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Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i.e without melting. There will be mineralogical, chemical and crystallographic changes. Image File history File links This is a lossless scalable vector image. ... This balancing rock, Steamboat Rock stands in Garden of the Gods park in Colorado Springs, CO The rocky side of a mountain creek near Orosí, Costa Rica. ... A mineral is a naturally occurring substance formed through geological processes that has a characteristic chemical composition, a highly ordered atomic structure and specific physical properties. ... Crystallography (from the Greek words crystallon = cold drop / frozen drop, with its meaning extending to all solids with some degree of transparency, and graphein = write) is the experimental science of determining the arrangement of atoms in solids. ...

Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism.

Limits of metamorphism

The temperature lower limit of metamorphism is considered to be between 100 - 150°C, to exclude diagenetic changes, due to compaction, which result in sedimentary rocks. There is no agreement as for a pressure lower limit. Some workers argue that changes in atmospheric pressures are not metamorphic, but some types of metamorphism can occur at extremely low pressures (see below). In geology and oceanography, diagenesis is any chemical, physical, or biological change undergone by a sediment after its initial deposition and during and after its lithification, exclusive of surface alteration (weathering) and metamorphism. ... Two types of sedimentary rock: limey shale overlaid by limestone. ...

The upper boundary of metamorphic conditions is related to the onset of melting processes in the rock. The temperature interval is between 700 - 900°C, with pressures that depend on the composition of the rock. Migmatites are rocks formed on this borderline. They present both melting and solid-state features. Ptygmatic folding in migmatite Migmatite on the coast of Saaremaa. ...

Kinds of metamorphism

Regional metamorphism

Regional or Barrovian metamorphism covers large areas of continental crust typically associated with mountain ranges, particularly subduction zones or the roots of previously eroded mountains. Conditions producing widespread regionally metamorphosed rocks occur during an orogenic event. The collision of two continental plates or island arcs with continental plates produce the extreme compressional forces required for the metamorphic changes typical of regional metamorphism. These orogenic mountains are later eroded, exposing the intensely deformed rocks typical of their cores. The conditions within the subducting slab as it plunges toward the mantle in a subduction zone also produce regional metamorphic effects. The techniques of structural geology are used to unravel the collisional history and determine the forces involved. Regional metamorphism can be described and classified into metamorphic facies or zones of temperature/pressure conditions throughout the orogenic terrane. The thickness of the Earths crust (km). ... Severe soil erosion in a wheat field near Washington State University, USA. For erosion as an operation of Mathematical morphology, see Erosion (morphology) Erosion is displacement of solids (soil, mud, rock and other particles) by the agents of ocean currents, wind, water, or ice by downward or down-slope movement... // Orogeny (Greek for mountain generating) is the process of mountain building, and may be studied as a tectonic structural event, as a geographical event and a chronological event, in that orogenic events cause distinctive structural phenomena and related tectonic activity, affect certain regions of rocks and crust and happen within... The tectonic plates of the world were mapped in the second half of the 20th century. ... An island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. ... Earth cutaway from core to exosphere. ... Categories: Geology stubs | Plate tectonics ... Structural geology is the study of the three dimensional distribution of rock bodies and their planar or folded surfaces, and their internal fabrics. ...

Metamorphic facies
Metamorphic facies are recognizable terranes or zones with an equilibrium assemblage of key minerals that were in equilibrium under specific range of temperature and pressure during a metamorphic event. The facies are named after the metamorphic rock formed under those facies conditions from basalt. Facies relationships were first described by Eskola (1920). Basalt Basalt (IPA: ) is a common gray to black extrusive volcanic rock. ...

Facies:

• Low T - low P : Zeolite
• Mod - high T - low P : Prehnite-Pumpellyite
• High-P low T : Blueschist
• Mod P - Mod to high T: Greenschist - Amphibolite - Granulite
• High P - Mod - high T : Eclogite

Zeolite facies describes the mineral assemblage resulting from the pressure and temperature conditions of low-grade metamorphism. ... The prehnite-pumpellyite facies is a metamorphic facies typical of subseafloor alteration of the oceanic crust around mid-ocean ridge spreading centres. ... Blueschist is a rock that forms by the metamorphism of sodium-rich basic rocks at high pressures and low temperatures, approximately corresponding to a depth of 15 to 30 kilometers and 200 to 400 degrees Celsius (cool by metamorphic standards). ... Greenschist is a general field petrologic term applied to metamorphically altered mafic volcanic rock. ... Amphibolite Amphibolite (IPA: , ) is the name given to a rock consisting mainly of hornblende amphibole, the use of the term being restricted, however, to metamorphic rocks. ... Modern petrology defnes a granulite sensuo stricto as a coarse grained, high-grade metamorphic rock composed primarily of pyroxene, plagioclase feldspar and accessory garnet, oxide and amphibole. ... Eclogite is a coarse-grained, mafic-to-ultramafic grouping of metamorphic rocks of special interest on account of the variety of minerals they contain and their microscopic structures and geological relationships. ...

Metamorphic grades

In the Barrovian sequence (described by George Barrow in zones of progressive metamorphism in Scotland), metamorphic grades are also classified by mineral assemblage based on the appearance of key minerals in rocks of pelitic (shaly, aluminous) origin:

Low grade ------------------- Intermediate --------------------- High grade

Greenschist ------------- Amphibolite ----------------------- Granulite

Slate --- Phyllite ---- Schist --------- Gneiss -----------------------Migmatite(partial metling) >>>melt

Chlorite zone

Biotite zone

Garnet zone

Staurolite zone

Kyanite zone

Sillimanite zone

Slate Slate Macro Slate roof Slate is a fine-grained, homogeneous, metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low grade regional metamorphism. ... Phyllite Phyllite is a type of foliated metamorphic rock primarily composed of quartz, sericite mica, and chlorite; the rock represents a gradiation in the degree of metamorphism between slate and mica schist. ... Schist The schists form a group of medium-grade metamorphic rocks, chiefly notable for the preponderance of lamellar minerals such as micas, chlorite, talc, hornblende, graphite, and others. ... Gneiss Gneiss (IPA: ) is a common and widely distributed type of rock formed by high-grade regional metamorphic processes from preexisting formations that were originally either igneous or sedimentary rocks. ... Ptygmatic folding in migmatite Migmatite on the coast of Saaremaa. ... Chlorite is a group of phyllosilicate minerals often classified as clays. ... A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... Garnet is a group of minerals that have been used since the Bronze Age as gemstones and abrasives. ... Staurolite Staurolite is a red brown to black mostly opaque nesosilicate mineral with a white streak. ... Kyanite, whose name derives from the Greek, kyanos, meaning blue, is a typically blue silicate mineral, commonly found in aluminium-rich metamorphic pegmatites and/or sedimentary rock. ... Sillimanite: Biotite gneiss (Mesozoic and Paleozoic) Sillimanite is an alumino-sillicate mineral with the chemical formula Al2SiO5. ...

Contact (Thermal) metamorphism

Contact metamorphism occurs typically around intrusive igneous rocks as a result of the temperature increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion (called aureoles) where the contact metamorphism effects are present is called the metamorphic aureole. Contact metamorphic rocks are usually known as hornfels. Rocks formed by contact metamorphism may not present signs of strong deformation and are often fine-grained. Pluton redirects here. ... Volcanic rock on North America Plutonic rock on North America Igneous rocks form 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. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... Country rock is a geological term meaning the rock native to an area. ... Hornfels (German, meaning hornstone) is the group designation for a series of contact metamorphic rocks that have been baked and indurated by the heat of intrusive granitic masses and have been rendered massive, hard, splintery, and in some cases exceedingly tough and durable. ...

Contact metamorphism is greater adjacent to the intrusion and dissipates with distance from the contact. The size of the aureole depends on the heat of the intrusive, its size, and the temperature difference with the wall rocks. Dykes generally have small aureoles with minimal metamorphism whereas large ultramafic intrusions can have significantly thick and well-developed contact metamorphism. This article does not cite any references or sources. ... It has been suggested that this article or section be merged with Ultramafic intrusion. ...

The metamorphic grade of an aureole is measured by the peak metamorphic mineral which forms in the aureole. This is usually related to the metamorphic temperatures of pelitic or alumonisilicate rocks and the minerals they form. The metamorphic grades of aureoles are andalusite hornfels, sillimanite hornfels, pyroxene hornfels.

Magmatic fluids coming from the intrusive rock may also take part in the metamorphic reactions. Extensive addition of magmatic fluids can significantly modify the chemistry of the affected rocks. In this case the metamorphism grades into metasomatism. If the intruded rock is rich in carbonate the result is a skarn. Fluorine-rich magmatic waters which leave a cooling granite may often form greisens within and adjacent to the contact of the granite. Metasomatic altered aureoles can localize the deposition of metallic ore minerals and thus are of economic interest. A metamorphic reaction is a chemical reaction that takes place during the geological process of metamorphism in an amalgamate of minerals that helps determine the final stable state of the resulting metamorphic rock. ... Metasomatism is a geologic process where metamorphism causes an alteration in a mineral or rock mass that involves a chemical change of the substance with the addition of material, as when chrysolite (olivine) is converted to serpentine basically by the addition of water. ... In organic chemistry, a carbonate is a salt of carbonic acid. ... Skarn is a fine grained metamorphic rock that is usually variably colored green or red, occasionally grey, black, brown or white. ... General Name, Symbol, Number fluorine, F, 9 Chemical series halogens Group, Period, Block 17, 2, p Appearance Yellowish brown gas Atomic mass 18. ... Greisen is a highly altered granitic rock or pegmatite. ... Iron ore (Banded iron formation) Manganese ore Lead ore Gold ore An ore is a volume of rock containing components or minerals in a mode of occurrence which renders it valuable for mining. ...

Hydrothermal metamorphism

Hydrothermal metamorphism is the result of the interaction of a rock with a high-temperature fluid of variable composition. The difference in composition between existing rock and the invading fluid triggers a set of metamorphic and metasomatic reactions. The hydrothermal fluid may be magmatic (originate in an intruding magma), circulating groundwater, or ocean water. Convective circulation of water in the ocean floor basalts produces extensive hydrothermal metamorphism adjacent to spreading centers and other submarine volcanic areas. The patterns of this hydrothermal alteration is used as a guide in the search for deposits of valuable metal ores. Hydrothermal circulation in the oceans is the passage of the water through mid-ocean Ridge (MOR) systems. ... Metasomatism is a geologic process where metamorphism causes an alteration in a mineral or rock mass that involves a chemical change of the substance with the addition of material, as when chrysolite (olivine) is converted to serpentine basically by the addition of water. ... Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of geologic formations. ... Basalt Basalt (IPA: ) is a common gray to black extrusive volcanic rock. ...

Impact metamorphism

This kind of metamorphism occurs when either an extraterrestrial object (a meteorite for instance) collides with the Earth's surface or during an extremely violent volcanic eruption. Impact metamorphism is, therefore, characterized by ultrahigh pressure conditions and low temperature. The resulting minerals (such as SiO₂ polymorphs coesite and stishovite) and textures are characteristic of these conditions. Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ... For other uses, see Volcano (disambiguation). ... Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. ... Coesite is a form of silicon dioxide that is formed when very high pressure (2–3 gigapascals) and moderately high temperature (700 °C) are applied to quartz. ... Stishovite is a form of silicon dioxide that is formed at very high pressure (~ 100 kbar) and temperature (> 1200 ° C), so far as is known only in meteorite impact craters and their ejecta. ...

Dynamic metamorphism

Dynamic metamorphism is associated with major fault planes. Metamorphism is localised adjacent to the fault plane and is caused by frictional heat generated by the fault movement. Cataclasis, crushing and grinding of rocks into angular fragments, occurs in dynamic metamorphic zones, giving cataclastic texture. Old fault exposed by roadcut near Harrisburg, Pennsylvania. ... Cataclastic rocks contain angular fragments formed by cataclasis. ...

The textures of dynamic metamorphic zones are dependent on the depth at which they were formed, as the confining pressure determines the deformation mechanisms which predominate. Within depths less than 5km, dynamic metamorphism is not often produced because the confining pressure is too low to produce frictional heat. Instead, a zone of breccia or cataclasite is formed, with the rock milled and broken into random fragments. This generally forms a mélange. At depth, the angular breccias transit into a ductile shear texture and into mylonite zones. Breccia, derived from the Latin word for broken, is a sedimentary rock composed of angular fragments in a matrix that may be of a similar or a different material. ... Cataclasite is a metamorphic rock that is formed by mechanical shear stress during faulting [1]. It is either incohesive or cohesive with poor schistosity. ... In geologic context, mélange is a large scale breccia formed in the accretionary wedge above a subduction zone. ...

Within the depth range of 5-10km pseudotachylite is formed, as the confining pressure is enough to prevent brecciation and milling and thus energy is focused into discrete fault planes. The frictional heating in this case may melt the rock to form pseudotachylite glass or mylonite, and adjacent to these zones, result in growth of new mineral assemblages. Pseudotachylite is a fault rock that has the appearance of the basaltic glass, tachylyte. ...

Within the depth range of 10-20km, deformation is governed by ductile deformation conditions and hence frictional heating is dispersed throughout shear zones, resulting in a weaker thermal imprint and distributed deformation. Here, deformation forms mylonite, with dynamothermal metamorphism observed rarely as the growth of porphyroblasts in mylonite zones. Study of geological shear is related to the study of structural geology, rock microstructure or rock texture and fault mechanics. ... Mylonite is a fine-grained, compact rock without cleavage or crystals. ... A porphyroblast is a large mineral crystal of metamorphic origin which has grown within the finer grained groundmass of a metamorphic rock as a response to the stresses or heat of metamorphism. ...

Overthrusting may juxtapose hot lower crustal rocks against cooler mid and upper crust blocks, resulting in conductive heat transfer and localised contact metamorphism of the cooler blocks adjacent to the hotter blocks, and often retrograde metamorphism in the hotter blocks. The metamorphic assemblages in this case are diagnostic of the depth and temperature and the throw of the fault and can also be dated to give an age of the thrusting. A thrust fault is a particular type of fault, or break in the fabric of the Earths crust with resulting movement of each side against the other, in which a lower stratigraphic position is pushed up and over another. ... Radiometric dating is a technique used to date materials based on a knowledge of the decay rates of naturally occurring isotopes, and the current abundances. ...

Prograde and retrograde metamorphism

Metamorphism is further divided into prograde and retrograde metamorphism. Prograde metamorphism involves the change of mineral assemblages (paragenesis) with increasing temperature and (usually) pressure conditions. These are solid state dehydration reactions, and involve the loss of volatiles such as water or carbon dioxide. Prograde metamorphism results in a rock representing the maximum pressure and temperature experienced. These rocks often return to the surface without undergoing retrograde metamorphism , where the mineral assemblages would become more stable under lower pressures and temperatures. Paragenesis is a petrologic concept meaning an equilibrium assemblage of mineral phases. ...

Retrograde metamorphism involves the reconstitution of a rock under decreasing temperatures (and usually pressures) where revolatisation occurs; allowing the mineral assemblages formed in prograde metamorphism to return to more stable minerals at the lower pressures. This is a relatively uncommon process, because volatiles must be present for retrograde metamorphism to occur. Most metamorphic rocks return to the surface as a representation of the maximum pressures and temperatures they have undergone.

See also

• Metamorphic rock
• Metasomatism
• Recrystallization
• Geothermobarometry

Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... Metasomatism is a geologic process where metamorphism causes an alteration in a mineral or rock mass that involves a chemical change of the substance with the addition of material, as when chrysolite (olivine) is converted to serpentine basically by the addition of water. ... Insulin crystals Recrystallization is an essentially physical process that has meanings in chemistry, metallurgy and geology. ... Geothermobarometry is the science of measuring the previous pressure and temperature history of a metamorphic or intrusive igneous rocks. ...

References

Eskola P. 1920. The mineral facies of rocks. Norsk. Geol. Tidsskr., 6, 143-194.

Winter J.D., 2001. An introduction to Igneous and Metamorphic Petrology. Prentice-Hall Inc. , 695 pages. ISBN 0-13-240342-0.

External links

• James Madison University: Metamorphism
• BARROVIAN METAMORPHISM: Brock Univ.
• Metamorphism of Carbonate Rocks: University of Wisconsin - Green Bay