Crustal Structure and Tectonic Evolution of the East Sea

Abstract

The East Sea (Japan Sea) is a back-arc basin lying on the southeastern Amur plate, separated from the Philippine Sea, Eurasia, and Pacific-Okhotsk plates by a complex border. The opening of the East Sea was initiated in the Early Oligocene by rifting and extension in the Japan Basin, followed by seafloor spreading in the Late Oligocene. The opening of the Japan Basin was achieved by a counterclockwise rotation of the NE Japan Arc. The extension in the Japan Basin propagated southwestward toward the northern part of the eastern Korean margin, inducing NW-SE rifting in the South Korea Plateau. In contrast, the southern part of the Korean margin underwent E-W extension before the Early Miocene, probably due to the N-S trending subduction off the SW Japan Arc. Back-arc rifting at the Korean margin gave way to breakup at the base of the continental slope, after which the SW Japan Arc was separated southeastward with a clockwise rotation, opening the Ulleung Basin. Part of the Ulleung Basin is underlain by thicker-than-normal oceanic crust generated by seafloor spreading with hotter-than-normal mantle temperature. The plate reorganization in East Asia in the early Middle Miocene led to the East Sea closure. The anticlinal structures in the southwestern Ulleung Basin margin show NW-SE or N-S compression in the Middle Miocene-Early Pliocene and NE-SW or E-W compression since the Late Pliocene. The incipient subduction along the eastern margin of the East Sea also suggests E-W compression since the Late Pliocene. The E-W compression is probably due to the eastward movement of the Amur plate that began in the Pliocene.