In the Hidaka Collision Zone of Hokkaido, northern Japan, the Kuril island are collides with the northeast Japan arc. In order to better understand the collision process, new high resolution information about lithospheric structure was obtained by means of a series of seismic reflection surveys. These seismic profiles reveal distinct zones of seismic lamination in the lower crust of the Kuril arc. The upper portion of the lower crust is characterized by numerous east-dipping reflectors. In contrast, west-dipping reflectors dominate the lower part of the lower crust. From this reflector configuration, the lower crust of the Kuril arc is interpreted to be delaminated by the collision. The geometry of delamination is consistent with other geophysical data, as well as the peak metamorphic grades exposed in the Hidaka mountains. As earthquakes indicate that delamination here is ongoing, the Hidaka Collision Zone represents an active model for continental growth by arc accretion with delamination of lower arc crust. ¿ 1999 American Geophysical Union