By Robert S. Hildebrand
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Extra resources for Did Westward Subduction Cause Cretaceous-Tertiary Orogeny in the North American Cordillera? (Special Paper (Geological Society of America))
1992, 2004). The shutdown of arc magmatism just before the Late Cretaceous, the rapid exhumation of the central gneiss complex between 60 and 50 Ma, the voluminous Late Cretaceous–early Tertiary magmatism, and the colocation of the apparent western edge of cratonic North America in the subsurface combine to identify one region of slab failure during the Cordilleran orogeny. , 1991). , Barker and Arth, 1990). Overall, the linear belt, some 1500 km long, of Late Cretaceous–early Tertiary plutons within the Coast Range Complex may be the best-exposed example of slab failure magmatism anywhere on Earth.
On the other hand, as the lower plate rose, and a greater area of it contacted the base of the upper plate such that continued movement—most likely because the failure was diachronous (Fig. , 2005)—produced much stronger coupling between the plates. This generated consistently increasing frictional drag and shear traction forces between the plates, which caused the entire crust of the lower plate to enter a progressively heightened compressive state, at least until horizontal convergence between the two plates ceased.
Inset (A) Distribution of Cordilleran-type batholiths and 53–40 Ma arc magmatism. Inset (B) separations of Cordilleran batholiths and Tethyan-McCloud terranes along Lewis and Clark lineament (L&C) and the proposed Snake River fault (SRF). Note that the western part of the Columbia triangle is filled with Tertiary basalt. Archeocyathid-bearing limestones and Neoproterozoic diamictite occur all along the Cordillera, but they are missing from the Columbia triangle. ATL—Atlanta lobe of Idaho batholith; B—Butte, Montana; BB—Boulder batholith; BIT—Bitterroot lobe of Idaho batholith; BM—Blue Mountain–Wallowa terranes; C—North Cascades; O— Orcas Island; SRF—approximate trace of proposed Snake River fault; wisz—Western Idaho shear zone.
Did Westward Subduction Cause Cretaceous-Tertiary Orogeny in the North American Cordillera? (Special Paper (Geological Society of America)) by Robert S. Hildebrand