The Origin of the Modern Kamchatka Subduction Zone

Within the Kuril-Kamchatka arc, its northern segment has a few conspicuous features lacking to the south of it: the second Quaternary volcanic belt, which ceased its activity only in the Holocene; three peninsulas (Shipunski, Kronotski and Kamchatski Mys) on the Pacific side of Kamchatka composed of the Paleocene-Eocene volcanic-sedimentary formation lacking elsewhere in Kamchatka; the significant decrease of the seismic zone depth from 650 km in the southern segment of the arc to 150-450 km beneath Kamchatka. All these features can be explained by a recent collision of the "Kronotski Arc terrain" with Kamchatka that caused the extinction of the northern part of the older subduction zone and the formation of the modern subduction zone about 150 km eastward. As the result of that, the older Central-Kamchatka volcanic belt gradually ceased its activity and a new Eastern volcanic belt formed at the same distance from the old one. A set of independent lines of evidence supports this model and gives several estimates for the age of the collision. Based on the ages of deformed deposits and the overlying volcanic rocks the time of the collision for the southern part of the Kronotski arc is 5-10 Ma. Calculations based on plate kinematics suggest the time interval of 0-10 Ma, which is in good agreement with the paleomagnetic data. A more accurate estimate was made by using the along-dip extension of the present-day slab to calculate the amount of time since the beginning of subduction: 7 Ma, 5 Ma, and 2 Ma for Shipunski, Kronotski and Kamchatski Mys segments, respectively.