Солтүстік Америкадағы Невада тау жасалу оқиғасы

Mountain building event in North America
The Nevadan orogeny occurred along the western margin of North America during the Late Jurassic to Early Cretaceous approximately 155 Ma to 145 Ma. It is noted that the Klamath Mountains and the Sierra Nevada share similar stratigraphy indicating that they were both formed by the Nevadan orogeny. In comparison with other orogenic events, it appears that the Nevadan Orogeny occurred rather quickly taking only about 10 million years as compared to hundreds of millions of years for other orogenies around the world (ex. Trans Hudson orogeny).

The Nevadan Orogeny began with the formation of a continental volcanic arc due to east dipping subduction of the Farallon Plate beneath the North American Plate. The accretion of arc terranes resulted in the generation of three distinct belts in the Sierra Nevada: the Western belt, Central belt, and Eastern Belt. This melting may be assisted by the presence of water in what is known as flux melting. It was determined that the deformation was minimal in the Eastern Belt by looking at dikes that had intruded the rocks which appeared to be mostly undeformed. The Calaveras greenschist complex is located in the western half of the Central Belt and essentially consists of volcanic arc rocks along with small amounts of chert and argillite. In the southern part of the Western Belt the rocks have undergone folding as the main type of deformation. The age of these rocks was dated using potassium argon dating (K Ar). These dikes are proposed to have been formed when the North American plate underwent a change in motion direction so that subduction was no longer occurring in a northeast direction but in the southeast direction. Once the Western Hayfork Terrane was formed (and had subsequently stopped forming) the region was intruded by mafic dikes attributed to some form of extension at approximately 160 Ma. Rather than being thrust on top of North America, the Josephine Ophiolite was accreted through a different process that involved being thrust underneath North America and then eventually being exhumed at the surface. Using the potassium argon (K Ar) method of isotopic dating on phyllite, the age of metamorphism in the Stuart Fork Formation was determined to be about 148 Ma. The metamorphism related to the phyllite in the Stuart Fork Formation is from the older Abrams and Salmon mica schists being thrust on top of the Stuart Fork rocks during the end of the Nevadan Orogeny.

The Sierra Nevada and the Klamath Mountains were the result of continental magmatic arc and then oceanic arc accretion during the Nevadan Orogeny between 155 and 145 Ma. At nearly the same time the Eastern Belt of the Sierra Nevada was forming, the Western Hayfork Terrane of the Klamath Mountains was being constructed. As the Nevadan Orogeny progressed, the Tuolumne River Terrane was accreted to the Sierra Nevada at approximately the same time as the formation of the Josephine Ophiolite in the Klamath Mountains (150 155 Ma). During the last stages of orogenesis, the sedimentary rocks of the Western Belt were accreted to the Sierra Nevada while the Abrams and Salmon mica schists were thrust on top of the Stuart Fork Formation in the Klamath Mountains.