Andesite () is a
volcanic rock
Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic r ...
of
intermediate composition In igneous petrology, an intermediate composition refers to the chemical composition of a rock that has 5263 wt% SiO2 being an intermediate between felsic and mafic compositions. Typical intermediate rocks include andesite, dacite, and trachya ...
. In a general sense, it is the intermediate type between
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
-poor
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
and silica-rich
rhyolite
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
. It is fine-grained (
aphanitic
Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This geologic ...
) to
porphyritic
Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all ...
in texture, and is composed predominantly of sodium-rich
plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...
plus
pyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
or
hornblende
Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...
.
Andesite is the extrusive equivalent of
plutonic
Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form '' intrusions'', such as batholiths, dikes, sills, laccoliths, and volcanic necks.Intrusive RocksIntrusive rocks accessdate: March ...
diorite
Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-silic ...
. Characteristic of
subduction
Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, the ...
zones, andesite represents the dominant rock type in
island arc
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...
s. The average composition of the
continental crust
Continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the geological continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called ''sial'' be ...
is andesitic. Along with basalts, andesites are a component of the
Martian crust.
The name ''andesite'' is derived from the
Andes
The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
mountain range, where this rock type is found in abundance. It was first applied by
Christian Leopold von Buch
Christian Leopold von Buch (26 April 1774 – 4 March 1853), usually cited as Leopold von Buch, was a German geologist and paleontologist born in Stolpe an der Oder (now a part of Angermünde, Brandenburg) and is remembered as one of the most im ...
in 1826.
Description
Andesite is an
aphanitic
Aphanites (adj. ''aphanitic''; ) are igneous rocks that are so fine-grained that their component mineral crystals are not visible to the naked eye (in contrast to phanerites, in which the crystals are visible to the unaided eye). This geologic ...
(fine-grained) igneous rock that is intermediate in its content of
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
and low in
alkali metals
The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...
. It has less than 20% quartz and 10%
feldspathoid
The feldspathoids are a group of tectosilicate minerals which resemble feldspars but have a different structure and much lower silica content. They occur in rare and unusual types of igneous rocks, and are usually not found in rocks containing prim ...
by volume, with at least 65% of the
feldspar
Feldspars are a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. The most common members of the feldspar group are the ''plagioclase'' (sodium-calcium) feldsp ...
in the rock consisting of
plagioclase
Plagioclase is a series of tectosilicate (framework silicate) minerals within the feldspar group. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a continuous solid solution series, more prope ...
. This places andesite in the
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
/andesite field of the
QAPF diagram
A QAPF diagram is a double ternary diagram which is used to classify igneous rocks based on mineralogic composition. The acronym QAPF stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)". These are the mineral groups used for ...
. Andesite is further distinguished from basalt by its silica content of over 52%.
However, it is often not possible to determine the mineral composition of volcanic rocks, due to their very fine grain size, and andesite is then defined chemically as volcanic rock with a content of 57% to 63% silica and not more than about 6% alkali metal oxides. This places andesite in the O2 field of the
TAS classification
The TAS classification can be used to assign names to many common types of volcanic rocks based upon the relationships between the combined alkali content and the silica content. These chemical parameters are useful, because the relative proportio ...
.
Basaltic andesite
Basaltic andesite is a volcanic rock that is intermediate in composition between basalt and andesite. It is composed predominantly of augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central Amer ...
, with a content of 52% to 57% silica, is represented by the O1 field of the TAS classification but is not a distinct rock type in the QAPF classification.
Andesite is usually light to dark gray in colour, due to its content of
hornblende
Hornblende is a complex inosilicate series of minerals. It is not a recognized mineral in its own right, but the name is used as a general or field term, to refer to a dark amphibole. Hornblende minerals are common in igneous and metamorphic rocks ...
or
pyroxene
The pyroxenes (commonly abbreviated to ''Px'') are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. Pyroxenes have the general formula , where X represents calcium (Ca), sodium (Na), iron (Fe II) ...
minerals.
but can exhibit a wide range of shading. Darker andesite can be difficult to distinguish from basalt, but a common
rule of thumb
In English, the phrase ''rule of thumb'' refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various t ...
, used away from the laboratory, is that andesite has a
color index
In astronomy, the color index is a simple numerical expression that determines the color of an object, which in the case of a star gives its temperature. The lower the color index, the more blue (or hotter) the object is. Conversely, the large ...
less than 35.
[Philpotts and Ague 2009, p. 139]
The plagioclase in andesite varies widely in sodium content, from
anorthite to
oligoclase
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite ( Na Al Si3 O8) and anorthite ( CaAl2Si2O8). The albite:an ...
, but is typically
andesine
Andesine is a silicate mineral, a member of the plagioclase feldspar solid solution series. Its chemical formula is ( Ca, Na)( Al, Si)4 O8, where Ca/(Ca + Na) (% anorthite) is between 30–50%. The formula may be written as Na0.7-0.5Ca0.3-0.5Al ...
, in which
anorthite makes up about 40
mol%
In chemistry, the mole fraction or molar fraction (''xi'' or ) is defined as unit of the amount of a constituent (expressed in moles), ''ni'', divided by the total amount of all constituents in a mixture (also expressed in moles), ''n''tot. This ex ...
of the plagioclase. The pyroxene minerals that may be present include
augite,
pigeonite
Pigeonite is a mineral in the clinopyroxene subgroup of the pyroxene group. It has a general formula of . The calcium cation fraction can vary from 5% to 25%, with iron and magnesium making up the rest of the cations.
Pigeonite crystallizes in th ...
, or
orthopyroxene.
Magnetite
Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the ...
,
zircon
Zircon () is a mineral belonging to the group of nesosilicates and is a source of the metal zirconium. Its chemical name is zirconium(IV) silicate, and its corresponding chemical formula is Zr SiO4. An empirical formula showing some of the r ...
,
apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
,
ilmenite
Ilmenite is a titanium-iron oxide mineral with the idealized formula . It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing ...
,
biotite
Biotite is a common group of phyllosilicate minerals within the mica group, with the approximate chemical formula . It is primarily a solid-solution series between the iron-endmember annite, and the magnesium-endmember phlogopite; more alumino ...
, and
garnet
Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives.
All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...
are common accessory minerals.
Alkali feldspar may be present in minor amounts.
Andesite is usually
porphyritic
Porphyritic is an adjective used in geology to describe igneous rocks with a distinct difference in the size of mineral crystals, with the larger crystals known as phenocrysts. Both extrusive and intrusive rocks can be porphyritic, meaning all ...
, containing larger crystals (
phenocryst
300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...
s) of plagioclase formed prior to the extrusion that brought the magma to the surface, embedded in a finer-grained
matrix
Matrix most commonly refers to:
* ''The Matrix'' (franchise), an American media franchise
** ''The Matrix'', a 1999 science-fiction action film
** "The Matrix", a fictional setting, a virtual reality environment, within ''The Matrix'' (franchis ...
. Phenocrysts of pyroxene or hornblende are also common.
[Blatt and Tracy 1996, p.57] These minerals have
the highest melting temperatures of the typical
mineral
In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ( ...
s that can crystallize from the melt
and are therefore the first to form solid crystals. Classification of andesites may be refined according to the most abundant
phenocryst
300px, feldspathic phenocrysts. This granite, from the Switzerland">Swiss side of the Mont Blanc massif, has large white plagioclase phenocrysts, triclinic minerals that give trapezoid shapes when cut through). 1 euro coins, 1 euro coin (diameter ...
. For example, if hornblende is the principal phenocryst mineral, the andesite will be described as a ''hornblende andesite''.
Andesitic volcanism
Andesite lava typically has a viscosity of 3.5 × 10
6 cP at . This is slightly greater than the viscosity of smooth
peanut butter. As a result, andesitic volcanism is often explosive, forming
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock cont ...
s and
agglomerates. Andesite vents tend to build up
composite volcano
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava and tephra. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and peri ...
es rather than the
shield volcano
A shield volcano is a type of volcano named for its low profile, resembling a warrior's shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more v ...
es characteristic of basalt, with its much lower viscosity resulting from its lower silica content and higher eruption temperature.
Block lava flows are typical of andesitic lavas from composite volcanoes. They behave in a similar manner to
ʻaʻā
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...
flows but their more viscous nature causes the surface to be covered in smooth-sided angular fragments (blocks) of solidified lava instead of clinkers. As with ʻaʻā flows, the molten interior of the flow, which is kept insulated by the solidified blocky surface, advances over the rubble that falls off the flow front. They also move much more slowly downhill and are thicker in depth than ʻaʻā flows.
Generation of melts in island arcs
Though andesite is common in other tectonic settings, it is particularly characteristic of
convergent plate margins. Even before the
Plate Tectonics Revolution
The Plate Tectonics Revolution was the scientific and cultural change which developed from the acceptance of the plate tectonics theory. The event was a paradigm shift and scientific revolution.
By 1967 most scientists in geology accepted the the ...
, geologists had defined an ''
andesite line'' in the western Pacific that separated
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
of the central Pacific from andesite further west. This coincides with the
subduction zones at the western boundary of the
Pacific Plate
The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At , it is the largest tectonic plate.
The plate first came into existence 190 million years ago, at the triple junction between the Farallon, Phoenix, and Iza ...
.
Magmatism
Magmatism is the emplacement of magma within and at the surface of the outer layers of a terrestrial planet, which solidifies as igneous rocks. It does so through magmatic activity or igneous activity, the production, intrusion and extrusion of ...
in
island arc
Island arcs are long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries. Most island arcs originate on oceanic crust and have resulted from the descent of the lithosphere into the mantle alon ...
regions comes from the interplay of the
subducting plate and the ''
mantle wedge
A mantle wedge is a triangular shaped piece of mantle that lies above a subducting tectonic plate and below the overriding plate. This piece of mantle can be identified using seismic velocity imaging as well as earthquake maps. Subducting oceanic ...
'', the wedge-shaped region between the subducting and overriding plates. The presence of convergent margins dominated by andesite is so characteristic of the Earth's unique
plate tectonic
Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...
s that the Earth has been described as an "andesite planet".
During subduction, the subducted
oceanic crust
Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumu ...
is subjected to increasing pressure and temperature, leading to
metamorphism
Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...
.
Hydrous
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was underst ...
minerals such as
amphibole
Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...
,
zeolite
Zeolites are microporous, crystalline aluminosilicate materials commonly used as commercial adsorbents and catalysts. They mainly consist of silicon, aluminium, oxygen, and have the general formula ・y where is either a metal ion or H+. These p ...
s, or
chlorite (which are present in the
oceanic lithosphere
A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion of the upper mantle (geology), mantle that behaves elastically on time sca ...
) dehydrate as they change to more stable, anhydrous forms, releasing water and soluble elements into the overlying wedge of mantle. Fluxing water into the wedge lowers the
solidus
Solidus (Latin for "solid") may refer to:
* Solidus (coin), a Roman coin of nearly solid gold
* Solidus (punctuation), or slash, a punctuation mark
* Solidus (chemistry), the line on a phase diagram below which a substance is completely solid
* ...
of the
mantle material and causes partial melting. Due to the lower density of the partially molten material, it rises through the wedge until it reaches the lower boundary of the overriding plate. Melts generated in the mantle wedge are of basaltic composition, but they have a distinctive enrichment of soluble elements (e.g.
potassium
Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...
(K),
barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in group 2 and is a soft, silvery alkaline earth metal. Because of its high chemical reactivity, barium is never found in nature as a free element.
Th ...
(Ba), and
lead
Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...
(Pb)) which are contributed from sediment that lies at the top of the subducting plate. Although there is evidence to suggest that the subducting oceanic crust may also melt during this process, the relative contribution of the three components (crust, sediment, and wedge) to the generated basalts is still a matter of debate.
Basalt thus formed can contribute to the formation of andesite through fractional crystallization, partial melting of crust, or magma mixing, all of which are discussed next.
Genesis
Intermediate volcanic rocks are created via several processes:
#
Fractional crystallization of a mafic parent magma.
# Partial melting of crustal material.
# Magma mixing between felsic
rhyolitic
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
and mafic
basalt
Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
ic magmas in a magma reservoir
# Partial melting of metasomatized mantle
Fractional crystallization
To achieve andesitic composition via
fractional crystallization, a basaltic magma must crystallize specific minerals that are then removed from the melt. This removal can take place in a variety of ways, but most commonly this occurs by crystal settling. The first minerals to crystallize and be removed from a basaltic parent are
olivine
The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...
s and
amphibole
Amphibole () is a group of inosilicate minerals, forming prism or needlelike crystals, composed of double chain tetrahedra, linked at the vertices and generally containing ions of iron and/or magnesium in their structures. Its IMA symbol is A ...
s. These mafic minerals settle out of the magma, forming mafic cumulates. There is geophysical evidence from several arcs that large layers of mafic cumulates lie at the base of the crust. Once these mafic minerals have been removed, the melt no longer has a basaltic composition. The silica content of the residual melt is enriched relative to the starting composition. The
iron
Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...
and
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
contents are depleted. As this process continues, the melt becomes more and more evolved eventually becoming andesitic. Without continued addition of mafic material, however, the melt will eventually reach a
rhyolitic
Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained (aphanitic) in texture, but may be porphyritic, containing larger mineral crystals (phenocrysts) in an otherwise fine-grained groundmass. The mineral ...
composition. This produces the characteristic basalt-andesite-rhyolite association of island arcs, with andesite the most distinctive rock type.
Partial melting of the crust
Partially molten basalt in the mantle wedge moves upwards until it reaches the base of the overriding crust. Once there, the basaltic melt can either
underplate the crust, creating a layer of molten material at its base, or it can move into the overriding plate in the form of
dykes. If it underplates the crust, the basalt can (in theory) cause partial melting of the lower crust due to the transfer of heat and volatiles. Models of heat transfer, however, show that arc basalts emplaced at temperatures 1100–1240 °C cannot provide enough heat to melt lower crustal
amphibolite
Amphibolite () is a metamorphic rock that contains amphibole, especially hornblende and actinolite, as well as plagioclase feldspar, but with little or no quartz. It is typically dark-colored and dense, with a weakly foliated or schistose (flaky ...
. Basalt can, however, melt
pelitic
A pelite (Greek: ''pelos'', "clay") or metapelite is a metamorphosed fine-grained sedimentary rock, i.e. mudstone or siltstone. The term was earlier used by geologists to describe a clay-rich, fine-grained clastic sediment or sedimentary rock ...
upper crustal material.
Magma mixing
In continental arcs, such as the
Andes
The Andes, Andes Mountains or Andean Mountains (; ) are the longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range is long, wide (widest between 18°S – 20°S ...
, magma often pools in the shallow crust creating magma chambers. Magmas in these reservoirs become evolved in composition (dacitic to rhyolitic) through both the process of fractional crystallization and partial melting of the surrounding
country rock
Country rock is a genre of music which fuses rock and country. It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal s ...
. Over time as crystallization continues and the system loses heat, these reservoirs cool. In order to remain active, magma chambers must have continued recharge of hot basaltic melt into the system. When this basaltic material mixes with the evolved rhyolitic magma, the composition is returned to andesite, its intermediate phase. Evidence of magma mixing is provided by the presence of phenocrysts in some andesites that are not in chemical equilibrium with the melt in which they are found.
Partial melting of metasomatized mantle
High-magnesium andesites (''
boninite
Boninite is an extrusive rock high in both magnesium and silica, thought to be usually formed in fore-arc environments, typically during the early stages of subduction. The rock is named for its occurrence in the Izu-Bonin arc south of Japan. ...
s'') in island arcs may be primitive andesites, generated from metasomatized mantle.
Experimental evidence shows that depleted mantle rock exposed to alkali fluids such as might be given off by a subducting slab generates magma resembling high-magnesium andesites.
Extraterrestrial samples
In 2009, researchers revealed that andesite was found in two meteorites (numbered GRA 06128 and GRA 06129) that were discovered in the
Graves Nunataks The Graves Nunataks () are a small group of nunataks near the edge of the Antarctic polar plateau, lying east-southeast of Beard Peak, La Gorce Mountains, in the Queen Maud Mountains of Antarctica. It was mapped by the United States Geological Sur ...
icefield during the US
Antarctic Search for Meteorites 2006/2007 field season. This possibly points to a new mechanism to generate andesite crust.
Along with basalts, andesites are a component of the
Martian crust. The presence of distinctive steep-sided domes on
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
suggests that andesite may have been erupted from large magma chambers where crystal settling could take place.
See also
*
*
*
*
*
References
External links
Origins of the Continental Crust, AbstractOrigins of the Continental Crust, Full paperIsland arc magmatism Experimental and Theoretical Constraints on Peridotite Partial Melting in the Mantle Wedge
{{Authority control
Aphanitic rocks
Porphyritic rocks
Intermediate rocks
Volcanic rocks
Subvolcanic rocks