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Inconsistencies between regional seismicity and block tectonic models, the recent recognition of the Bering plate, and the availability of global positioning system data motivated a large-scale kinematic analysis of Alaska and western Canada. We provide a synoptic view of the neotectonics of the region through kinematic modeling of the longterm strain rate and velocity field constrained by geologic and geophysical observations. Our results provide evidence that a wide zone of diffuse deformation defines the boundaries between the North America, Pacific, and Bering plates, and that the relative motion between these plates may be the source for much of the modern deformation. [ABSTRACT FROM AUTHOR]

The northern Cordilleran fold-and-thrust belt in Canada and Alaska is at the boundary between the broad continental margin mobile belt and the stable North American craton. The fold-and-thrust belt is marked by several significant changes in geometry: cratonward extensions in the central Yukon Territory and northeastern Alaska are separated by marginward re-entrants. These geometric features of the Cordilleran mobile belt are controlled by relations between lithospheric strength and compressional tectonic forces developed along the continental margin. Regional magnetic anomalies indicate deep thermal and compositional characteristics that contribute to variations in crustal strength. Our detailed analysis of one such anomaly, the North Slope deep magnetic high, helps to explain the geometry of the fold-and-thrust front in northern Alaska. This large magnetic anomaly is inferred to reflect voluminous mafic magmatism in an old (Devonian?) extensional domain. The presence of massive amounts of mafic material in the lower crust implies geochemical depletion of the underlying upper mantle, which serves to strengthen the lithosphere against thermal erosion by upper mantle convection. We infer that deep-source magnetic highs are an important indicator of strong lower crust and upper mantle. This stronger lithosphere forms buttresses that play an important role in the structural development of the northern Cordilleran fold-and-thrust belt. [ABSTRACT FROM AUTHOR]