Magma (Plurals: magmas and magmata) is molten rock that sometimes forms beneath the surface of the earth (or any other terrestrial planet) that often collects in a magma chamber inside a volcano. In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our A magma chamber is a large underground pool of molten rock lying under the surface of the earth's crust Magma may contain suspended crystals and gas bubbles. By definition, all igneous rock is formed from magma. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock

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

Magma is a complex high-temperature fluid substance. Extrusive refers to the mode of Igneous Volcanic rock formation in which hot Magma from inside the Earth flows out (extrudes onto the surface 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. Carbonatites (kɑrˈbɒnətaɪt are Intrusive or extrusive Igneous rocks defined by mineralogy that comprises more than 50 volume-% Carbonate Komatiites are Ultramafic mantle-derived Volcanic rocks They have low SiO2 low K2O low Al2O3 and high to extremely high Most are silicate solutions. For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances

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. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Tephra is 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 Clastic rocks

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. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other In Geology, a rift is a place where the Earth 's crust and Lithosphere are being pulled apart and is an example of Extensional tectonics A mid-ocean ridge or mid-oceanic ridge is an underwater Mountain range typically having a valley known as a Rift running along its axis formed by In Geology, a hotspot is a location on the Earth's surface that has experienced active volcanism for a long period of time A mantle plume is an upwelling of abnormally hot rock within the Earth's mantle. Environments are discussed in the entry on igneous rock. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Magma compositions may evolve after formation by fractional crystallization, contamination, and magma mixing. Fractional crystallization is one of the most important geochemical and physical processes operating within the Earth's crust and mantle.

Contrary to some impressions, the bulk of the Earth's crust and mantle is not molten. In Geology, a crust is the outermost solid shell of a planet or moon The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Rather, the bulk of the Earth takes the form of a rheid, a form of solid that can move or deform under pressure. In Geology, a rheid is a Solid material that deforms by viscous flow Magma, as liquid, preferentally forms in high temperature, low pressure environments within several kilometers of the Earth's surface.

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. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock

Temperature

At any given pressure and for any given composition of rock, a rise in temperature past the solidus will cause melting. In Chemistry, Materials science, and Physics, the solidus is a temperature (a line on a Phase diagram) below which a given substance is completely 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 is the rate of increase in temperature per unit depth in the Earth. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. 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.

Pressure

As magma buoyantly rises it will cross the solidus-liquidus and its temperature will reduce by adiabatic cooling. At this point it will liquify and if erupted onto the surface will form lava. Melting can also occur due to a reduction in pressure by a process known as decompression melting. ^[1]

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. Water is a common Chemical substance that is essential for the survival of all known forms of Life. Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single

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 solidify.

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. In Physical chemistry, Mineralogy, and Materials science, a phase diagram is a type of graph used to show the equilibrium conditions 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.

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 diapir (ˈdaɪəpɪər) ( French, from Greek diapeirein, to pierce through is an Intrusion caused by Buoyancy and Pressure

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. Migmatite is a rock at the frontier between igneous and Metamorphic rocks They can also be known as diatexite. 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. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided

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. Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Barium (ˈbɛəriəm is a Chemical element. It has the symbol Ba, and Atomic number 56 Caesium or cesium (ˈsiːziəm is the Chemical element with the symbol Cs and Atomic number 55 Rubidium (ruːˈbɪdiəm /rəˈbɪdiəm/ is a Chemical element with the symbol Rb and Atomic number 37

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). The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 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. Lamprophyres ( Greek λαµπρός (lamprós = "bright" and φύρω (phýro = to mix are uncommon small volume ultrapotassic Igneous rocks Lamproites are ultrapotassic mantle -derived volcanic rocks. They have low CaO Al2O3 Na2O high K2O/Al2O3 Kimberlite is a type of potassic Volcanic rock best known for sometimes containing Diamonds It is named after the town of Kimberley in South Africa Nepheline, also called nephelite (from Greek: nephos, "cloud" is a Feldspathoid: a silica-undersaturated aluminosilicate Na In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. Essexite (ˈɛsəksaɪt also called nepheline monzogabbro (/ˈnɛfəliːn ˌmɒnzoʊˈgæbroʊ/ is a dark gray or black Holocrystalline Plutonic Carbonatites (kɑrˈbɒnətaɪt are Intrusive or extrusive Igneous rocks defined by mineralogy that comprises more than 50 volume-% Carbonate

Pegmatite may be produced by low degrees of partial melting of the crust. Pegmatite is a very coarse-grained Igneous rock that has a grain size of 20 mm or more such rocks are referred to as pegmatitic. 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. Granite (ˈɡrænɪt is a common and widely occurring type of intrusive, Felsic, igneous rock. 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. Tonalite is an igneous, Plutonic ( Intrusive) rock, of Felsic composition with Phaneritic texture Granodiorite (ˌgrænəˈdaɪəraɪt/ /ˌgreɪn- is an intrusive Igneous rock similar to Granite, but contains more Plagioclase than Potassium feldspar Monzonite is an intermediate Igneous Intrusive rock composed of approximately equal amounts of sodic to intermediate Plagioclase and Orthoclase

At high degrees of partial melting of the mantle, komatiite and picrite are produced. Komatiites are Ultramafic mantle-derived Volcanic rocks They have low SiO2 low K2O low Al2O3 and high to extremely high Picrite basalt is a variety of high-magnesium olivine Basalt that is very rich in the mineral Olivine. so

Composition and melt structure and properties

Silicate melts are composed mainly of silicon, oxygen, aluminium, alkalis (sodium, potassium, calcium), magnesium and iron. Silicon (ˈsɪlɪkən or /ˈsɪlɪkɒn/ silicium is the Chemical element that has the symbol Si and Atomic number 14 Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the WikipediaNaming Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Magnesium (mægˈniːziəm is a Chemical element with the symbol Mg, Atomic number 12 Atomic weight 24 Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 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 silicate minerals make up the largest and most important class of rock-forming Minerals They are classified based on the structure of their silicate Ion group The physical behaviours of melts depend upon their atomic structures as well as upon temperature and pressure and composition. ^[2]

Viscosity is a key melt property in understanding the behaviour of magmas. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. 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.

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. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Low viscosity leads to gentler, less explosive eruptions.

Main article: Igneous differentiation

Characteristics of several different magma types are as follows:

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

See also

• Igneous differentiation
• Cumulate rocks
• Fractional crystallization (geology)
• Igneous rocks
• Lava
• Intrusion
• Ultramafic to mafic layered intrusions

References

1. ^ Geological Society of America, Plates, Plumes, And Paradigms, p. Igneous differentiation is an umbrella term for the various processes by which Magmas undergo bulk chemical change during the Partial melting process cooling Ultramafic (also referred to as ultrabasic) rocks are igneous and meta -igneous rocks with very low Silica content (less than 45% generally Picrite basalt is a variety of high-magnesium olivine Basalt that is very rich in the mineral Olivine. Komatiites are Ultramafic mantle-derived Volcanic rocks They have low SiO2 low K2O low Al2O3 and high to extremely high The geothermal gradient is the rate of increase in temperature per unit depth in the Earth. Mafic is an adjective describing a Silicate mineral or rock that is rich in magnesium and iron the term was derived by contracting "magnesium" and "ferric" Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate Felsic is a term used in Geology to refer to Silicate minerals, Magma, and rocks which are enriched in the lighter elements such as Silicon Igneous differentiation is an umbrella term for the various processes by which Magmas undergo bulk chemical change during the Partial melting process cooling Cumulate rocks are Igneous rocks formed by the accumulation of Crystals from a Magma either by settling or floating Fractional crystallization is one of the most important geochemical and physical processes operating within the Earth's crust and mantle. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures In Geology, an intrusion is a body of Igneous rock that has Crystallized from molten Magma below the surface of the Earth. Ultramafic to mafic layered intrusions are found in typically ancient Cratons and are rare but worldwide in distribution 590 ff. , 2005, ISBN 0813723884
2. ^ E. B. Watson, M. F. Hochella, and I. Parsons (editors), Glasses and Melts: Linking Geochemistry and Materials Science, Elements, volume 2, number 5, (October 2006) pages 259-297