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During the Mesozoic, the North American tectonic plate migrated westward from its accretionary eastern margin at the Mid-Atlantic Ridge, over the Kula-Farallon oceanic plates at its consuming western margin. The east-dipping Andean-type subduction at this western margin produced the igneous arc rocks of the Sierra Nevada-Idaho batholith. The accompanying horizontal shortening in the North American plate was manifested farther east in the generally eastward-younging thrust faulting of the Nevadan, Sevier, and Laramide events.

During Tertiary time, continued westward movement of the North American plate brought it over a large mantle hot-spot system. As the North America lithosphere delaminated, its upper crustal part moved westward over the hot-spot material and its lower, mantle lithosphere moved westward beneath the hot-spot material. The associated heating of the western part of the North American crust triggered the formation of ignimbrites in the Great Basin and produced thermal uplift of the entire Western Cordillera. Hot-spot activity also induced a westward-directed extensional tectonic regime in the overlying plate, which produced normal faulting in the brittle upper crust and ductile stretching in the lower crust. The crustal thinning caused by this extension resulted in downward migration of the brittle-ductile transition zone, apparently in a discontinuous manner, such that older and higher brittle-ductile transition detachments, where present, are involved in the hanging walls of deeper and younger brittle-ductile transition detachments. This delamination and extensional activity is continuing today.

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