INVESTIGATING LANDSCAPE ANTIQUITY AND CENOZOIC DRAINAGE DEVELOPMENT OF SOUTHERN YUKON (CANADA), THROUGH RESTORATION MODELING OF THE CORDILLERAN-SCALE TINTINA FAULT

This study of southern Yukon (Canada) challenges the notion that the landscape in the long-lived, tectonically active, northern Canadian Cordillera is implicitly young. The impact of Cenozoic displacement along the continental- scale Tintina Fault on the development of the Yukon River and drainage basins of central Yukon is investigated through geophysical and hydrological modeling of digital terrain model data. Regional geological evidence suggests that the age of the planation of the Yukon plateaus is at least Late Cretaceous, rather than Neogene as previously concluded, and that there has been little penetrative deformation or net incision in the region since the late Mesozoic. The Tintina Fault has been previously interpreted as having experienced ~430 km of dextral displacement, primarily during the Eocene. However, the alignment of river channels across the fault at specific displacements, coupled with recent seismic events and related fault activity, indicate that the fault may have moved in stages over a longer time span.

Topographic restoration and hydrological models show that the drainage of the Yukon River northwestward into Alaska via the ancestral Kwikhpak River was only possible at restored displacements of up to ~50-55 km on the Tintina Fault. We interpret the published drainage reversals convincingly attributed to the effects of Pliocene glaciation as an overprint on earlier Yukon River reversals or diversions attributed to tectonic displacements along the Tintina Fault. At restored fault displacements of between 230 and 430 km, our models illustrate that paleo Yukon River drainage conceivably may have flowed eastward into the Atlantic Ocean via an ancestral Liard River which was a tributary of the paleo Bell River system.

The revised drainage evolution, if correct, requires wide-reaching reconsideration of surficial geology deposits, the flow direction and channel geometries of the region’s ancient rivers, and importantly, exploration strategies of placer gold deposits.