Late Cretaceous - Eocene evolution of the Kronotsk arc

Eastern peninsulas of Kamchatka and probably Komandorskiy Islands form Kronotsk paleoarc. Main components uniting these blocks in a single structure are Paleocene-Eocene subduction-related volcanics. The lowest part of this formation on the Kronotsk peninsula was dated as the Late Senonian. Paleomagnetic data show that, 60-40 Myr ago, Kronotsk arc undergo large northern drift after a nearly equal period of southern drift. The southern part of the Kamchatskiy Mys peninsula, Africa block, is interpreted as a fragment of the accretionary prism of the Kronotsk arc, related to period of the southern drift. There are five main parts of this prism: Olenegorsk gabbro (50-70 Ma); Smaginsk Fm (Albian-Senomanian, 110-95 Ma): hot-spot basaltes and pelagic sediments; Pickezh Fm (Campanian - Maastrichtian, 85-65 Ma): tuffites in the lower part and subarcosic sandstones in the upper; and Soldatsk ultramafics. These parts of the prism are mostly separated by the large thrusts, but locally we saw the konglobrechia with gabbroic and diabasic clasts in the lowest parts of the Smaginsk and Pickezh sequences. The transition from the Pickezh Fm to Pickezh sanstones was always described as gradual. Six published paleomagnetic determinations (from Campanian to Bartonian, 80-40 Ma) of Kronotsk arc volcanics, kinematics of the large plates in the Northern Pacific, and some geological data allow us to reconstruct the drift of the Kronotsk arc at the end of Cretaceous and the first half of Paleogene. 80-60 Myr ago, Kronotsk arc marked a southern margin of the North American Plate (or a little plate with the very similar kinematics) when the Kula plate was consumed in the Kronotsk while the Kula-Pacific Ridge and Hawaiian hot spot were placed to the south. The apron of tuffs and tuffites overlapped the slopes of the newly arc and neighboring oceanic structures. One of the latter, Smaginsk oceanic plateau on the Kula plate was partly separated from this plate and attached to the Kronotsk accretionary prism. Simultaneously with these intra-oceanic events, there was a maximum of Laramie orogeny on the nearest North American continent. A huge sequence of turbidit fans was formed along western margin of Cordilleras. The Upper Pickezh sanstones are probably a small part of one of these fan included in the Kronotsk accretionary prism. At the Late Cretaceous and beginning of the Paleogene, the Kula-Pacific Ridge moved aside Obrutchev Rise and approached the Kronotsk. Therefore, the part of Kula plate south of the Kronotsk arc was constantly diminishing. As a result, 60-55 Myr ago, the subduction zone was blocked by the ridge and the western part of Kula plate was attached to the Pacific plate. This collision is the most probable cause of the strong deformation of the accretionary prism and of the emergence of the outer nonvolcanic arc that supplied the intra-arc basin (Stolbovsk Series of the Kamchatskiy Mys peninsula) with the ofiolitoclastics. The continuation of the Kronotsk volcanism after this collision is probably caused by a new subduction zone placed north of the Kronotsk arc.