Tectonic and sedimentary evolution of the Korean peninsula: a review and new view

This review focuses on the tectonics and sedimentation of major sedimentary basins and orogenic belts (Late Proterozoic-Neogene) in the Korean peninsula. The Korean peninsula is part of the Amuria Plate and represents an important link between continental blocks of North and South China and the island arcs of Japan. The basement rocks, exposed in the Kyonggi and Yongnam massifs, consist of 2.7 to 1.1 Ga high-grade gneiss and schist. These massifs are separated by the Okchon Fold Belt which comprises metasedimentary rocks and bimodal meta-volcanic rocks. The stratigraphy of the Okchon Group is unclear at present. The Okchon Basin was probably initiated as an intraplate rift prior to the Late Proterozoic. The Hwanggangri Formation (clast-bearing phyllite) most likely represents deposition by subaqueous debris flows in slope environments of an enclosed basin. The stratigraphic relationship between the Okchon Group and the Chosen Supergroup (Cambro-Ordovician) of the Taebaeksan Basin is poorly constrained. The Chosen Supergroup unconformably overlies the Yongnam Massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tidal environments, reflecting numerous sea-level fluctuations. The sequence is disconformably overlain by siliciclastic sequence of Pyongan Supergroup (Carboniferous-?Triassic) which formed most likely in shallow marine, deltaic, and fluvial environments. The Imjingang Belt is an east-trending fold and thrust zone and consists of metasedimentary rocks and volcaniclastics (Devonian-Carboniferous), underlain unconformably by Proterozoic basement rocks. Late Proterozoic amphibolites of oceanic affinity were metamorphosed at about 8-13 kbar and 630-740 degreesC during the late Permian to the early Triassic. The south-vergent contraction and top-down-to-the-north normal faulting are suggestive of a suture belt between the North China Block (Sino-Korea Craton) and the South China Block (Yangtze Craton), an extension of Sulu Belt across the Yellow Sea. Entire peninsula experienced strong deformation and metamorphism during the suturing event, namely Songrim orogeny. During this orogenic event, the Kyonggi Massif (and the Okchon Basin) accreted to the Yongnam Massif (and Taebaeksan Basin) along the South Korean Tectonic Line running northeast-southwest. A series of northward-trending thrust formed along the boundary zone to the east (Kaktong and Kongsuwon thrusts and others). Piggyback basins locally developed along the thrust faults, forming the Taedong Group. The crustal deformation resumed in the early to late Jurassic (Daebo event) under contractional setting. Dextral ductile shearing associated with thrusting and folding continued in the mid-southern part of the peninsula. It was due to orthogonal (northwestward) subduction of the Izanagi Plate under the Asian continent. The Yongnam Massif experienced continuous dextral offset along the Honam Shear Zone. In the early Cretaceous, the Izanagi Plate began to subduct northward and caused formation of strike-slip basins in retroarc setting, i.e., Kyongsang Basin in the southeastern part and a number of small-scale basins in the mid-southwestern part of the peninsula. Small-scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephemeral lacustrine systems under semiarid to arid conditions. Extensive intrusion of granitoids occurred from Triassic to Early Tertiary with a gap between 160 and 100 Ma, representing continental magmatic are. In the Tertiary, the southeastern margin of the Korean peninsula experienced back-are opening. Pull-apart basins formed in the Miocene, bounded by the Yangsan and Hupo faults. The Yonil Group, sedimentary fill of the Pohang Basin, comprises more than 1-km-thick siliciclastic sequence which represents deposition in fan-delta systems on the hanging wall of the Yangsan fault. Thick (more than 10 km thick) sediments in the Ulleung Basin margin were deformed in the late Miocene due to the northward movement of Kyushu Block. Quarternary volcanic events in Cheju Island represent intraplate hot spots. (C) 2000 Elsevier Science B.V. All rights reserved.