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A batholith is a large emplacement of igneous intrusive (also called plutonic) rock that forms from cooled magma deep in the Earth's crust. Batholiths are almost always made mostly of felsic or intermediate rock-types, such as granite, diorite or lighter colored forms of andesite. In spite of their apparent uniformity, batholiths are in fact structures with complex histories and compositions. They are composed of multiple blobs, or plutons, of magma that traveled toward the surface from a zone of partial melting at the base the Earth's crust. While moving, these plutons of relatively buoyant magma are called plutonic diapirs (not to be confused with diaper). Because the diapirs are liquefied and very hot, they tend to rise through the surrounding country rock, pushing it aside and partially melting it. Most diapirs do not reach the surface to form volcanoes, but instead slow down, cool and usually solidify 5 to 30 kilometers underground as plutons (hence the use of the word pluton; in reference to the Roman god of the underword Pluto).
A batholith is formed when many plutons converge together to form a huge expanse of granitic rock. Some batholiths are mammoth, paralleling past and present subduction zones and other heat sources for hundreds of kilometers in continental crust. One such batholith is the Sierra Nevada Batholith , which is a continuous granitic formation that forms much of the Sierra NevadaThe Sierra Nevada is a mountain range that is mostly in eastern California. The range is also known as The Sierra . Geography The Sierra Nevada stretches 400 miles (650km), from Fredonyer Pass in the North to Tehachapi Pass in the South. The Sierra Nevadas in CaliforniaCalifornia is a state located in the western United States, bordering the Pacific Ocean. The most populous and third largest state in the U. California is both physically and demographically diverse. The state's official nickname is "The Golden State", wh. An even larger batholith, found predominantly in the mountains of western CanadaCanada historically the Dominion of Canada is the second-largest, and northernmost, country in the world. It is a decentralized federation of 10 provinces and 3 territories, governed as a constitutional monarchy, and formed in 1867 through an act of Confe, extends for 1,800 kilometers and reaches into southeastern AlaskaOn January 3, 1959, Alaska was admitted to the United States as the 49th state. The population of the state is 626,932, as of 2000. The name "Alaska" is most likely derived from the Aleut word for "great country" or "mainland. The natives called it "Alyes.
There is also an important geographic usage of the term batholith. For a geographer, a batholith is an exposed area of mostly continuous plutonic rock that covers an area larger than 100 square kilometers. Areas smaller than 100 kilometers are called stocks. However, the majority of batholiths visible at the surface (via outcroppings) have areas far greater than 100 square kilometers. These areas are exposed to the surface through the process of erosionErosion is the displacement of solids ( soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravity. Although the processes may be simultaneous, erosion is to be distinguished from weathering, which is the decompos accelerated by continental upliftOrogeny is a geologic term associated with periods of mountain building. An orogenic belt therefore, is a geologic structure associated with continental collisions and mountain building. Generally orogenic belts consist of long parallel strips of rock exh acting over many tens of millions to hundreds of millions of years. This process has removed several tens of kilometers of overlying rock in many areas, exposing the once deeply buried batholiths.
Batholiths exposed at the surface are also subjected to huge pressure differences between their former homes deep in the earth and their new homes at or near the surface. As a result, their crystal structureIn mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. A crystal structure is composed of a unit cell a set of atoms arranged in a particular way, which is periodically repeated in three dimensions on a latti expands slightly and over time. This manifests itself by a form of mass wasting called exfoliationExfoliation has at least two meanings: In cosmetology, exfoliation is a cosmetic technique which is aimed at removing dead skin cells from the face and body. Removing these excess dead skin cells is reasoned to reveals more younger and healthy-looking ski. This form of erosion causes convex and relatively thin sheets of rock to slough off the exposed surfaces of batholiths (a process accelerated by frost wedging ). The result is fairly clean and rounded rock faces. A famous example of the result of this process is Half Dome, which located in the world-famous Yosemite Valley (see picture).
