MESOZOIC TECTONICS IN KOREA

Mesozoic tectonism in Korea is characterized by polycyclic and reitera ted intracratonic deformations, which include (a) strike-slip movement of ductile or brittle-ductile shearings, (b) compressive phase of fol ding, thrusting and transpression of strike-slip movement and (c) exte nsional phase of basin formation by normal or domino fault system and transtension of strike-slip movement. It occurred during three events: Songnim, Daebo and Bulgugsa orogenies. Late Permian to Early Triassic Songnim orogeny can be divided into two stages. In the early stage, d uctile shearing has affected the southwestern part of the Ogcheon Belt and northwest-trending folds developed in the Paleozoic sedimentary s equences. During the late stage, folding and thrust movement have affe cted the Paleozoic rocks and produced northwest-trending folds and thr usts which moved toward the southeast. When the Songmin orogeny was di minished, post-tectonic granites were emplaced and the Daedong basins were formed by extensional tectonic fields. The Daebo orogeny follows the deposition of the Late Triassic to Early Jurassic Daedong Group, w hich includes northeast-trending folds and thrusts. This phase was con tinued on the Songnim phase, in which folds and thrust faults had simi lar trends and transport directions. The Songnim phase was then associ ated with high angle thrust faults. During the late stage, brittle-duc tile strike-slip faults predominated, and produced pull-apart basins a long the contact boundary of the Ogcheon belt. S-type granites were em placed with the northeast trend. From the Late Cretaceous to Early Ter tiary periods, the Bulgugsa orogeny produced east-west trending folds and thrusts. Thrust movements prevailed in the northeastern part of th e Ogcheon belt, whereas other areas were affected by east-west trendin g folds. Sedimentary rocks in the pull-apart basins were affected by t ranspression and produced en-echelon arrays of folds and flower struct ures. Mesozoic tectonism in Korea can be correlated to Indosinian, Yan shanian, and Sichuanian tectonisms in China. Copyright (C) 1996 Elsevi er Science Ltd