| Abstract: | Based on fault geometry, petrography, and geochronology of granitic rocks as well as palaeomagnetic data from the Gyeongsang Basin, two conjugate fault sets are explained as a reflection of NNE-trending right-lateral wrench tectonics. According to this interpretation, the Gaum and Yangsan fault sets correspond to antithetic faulting by R′-shear and synthetic faulting by R-shear, respectively; they have rotated clockwise and counterclockwise, respectively, due to NE–SW compression (shortening), as a result of a NNE-trending wrenching force (simple shear). During progressive deformation, NS- or NNW-trending strike–slip faulting by P-shear occurred in the Yeongyang sub-basin, and finally the Yangsan fault formed as a wrench fault bisecting the P-shear and R-shear directions. Extension of the faults (R-shear, striking ～N22°E) generated by block rotation on the east side of the Yangsan fault (wrench fault, striking ～N13°E) resulted in convex eastward deflections. We suggest that this was caused by oroclinal bending of the existing faults generated by block rotations in opposite directions and is inferred to have been closely related to the East Sea (i.e. Sea of Japan) opening. |
