Cenozoic northward translation of the Kitakami massif in northeast Japan: paleomagnetic evidence

Paleogene and early Cretaceous welded tuffs have been sampled from eleven sites at the Omoe Peninsula (39.6°N, 142.0°E) in the Kitakami massif of northeast Japan for paleomagnetic study. Characteristic paleomagnetic directions with a high unblocking temperature component above 560°C are isolated: Westerly declinations with shallow inclination are identified after tilt correction in the 62–71 Ma Heizaki volcanics (D=283.5°, I=9.4°, α95=8.0°) and in the 114–119 Ma Harachiyama Formation (D=274.2°, I=−20.4°). The shallow inclination, which was previously reported from early Cretaceous plutonic rocks without tilt correction in the Kitakami massif, has been discovered in the tilt-corrected paleomagnetic directions. The presence of both normal and reversed polarities suggests reliability of this shallow and westerly paleomagnetic direction. The shallow inclination indicates that the Kitakami massif was located at low latitude (5°±4°N) at 71–62 Ma. Taking into account a reference paleomagnetic pole of the Paleocene expected from Sikhote Alin, the Kitakami massif was translated northward over 25° in latitude since 65 Ma. The Kitakami massif can be subjected to latitudinal northward motion more than 24° during the last 70 Ma, when it was transported by push of the moving Pacific plate and reached the Asian continental margin near Sikhote Alin later than 30 Ma. We conclude that the Kitakami massif was incorporated into northeast Japan at some time between 30 and 22 Ma after the Cenozoic northward translation.