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( Francois Hategekimana ),( Young-seog Kim ) 대한지질공학회 2021 지질공학 Vol.31 No.3
Kinematic analyses of magmatic intrusions and faults can provide useful information on stress conditions and chronological relationships between dike emplacement and brittle deformation events. We studied structures in rocks exposed on a coastal platform in Geoje Island off the southern Korean Peninsula because of its well-developed dikes and faults. The geology of the study area includes the Cretaceous Seongpo-ri Formation, which is composed mostly of shale, sandstone, and hornfels intruded by magmatic dikes. Most of the dikes are developed along pre-existing structural features (faults and fractures), indicating that their emplacements were structurally controlled. Because dikes commonly open along the direction of the minimum principal stress, the direction of this stress can be obtained from dike geometry and orientation through the matching of piercing points on either side of a dike. In addition, the deformed dikes can give information regarding later deformation. On the basis of the kinematic analyses, we identified five deformation events in the study area, which are kinematically related to changes of the regional maximum principal stress. Results indicate that the structures in the study area have been controlled predominantly by episodes of reactivation of the NNE-trending Yangsan strike-slip fault, located to the northeast of the study area, under different stress regimes. In a wider tectonic context, the brittle deformation of the rocks of Geoje Island was probably induced by interactions among the Philippine Sea, Pacific, and Eurasian plates, including changes in subduction parameters with respect to the latter two plates over time.
Francois Hategekimana,MOHAMMED SAIF ALDIN MOHAMMED ADAM,김영석 한국지구과학회 2023 한국지구과학회지 Vol.44 No.4
Structural inversion refers to the reverse reactivation of extensional faults that influence basin shorteningaccommodated by contractional faults or folds. On the Korean peninsula, Miocene inversion structures have been found,but the Cretaceous rocks on Geoje Island may have undergone inversion as early as the Upper Cretaceous. To evaluatethe structural inversion on Geoje Island, located on the eastern side of South Korea, and to determine the effects of preexistingweakness zones, field-based geometric and kinematic analyses of faults were performed. The lithology of GeojeIsland is dominated by hornfelsified shale, siltstone, and sandstone in the Upper-Cretaceous Seongpori formation. NE andNW-oblique normal faults, conjugate strike-slip (NW-sinistral transpressional and E-W-dextral transtensional) faults, andNE-dextral transpressional faults are the most prominent structural features in Geoje Island. Structural inversion on GeojeIsland was evidenced by the sinistral and dextral transpressional reactivation of the NW and NE-trending oblique normalfaults respectively, under WNW-ESE/NW-SE compression, which was the orientation of the compressive stress during theLate Cretaceous to Early Cenozoic.