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4. Although they collided with North America in the Great Basin
sector at about 125 Ma, the upper plate rocks accreted to
North America during the Sevier event migrated northward
during the Laramide and, because the various terranes in the
upper plate were amalgamated prior to the Laramide event
(Hildebrand, 2013), now span nearly the entire width of the
Canadian Cordillera.
5. The Cordilleran fold-thrust belt, located in the eastern
Cordillera from about Las Vegas northward, typically has no
associated magmatism and is a Laramide transpressive feature
accommodating the northward migration of rocks previously
accreted to the Great Basin sector of the margin during the
125–110 Ma Sevier event.
6. If the rapid northward migration of the Kula plate drove the
Cordilleran block northward as many believe, then the model
constrains the long-uncertain position of the Kula-Farallon
spreading ridge (Engebretson et al., 1985) to have been at least
1300 km south of the current location of the Cordilleran
block—about the latitude of La Paz, Mexico (Fig. 4).
7. Some Eocene and younger rocks, such as those of the Columbia
River Basalt Group, the Ancestral Cascades, and Siletzia, abut
directly against the remaining south-facing margin, illustrating
that the transform margin maintained a strong influence on the
distribution of geological units for about 100 m.y.
ACKNOWLEDGMENTS
Randy Enkin, Charlie Kerans, Dennis Kent, Eldridge Moores, and Charlie
Roots read the first draft and suggested improvements. Robert Hatcher
and Stephen Johnston critically reviewed the manuscript and made helpful
comments. I dedicate this paper to the memory of Ted Irving.
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