In geology, an intrusion is a body of igneous rock that has crystallized from molten magma below the surface of the Earth. Geology (from Greek γη gê, "earth" and λόγος Logos, "speech" lit Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock In Materials science, a crystal is a Solid in which the constituent Atoms Molecules or Ions are packed in a regularly ordered repeating Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 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 pluton in Geology is an Intrusive Igneous rock body that crystallized from a Magma slowly cooling below the surface of the Earth Pluto was the Roman god of the underworld known in Latin as Tertius the counterpart of the Greek Hades. Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its In the study of Mythology and Religion, the underworld (gr κάτω κόσμος) is a generic term approximately equivalent to the lay term Afterlife Correspondingly, rocks of this kind are also referred to as igneous plutonic rocks or igneous intrusive rocks. This is to be contrasted with extrusive rocks. Extrusive refers to the mode of Igneous Volcanic rock formation in which hot Magma from inside the Earth flows out (extrudes onto the surface The rock surrounding a pluton is called country rock. Country rock is a geological term meaning the rock native to an area
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Varieties
In composition, intrusive rocks 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. A peridotite is a dense coarse-grained Igneous rock, consisting mostly of the minerals Olivine and Pyroxene. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. Syenite is a coarse-grained intrusive Igneous rock of the same general composition as Granite but with the Quartz either absent or present in relatively A well-known example of an igneous intrusion is Devil's Tower in Wyoming, USA. Devils Tower ( Lakota: Mato Tipila, which means “Bear Tower” is a Monolithic igneous Intrusion or Volcanic The State of Wyoming ( is a sparsely populated state in the western region of the United States. The United States of America —commonly referred to as the
Structural types
Intrusive rocks also exist in a wide range of forms from mountain range sized batholiths to thin vein-like fracture fillings of aplite. In Geology, a vein is a finite volume within a rock, having a distinct shape filled with Crystals of one or more Minerals which were precipitated Intrusive structures are often classified according to whether or not they are parallel to the bedding planes or foliation of the country rock: if the intrusion is parallel, the body is concordant, while if it cuts across the country rock, it is discordant. In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes In Mathematics, a foliation is a geometric device used to study manifolds Informally speaking a foliation is a kind of "clothing" worn on a manifold Structural types include:
- batholith: large irregular discordant intrusions. A batholith (from Greek bathos, depth + lithos, rock is a large emplacement of Igneous intrusive (also called plutonic rock that forms
- stock: smaller irregular discordant intrusions.
- dike: a relatively narrow tabular discordant body, often with near-vertical attitude. A dike or dyke in Geology is a type of Sheet intrusion referring to any geologic body that cuts Discordantly ' across planar
- sill: a relatively thin tabular concordant body intruded along bedding planes, often near-horizontal when emplaced, but may be intruded into tilted beds or the entire package may be tilted by later deformation. In Geology, a sill is a tabular Pluton that has intruded between older layers of Sedimentary rock, beds of Volcanic
- pipe or volcanic neck: circular or tube shaped nearly vertical body which may have been a feeder vent for a volcano. A volcanic plug, also called a volcanic neck or lava neck, is a volcanic landform created when Lava hardens within a Vent on Plate tectonics and hotspots Divergent plate boundaries At the
- laccolith: concordant body with essentially flat base and dome shaped upper surface, usually has a feeder pipe below. A laccolith is an Igneous intrusion (or concordant Pluton) that has been injected between two layers of Sedimentary rock.
- lopolith: concordant body with a relatively flat to sagging top and a shallow covex base (spoon-shaped), may have a feeder dike or pipe below. A lopolith is a large Igneous Intrusion which is lenticular in shape with a depressed central region
- phacolith: a concordant lens-shaped pluton that typically occupies the crest of an anticline or the trough of a syncline. A phacolith is a pluton parallel to the bedding plane or Foliation of folded country rock. In Structural geology, an anticline is a fold that is convex up and has its oldest beds at its core In Structural geology, a syncline is a downward-curving fold, with layers that dip toward the center of the structure
Characteristics
Deep-seated intrusive rock formations are shown by the way in which they have burst through the superincumbent strata. The ramifying veins resulted from filled cracks. That they were at a very high temperature is equally clear from the changes that have been induced in the rocks that were in contact with them. But since heat can only dissipate slowly, and since the rock is under pressure, crystals form and no vitreous rapidly chilled matter is present. As they have had time to rest before crystallizing, they are not fluidal. Their contained gases have not been able to escape through the thick layer of strata, beneath which they were injected. Such gases form cavities, which can often be observed in these minerals. Such gases have also resulted in many important modifications in the crystallization of the rock. Because their crystals are of approximately equal size these rocks are said to be granular. There is typically no distinction between a first generation of large well-shaped crystals and a fine-grained ground-mass. Their minerals have formed, however, in a definite order, and each has had a period of crystallization which may be very distinct or may have coincided with or overlapped the period of formation of some of the other ingredients. The earlier crystals originated at a time when most of the rock was still liquid and are more or less perfect. The later crystals are less regular in shape because they were compelled to occupy the interspaces left between the already formed crystals. The former is said to be idiomorphic (or automorphic), the latter is anidiomorphic (allotriomorphic, xenomorphic). There are also many other characteristics which serve to distinguish the members of these two groups. Orthoclase, for example, is typically feldspar from granite, while its modifications occur in lavas of similar composition. The same distinction holds between elaeolite and nepheline. Leucite is common in lavas, but very rare in plutonic rocks. Muscovite is confined to the intrusions. These differences show the influence of the physical conditions under which consolidation takes place.
There is a certain class of intrusive rocks which have risen upwards towards the surface, but have failed to reach it, and have solidified in fissures as dikes and intrusive sills at no great depth. These types are given the name "intrusive" (or "hypabyssal") or "plutonic" (or "abyssal") which formed at greater depths. As might be expected, they show structures intermediate between those of the effusive and the plutonic rocks. They are very commonly porphyritic, vitreous, and sometimes even vesicular. In fact, many of them are petrologically indistinguishable from lavas of similar composition. [1]
See also
References
- ^ This article incorporates text from the Encyclopædia Britannica Eleventh Edition article "Petrology", a publication now in the public domain. A diapir (ˈdaɪəpɪər) ( French, from Greek diapeirein, to pierce through is an Intrusion caused by Buoyancy and Pressure Note See the Volcano article for information on Magmatic volcanoes such as Mount St A pluton in Geology is an Intrusive Igneous rock body that crystallized from a Magma slowly cooling below the surface of the Earth Ultramafic to mafic layered intrusions are found in typically ancient Cratons and are rare but worldwide in distribution The Encyclopædia Britannica Eleventh Edition (1910–1911 is a 29-volume reference work that marked the beginning of the Encyclopædia Britannica The public domain is a range of abstract materials &ndash commonly referred to as Intellectual property &ndash which are not owned or controlled by anyone
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