Nevadan orogeny
Encyclopedia
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
(between about 180 and 140 million years ago). The Nevadan orogeny
was the first of three major mountain building episodes to transform Western North America between the Late Mesozoic
and Early Cenozoic
Eras, the latter two being the Sevier
and Laramide orogeny
, chronologically. Much like the two orogenies that followed, the Nevadan was caused by the subduction
of oceanic lithosphere
at a subduction zone running along the edge of the North American continent. This resulted in relatively cool oceanic crust
descending into the lithosphere
very quickly, and steeply beneath the edge of the continent
. Due to dehydration and release of volatiles from the subducted plate, the mantle above the down-going plate was melted. This magma
rose through the mantle wedge
and the continental crust
to produce an arc of extrusive volcanoes with large intrusive batholith
s beneath. These intrusive batholiths are presently exposed as the Sierra Nevada batholith
s. Due to the steep angle of the subducted plate, these were located relatively close to continent's edge.
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
between the Mid to Late Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
(between about 180 and 140 million years ago). The Nevadan orogeny
Orogeny
Orogeny refers to forces and events leading to a severe structural deformation of the Earth's crust due to the engagement of tectonic plates. Response to such engagement results in the formation of long tracts of highly deformed rock called orogens or orogenic belts...
was the first of three major mountain building episodes to transform Western North America between the Late Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
and Early Cenozoic
Cenozoic
The Cenozoic era is the current and most recent of the three Phanerozoic geological eras and covers the period from 65.5 mya to the present. The era began in the wake of the Cretaceous–Tertiary extinction event at the end of the Cretaceous that saw the demise of the last non-avian dinosaurs and...
Eras, the latter two being the Sevier
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 tectonic activity between approximately 140 million years ago and 50 Ma. The Sevier River area of central Utah...
and Laramide orogeny
Laramide orogeny
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, as is the cause. The Laramide...
, chronologically. Much like the two orogenies that followed, the Nevadan was caused by the subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
of oceanic lithosphere
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
at a subduction zone running along the edge of the North American continent. This resulted in relatively cool oceanic crust
Oceanic crust
Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
descending into the lithosphere
Lithosphere
The lithosphere is the rigid outermost shell of a rocky planet. On Earth, it comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater.- Earth's lithosphere :...
very quickly, and steeply beneath the edge of the continent
Continent
A continent is one of several very large landmasses on Earth. They are generally identified by convention rather than any strict criteria, with seven regions commonly regarded as continents—they are : Asia, Africa, North America, South America, Antarctica, Europe, and Australia.Plate tectonics is...
. Due to dehydration and release of volatiles from the subducted plate, the mantle above the down-going plate was melted. This magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
rose through the mantle wedge
Mantle wedge
A mantle wedge is a zone of mantle, triangular in cross–section, that lies between subducting and overriding tectonic plates. Flow inside the wedge is aligned with plate motions. Flux melting of material within wedge due to the release of volatiles from the underlying subducting slab results in...
and the continental crust
Continental crust
The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
to produce an arc of extrusive volcanoes with large intrusive batholith
Batholith
A batholith is a large emplacement of igneous intrusive rock that forms from cooled magma deep in the Earth's crust...
s beneath. These intrusive batholiths are presently exposed as the Sierra Nevada batholith
Sierra Nevada Batholith
The Sierra Nevada Batholith is a large batholith which forms the core of the Sierra Nevada mountain range in California, USA, exposed at the surface as granite....
s. Due to the steep angle of the subducted plate, these were located relatively close to continent's edge.