Multiple deformations along the Honam shear zone in southwestern Korea constrained by Rb–Sr dating of synkinematic fabrics: Implications for the Mesozoic tectonic evolution of northeastern Asia

The Honam shear zone, dextrally running along the southern margin of the Ogcheon belt, Korea, has drawn much attention in reconstructing the Mesozoic tectonic framework of northeastern Asia. Here we present Rb–Sr data for the middle to southwestern part of the Honam shear zone, in an attempt to directly determine ages of deformation. In the middle part, the younger limit of deformation is constrained to be 162 ± 11 Ma by feldspar–biotite Rb–Sr dating of the deformed Sunchang granodiorite. On the other hand, an early Cretaceous deformation age is estimated for synkinematic fibers in ultramylonites from the southwestern part by two reproducible Rb–Sr errorchrons at 138 ± 4 and 139 ± 23 Ma. This deformational time scale is consistent with earlier interpretations based on field evidence, magnetic susceptibility data, and age data for Jurassic plutons within the shear zone. Our data demonstrate that the Honam shear zone is not a Permian to Triassic tectonic feature related to the Chinese continental collision.