Editing Laramide orogeny (section)

{{Short description|Period of mountain building in North America}}

The '''Laramide orogeny''' was a time period of [[mountain building]] in western [[North America]], which started in the [[Late Cretaceous]], 80 to 70 million years ago, and ended 55 to 35 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 in time and space.<ref>{{harvnb|Willis|2000}}</ref>
[[File:Shallow subduction Laramide orogeny.gif|thumb|right|upright=1.333|The Laramide orogeny was caused by subduction of a plate at a shallow angle.]]
The orogeny is commonly attributed to events off the west coast of North America, where the [[Kula Plate|Kula]] and [[Farallon Plate]]s were sliding under the [[North American Plate]]. Most hypotheses propose that oceanic crust was undergoing [[flat-slab subduction]], that is, [[subduction]] at a shallow angle. 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.

Magmatism associated with subduction occurred not near the plate edges (as in the [[volcanic arc]] of the [[Andes]], for example), but far to the east, along the [[Colorado Mineral Belt]].<ref name="JonesEtal2012">{{cite journal |last1=Jones |first1=Craig |last2=Farmer |first2=Lang |last3=Sageman |first3=Brad |last4=Zhong |first4=Shijie |title=Hydrodynamic mechanism for the Laramide orogeny |journal=Geosphere |date=2012 |volume=7 |issue=1 |pages=183 |doi=10.1130/GES00575.1|doi-access=free }}</ref> Geologists call such a lack of volcanic activity near a [[subduction zone]] a [[magmatic gap]]. This particular gap may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter [[asthenosphere]].<ref>{{harvnb|Dumitru|Gans|Foster|Miller|1991}}</ref> One result of shallow angle of subduction and the drag that it caused was a broad belt of mountains, some of which were the progenitors of the [[Rocky Mountains]]. Part of the proto-Rocky Mountains would be later modified by extension to become the [[Basin and Range Province]].