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Encyclopedia > Magma

Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. Magma may contain suspended crystals and gas bubbles. By definition, all igneous rock is formed from magma. The rocky side of a mountain creek near Orosí, Costa Rica. ... Adjectives: Terrestrial, Terran, Telluric, Tellurian, Earthly Atmosphere Surface pressure: 101. ... The inner planets, Mercury, Venus, Earth, and Mars, their sizes to scale. ... A magma chamber is a chamber typically between 1 km and 10 km beneath the surface of the Earth formed as rising magma forms a reservoir if it is unable to rise any further. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ...

Hawaiian lava flow (lava is the extrusive equivalent of magma)

Magma is a complex high-temperature fluid substance. Temperatures of most magmas are in the range 700°C to 1300°C, but very rare carbonatite melts may be as cool as 600°C, and komatiite melts may have been as hot at 1600°C. Most are silicate solutions. Download high resolution version (1280x1024, 452 KB)Marvel superhero Magma. ... Download high resolution version (1280x1024, 452 KB)Marvel superhero Magma. ... Extrusive refers to a mode of igneous rock formation, in which hot magma from inside the Earth flows out (extrudes) onto the surface. ... Carbonatites are intrusive igneous rock structures with more than 50% carbonate content, many of which contain distinctive abundances of apatite, magnetite, barite, and fluorite, that may contain economic or anomalous concentrations of rare earth elements, phosphorus, niobium, uranium, thorium, copper, iron, titanium, barium, fluorine, zirconium, and other rare or incompatible... Komatiites are ultramafic mantle-derived volcanic rocks. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ... Dissolving table salt (NaCl) in water This article is about a chemical solution; for other uses of the term solution, see solution (disambiguation). ...


It is capable of intrusion into adjacent rocks or of extrusion onto the surface as lava or ejected explosively as tephra to form pyroclastic rock. Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ... Pyroclastic rocks or pyroclastics (derived from the Greek πῦρ, meaning fire, and κλαστός, meaning broken) are debris thrown from volcanoes during an eruption. ...


Environments of magma formation and compositions are commonly correlated. Environments include subduction zones, continental rift zones, mid-oceanic ridges, and hotspots, some of which are interpreted as mantle plumes. Environments are discussed in the entry on igneous rock. Magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. Categories: Geology stubs | Plate tectonics ... It has been suggested that this article or section be merged with Rift valley. ... Courtesy USGS The Mid-Atlantic Ridge is an underwater mountain range of the Atlantic Ocean that runs from Iceland to Antarctica, and is the longest mountain range on Earth. ... In geology, a hotspot is a location on the Earths surface that has experienced active volcanism for a long period of time. ... A lava lamp illustrates the basic concept of a mantle plume. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ...

Contents

Melting of solid rock

Melting of solid rock to form magma is controlled by three physical parameters: its temperature, pressure, and composition. Mechanisms are discussed in the entry for igneous rock.Magma is hottt. Volcanic rock on North America Plutonic rock on North America Igneous rocks are formed when rock (magma) cools and solidifies, with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ...


Temperature

At any given pressure and for any given composition of rock, a rise in temperature past the solidus will cause melting. Within the solid earth, the temperature of a rock is controlled by the geothermal gradient and the radioactive decay within the rock. The geothermal gradient averages about 25°C/km with a wide range from a low of 5-10°C/km within oceanic trenches and subduction zones to 30-80°C/km under mid-ocean ridges and volcanic arc environments. In chemistry, materials science, and physics, the solidus is a line on a phase diagram below which a given substance is stable in the solid phase. ... penis, hahaha big long penis. ... Radioactive decay is the process in which an unstable atomic nucleus loses energy by emitting radiation in the form of particles or electromagnetic waves. ...


Pressure

Melting can also occur when a rock rises through the solid earth by a process known as decompression melting.


Composition

It is usually very difficult to change the bulk composition of a large mass of rock, so composition is the basic control on whether a rock will melt at any given temperature and pressure. The composition of a rock may also be considered to include volatile phases such as water and carbon dioxide. Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ...


The presence of volatile phases in a rock under pressure can stabilize a melt fraction. The presence of even 0.8% water may reduce the temperature of melting by as much as 100°C. Conversely, the loss of water and volatiles from a magma may cause it to essentially freeze or soldify.


Partial melting

When rocks melt they do so incrementally and gradually; most rocks are made of several minerals, all of which have different melting points, and the phase diagrams that control melting commonly are complex. As a rock melts, its volume changes. When enough rock is melted, the small globules of melt (generally occurring in between mineral grains) link up and soften the rock. Under pressure within the earth, as little as a fraction of a percent partial melting may be sufficient to cause melt to be squeezed from its source. In physical chemistry and materials science, a phase diagram is a type of graph used to show the equilibrium conditions between the thermodynamically-distinct phases. ...


Melts can stay in place long enough to melt to 20% or even 35%, but rocks are rarely melted in excess of 50%, because eventually the melted rock mass becomes a crystal and melt mush that can then ascend en masse as a diapir, which may then cause further decompression melting. A lava lamp illustrates the basic principle of diapirism. ...


Primary melts

When a rock melts, the liquid is known as a primary melt. Primary melts have not undergone any differentiation and represent the starting composition of a magma. In nature it is rare to find primary melts. The leucosomes of migmatites are examples of primary melts. Primary melts derived from the mantle are especially important, and are known as primitive melts or primitive magmas. By finding the primitive magma composition of a magma series it is possible to model the composition of the mantle from which a melt was formed, which is important in understanding evolution of the mantle. Ptygmatic folding in migmatite Migmatite on the coast of Saaremaa. ... Earth cutaway from core to exosphere. ...


Parental melts

Where it is impossible to find the primitive or primary magma composition, it is often useful to attempt to identify a parental melt. A parental melt is a magma composition from which the observed range of magma chemistries has been derived by the processes of igneous differentiation. It need not be a primitive melt.


For instance, a series of basalt flows are assumed to be related to one another. A composition from which they could reasonably be produced by fractional crystallization is termed a parental melt. Fractional crystallization models would be produced to test the hypothesis that they share a common parental melt.


Geochemical implications of partial melting

The degree of partial melting is critical for determining what type of magma is produced. The degree of partial melting required to form a melt can be estimated by considering the relative enrichment of incompatible elements versus compatible elements. Incompatible elements commonly include potassium, barium, caesium, rubidium. In geochemistry, compatibility is a measure of how readily a particular trace element will substitute for a major element within a mineral. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Standard atomic weight 39. ... General Name, Symbol, Number barium, Ba, 56 Chemical series alkaline earth metals Group, Period, Block 2, 6, s Appearance silvery white Atomic mass 137. ... General Name, Symbol, Number caesium, Cs, 55 Chemical series alkali metals Group, Period, Block 1, 6, s Appearance silvery gold Atomic mass 132. ... General Name, Symbol, Number rubidium, Rb, 37 Chemical series alkali metals Group, Period, Block 1, 5, s Appearance grey white Atomic mass 85. ...


Rock types produced by small degrees of partial melting in the Earth's mantle are typically alkaline (Ca, Na), potassic (K) and/or peralkaline (high aluminium to silica ratio). Typically, primitive melts of this composition form lamprophyre, lamproite, kimberlite and sometimes nepheline-bearing mafic rocks such as alkali basalts and essexite gabbros or even carbonatite. Earth cutaway from core to exosphere. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Standard atomic weight 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Standard atomic weight 39. ... Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ... Lamproite is a peralkaline volcanic rock. ... Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... A big crystal of Nepheline from Canaã Massif, Brazil Nepheline, also called nephelite (from Greek: nephos, cloud), is a feldspathoid: a silica-undersaturated aluminosilicate, Na3KAl4Si4O16, that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. ... In chemistry, an alkali (from Arabic: al-qalyالقلوي, القالي ) is a basic, ionic salt of an alkali metal or alkali earth metal element. ... Basalt Basalt (IPA: ) is a common gray to black volcanic rock. ... Essexite (IPA: ), also called nepheline monzogabbro (IPA: ) is a dark gray or black holocrystalline plutonic igneous rock. ... Carbonatites are intrusive igneous rock structures with more than 50% carbonate content, many of which contain distinctive abundances of apatite, magnetite, barite, and fluorite, that may contain economic or anomalous concentrations of rare earth elements, phosphorus, niobium, uranium, thorium, copper, iron, titanium, barium, fluorine, zirconium, and other rare or incompatible...


Pegmatite may be produced by low degrees of partial melting of the crust. Some granite-composition magmas are eutectic (or cotectic) melts, and they may be produced by low to high degrees of partial melting of the crust, as well as by fractional crystallization. At high degrees of partial melting of the crust, granitoids such as tonalite, granodiorite and monzonite can be produced, but other mechanisms are typically important in producing them. This article or section does not cite its references or sources. ... Close-up of granite from Yosemite National Park, valley of the Merced River Quarrying granite for the Mormon Temple, Utah Territory. ... A eutectic or eutectic mixture is a mixture of two or more elements which has a lower melting point than any of its constituents. ... In chemistry, Fractional Crystallization is a method of refining substances based on differences in soluability. ... Tonalite is an igneous, plutonic (intrusive) rock, of felsic composition, with phaneritic texture. ... A sample of granodiorite rock Granodiorite (IPA: ) is an intrusive igneous rock similar to granite, but contains more plagioclase than potassium feldspar. ... Figure 1. ...


At high degrees of partial melting of the melito, komatiite and picrite are produced. Komatiites are ultramafic mantle-derived volcanic rocks. ... Picrite is an intrusive and extrusive igneous rock. ...


Composition and melt structure and properties

Silicate melts are composed mainly of silicon, oxygen, aluminum, alkalis (sodium, potassium, calcium), magnesium and iron. Silicon atoms are in tetrahedral coordination with oxygen, as in almost all silicate minerals, but in melts atomic order is preserved only over short distances. The physical behaviours of melts depend upon their atomic structures as well as upon temperature and pressure and composition (e.g., Watson and others, 2006) It has been suggested that Silicons ranking be merged into this article or section. ... General Name, Symbol, Number oxygen, O, 8 Chemical series nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Standard atomic weight 15. ... Aluminum is a soft and lightweight metal with a dull silvery appearance, due to a thin layer of oxidation that forms quickly when it is exposed to air. ... General Name, Symbol, Number sodium, Na, 11 Chemical series alkali metals Group, Period, Block 1, 3, s Appearance silvery white Standard atomic weight 22. ... General Name, Symbol, Number potassium, K, 19 Chemical series alkali metals Group, Period, Block 1, 4, s Appearance silvery white Standard atomic weight 39. ... General Name, Symbol, Number calcium, Ca, 20 Chemical series alkaline earth metals Group, Period, Block 2, 4, s Appearance silvery white Standard atomic weight 40. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Standard atomic weight 24. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Standard atomic weight 55. ... In chemistry, a silicate is a compound containing an anion in which one or more central silicon atoms are surrounded by electronegative ligands. ...


Viscosity is a key melt property in understanding the behaviour of magmas. More silica-rich melts are typically more polymerized, with more linkage of silica tetrahedra, and so are more viscous. Dissolution of water drastically reduces melt viscosity. Higher-temperature melts are less viscous. Viscosity is a measure of the resistance of a fluid to deform under shear stress. ...


Generally speaking, more mafic magmas, such as those that form basalt, are hotter and less viscous than more silica-rich magmas, such as those that form rhyolite. Low viscosity leads to gentler, less explosive eruptions. Basalt Basalt (IPA: ) is a common gray to black volcanic rock. ... Rhyolite This page is about a volcanic rock. ...

Main article: Igneous differentiation

Characteristics of several different magma types are as follows: Igneous differentiation is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement of eruption. ...

Ultramafic (picritic)
SiO2 < 45%
Fe-Mg >8% up to 32%MgO
Temperature: up to 1500°C
Viscosity: Very Low
Eruptive behavior: gentle or very explosive (kimberilites)
Distribution: divergent plate boundaries, hot spots, convergent plate boundaries; komatiite and other ultramafic lavas are mostly Archean and were formed from a higher geothermal gradient and are unknown in the present
Mafic (basaltic)
SiO2 < 50%
FeO and MgO typically < 10 wt%
Temperature: up to ~1300°C
Viscosity: Low
Eruptive behavior: gentle
Distribution: divergent plate boundaries, hot spots, convergent plate boundaries
Intermediate (andesitic)
SiO2 ~ 60%
Fe-Mg: ~ 3%
Temperature: ~1000°C
Viscosity: Intermediate
Eruptive behavior: explosive
Distribution: convergent plate boundaries
Felsic (rhyolitic)
SiO2 >70%
Fe-Mg: ~ 2%
Temp: < 900°C
Viscosity: High
Eruptive behavior: explosive
Distribution: hot spots in continental crust (Yellowstone National Park), continental rifts, island arcs

Ultramafic (or ultrabasic) rocks are igneous rocks with very low silica content (less than 45%), generally >18% MgO, high FeO, low potassium and are composed of usually greater than 90% mafic minerals (dark colored, high magnesium and iron content). ... Picrite is an intrusive and extrusive igneous rock. ... Komatiites are ultramafic mantle-derived volcanic rocks. ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... Geothermal power is electricity generated by utilizing naturally occurring geological heat sources. ... In geology, mafic minerals and rocks are silicate minerals, magmas, and volcanic and intrusive igneous rocks that have relatively high concentrations of the heavier elements. ... Basalt Basalt (IPA: ) is a common gray to black volcanic rock. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Felsic is a term used in geology to refer to silicate minerals, magmas, and rocks which are enriched in the lighter elements such as silica, oxygen, aluminium, sodium, and potassium. ... Yellowstone National Park is the centerpiece of the Greater Yellowstone Ecosystem, the largest intact ecosystem in the Earths northern temperate zone. ...

References

  • E. B. Watson, M. F. Hochella, and I. Parsons, editors, Glasses and Melts: Linking Geochemistry and Materials Science. Elements, v. 2, pages 259-297 (2006). http://www.elementsmagazine.org/

See also


  Results from FactBites:
 
Magma - Wikipedia, the free encyclopedia (1605 words)
Magma is a complex high-temperature (between 650 and 1200 °C) silicate solution that is ancestral to all igneous rocks.
Magma rises primarily because a melt is less dense than its source rock, it is propelled upward through the lithosphere by the buoyancy that its lower density creates (the way less dense wood is pushed up and floats in denser water).
Magma is composed mainly of silica; alkalis (sodium, potassium, calcium, magnesium) and iron.
Magma - definition of Magma in Encyclopedia (163 words)
Magma is molten rock often located inside a magma chamber beneath the surface of the Earth.
Magma is a complex high-temperature silicate solution that is ancestral to all igneous rocks, both intrusive and extrusive.
Magma is under high pressure and sometimes emerges through volcanic vents in the form of flowing lava and pyroclastic ejecta.
  More results at FactBites »

 
 

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