Intrusion

:Pluton redirects here. For the ancient Roman god, see Pluto. For the French nuclear missile system, see Pluton missile. For the physical act of trespass with a possible intent to steal, see intruder.

Related Topics:
Pluto - Pluton missile - Intruder

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In geology an intrusion is usually a body of igneous rock that has crystallized from a molten magma below the surface of the Earth. Intrusive rocks include all varieties of igneous rocks from coarse-grained, phaneritic granites of large batholiths to very fine grained, aphanitic, rhyolites in volcanic necks or feeder pipes. In composition, intrusive rocks also include the entire sequence of igneous rock types from the dense and dark ultramafic peridotites to the very light-colored and low-density alkali granites and syenites. Bodies of magma that solidify underground before they reach the surface of the earth are called plutons, named for Pluto, the Roman god of the underworld. A well-known example of an igneous intrusion is Devil's Tower in Wyoming, USA.

Related Topics:
Geology - Igneous rock - Crystal - Magma - Earth - Granite - Batholith - Rhyolite - Volcanic - Peridotite - Syenite - Pluto - Roman god - Underworld - Devil's Tower - Wyoming - USA

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Intrusive rocks also exist in a wide range of forms from mountain range sized batholiths to thin vein-like fracture fillings of aplite. Structural types include:

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• batholith: large irregular intrusions.
• stock: smaller irregular disordant intrusions.
• dike: a relatively narrow tabular discordant body with near vertical attitude.
• sill: a relatively thin tabular concordant body intruded along bedding planes, horizontal attitude.
• pipe or volcanic neck: circular or tube shaped nearly vertical body which may have been a feeder vent for a volcano.
• laccolith: concorant body with essentially flat base and dome shaped upper surface, usually has a feeder pipe below.
 
Intrusion: Diapir ►