Origin of volcaniclastics in the central part of a pull-apart basin, the Cretaceous Eumsung Basin, Korea

There are coarse-grained deposits, especially composed entirely of volcaniclastics in the central part of the Cretaceous Eumsung Basin, far away from the basinal margins. Primary volcanic masses are not exposed on the surface in the adjacent areas. For unraveling the origin of the volcaniclastics, subsurface magnetotelluric as well as surface sedimentological data were examined. Two resistivity profiles of crossed lines ES2 and ES9 represent subsurface basinal and basin-fill structures of the Eumsung Basin. In the basin fills, four high-resistivity bodies of A, B, C, and D were found. Considering the basin-scale structure and forming process of the pull-apart Eumsung Basin, it is reasonable to infer that these isolated high-resistivity bodies formed as a result of volcanic intrusion/ extrusion into/upon the basin-fill. Therefore, the coarse-grained volcaniclastic deposits in the central part of the Eumsung Basin can be interpreted as the product of syn-sedimentary deposition of volcaniclastic material that was shed from an exposed part of subsurface volcanics in a relatively short distance.