CENOZOIC NORTHWARD TRANSLATION OF THE KITAKAMI MASSIF IN NORTHEAST JAPAN - PALEOMAGNETIC EVIDENCE

Paleogene and early Cretaceous welded tuffs have been sampled from ele ven sites at the Omoe Peninsula (39.6 degrees N, 142.0 degrees E) in t he Kitakami massif of northeast Japan for paleomagnetic study. Charact eristic paleomagnetic directions with a high unblocking temperature co mponent above 560 degrees C are isolated: Westerly declinations with s hallow inclination are identified after tilt correction in the 62-71 M a Heizaki volcanics(D = 283.5 degrees, l = 9.4 degrees, alpha(95) = 8. 0 degrees) and in the 114-119 Ma Harachiyama Formation (D = 274.2 degr ees, l = -20.4 degrees), 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 pal eomagnetic directions. The presence of both normal and reversed polari ties suggests reliability of this shallow and westerly paleomagnetic d irection. The shallow inclination indicates that the Kitakami massif w as located at low latitude (5 degrees +/- 4 degrees N) at 71-62 Ma. Ta king into account a reference paleomagnetic pole of the Paleocene expe cted from Sikhote Alin, the Kitakami massif was translated northward o ver 25 degrees in latitude since 65 Ma. The Kitakami massif can be sub jected to latitudinal northward motion more than 24 degrees during the last 70 Ma, when it was transported by push of the moving Pacific pla te and reached the Asian continental margin near Sikhote Alin later th an 30 Ma. We conclude that the Kitakami massif was incorporated into n ortheast Japan at some time between 30 and 22 Ma after the Cenozoic no rthward translation. (C) 1997 Elsevier Science B.V.