Sierra Nevada Batholith
The Sierra Nevada Batholith is a large
batholithwhich forms the core of the Sierra Nevada mountain range in California, USA, exposed at the surface as granite.
The batholith is composed of many individual masses of rock called "
plutons", which formed deep underground during separate episodes of magma intrusion, millions of years before the Sierra itself first began to rise. The extremely hot, more buoyant plutons, also called "plutonic diapirs", intruded through denser, native country rock, never reaching the surface. At the same time, some magma managed to reach the surface as volcanic lava flows, but most of it cooled and hardened below the surface and remained buried for millions of years.
The batholith---the combined mass of subsurface plutons---became exposed as
tectonicforces initiated the formation of the Basin and Rangegeologic province, including the Sierra Nevada. As the mountains rose, the forces of erosioneventually wore down the material which had covered the batholith for millions of years. The exposed portions of the batholith became the familiar granite peaks of the High Sierra, including for example, Mount Whitney, Half Domeand El Capitan. However, most of the batholith remains below the surface.
Research thus far indicates that the Sierra batholith was formed from heating as the
Farallon Platesubducted below the North American Plate. The episodic nature of the formation of the plutons is not yet well-explained. It may involve the effects of the emplacement of various terranes along the margin of the continent. Termination of the formation process occurred as the Farallon Plate was fully subducted along the Pacific coastline west of the Sierras.
Geologic timeline of Western North America
* [http://www.nps.gov/archive/yose/education/glance/geology/sierra_nev.htm US National Park site ]
* [http://virtual.yosemite.cc.ca.us/ghayes/granite.htm Yosemite site]
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