TOWARDS A CRETACEOUS PALEOGEOGRAPHY OF NW LAURENTIA: UNTYING THE TINTINA-KALTAG-KOBUK KNOT

Alaska and Yukon are traversed by several major Cenozoic faults that obliquely truncate a complex distribution of terranes of different paleogeographic affinities. These include strike-slip faults such as the Tintina, Kaltag, Kobuk, and Denali faults in central and northern Alaska, as well as thrust faults at the leading edge of the Brooks Range – North Yukon fold and thrust belts. The relationship between these structures is not understood but is key to paleogeographic reconstruction. The Tintina is a northwest-striking dextral strike-slip fault with about 430 km of early Tertiary displacement. The trace of the Tintina converges with the merged traces of two northeast-striking faults, the Kaltag and Iditarod-Nixon Fork (KINF), with a cumulative displacement of about 220 km. Poor exposure characterizes the area of convergence. Some models portray the Tintina and KINF as a single fault system, connected through a 55 degree bend by the Victoria Creek fault. However, the disparity between KINF and Tintina displacements is great and coeval restraining bend structures sufficiently important to accommodate the difference have yet to be identified. Other interpretations consider the E-W-striking Kobuk fault a segment of the Tintina system offset by the younger KINF. In this interpretation, the KINF serves as the southern wrench boundary for the mid-Tertiary North Yukon thrust belt, required at a location near where the KINF would project through the Yukon Flats basin.

A new Cretaceous paleogeographic restoration, created using elements of previous kinematic models, yields insights into Laurentian - Eurasian terrane relationships. These include: 1) the eastern contact of the Eurasian Farewell terrane with the truncated edge of Laurentia is a post-Permian, pre-Early Jurassic structure; the lack of oceanic rocks along it suggests a strike-slip fault; 2) the timing of Farewell-Laurentian juxtaposition is similar to the re-attachment of Yukon-Tanana terrane to Laurentia by the closure of the Slide Mountain ocean, suggesting that the events may be kinematically linked, and 3) the timing of the Farewell-Laurentia juxtaposition means that Eurasian terranes attached to Laurentia on more than one occasion as the Arctic-Alaska-Laurentia boundary is a pre-Late Devonian feature.