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[1] A stochastic relationship between topography and Bouguer gravity is used to calculate high-resolution variations in effective elastic thickness, T e , of the lithosphere in western Canada. The topography-gravity coherence is calculated using a two-dimensional, maximum-entropy-based spectral estimator. This method allows for smaller data windows and provides T e determinations with higher spatial resolution than standard Fourier spectral estimators. Our analysis shows significant variations in T e in western Canada. T e increases from $20-40 km in the weak, young portions of the Cordillera to 100 km and greater in the strong, old Canadian Shield. T e estimates are in good agreement with lithospheric temperatures calculated from surface heat flow and radioactive heat generation data. Our calculated T e distribution also shows strong correlation with other thermally related geophysical parameters, such as lithospheric age, regional heat flow, seismicity, seismic properties, and the stress field. Consequently, we infer that lithospheric temperatures exert a primary control on large-scale variations in T e . Collectively, the correlations readily explain why the Craton continues to be stable and undeformed, whereas the Cordillera has continued to be deformed through the Cenozoic. An exception is the Wopmay Orogen, which includes the easternmost part of the northern Cordillera. There T e is $90 km, although the surface heat flow is $90 mW/m 2 . We infer that the high heat flow in this region is caused primarily by very high radioactive heat generation in the upper crust and that deep lithospheric temperatures are moderately low as expected from its age and long-term geological stability.

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.