolution of the Korean Peninsula: A new paradigm for critical building blocks of East Asia

Abstract

The Korean Peninsula occupies a critical part of East Asia, and thus understanding its tectonic development has a significant impact on comprehending the crustal evolution of the entire East Asia. However, there is still contention surrounding the formation of the Korean Peninsula during the Permian-Triassic collision of the Sino-Korean (North China) Craton (SKC) and the South China Craton (SCC). Various hypotheses have been proposed regarding the tectonic affinity of different parts of the Korean Peninsula, complicating the proper understanding of the tectonic evolution in East Asia. This is partly due to a pre-existing geological framework that has played a pivotal role in the tectonic understanding of the Korean Peninsula, originally suggested during the age of the ‘geosyncline.’ This framework involves the tripartite division of the basement rocks into the Nangrim, Gyeonggi, and Yeongnam “massifs.” Not bound by this pre-existing paradigm, here we provide a new perspective on the tectonic evolution of the Korean Peninsula based on multidisciplinary geological data, including paleontology, sedimentology, petrology, and geochronology. An integrative reinterpretation of the data has led to the recognition of critical insights on the development of the Korean Peninsula: (1) the Paleoproterozoic crystalline rocks of the two Gyeonggi ‘blocks’ were basement rocks of the SKC southern margin that were dragged down by the subduction of the eastern tip of the SCC crust during the Permo-Triassic collision and then exhumed during the Late Triassic extensional regime; (2) continental core complexes of various sizes developed near the tectonic boundaries during the Late Triassic and Cretaceous extensional regimes, resulting in the formation of coeval small non-marine basins throughout the Korean Peninsula; (3) the Cathaysia Block-affinity rocks in the midwestern part of South Korea were brought up to the surface by the Late Triassic Hongseong Core Complex, and; (4) the Hwanghae-Taean Belt around the western coast of the Korean Peninsula was formed by a Late Cretaceous ‘continental crust spreading’ event. Accordingly, a new subdivision of tectonic provinces of the Korean Peninsula is presented, which does not accord with the previous tectonic models that proposed either a simple collision belt running through the peninsula or the entire peninsula belonging to the SKC. We present retrograde reconstructions of the Korean Peninsula, representing the geological components from the Late Cretaceous to Permian, and integrate the results with the framework of the Permo-Triassic collision between the SKC and the SCC. Under the new perspective, geological aspects and events known in the Korean Peninsula can be revisited. Except for the northeastern terranes, the Macheollyeong Block, the Gwanmo Massif, and the Dumangang Belt, the tectonic provinces of the Korean Peninsula, from northwest to southeast, consist of the Nangrim Spread Crustal Region (SCR) (including the Pyeongnam District), Hwanghae District, Imjingang Belt, Western Gyeonggi Block, Central Gyeonggi Block, Okcheon Belt (including the Taebaeksan Complex), and Yeongnam Block. The metasedimentary rocks with the SCC-affinity in the Imjingang Belt and the Okcheon Metamorphic Belt were the Devonian-Carboniferous passive margin sediments and their substratum-forming pre-Devonian rocks in the northern margin of the SCC, which were subducted during the continental collision and exhumed in the Late Triassic. A continental arc system was formed as the SCC approached the SKC in the late Paleozoic, and the late Paleozoic Pyeongan Supergroup was formed in forearc basins developed at the southern margin of the SKC before the continental collision. The supracrustal boundary of the SKC and the SCC runs across the ‘Taebaeksan Complex,’ which is marked by the boundary between the SCC-derived Yeongwol Group and the SKC-derived Taebaek Group and Pyeongan Supergroup. Most importantly, the three renowned orogenies in the Korean Peninsula are redefined. The Songrim Orogeny encompasses the events related to the Permo-Triassic collision between the SKC and the SCC and is subdivided into the Early, Middle, and Late phases. The Early and Middle phases represent the accretionary wedge-induced metamorphism and the main continental collision events, respectively, while the Late Phase is represented by post-collisional exhumation events and core complex developments. The Jurassic Daebo Orogeny was caused by the flat subduction of the Paleo-Pacific (Izanagi) Plate that formed the widespread Jurassic granitoids across the peninsula, the thrust-fault systems in the Okcheon Belt, and the ductile Honam Shear Zone. The Cretaceous Bulguksa Orogeny represents the extensional regime caused by the rollback of the Paleo-Pacific (Izanagi) Plate, which progressively developed core complexes from northwest to southeast and likely triggered an epeirogeny in the early phase of the orogeny. The new tectonic perspective of the Korean Peninsula will provide a critical new basis for the tectonic understanding of the Korean Peninsula, as well as a new insight into the tectonics of East Asia.