Current tectonics of the northern Canadian Cordillera

Abstract

The northern Canadian Cordillera is remarkably tectonically and seismically active, extending from a terrane collision zone on the continental margin to an active fold and thrust belt at the eastern mountain front. The source and distribution of the deformation are constrained by (i) precision global positioning system (GPS) measurements; (ii) the seismicity distribution, mechanisms, and rates; (iii) the thermal regime; (iv) estimates of lithosphere thickness and strength; and (v) topography and gravity. The ongoing oblique collision of the Yakutat block in the northeast corner of the Gulf of Alaska has produced large deformation and uplift in the adjacent Saint Elias and Chugach mountains and appears to be responsible for the current deformation 800 km to the northeast. Northern Cordillera GPS velocities are ∼5 mm/year northeast relative to the North American Craton. Deformation rates across the eastern mountain front from earthquake statistics are similar, i.e., ∼4 mm/year of thrust shortening across the Mackenzie Mountains and right-lateral strike-slip in the Richardson Mountains. This large-scale motion is explained by a quasi-rigid displacement of the upper crust over a lower crust detachment. The detachment zone is a consequence of the high temperature of the northern Cordillera lithosphere and a weak eastern Cordillera deformation front. Regional Moho temperatures of 800–950 °C are indicated by very high heat flow and other indicators of deep temperature and by the thin lithosphere effective thickness (Te). The northern Cordillera model may have application in other areas, such as the earlier thrusting in the southern Canadian Rocky Mountains driven by terrane collision along the Pacific margin.

Current deformation in the northern Canadian Cordillera inferred from GPS measurements

“…However, plate boundary deformation is far reaching, with significant right‐lateral motion along the inland Denali fault, and current deformation across the whole northern Cordillera, apparently due to far‐field effects of the Yakutat collision far to the south. The transfer of strain from the collision zone to the eastern foreland belt (Mackenzie and Richardson Mountains) and possibly as far north as the Beaufort Sea was previously suggested by Mazzotti and Hyndman [2002] and Hyndman et al [2005a]. The current tectonics and seismicity of the region are discussed further in section 2.…”

The underestimated Proterozoic component of the Canadian Cordillera accretionary margin

“…4). It and its underlying mantle have sufficient strength or viscosity to buttress the present-day North America plate margin against convergence of the Kula-Pacific oceanic plate, but high regional geotherms suggest dynamic support, high degrees of melting and generally low viscosities (Hyndman et al 2005).…”

Foreland and Hinterland basins: what controls their evolution?

“…Due to a corner effect of the Pacific subduction, hot mantle is progressively thinning and uplifting the North American lithosphere over an extremely wide surface, accounting for the post-Laramian collapse of the Cordilleran orogen coeval with the development of metamorphic core complexes and basin and range-type extension, for recent volcanic activity, but also for the wide doming and unroofing observed in the foreland, from Canada to southern Mexico (Price 1986;Hyndman et al 2005; Fig. 15c).…”