HR: 17:00h
AN: GP44A-05    [Abstracts]
TI: Paleomagnetism of the Kamchatka region, northeastern Russia: Implications for the evolution of the northwest Pacific Basin
AU: * Harbert, W
EM: harbert@pitt.edu
AF: Department of Geology and Planetary Science, University of Pittsburgh, 200 SRCC, Pittsburgh, PA 15260 United States
AB: The Kamchatka Peninsula of northeastern Russia is located along the northwestern margin of the Bering Sea and consists of zones of complexly deformed accreted terranes. Along the northern portion of the peninsula, progressing from the northwestern Bering Sea inland the Olyutorsky, Ukelayat, and Koryak superterranes are accreted to the Okhotsk-Chukotsk volcanic-plutonic belt in northern-most Kamchatka. Together paleomagnetic results and their close agreement with the calculated terrane trajectories strongly suggest that an island arc system moving with the Kula plate collided with this region of North American plate approximately 50 Ma (Middle Eocene). Previously published plate motion models for oceanic plate systems in this region have suggested such a subduction boundary between the Izanagi and Farallon plates. In the model of Engebretson et al. [1985] this region becomes part of the Kula plate at 85 Ma, after initiation of Kula-Farallon motion. Paleomagnetic data show that fragments of an island arc are present in the Olyutorsky superterrane and East Kamchatka superterrane as predicted by this model; perhaps the tectonostratigraphic terranes of the northern Kamchatka represent an accreted fragment of an oceanic island arc system between the Izanagi and Kula plates. The coincidence of this age of accretion (approximately 50 Ma) and the age of initiation of subduction along the Aleutian arc (estimated as Late Paleocene to Early Eocene) suggests the possibility of a causal relationship. The small circle geometry of the present day Aleutian arc and the right angle intersection of magnetic anomalies interpreted, over the oceanic plate presently beneath the eastern Bering Sea, with the arc both strongly suggest that the region now occupied by the Aleutian arc subduction zone was originally a transform fault within an oceanic plate. Given this pre-existing zone of weakness within the subducting oceanic plate and its apparent close proximity to the region undergoing obduction of the Olyutorsky superterrane during the Early Eocene, we strongly favor this model for formation of the present-day Aleutian arc subduction zone. A plate tectonic animation of this scenario will be shown.
UR: http://harbert.geology.pitt.edu
DE: 9320 Asia
DE: 8157 Plate motions--past (3040)
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting