Evidences of Brittle deformation associated with Reactivation and Tectonic Inversion in Geoje Island, SE Korea

Abstract

Kinematic analyses of magmatic intrusions and faults can provide useful information on the stress conditions and the chronological relationships between dike emplacement, fault reactivation, tectonic inversion hence deducing brittle deformation events within rocks. A well exposed coastal platform in Geoje island is selected for this study, because there are well developed dykes and faults. The study area is mainly composed of Cretaceous Seongpo-ri formation, which is mostly composed of shale, sandstone and hornfels intruded by magmatic dikes. Most of the magmatic dikes are developed along pre-existing structural features (faults and fractures) indicating that their emplacements were structurally controlled, while others created their own paths. Because dike commonly opens to the least principal stress, the direction of the least principal stress can be obtained from dike geometry and orientation through matching of piercing points located on both sides across a dyke. Also, the deformed dikes can give more information associated with the later deformations. Brittle deformation history can also be studied using fault reactivation and tectonic inversion. Identifying the kinematic indicators along the faults provides enough information about the faulting events. Based on these analyses, we extracted seven deformation events from the study area, which are kinematically related to the change of maximum regional principal stress. The results indicate that the structures of the study area are mostly controlled by the reactivation of the NNE-trending Yangsan strike-slip fault located to the northeast from the study area. Tectonically, the brittle deformation in Geoje island was probably induced by the relative stress relationship between Philippine sea plate and Pacific plate subducting under Eurasian plate.