Rifting to spreading at the Korean margin

Abstract

While diverse opening models of the East Sea (Japan Sea) have been proposed so far, the structural evolution of the eastern Korean margin has not been investigated where back-arc rifting and breakup leading to the separation of the Japan Arc from the Korean Peninsula took place. We interpreted marine seismic profiles in conjunction with swath bathymetry and magnetic data to address rifting to breakup processes at the Korean margin. Changes in rift structure are recognized between the northern and southern parts of the margin. In the northern part, rifting occurred in the Korea Plateau, a continental fragment extended and partially segmented from the Korean Peninsula, that provided a relatively broader zone of extension resulting in a number of rifts. Two distinguished rift basins (Onnuri and Bandal Basins) in the Korea Plateau are bounded by major synthetic and smaller antithetic faults, creating wide and symmetric profiles. The large-offset border fault zones of these basins have convex dip slopes and demonstrate a zig-zag arrangement along strike. In contrast, the southern margin is engraved along its length with a single narrow rift basin (Hupo Basin) that is an elongated asymmetric half-graben. The rifting architecture at the Korean margin exhibits fundamental elements comprizing a seaward succession of a rift basin and an uplifted rift flank passing into the slope. Breakup is interpreted to have occurred along the base of the slope. Rifting was primarily controlled by normal faulting resulting from extension orthogonal to the line of breakup. Although rifting involved no significant volcanism, the inception of sea floor spreading documents a pronounced volcanic phase which seems to reflect slab-induced asthenospheric upwelling as well as rift-induced convection. We suggest that structural and igneous evolution of the Korean margin can be explained by the processes occurring at the passive continental margin with magmatism intensified by asthenospheric upwelling