Miocene dislocations during the formation of the Sea of Japan basin: Case study of Tsushima Island

Abstract

Lower Miocene rocks of the Taishu Group accumulated in the Tsushima pull-apart graben, which downwarped and was filled with sediments at a particularly high rate (about 2700 m/Ma), in the background of northeastern regional shortening. A considerable part of the sedimentary prism is composed of material supplied by landslide blocks from the shallow shelf. Folding and penetration of granite intrusions on Tsushima Island occurred ca. 15 Ma ago, simultaneously with the main phase of opening of the Sea of Japan, in the field of different, northwestern shortening, which had a local character and was related to clockwise rotation of the Southwestern Japan block. These rotations in turn could have been the result of an intensive rifting episode in the Central and Honshu basins of the Sea of Japan, which are located north of Tsushima Island.