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 peninsu la. The Korean peninsula is part of the Amuria Plate and represents an impo rtant link between continental blocks of North and South China and the isla nd arcs of Japan. The basement rocks, exposed in the Kyonggi and Yongnam ma ssifs, 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 rock s and bimodal meta-volcanic rocks. The stratigraphy of the Okchon Group is unclear at present. The Okchon Basin was probably initiated as an intraplat e rift prior to the Late Proterozoic. The Hwanggangri Formation (clast-bear ing 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 Supe rgroup (Cambro-Ordovician) of the Taebaeksan Basin is poorly constrained. T he Chosen Supergroup unconformably overlies the Yongnam Massif and consists mainly of carbonate sequence that formed mostly in shallow marine and tida l environments, reflecting numerous sea-level fluctuations. The sequence is disconformably overlain by siliciclastic sequence of Pyongan Supergroup (C arboniferous-?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), underl ain unconformably by Proterozoic basement rocks. Late Proterozoic amphiboli tes of oceanic affinity were metamorphosed at about 8-13 kbar and 630-740 d egreesC during the late Permian to the early Triassic. The south-vergent co ntraction and top-down-to-the-north normal faulting are suggestive of a sut ure belt between the North China Block (Sino-Korea Craton) and the South Ch ina Block (Yangtze Craton), an extension of Sulu Belt across the Yellow Sea . Entire peninsula experienced strong deformation and metamorphism during t he suturing event, namely Songrim orogeny. During this orogenic event, the Kyonggi Massif (and the Okchon Basin) accreted to the Yongnam Massif (and T aebaeksan Basin) along the South Korean Tectonic Line running northeast-sou thwest. A series of northward-trending thrust formed along the boundary zon e 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 thru sting and folding continued in the mid-southern part of the peninsula. It w as due to orthogonal (northwestward) subduction of the Izanagi Plate under the Asian continent. The Yongnam Massif experienced continuous dextral offs et along the Honam Shear Zone. In the early Cretaceous, the Izanagi Plate began to subduct northward and c aused 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 mi d-southwestern part of the peninsula. Small-scale alluvial fans and fluvial channel networks formed in the basin margin and were transitional to ephem eral 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. I n 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 Ba sin, 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 de formed in the late Miocene due to the northward movement of Kyushu Block. Q uarternary volcanic events in Cheju Island represent intraplate hot spots. (C) 2000 Elsevier Science B.V. All rights reserved.