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rocks located in the Canadian Cordillera north of Whitehorse Figure 3. Google Earth® map showing key paleomagnetic results for mid- to GSA TODAY | www.geosociety.org/gsatoday
(Fig. 3). Rocks of the group sit unconformably on rocks of the Upper Cretaceous rocks and separation of Late Cretaceous–Early Cenozoic
Yukon-Tanana terrane, which collided and joined with Cassiar Laramide slab failure rocks. Symbols without inner black dots are current
platform and Selwyn basin during the Late Permian (Berenek and locations, whereas those with dots are their paleomagnetically restored
Mortensen, 2011); were all overlapped by Triassic conglomerate latitudes. Note that restoring the Lewis & Clark zone with the Texas Lineament
(Berenek and Mortensen, 2007); and cut by abundant mid-Creta- is consistent with the paleomagnetic data and also reunites the Laramide
ceous plutons (Rasmussen, 2013). Thus, the paleomagnetic results magmatic belt. Leaf margin data from Miller et al. (2006); Nanaimo points
from much younger rocks of the Carmacks Group apply to those from Kent and Irving (2010) and Kim and Kodama (2004); Carmacks from
terranes as well (Gladwin and Johnston, 2006). The results, Enkin et al. (2006a); Silverquick–Powell Creek from Enkin et al. (2006b);
supported by data from earlier, but less conclusive, studies farther Fernie, British Columbia (BC), from Enkin et al. (2000); Blue Mountains from
south in the Canadian Front Ranges (Enkin et al., 2000) led Housen and Dorsey (2005).
Randy Enkin to conclude that the majority of northward transla-
tion took place on “unidentified structures located east of the America, respectively (Housen and Dorsey, 2005; Enkin et al.,
Selwyn basin” (Enkin et al., 2006a). 2006a) so they support the geological restoration. Thus, the trans-
verse zones provide a piercing point consistent with the paleo­
Paleomagnetic studies farther south in Albian-Cenomanian magnetic data (Fig. 3).
turbiditic rocks of the Blue Mountain terranes, Oregon, yielded
paleopoles 1760 ± 460 km discordant to North American poles I propose that the restored transverse zone represents a step in
at about 93 Ma (Housen and Dorsey, 2005). Rocks of the Blue the southern margin of North America, and—because the oldest
Mountains–Riggins terranes were joined to rocks of the Belt known rocks to exhibit sinistral separation across the zone are
Supergroup along the Salmon River suture between 111 and Callovian salt deposits beneath the Gulf of Mexico—that it
90 Ma (Manduca et al., 1993; Unruh et al., 2008), and, because formed as a sinistral transform fault during Jurassic opening of
rocks of the Belt Supergroup form one giant allochthon (Sears, the central Atlantic Ocean. The northwest extent of the zone is
2007; Fuentes et al., 2012) that was thrust over Upper Cretaceous located today around southern Vancouver Island, but the
sedimentary rocks in the Cordilleran fold-thrust belt, the
paleomagnetic results from the Ochoco Basin should apply to
rocks of the Belt Supergroup as well. These results are consistent
with the Carmacks results and together indicate that northward
migration of the entire Cordilleran tectonic collage took place
along faults within or east of the Cordilleran fold-thrust belt after
about 70 Ma.

I recognized (Hildebrand, 2013, 2014) that the 125–105 Ma
Sevier event was separate and distinct from the 80–58 Ma
Laramide event and confined to the Great Basin sector of the
orogen. And, based on geological and geophysical features, such
as the distribution of eastwardly vergent thrusts, the lack of
an arc on North American crust, and compelling new mantle
tomography (Sigloch and Mihalynuk, 2013), I argued that
subduction was westerly dipping. I also noted that slab-failure
magmatism and thrust faults related to the Sevier event are not
found in the Great Basin west of the fold-thrust belt where
expected, but instead are located in the Canadian Cordillera.
This, along with the Carmacks paleomagnetic data, and evidence
that the Laramide foredeep migrated northward during the
latest Cretaceous–Paleocene (Cataneanu et al., 2000; Roberts and
Kirschbaum, 1995), led me to argue that the entire Cordillera
migrated northward during the Laramide event (Hildebrand,
2014). However, other than the band of likely slab-failure plutons
and the mismatched thrust belts, I presented no real piercing
points, so the arguments, although cogent to some, were not
compelling to all.

The left-stepping nature of the geology along both the Lewis
& Clark transverse zone and the Texas Lineament, their similar
orientations, and the observation that both appear to be truncated
at the Laramide fold-thrust belt, suggest that the two zones were
once continuous and separated during the Laramide event on one
or more faults in, or adjacent to, the thrust belt. Currently, the two
zones are ~1300 km apart. Paleomagnetic studies from the
Carmacks volcanics and the Blue Mountains terranes have paleo-
poles 1760 ± 460 and 1950 ± 600 km discordant to cratonic North

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