Development of the intracontinental, continuous, narrow transpressional zone along the Sinnyeong Fault in the Cretaceous Gyeongsang Basin, SE Korea

The WNW-ESE-striking Sinnyeong Fault, the most conspicuous fault of the Gaeum Fault System in the Cretaceous Gyeongsang Basin of Korea, provides an opportunity to understand the architectures and evolution of an intracontinental transpressional fault zone. We focus on the structural characteristics of the Sinnyeong Fault based on detailed field observations and magnetic fabric analysis. Its main movement is interpreted as sinistral slip with a small reverse component, although it could also have been active before the main movement. The deformation zone is asymmetric about the fault core. Sedimentary strata of the southern deformation zone are more extensively folded and deformed than those of the northern part, and the southern zone is much wider than the northern zone. NW-SE-trending en-echelon folds are limited to the southern periphery of the fault zone, where it is narrow, and underwent rotation toward the fault surface. These contractional deformations along the entire length of the fault are interpreted to have formed approximately coevally with the sinistral faulting. Newly observed WNW-ESE-striking mappable faults show a similar structural feature. Our results suggest that the damage asymmetry resulted from the eastward transport direction and relative uplift of south blocks of the faults under NE-SW compressive stress, which oriented at high angle (60–70°) to pre-existing strike of the faults. During progressive deformation, continuing slip accumulation along vertically tilted and fault-parallel sedimentary strata located directly south of the fault cores was responsible for the larger motions of the southern blocks of the faults rather than the relatively fixed northern blocks. We highlight that the sinistral reactivation of the Sinnyeong Fault formed a continuous, narrow transpressional zone during its long-term evolution.