COLLISION OF THE OLYUTORSKY TERRANE, KAMCHATKA

The accretion of the Olyutorsky terrane is a defining event in the northern Pacific and the north-westernmost North American Cordillera. The suture zone extends for about 3000 km along the Kamchatka Peninsula and into the Bering Sea where is ends against the Aleutian arc. The Olyutorsky collision zone, consists of the Olyutorsky arc in the hangingwall and the Ukelayat flysch in the footwall. The suture zone is intermittently exposed onland and is mapped at the Vatyna and Lesnaya thrusts. The Olyutorsky arc has low-latitude paleomagnetic signature and traveled rapidly on Pacific plates to the NE Asian margin. The footwall of the collision zone in Kamchatka is marked by the Ukelayat flysch and its stratigraphic equivalents, which are overthrust by the Olyutorsky arc. The Ukelayat flysch is a 10-to-15-km-thick zone of deformed turbidites that accumulated in forearc region of the Okhotsk-Chukotka continental Arc that was active in the mid to Late Cretaceous and extends across NE Asia eastward to the western Alaskan margin. Detailed geochronology along the suture zone in a number of study areas in Kamchatka suggest that the collision proceeded from south to north. In southern Kamchatka (Sredinny Range), collision is inferred to be to be synchronous with peak metamorphic conditions attained in the Early Eocene (~52 Ma) while post orogenic exhumation occurred in the middle to late Eocene (~40-42 Ma). In central and northern Kamchatka, collision occurred slightly later (~45 Ma), and the suture is only shallowly exhumed (~3-4 km). The Shirshov and Bowers ridges in the Bering Sea may represent the submarine continuation of the Olyutorsky arc. If this is the case, collision must have predated the establishment of the Aleutian Ridge; in fact it is likely that collision of the Olyutorsky terrane changed the plate geometry and forced the initiation of outboard subduction at ~45 Ma.