Paleozoic rocks of northern Chukotka Peninsula, Russian Far East: Implications for the tectonics of the arctic region

Paleozoic rocks exposed across the northern flank of the mid-Cretaceous to Late Cretaceous Koolen metamorphic dome make up two structurally superimpos ed tectonic units: (1) weakly deformed Ordovician to Lower Devonian shallow marine carbonates of the Chegitun unit which formed on a stable shelf and (2) strongly deformed and metamorphosed Devonian to Lower Carboniferous phy llites, limestones, and andesite tuffs of the Tanatap unit Trace element ge ochemistry, Nd isotopic data; and textural evidence suggest that the Tanata p tuffs are differentiated calc-alkaline volcanic rocks possibly derived fr om a magmatic are. We interpret the associated sedimentary facies as indica tive of deposition in a basinal setting, probably a back are basin. Orthogn eisses in the core of the Koolen dome yielded a Devonian (between similar t o 369 and similar to 375 Ma) U-Pb zircon age which is similar to the ages o f the Tanatap tuffs as well as granitic plutons formed within a Devonian ac tive continental margin of northern Alaska. The stratigraphy of the Chegitu n unit is similar to that of the Novosibirsk carbonate platform which overl ies the Late Precambrian Bennett-Barrovia block. The basement of the block is exposed in Chukotka where ortogneiss in the Chegitun River valley yielde d Late Proterozoic (similar to 650 to 550 Ma) U-Pb ages. These two tectonic units form the shelf of the Chukchi and East Siberian Seas and may continu e into northern Alaska as the Hammond subterrane. The deep-water Tanatap un it can be traced along the southern boundary of the Bennett-Barrovia block from the Novosibirsk Islands to northern Alaska This basin was paired with a Devonian magmatic are that existed farther to the south. The northern mar gin of the Bennett-Barrovia block: collided with North America in the Late Silurian to Early Devonian. In Chukotka, during Middle to Late Carboniferou s time the re constructed Devonian arc-trench system at the southern edge o f the Bennett-Barrovia block collided with an unknown continental object, f ragments of which now occur to the south of the South Anyui suture. Triassi c to Cretaceous deformation strongly modified the Paleozoic units. Our resu lts provide new constraints on the geometry and Paleozoic history of the Ch ukotka-Arctic Alaska block the essential element involved in the opening of the Canada basin.