TIME-SLICE MAPS SHOWING THE DISTRIBUTION OF CONTRACTIONAL DEFORMATION IN ALASKA NORTH OF 60°N

The structural architecture of Alaska is the product of a complex history of deformation that occurred along both the Cordilleran and Arctic margins of North America through interactions with ancient and modern-day ocean basins and with continental elements derived from Laurentia, Siberia, and Baltica. To analyze these events, contractional structures are assigned to 13 specified intervals of geologic time and their distributions mapped in Alaska. In general, the new maps reveal that the geology of Alaska can be divided into three domains with differing deformational histories. The northern domain consists of terranes that were involved in arc-continent collision events that produced the Early Cretaceous Brookian orogeny. This deformation impacted most terranes north of the Tintina and Kaltag faults and resulted from the subduction of the outboard northern margin of North America beneath oceanic arcs of the Paleo-Pacific Ocean. The second domain lies south of the Denali Fault in southern Alaska and includes the Peninsular-Wrangellia oceanic magmatic arc terrane and its associated Chugach accretionary prism. The Peninsular and Wrangellia terranes were amalgamated by Middle or Late Jurassic tectonic events. Chugach forearc accretion occurred episodically since the Early Jurassic, interrupted by episodes of subduction erosion, ridge subduction in the Paleogene, and collision with the Yakutat terrane in the Neogene. The third domain, situated between the first two domains and roughly bounded by the Denali and Tintina faults includes the large Farewell and Yukon-Tanana terranes. Both terranes display a locally important episode of Permian collisional deformation (Browns Fork and Klondike orogenies). However, a later episode of Middle Jurassic deformation affected only the Yukon-Tanana terrane. Our maps reveal little evidence for final assembly by collisional processes in this domain, although overlapping sedimentary basins indicate that assembly occurred by the Late Cretaceous. This indicates that this part of Alaska was assembled mainly by strike-slip tectonics. Folding and thrusting of the basinal strata within and between these three domains in the Late Cretaceous may mark the final collision and consolidation the southern domain with the remainder of Alaska.