Abstract
Paleo-and rock magnetic experiments were carried out on the Cretaceous Yezo Supergroup in the Urakawa area (southern central Hokkaido) in order to detect tectonic episodes of the ancient eastern Eurasian margin. Characteristic remanent magnetization determined for five sites resides in magnetite, and has primary origin as indicated by positive result of tilting test. Bedding-parallel fabric of anisotropy of magnetic susceptibility and anisotropic acquisition of isothermal remanent magnetization (IRM) indicate significant inclination shallowing after deposition and lock-in of remanence. Shallowing ranges from 4° to 11° for the five sites on the basis of IRM anisotropy. The flattening-corrected mean inclination is still anomalously shallow (31°). Considering the correlation between the obtained inclination data and the geomagnetic polarity Chron C33r−C32r, a block containing the Urakawa area was located at a low latitude (16.7°N) during Campanian and then has experienced at largest 3400 km northward transportation. Transcurrent fault motions along the continental margin may be responsible for the transportation, as inferred from extremely large rotational motion (−161°). The Cretaceous Yezo forearc basin contains an exotic landmass that had evolved along a remote continental margin, then been transported as a result of oblique subduction.
