The
Laramide orogeny was a period of
mountain building in western
North America, which started in the
Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the orogeny are in dispute. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this
orogeny was deep-seated,
thick-skinned deformation, with evidence of this orogeny found from
Canada to northern
Mexico, with the easternmost extent of the mountain-building represented by the
Black Hills of
South Dakota. The phenomenon is named for the
Laramie Mountains of eastern
Wyoming. The Laramide orogeny is sometimes confused with the
Sevier orogeny, which partially overlapped it in time and space. The orogeny is commonly attributed to events off the west coast of North America, where the
Kula and
Farallon Plates were sliding under the
North American plate. Most hypotheses propose that oceanic crust was undergoing
flat-slab subduction, i.e., with a shallow
subduction angle, and as a consequence, no
magmatism occurred in the central west of the continent, and the underlying oceanic
lithosphere actually caused drag on the root of the overlying continental lithosphere. One cause for shallow subduction may have been an increased rate of plate convergence. Another proposed cause was subduction of thickened oceanic crust.