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 (between about 180 and 140 million years ago).^[1] 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 orogeny and Laramide orogeny, chronologically. The Nevadan orogeny is unique among the three in that it produced Andean-style stratovolcanoes, possibly reaching up to 20,000 feet (6,100 m), while the other orogenies were compressional events. The massive series of exposed batholiths that currently make up most of the high Sierra Nevada was formed during this event.

In the same way as 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 oceanic crust, being more dense than the mantle, 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 underwent partial melting. This magma rose through the mantle wedge and the continental crust to produce an arc of extrusive volcanoes with large intrusive batholiths beneath. These intrusive batholiths are presently exposed as the Sierra Nevada batholiths. Due to the steep angle of the subducted plate, these were located relatively close to continent's edge.

See also

• Nevadan Belt of the North American Cordillera
• Sierran Arc

References

1. Shaffer, Jeffrey P. "Evolution of the Yosemite Landscape — The Nevadan Orogeny". One Hundred Hikes in Yosemite.