Metamorphic petrology

rock arising from metamorphism of original rock under high heat and pressure

thumb|upright=1.35|Schematic representation of a metamorphic reaction. Abbreviations of minerals: act = [[actinolite; chl = chlorite; ep = epidote; gt = garnet; hbl = hornblende; plag = plagioclase. Two minerals represented in the figure do not participate in the reaction, they can be quartz and K-feldspar. This reaction takes place in nature when a mafic rock goes from amphibolite facies to greenschist facies.]]

thumb|Amphibolite from Cape Cod, [[Massachusetts]] thumb|Garnet bearing amphibolite from Val di Fleres, Italy

right|thumb|Serpentinite from the Maurienne valley, [[Savoie, French Alps]] right|thumb|Sample of serpentinite from the Golden Gate National Recreation Area, California, United States thumb|Chromite|Chromitic serpentinite ( across), [[Styria Province, Austria. Protolith was a Proterozoic-Early Paleozoic upper mantle dunite peridotite that has been multiply metamorphosed during the Devonian, Permian, and Mesozoic.]] thumb|Tightly folded serpentinite from the Tux Alps, [[Austria. Closeup view about .]]

thumb|Ptygmatic folding in migmatite on Naissaar Island, Estonia thumb|Migmatite on the coast of Saaremaa, Estonia thumb|Intricately-folded migmatite from near Geirangerfjord, Norway

thumb|300px|right|Eclogite from Norway with a garnet (red) and [[omphacite (greyish-green) groundmass. The sky-blue crystals are kyanite. Minor white quartz is present, presumably from the recrystallization of coesite. A few gold-white phengite patches can be seen at the top. A coin added for scale.]]

Metasomatism (from the Greek μετά metá "change" and σῶμα sôma "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is traditionally defined as metamorphism which involves a change in the chemical composition, excluding volatile components. It is the replacement of one rock by another of different mineralogical and chemical composition. The minerals which compose the rocks are dissolved and new mineral formations are deposited in their place. Dissolution and deposition occur simultaneously and the rock remains solid.

repetitive layering in metamorphic rocks

thumb|right|chlorite group|Chlorite [[schist, a type of greenschist]] thumb|Greenschist (prasinite) at Cap Corse in Corsica, France thumb|Greenschist (epidote) from Itogon, Benguet, Philippines

zone of variably metamorphosed (ultra)mafic volcanic sequences with associated sedimentary rocks occurring in Archaean and Proterozoic cratons between granite and gneiss bodies, typically dozens to thousands of kilometres long

Anatexis (via Latin from Greek roots meaning 'to melt down') is the partial melting of rocks. Traditionally, anatexis is used specifically to discuss the partial melting of crustal rocks, while the generic term "partial melting" refers to the partial melting of all rocks, in both the crust and mantle.

thumb|right|Blueschist on Île de Groix, France thumb|right|Photomicrograph of a [[thin section of blueschist facies metamorphosed basalt, from Sivrihisar, Turkey]]

Pneumatolysis is an obsolete geologic term for magma emitting gasses that alter surrounding rock or crystallize minerals. Pneumatolysis is now considered a type of hydrothermal interaction.

chemical reaction adding water to a mineral's crystal structure

set of metamorphic mineral assemblages that are formed under similar pressures and temperatures

thumb|300px|Thin section of a garnet porphyroblast (black) in a mica schist that contains foliated trails of small inclusions (white and grey)

Geothermobarometry is the methodology for estimating the pressure and temperature history of rocks (metamorphic, igneous, or sedimentary). Geothermobarometry is a combination of geobarometry, where the pressure attained (and retained) by a mineral assemblage is estimated, and geothermometry where the temperature attained (and retained) by a mineral assemblage is estimated. thumb|upright=1.35|An illustration of geothermobarometry. A line of temperature equilibrium (orange) and a line of pressure equilibrium (blue) of selected mineral assemblages found in the specimen are plotted on the P-T diag

metamorphic process that occurs under temperature and pressure where atoms of a mineral are reorganized by diffusion and/or dislocation glide

mineral used in geology to determine the degree of metamorphism a rock has experienced

Geological event leading to deep crust exhumation

thumb|350px|Augen mylonite from near Røragen, Norway. This deformed megacrystic [[granite has large alkali felspar and small plagioclase feldspar porphyroclasts. Sample 18 cm x 10 cm. Many of the larger porphyroclasts have a clear σ-type geometry, consistent with top to the right shear sense.]] thumb|350px|right|A mylonite showing a number of (rotated) porphyroclasts: a clear red [[garnet left in the picture while smaller white feldspar porphyroclasts can be found all over. Location: the tectonic contact between the autochthonous Western Gneiss Region and rocks of the allochthonous Blåhø nappe

describes the effects of shock-wave related deformation and heating during impact events

thumb|Chromite|Chromitic [[serpentinite from Styria Province, Austria]] Serpentinization is a hydration and metamorphic transformation of ferromagnesian minerals, such as olivine and pyroxene, in mafic and ultramafic rock to produce serpentinite. Minerals formed by serpentinization include the serpentine group minerals (antigorite, lizardite, chrysotile), brucite, talc, Ni-Fe alloys, and magnetite. The mineral alteration is particularly important at the sea floor at tectonic plate boundaries.

thumb|upright=1.3|Scanning Electron Microscope interface image of a fayalite-[[pyroxene symplectite (at right) in a Martian meteorite]] A symplectite (or symplektite) is a material texture: a micrometre-scale or submicrometre-scale intergrowth of two or more crystals. Symplectites form from the breakdown of unstable phases, and may be composed of minerals, ceramics, or metals. Fundamentally, their formation is the result of slow grain-boundary diffusion relative to interface propagation rate.

rock metamorphosed from sedimentary material

mass of metamorphic rock in which the formation pressure and temperature conditions can be established according to the minerals that compose it

changes of rock due to pressure and heat near a subduction zone

metamorphic rock from a volcanic precursor