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Batholith

Batholith

Batholiths are large bodies of intrusive igneous rock . Formed when magma cools and crystallizes beneath Earth's surface, batholiths are the largest type of pluton . By definition, a batholith must cover at least 39 mi2 (100 km2), although most are even larger. Many batholiths cover hundreds to thousands of square miles. The Idaho batholith, for example, has a surface area of over 15,500 mi2 (40,000 km2).

Batholiths are generally not comprised of one continuous magmatic intrusion; rather, they are produced by repeated intrusions, and most batholiths are made up of multiple individual plutons. Intruded rock cools and solidifies, later to be exposed at the surface through erosion . Because they cool beneath Earth's surface, batholiths have a coarse grained texture, and most are granitic in composition.

Usually associated with mountain building, batholiths are often emplaced near continental margins during periods of subduction. As the subducting slab descends, it begins to melt, and multiple plutons are intruded beneath the continent to form the core of the volcanic arc. The Sierra Nevada Mountains, for example, are comprised of a granitic batholith, which is made up of hundreds of individual plutons intruded over a period of several million years. Emplacement of the Sierra Nevada batholith occurred during a mountain building episode known as the Nevadan orogeny , initiated during the Jurassic. Uplift and erosion of the area later exposed the batholith, which now forms the spine of the famous mountains.

The Sierra Nevada batholith not only forms a major mountain chain, but also was responsible for driving the California gold rush. Precious minerals including gold are commonly associated with granitic batholiths. As mineral-rich solutions move along cracks in the rock body, gold, copper, and other minerals, especially quartz , precipitate out. Gold may be mined from deposits known as quartz veins that form along the fractures. The Mother Lode in the Sierra Nevada is possibly the most famous of such deposits.

Determining the mechanism for batholith emplacement has been a topic of much debate. When gigantic batholiths are intruded, the surrounding rock, known as the country rock , must somehow make room for the intrusion. Several models have been suggested, but most geologists now agree that a mechanism known as forceful injection is probably responsible for emplacement. Apparently, as the body of magma rises, it deforms the country rock, pushing it out of the way.

See also Intrusive cooling; Mineral deposits; Pluton and plutonic bodies

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batholith

batholith, enormous mass of intrusive igneous rock, that is, rock made of once-molten material that has solidified below the earth's surface (see rock). Batholiths usually are granitic (see granite) in composition, have steeply inclined walls, have no visible floors, and commonly extend over areas of thousands of square miles. Batholiths are formed either as one large mass or many smaller masses at great depths in the earth's crust and are exposed at the surface only after considerable erosion of the overlying mountain mass. They are commonly associated with lithospheric plate boundaries, where the interactions between plates can produce sufficient heat to melt crustal rocks on a large scale and form batholiths (see plate tectonics). One of the largest single batholiths in North America is the Coast Range batholith of W Canada and Alaska, encompassing an area of about 73,000 sq mi (182,500 sq km). Important batholiths in the United States include the Idaho batholith, 18,000 sq mi (45,000 sq km), and the Sierra Nevada batholith, 16,000 sq mi (40,000 sq km).

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batholith

batholith Huge mass of igneous rock at the Earth's surface that has an exposed surface of more than 100sq km (40sq mi). It may have originated as an intrusive igneous structure that was gradually eroded and became surface material. Most batholiths consist of granite rock types, and are associated with the mountain-building phases of plate tectonics.

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batholith

batholith Large (more than 100 km2) igneous intrusion, which may comprise several plutons amalgamated at depth. Most batholiths are granitic in composition and their genesis is linked with plate tectonics. Generally, batholiths cut across country rocks and therefore are discordant in nature.

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"batholith." A Dictionary of Earth Sciences. . Encyclopedia.com. 19 Aug. 2017 <http://www.encyclopedia.com>.

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"batholith." A Dictionary of Earth Sciences. . Retrieved August 19, 2017 from Encyclopedia.com: http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-press-releases/batholith