Geometric model of conjugate faulting in the Gyeongsang Basin, southeast Korea

Abstract

The NNE trending dextral Yangsan fault system and the WNW trending sinistral Gaum fault system comprise a conjugate set that cuts the Cretaceous Gyeongsang Basin along the SE margin of the Korean Peninsula. These faults evidently formed under compressional stress accompanied by a progressive 12° block rotation, calculated from a geometric model incorporating angles between conjugate fault sets, widths of fault domains, and measured fault displacements. The angle between paleomagnetic declinations in the set of conjugate fault domains increases with age, suggesting incremental block rotation that included overall rotation of the entire Gyeongsang Basin (or the Korean Peninsula) with respect to Eurasia. The model accounts for Yucheon Group volcanism, subsequent caldera subsidence in the Uiseong subbasin, and volcanism in the Miryang subbasin, all produced by regional tension. The tectonic regime of the Gyeongsang Basin apparently evolved from compression to extension at ∼50 Ma, reflecting India‐Eurasia collision and opening of the Sea of Japan (East Sea).