The Kongju basin of Cretaceous sedimentary rocks, which is located in the area between Ogcheon fold belt and Gyeonggi massif, is developed by the strike-slip fault and shows elongated rhombic shape trending roughly NE and SW with about 4㎞ in width and 25㎞ in length. Two stripes of ductile shear zone are traced in basement rocks along the boundary of basin. The shear sense of ductile shear zone is suggested to be sinistral. The Cretaceous sedimentary rocks within the Kongju Basin also exhibit deformed state in terms of developments of en-echelon arrayed folds, faults and various kinds of joint systems. The majority of joints is occupied by the fractures whose strikes are approximately normal to the directions of en-echelon arrayed fold axes. The shortening(α^(-1)) of fold system is most pronounced at the central part of the basin and gradually decreases toward both ends of the basin. Both of the strikes of fold axial planes and the azimuths of fold axes change discontinuously to form sigmoidal style of en-echelon arrayed folds. The en-echelon arrayed folds, all plunged towards SW direction, indicate that upper layers of the sedimentary rocks are more distributed in the SW area of the basin than in its NE area. The gravity anomaly around the Kongju basin shows 12∼17 mgal in the outer metamorphic zone and 8∼10 mgal in the basin; and its minimum value occurs in NE-SW direction along the western boundary of the sedimentary basin. The electric resistivity study on both boundaries of the basin shows 200∼300Ω-m in the boundary zone, 500∼600Ω-m in sedimentary rocks, and 1000Ω-m or more in the granite-gneiss region. These values indicate that the east boundary be gentle slope and the west one be steep fracture zone. 'These patterns of geophysical data implicates that the Kongju sedimentary basin should be dipping down to the west.

• 송무영
• 이제룡
• 이창진
• 이동의