Geodynamics of an Early Eocene arc–continent collision reconstructed from the Kamchatka Orogenic Belt, NE Russia

Abstract

The principal structures of the Central and Eastern Ranges of the Kamchatka orogenic belt were formed during collision of an Upper Cretaceous–Lower Paleocene island arc with the Asian continental margin during the Early Eocene. Two major syncollisional tectonic events are recognized: westward thrusting of the island arc onto the continental margin, and eastward thrusting on the eastern side of the deformed arc accompanied by tectonic accretion of eastward-derived slices of oceanic crust. Both tectonic processes occurred under upper to middle crustal conditions. Syntectonic, high temperature–medium pressure metamorphism (up to amphibolite and granulite facies) affected the units of the arc, its oceanic basement, and the continental margin. Synkinematic gabbro-plagiogranite intrusions occurred along major décollements of both vergences. According to the geodynamic model, both of the observed tectonic events (i.e. westward overthrusting of the arc and eastward thrusting at its eastern side) represent incremental stages of a single processes that lasted over 7 Ma, and was initiated by the arc–continent collision. The first stage corresponds to southeastward continent subduction under the arc, which was soon blocked, followed by reversal of subduction polarity and the beginning of northwestward oceanic subduction.