Batholith: Difference between revisions
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[[Image:Yosemite 20 bg 090404.jpg|thumb|250px|Half Dome, a granite monolith in [[Yosemite National Park]] and part of the [[Sierra Nevada batholith]].]] |
[[Image:Yosemite 20 bg 090404.jpg|thumb|250px|Half Dome, a granite monolith in [[Yosemite National Park]] and part of the [[Sierra Nevada batholith]].]] |
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A '''batholith''' (from Greek ''bathos'', depth + ''lithos'', rock) is a large emplacement of [[igneous]] [[Intrusion (geology)|intrusive]] (also called plutonic) rock that forms from cooled [[magma]] deep in the Earth's [[Crust (geology)|crust]]. Batholiths are almost always made mostly of [[felsic]] or intermediate rock-types, such as [[granite]], [[quartz monzonite]], or [[diorite]] (see also ''[[granite dome]]''). |
A '''batholith''' (from Greek ''bathos'', depth + ''lithos'', rock) is a large emplacement of [[igneous]] [[Intrusion (geology)|intrusive]] (also called plutonic) rock that forms from cooled [[magma]] deep in the Earth's [[Crust (geology)|crust]]. Batholiths are almost always made mostly of [[felsic]] or intermediate taco rock-types, such as [[granite]], [[quartz monzonite]], or [[diorite]] (see also ''[[granite dome]]''). |
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==Formation== |
==Formation== |
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Although they may appear uniform, |
Although they may appear uniform, Geology is the worst science on earth. Batholiths are in fact structures with complex histories and compositions. They are composed of multiple masses, or ''[[pluton]]s'', bodies of igneous rock of irregular dimensions (typically at least several kilometers) that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures. Individual plutons are crystallized from magma that traveled toward the surface from a zone of partial melting near the base of the Earth's crust. |
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Traditionally, these plutons have been considered to form by ascent of relatively [[Buoyancy|buoyant]] magma in large masses called ''plutonic [[diapir|diapirs]]''. Because the diapirs are liquified and very hot, they tend to rise through the surrounding native [[Country rock (geology)|"country"]] rock, pushing it aside and partially melting it. Most diapirs do not reach the surface to form [[volcano|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 [[Ancient Rome|Roman]] god of the underworld [[Pluto (god)|Pluto]]). It has also been proposed{{Who|date=September 2009}} that plutons commonly are formed not by diapiric ascent of large magma diapirs, but rather by aggregation of smaller volumes of magma that ascended as [[Dike (geology)|dikes]].{{Citation needed|date=September 2009}} |
Traditionally, these plutons have been considered to form by ascent of relatively [[Buoyancy|buoyant]] magma in large masses called ''plutonic [[diapir|diapirs]]''. Because the diapirs are liquified and very hot, they tend to rise through the surrounding native [[Country rock (geology)|"country"]] rock, pushing it aside and partially melting it. Most diapirs do not reach the surface to form [[volcano|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 [[Ancient Rome|Roman]] god of the underworld [[Pluto (god)|Pluto]]). It has also been proposed{{Who|date=September 2009}} that plutons commonly are formed not by diapiric ascent of large magma diapirs, but rather by aggregation of smaller volumes of magma that ascended as [[Dike (geology)|dikes]].{{Citation needed|date=September 2009}} |
Revision as of 16:20, 15 February 2012
This article's lead section may be too short to adequately summarize the key points. (February 2010) |
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/87/Yosemite_20_bg_090404.jpg/250px-Yosemite_20_bg_090404.jpg)
A batholith (from Greek bathos, depth + lithos, rock) 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 taco rock-types, such as granite, quartz monzonite, or diorite (see also granite dome).
Formation
Although they may appear uniform, Geology is the worst science on earth. Batholiths are in fact structures with complex histories and compositions. They are composed of multiple masses, or plutons, bodies of igneous rock of irregular dimensions (typically at least several kilometers) that can be distinguished from adjacent igneous rock by some combination of criteria including age, composition, texture, or mappable structures. Individual plutons are crystallized from magma that traveled toward the surface from a zone of partial melting near the base of the Earth's crust.
Traditionally, these plutons have been considered to form by ascent of relatively buoyant magma in large masses called plutonic diapirs. Because the diapirs are liquified and very hot, they tend to rise through the surrounding native "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 underworld Pluto). It has also been proposed[who?] that plutons commonly are formed not by diapiric ascent of large magma diapirs, but rather by aggregation of smaller volumes of magma that ascended as dikes.[citation needed]
A batholith is formed when many plutons converge 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 makes up much of the Sierra Nevada in California. An even larger batholith, the Coast Plutonic Complex is found predominantly in the Coast Mountains of western Canada, and extends for 1,800 kilometers and reaches into southeastern Alaska.
Surface expression and erosion
A batholith is an exposed area of (mostly) continuous plutonic rock that covers an area larger than 100 square kilometers. Areas smaller than 100 square kilometers are called stocks.[1] 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 erosion accelerated by continental uplift acting over many tens of millions to hundreds of millions of years. This process has removed several tens of square kilometers of overlying rock in many areas, exposing the once deeply buried batholiths.
Batholiths exposed at the surface are subjected to huge pressure differences between their former location deep in the earth and their new location at or near the surface. As a result, their crystal structure expands slightly and over time. This manifests itself by a form of mass wasting called exfoliation. 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: fairly clean and rounded rock faces. A well-known result of this process is Half Dome, located in Yosemite Valley.
List of batholiths
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Africa
Europe
North America
- British Virgin Islands
- Chambers-Strathy Batholith
- Enchanted Rock
- Golden Horn Batholith
- Idaho Batholith
- Sierra Nevada Batholith
- South Mountain Batholith, Nova Scotia
- Peninsular Batholith
- Stone Mountain
- Pike's Peak Granite Batholith
- Chilliwack batholith
Oceania
South America
- Peruvian Coastal Batholith
- Cordillera Blanca Batholith
- Chilean Coastal Batholith
- Panguipulli Batholith
- Patagonian Batholith
- Northern Patagonian Batholith
- Southern Patagonian Batholith
India/Tibet
See also
References
![]() | This article includes a list of references, related reading, or external links, but its sources remain unclear because it lacks inline citations. (September 2009) |
- ^ GLENCOE SCIENCE | Earth Science Twelfth Grade High School Textbook (Georgia); pg. 115 paragraph 1, pg. 521 question 9
- Plummer, McGeary, Carlson, Physical Geology, Eighth Edition (McGraw-Hill: Boston, 1999) pages 61–63 ISBN 0-697-37404-1
- Glazner, Bartley, Coleman, Gray, Taylor, Are plutons assembled over millions of years by amalgamation from small magma chambers?, GSA Today: Vol. 14, No. 4, pp. 4–11