CAUSES OF ALONG-STRIKE VARIATION IN THE BROOKS RANGE OROGEN OF NORTHERN ALASKA
Along-strike variation in the two orogenic belts differ because of the types of basement involved in their deformation and changes in the style of tectonism. The Early Cretaceous belt developed during subduction of the northern margin of North America prior to rifting of the Arctic Alaska terrane away from this margin. A linear pattern of deformation occurs in the eastern and central areas due to the presence of Neoproterozoic to middle Paleozoic slope facies and overlying Upper Paleozoic and Lower Mesozoic platform facies strata that were deposited along the North American craton margin. To the west, the basement includes thick Baltica-derived continental crust of the Chukchi platform, which may have produced the deflection of trends to the NW. Alternatively, Early Cretaceous deformation in Chukotka may have been caused by a westward change to Andean-style retroarc thrusting. In contrast, the more northerly propagation of Cenozoic shortening resulted in involvement of a rifted fragment of the craton-margin crust of North America in the northeastern Brooks Range. This produced higher uplift than where underlain by deformed slope deposits to the west. Farther west, the Cenozoic deformation terminates against the thick continental crust of the Chukchi platform.