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Laramide orogeny
 
 
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The Laramide orogeny was a period of mountain building in western North America
North America

North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere....
, which started in the Late Cretaceous
Late Cretaceous

Late Cretaceous refers to the second half of the Cretaceous Period , named after the famous white chalk cliffs of southern England, which date from this time....
, 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, as is the cause. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny
Orogeny

Orogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event: orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust, and happen within a specific period of time....
 was the Rocky Mountains
Rocky Mountains

The Rocky Mountains, often called the Rockies, are a mountain range in western North America. The Rocky Mountains stretch more than 4,800 kilometre from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States....
, but evidence of this orogeny can be found from Alaska
Alaska

Alaska is the largest U.S. state of the United States by area; it is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait....
 to northern Mexico
Mexico

The United Mexican States , commonly known as Mexico , is a federalism constitutionalism republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of Mexico....
, with the easternmost extent of the mountain-building represented by the Black Hills
Black Hills

The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States....
 of South Dakota
South Dakota

South Dakota is a U.S. state located in the Midwestern United States of the United States of America. It is named after the Lakota people and Sioux Sioux Native Americans in the United States tribes....
.






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The Laramide orogeny was a period of mountain building in western North America
North America

North America is the northern continent of the Americas, situated in the Earth's northern hemisphere and almost totally in the western hemisphere....
, which started in the Late Cretaceous
Late Cretaceous

Late Cretaceous refers to the second half of the Cretaceous Period , named after the famous white chalk cliffs of southern England, which date from this time....
, 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, as is the cause. The Laramide orogeny occurred in a series of pulses, with quiescent phases intervening. The major feature that was created by this orogeny
Orogeny

Orogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event: orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust, and happen within a specific period of time....
 was the Rocky Mountains
Rocky Mountains

The Rocky Mountains, often called the Rockies, are a mountain range in western North America. The Rocky Mountains stretch more than 4,800 kilometre from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States....
, but evidence of this orogeny can be found from Alaska
Alaska

Alaska is the largest U.S. state of the United States by area; it is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait....
 to northern Mexico
Mexico

The United Mexican States , commonly known as Mexico , is a federalism constitutionalism republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of Mexico....
, with the easternmost extent of the mountain-building represented by the Black Hills
Black Hills

The Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, United States....
 of South Dakota
South Dakota

South Dakota is a U.S. state located in the Midwestern United States of the United States of America. It is named after the Lakota people and Sioux Sioux Native Americans in the United States tribes....
. The phenomenon is named for the Laramie Mountains
Laramie Mountains

The Laramie Mountains are a mountain range of moderately high peaks on the eastern edge of the Rocky Mountains in the states of Wyoming and Colorado in the United States....
 of eastern Wyoming
Wyoming

The State of Wyoming is a sparsely populated U.S. state in the Northwestern United States of the United States. The majority of the state is dominated by the mountain ranges and rangelands of the Rocky Mountains, while the easternmost section of the state is a high altitude prairie region known as the High Plains ....
.

The orogeny is commonly attributed to events off the west coast of North America, where the Kula
Kula Plate

The Kula Plate is an oceanic tectonic plate under the northern Pacific Ocean south of the Near Islands segment of the Aleutian Islands. It is subduction under the North American Plate at the Aleutian Trench and is surrounded by the Pacific Plate....
 and Farallon Plate
Farallon Plate

The Farallon Plate was an ancient oceanic plate, which began subducting under the west coast of the North American Plate— then located in modern Utah— as Pangaea broke apart during the Jurassic period....
s were sliding under the North American plate
North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland and part of Siberia. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia....
. Most hypotheses propose that the angle of subduction
Subduction

In geology, subduction is the process that takes place at convergent boundary by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge....
 became shallow, and as a consequence, no magmatism occurred in the central west of the continent, and the underlying oceanic lithosphere
Lithosphere

File:Plates tect2 en.svgFile:Earth-crust-cutaway-english.svgThe lithosphere is the rigid outermost shell of a rocky planet....
 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
Volcanic arc

A volcanic arc is a chain of volcanos or mountains formed by plate tectonics as an oceanic tectonic plate subduction under another tectonic plate and produces magma....
 of the Andes
Andes

The Andes form the world's longest exposed mountain range. They lie as a continuous chain of highland along the western coast of South America. The range is over 7,000 km long, 200-700 km wide , and of an average height of about 4,000 m ....
, for example), but far to the east, called the Coast Range Arc
Coast Range Arc

The Coast Range Arc was a large volcanic arc system, extending from northern Washington through British Columbia and the Alaska Panhandle to southwestern Yukon, a distance more than ....
. Geologists call such a lack of volcanic activity near a subduction zone a magmatic null. This particular null may have occurred because the subducted slab was in contact with relatively cool continental lithosphere, not hotter asthenosphere
Asthenosphere

The asthenosphere is the mechanically weak ductily-deforming region of the upper Mantle of the Earth. It lies below the lithosphere, at depths between 100 and 200 km below the surface, but perhaps extending as deep as 400 km ....
. 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.

Compare the earlier Sevier orogeny
Sevier orogeny

The Sevier orogeny was a mountain-building event that affected western North America from Canada to the north to Mexico to the south. This orogeny was the result of convergent boundary tectonism between approximately 140 million years ago, and 50 Ma....
 and the still-earlier Nevadan orogeny
Nevadan orogeny

The Nevadan Orogeny was a major mountain building event that took place along the western edge of ancient North America between the Mid to Late Jurassic ....
 of the late Jurassic
Jurassic

The Jurassic is a geologic period that extends from about annum to  Ma, that is, from the end of the Triassic to the beginning of the Cretaceous....
 — early Cretaceous
Cretaceous

The Cretaceous , usually abbreviated K for its German translation Kreide, is a geologic period from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period....
.

See also

  • Geology of the Rocky Mountains
    Geology of the Rocky Mountains

    The geology of the Rocky Mountains reveals a discontinuous series of mountain ranges with distinct geological origins. Collectively these make up the Rocky Mountains, a mountain system that stretches from Canada through central New Mexico and which is part of the great mountain system known as the Western Cordillera ....
  • Geology of the Pacific Northwest
    Geology of the Pacific Northwest

    The geology of the Pacific Northwest refers to the study of the composition , structure, physical properties and the processes that shape the Pacific Northwest region of the United States and Canada....


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