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Reassessment of the Pyeongan Supergroup: Metamorphism and Deformation of the Songrim Orogeny
평안누층군의 재조명: 송림 조산운동의 변성작용과 변형작용
Econ. Environ. Geol. 2019 Oct;52(5):367-79
Published online October 31, 2019;  https://doi.org/10.9719/EEG.2019.52.5.367
Copyright © 2019 the Korean society of economic and environmental gelology.

Hyeong Soo Kim*
김형수*

Department of Earth and Environmental Sciences, Korea University
고려대학교 지구환경과학과
Received August 8, 2019; Revised September 22, 2019; Accepted October 4, 2019.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
 Abstract
Pyeongan Supergroup (PS) in the Taebaeksan basin preserves key geological evidences to understand the tectonometamorphic evolution of the Songrim orogeny that affected the formation of the Korean Peninsula during the late Paleozoic to early Mesozoic. The aims of this paper therefore are to investigate the characteristics of the Songrim orogeny based on the previous results of metamorphism and deformations of the PS, and then to review geological significance and research necessity of the PS. Age distributions and Th/U ratio of detrital zircon in the PS indicate that sedimentary environment of the Taebaeksan basin during the late Paleozoic was arc-related foreland basin and retro-arc foreland basin at the active continental margin. In addition, the main magmatic activities occurred in the early Pennsylvanian and Middle Permian, thus sedimentation and magmatic activities occurred simultaneously. The PS was affected by lower temperature–medium pressure (M1) and medium temperature and pressure (M2) regional metamorphism during the Songrim orogeny. During M1, slate and phyllite containing chloritoid, andalusite, kyanite porphyroblasts intensively deformed by E–W bulk crustal shortening combined with folding and shearing. And garnet and staurolite porphyroblasts were formed during the N–S bulk crustal shortening accompained by M2. Such regional metamorphism of the PS is interpreted to occur in an area where high strain zone is localized during ca. 220–270 Ma. In order to elucidate the evolution of the Taebaeksan basin and tectonic features of the Songrim orogeny, it is expected that the study will be carried out such as the regional distribution of metamorphic zones developed in the PS, characteristics and timing of deformations, and late Paleozoic paleogeography of the Taebaeksan basin.
Keywords : Taebaeksan basin, Pyeongan Supergroup, Songrim orogeny, metamorphism-deformation, detrital zircon

 

December 2019, 52 (6)