DOES THE BROOKS RANGE OROGEN EXTEND INTO CHUKOTKA?

TORO, Jaime, Department of Geology and Geography, West Virginia Univ, 425 White Hall, P.O. Box 6300, Morgantown, WV 26506-6300, [email protected], MILLER, Elizabeth, Geological and Environmental Sciences, Stanford Univ, Stanford, CA 94305-2115, and KATKOV, Sergey, Geological Institute, Russian Academy of Sciences/MGU, Pyzhevsky 7, Moscow, 119017, Russia

Models of the evolution of the circum-Arctic assume that the Brookian Orogen continues to the west as the Chukotka fold-belt of Russia. Although the two fold-belts are approximately coeval, they differ in geometry, kinematics, structural style, timing, and in the role of magmatism. Several of the lithotectonic belts of the Brooks Range have no clear counter parts in Chukotka or if there is an equivalent, significant tectonic differences exist. For example, although oceanic assemblages of the Angayucham terrane have been correlated with the South Anyui suture zone, a Late Jurassic-Early Cretaceous volcanic arc existed on the southern margin of Chukotka indicating that polarity of subduction during oceanic closure was opposite from that of the Brookian margin. The Schist and Central metamorphic belts of the Brooks Range have no equivalents in Chukotka where the mid-crustal portion was usually not exhumed. Instead, areas of high-grade metamorphism in Chukotka correspond to gneiss domes associated with large granitic plutons and with extensional deformation. The Chukotka fold-belt is peppered by Early to mid-Cretaceous granodioritic plutons presumably of a subduction-related origin while the Brooks Range lacks Cretaceous magmatism. The structural style of the Brooks Range fold-belt is characterized by a stack of far-traveled north-vergent allochthons involving Paleozoic to Jurassic rocks. In contrast, the bulk of the Chukotka fold-belt is developed in a thick basinal succession of Triassic-Jurassic turbidites. The early Triassic section contains abundant gabbro dikes and may be part of a failed-rift system that extends to the eastern side of the Urals. The presence of this thick clastic section had a profound effect on the structural style in Chukotka, where upright folding and penetrative deformation dominate in the southern part of the belt, while an internally imbricated thrust sheet (Myrgovan sheet) of Late Jurassic strata is found in the central part. To the north and west, early fabrics are overprinted by a subhorizontal foliation centered in the Alarmaut dome. Finally, syntectonic deposits equivalent to the Colville foreland basin of Northern Alaska are conspicuously absent in Chukotka. It is possible that this basin lies to the north in the East Siberian shelf, but it has not been unambiguously identified.