Tectonics of sedimentary basins in and around Japan since the opening of the Sea of Japan

Abstract

The opening of the Sea of Japan, associated with detachment of the Japan Arc from the Asian Continent, was the most significant Cenozoic event in Japan. Previous geophysical investigations in back-arc basins surrounding Japan have revealed that the Sea of Japan, the Shikoku Basin, and the Chishima Basin opened almost simultaneously from 24 to 15 Ma. However, the Sea of Japan’s opening mechanism and the paleoposition of the Shikoku Basin have been debated until now. Recently acquired high-resolution radiometric data have clarified that the Sea of Japan opened over multiple stages concurrent with repeated rifting events on land. Initial rifting occurred between 44 and 30 Ma, and its cessation is marked by an Oligocene unconformity (30-21 Ma). Rifting resumed at 21 Ma, increasing in intensity (18-15 Ma) before transitioning into a post-rift phase between 15 and 13.5 Ma.

High-resolution age data have clarified the multi-stage, post-rift development of northeast and southwest Japan. Compressional tectonics, starting at ~12 Ma in NE Japan, caused uplift of the Ou Backbone Range and subsidence of the Onnagawa Basin. These events also had a marked effect on the paleoenvironment of the Sea of Japan, resulting in the deposition of hydrocarbon source rocks. This compression gradually intensified from 6.5 Ma, with an oscillating stress state indicated by stepwise post-Miocene basin inversion and fold growth along the coastline of the Sea of Japan. In contrast, uplift in SW Japan (at ~15 Ma) was associated with compressional deformation, and outer-arc and Setouchi volcanism. Following north-south compression in the late Miocene, the tectonic regime switched to compressional and transcurrent deformation at 6 Ma, probably due to the resumption of movement of the Philippine Sea Plate.