報恩 炭田 西部地域의 地質構造

Structural geology in the western area of the Poun coal field

The study area is mainly composed of metasedimentary rocks which are included in Ogchon, Choson and Pyongan Groups. Because of thrust faults which are developed in this area, a coal bearing formation is repeatedly distributed two times, and Choson Group is thrusted over Pyongan Group. Deformation in this area was taken place in a series of three phases ((D₁, D₂ and D₃) ; D₁ was most intense whereas D₃ was weakest. Thrust faults developed in the upper curst during D₂ produced cataclastic rocks and fault breccia, truncating regional slaty cleavage and earlier folds which were formed during D₁ stage. The quartz microstructures of metapsammitic rocks in Choson and Pyongan Groups suggest that dislocation creep mechanism predominated early in fabric development, afterwards deformation mechanism was transfered to pressure solution which intensified the earlier fabrics. According to strain analysis using quartz grains and quartz aggregate grains, the strain magnitude(Es) of Pyongan Group represents larger values than that of Choson Group due to the contrast of constituent minerals, the size of original quartz grains and matrix content. Apparent flattening type in strain pattern appears in the whole area. It is suggested that the relationship between Ogchon Group and Choson Group may be thrust contact.