Arc deformation and marginal basin opening: Japan Sea as a case study

Abstract

We discuss the opening mechanism of the Japan Sea in Miocene time using (1) tectonic and published paleomagnetic data along the eastern margin from the north of Hokkaido Island to Sado Island, (2) a mechanical model which is tested by small‐scale physical modeling, and (3) crustal structure and bathymetric features in the Japan Sea which constrain our kinematic model and preopening reconstructions. Our main conclusions are the following. The eastern margin of the Japan Sea was, as a whole, a dextral shear zone about 100 km wide. This conclusion is supported by the existence of a ductile dextral shear zone in Central Hokkaido (Hidaka Mountains) and associated brittle deformation in western Hokkaido and northeastern Honshu. The stress field during the opening (which ended about 12 Ma ago at the end of the middle Miocene) changes from right‐lateral transpression in the north to right‐lateral transtension in the south. The western margin, along the Korean peninsula, during the same period, also was an active dextral shear zone. Paleomagnetic results indicate that clockwise rotations occurred in the south during the opening and counterclockwise rotations in the north. We propose a model of right‐lateral pull‐apart deformation with clockwise rotations of rigid blocks in the southern transtensional domain and counterclockwise rotations in the transpressional one. Small‐scale physical models show that the clockwise rotation in transtension is possible provided that the eastern boundary (Pacific side) is free of stress. The opening stopped and compression subsequently began about 12 Ma ago. Finally, we show that the dextral shear, which is distributed over the whole Japan Sea area, is accommodated by N‐S trending right‐lateral faults and rotation of blocks located between these right‐lateral faults.

Neogene Kinematics in the Japan Sea Region and Volcanic Activity of the Northeast Japan Arc

“…This major feature was active during the opening of the Japan Sea and implies a large north-south component for the displacement of Japan relative to Asia. As stated earlier in Lallemand and Jolivet (1985) and Jolivet et al (1991), this north-south motion is accommodated by dextral motion along the Yangsan and Tsushima north-south-trending faults between South Korea and Japan (Fig. 1).…”

“…The motion of Northeast Japan relative to Asia can be further constrained by the observation that the transfer faults that separate the en-echelon grabens have a changing orientation from north to south and fit very well in small circles about a pole located west of Korea (Fig. 4) (Jolivet et al, 1991). This is the pole we shall use in our reconstructions, thus assuming that these faults are purely dextral faults.…”

“…The crustal structure in the Figure 1. Tectonic map of the Japan Sea region showing the distribution of oceanic crust (dark) and continental blocks identified by Tamaki (1988), modified after Jolivet et al (1991). Sites 794 through 799 of Legs 127 and 128 are shown as well as Sites 436,438,440, and 584 of previous DSDP legs.…”

“…1 and 3). A study of brittle structures was then completed along the entire eastern margin from Rebun Island in the north to Noto Peninsula and Yatsuo Basin in the south (Jolivet et al, 1991;M. Fournier, unpub.…”

“…The geometry of our reconstructions is constrained by (1) the internal bathymetric features and crustal structures of the Japan Sea derived from geophysical studies (Tamaki, 1988), and (2) the deformation mechanism along the eastern margin of the Japan Sea (Jolivet et al, 1991) based on field data and small-scale physical modeling.…”