OROGEN-SCALE TRANSFORM FAULTS, OROCLINES AND MIS-ORIENTED THRUST BELTS, NORTHWESTERN NORTH AMERICAN CORDILLERA: THE PACIFIC-ARCTIC-ATLANTIC CONNECTION

The North American Cordillera is a complex collage of terranes of different paleogeographic origins and tectonic histories. Much of the complexity of this collage results from displacements on Paleogene orogen-scale transform faults and fault systems, structures that post-dated the initial juxtaposition of these terranes (e.g. Tintina, Denali). The complexity of the collage is exacerbated in Alaska by Paleogene oroclinal buckling of pre- and syn-Paleogene features around the N-closing Alaska embayment (AE) and the S-closing Bering salient (BS). A third order of complexity is introduced by Paleogene N-striking thrust-fold belts in northern Yukon (e.g. northern Ogilvie, Richardson).

Temporal overlap of transforms and oroclines is inferred from map geometry. At the hinge of the AE, the single-strand Tintina and Denali faults pass westwardly into radiating networks of SW-striking faults that largely converge with the western part of the Denali fault near its hinge in the BS. This geometry suggests that fault splays originated in alignment with transforms but rotated with oroclinal bending and were abandoned in favour of new aligned segments. The W-ward continuation of this network around the BS into the Bering shelf is not known but represents >900km of cumulative dextral displacement.

Temporal overlap of transforms and N-striking thrust-fold belts is inferred from cross-cutting relationships. Although the N-striking thrust-fold belts of northern Yukon are cut by the Tintina fault, the southern wrench boundary of the thrust system is geometrically constrained to be one of the SW splays of the Tintina network.

Following others, this network of structures is interpreted as an integrated kinematic response to: 1) E-W shortening between the Eurasian and North American portions of a continuous continental plate, to accommodate opening of the Eurasian and North Atlantic basins, and 2) NW-ward motion of the western part of North America while coupled to the plates of the Pacific ocean following Early Paleogene plate re-organization. The NW-ward motion of the coupled western North America and Pacific plates is manifest by the transform faults; E-W shortening between Eurasia and North America is manifest by the oroclinal buckling around N-striking axial surfaces and the N-striking thrust-fold belts of northern Yukon.