query: an existing rock that changes during metamorphism to create a metamorphic rock is called

pos: Metamorphic rock the foliation is called "gneissosity"), granoblastic (includes granulite, some marbles and quartzite), and hornfelsic (includes hornfels and skarn). Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by

pos: Metamorphic rock Metamorphic rock Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form". The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure ( or more), causing profound physical or chemical change. The protolith may be a sedimentary, igneous, or existing metamorphic rock. Metamorphic rocks make up a large part of the Earth's crust and form 12% of the Earth's land surface. They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath

pos: Metamorphism of the fault and can also be dated to give an age of the thrusting. Metamorphic rocks are classified by their mineral composition, the source rock, also known as a protolith, and the context (pressure, temperature, hydrological features, etc.) of its formation. Metamorphic facies are recognizable terranes or zones with an 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 Pentti Eskola in 1921. See diagram for more detail.

pos: Rock (geology) formed. This process is called metamorphism, meaning to "change in form". The result is a profound change in physical properties and chemistry of the stone. The original rock, known as the protolith, transforms into other mineral types or other forms of the same minerals, by recrystallization. The temperatures and pressures required for this process are always higher than those found at the Earth's surface: temperatures greater than 150 to 200 °C and pressures of 1500 bars. Metamorphic rocks compose 27.4% of the crust by volume. The three major classes of metamorphic rock are based upon the formation mechanism. An intrusion

pos: Metamorphism conditions. This is a relatively uncommon process, because volatiles must be present. Metamorphism Metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (protoliths), without the protolith melting into liquid magma (a solid-state change). The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. The chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earth's surface due to weathering or diagenesis are not classified as metamorphism. Metamorphism typically occurs between diagenesis (max.

pos: Metamorphism Metamorphism Metamorphism is the change of minerals or geologic texture (distinct arrangement of minerals) in pre-existing rocks (protoliths), without the protolith melting into liquid magma (a solid-state change). The change occurs primarily due to heat, pressure, and the introduction of chemically active fluids. The chemical components and crystal structures of the minerals making up the rock may change even though the rock remains a solid. Changes at or just beneath Earth's surface due to weathering or diagenesis are not classified as metamorphism. Metamorphism typically occurs between diagenesis (max. 200°C), and melting (~850°C). Three types of metamorphism exist: contact, dynamic, and

pos: Lawsonite a significant metamorphic mineral as it can be used as an index mineral for high pressure conditions. Index minerals are used in geology to determine the degree of metamorphism a rock has experienced. New metamorphic minerals form through solid-state cation exchanges following changing pressure and temperature conditions imposed upon the protolith (pre-metamorphosed rock). This new mineral that is produced in the metamorphosed rock is the index mineral, which indicates the minimum pressure and temperature the protolith must have achieved in order for that mineral to form. Lawsonite is known to form in high pressure, low temperature conditions, most commonly found

pos: Parent rock Parent rock Parent rock, also referred to as substratum, refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock (or parent material) normally has a large influence on the nature of the resulting soil. For example,clay soil is derived from shale while sandy soil comes from the weathering of sandstones. The term is also used in the context of metamorphic rocks where again the parent rock or protolith refers to the original rock before metamorphism takes place. Parent rocks can be sedimentary, igneous or metamorphic.

pos: Parent rock Parent rock Parent rock, also referred to as substratum, refers to the original rock from which something else was formed. It is mainly used in the context of soil formation where the parent rock (or parent material) normally has a large influence on the nature of the resulting soil. For example,clay soil is derived from shale while sandy soil comes from the weathering of sandstones. The term is also used in the context of metamorphic rocks where again the parent rock or protolith refers to the original rock before metamorphism takes place. Parent rocks can be sedimentary, igneous or metamorphic.

pos: Amphibolite metamorphic mapping based on amphibolite alone. Firstly, for an (ortho)amphibolite to be classed as a metamorphic amphibolite, it must be certain that the amphibole in the rock is a prograde metamorphic product, and not a retrograde metamorphic product. For instance, actinolite amphibole is a common product of retrograde metamorphism of metabasalt at (upper) greenschist facies conditions. Often, this will take on the crystal form and habit of the original protolith assemblage; actinolite pseudomorphically replacing pyroxene is an indication that the amphibolite may not represent a peak metamorphic grade in the amphibolite facies. Actinolite schist is often the result of hydrothermal

pos: Metamorphism involve the diffusion of atoms through solid crystals. Pressure solution is a metamorphic process that requires a rock to be under strong pressure from one direction and in the presence of hot water. During this process mineral of the protolith partially dissolve, diffuse through the water and precipitate elsewhere. In plastic deformation pressure is applied to the protolith, which causes it to shear or bend, but not break. In order for this to happen temperatures must be high enough that brittle fractures do not occur, but not so high that diffusion of crystals takes place. Metamorphism is further divided into

pos: Metamorphic zone index minerals have complicated chemical compositions. If not all necessary elements are abundant, the mineral will not grow. When mapping the metamorphic grade of a terrane, a geologist has to take the lithology of the rock in account. Lithologies are mainly dependent on the protolith, the original rock before metamorphism. The main lithologies are ultramafic, mafic, felsic (or quartzo-feldspatic), pelitic and calcareous. In all of these (and other) lithologies, different combinations of minerals occur at a certain grade. The metamorphic zones in these lithologies can also be different. The type of metamorphic zones in a terrane are also determined by

pos: Phyllite silky, sometimes golden sheen to the surfaces of cleavage, called "phyllitic luster". The word comes from the Greek "phyllon", meaning "leaf". The protolith (or parent rock) for phyllite is shale or pelite, or slate, which in turn came from a shale protolith. Its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a texture called "phyllitic sheen," and are usually classified as having formed through low-grade metamorphic conditions through regional metamorphism metamorphic facies. Phyllite has good fissility (a tendency to split into sheets). Phyllites are usually black

pos: Lithology naming can be based on texture, protolith, metamorphic facies, and/or the locations in which they are found. Naming based on texture and a pelite (e.g., shale, mudrock) protolith can be used to define slate and phyllite. Texture-based names are schist and gneiss. These textures, from slate to gneiss, define a continually-increasing extent of metamorphism. Metamorphic facies are defined by the pressure-temperature fields in which particular minerals form. Additional metamorphic rock names exist: greenstone (metamorphosed basalt and other extrusive igneous rock) is a classification based on composition and being located Precambrian terranes, while quartzite is based only on composition, as quartz

pos: Talc carbonate Talc carbonate Talc carbonates are a suite of rock and mineral compositions found in metamorphic ultramafic rocks. The term refers to the two most common end-member minerals found within ultramafic rocks which have undergone talc-carbonation or carbonation reactions, talc and the carbonate mineral magnesite. Talc carbonate mineral assemblages are controlled by temperature and pressure of metamorphism and the partial pressure of carbon dioxide within metamorphic fluids, as well as by the composition of the host rock. In a general sense, talc carbonate metamorphic assemblages are diagnostic of the magnesium content of the ultramafic protolith. Thus, the MgO content of a

pos: Amphibolite Amphibolite Amphibolite () is a metamorphic rock that contains amphibole, especially the species hornblende and actinolite, as well as plagioclase. Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspar, with little or no quartz. It is typically dark-colored and heavy, with a weakly foliated or schistose (flaky) structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance. Amphibolite need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals entirely based upon the chemistry of the protolith, certain 'dirty marls' and volcanic sediments may actually metamorphose to an

pos: Monazite geochronology These distinctive features can be easily identified with textual and compositional analysis in monazite geochronology. Monazite geochronology is generally regarded as a powerful tool to reveal metamorphic history. Metamorphism is the mineral change of textural change in preexisting rocks in response to a change in environment with different temperatures and pressures. It occurs at a temperature above diagenesis (~200 °C) and below melting (>800 °C). The mineral assemblage formed under metamorphism depends on the composition of the parent rock (protolith) and more importantly, the stability of different minerals in varying temperature and pressure (P-T). A set of mineral assemblage that

pos: Metamorphism Metamorphic grade is an informal indication of the amount or degree of metamorphism. A more complete indication of this intensity or degree is provided with the concept of metamorphic facies. 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 During recrystallization, the grains making up the protolith change shape and size. The identity of the mineral does not change during this process, only the texture.

neg: Diagenesis Diagenesis Diagenesis () is the change of sediments or existing sedimentary rocks into a different sedimentary rock during and after rock formation (lithification), at temperatures and pressures less than that required for the formation of metamorphic rocks. It does not include changes from weathering. It is any chemical, physical, or biological change undergone by a sediment after its initial deposition, after its lithification. This process excludes surface alteration (weathering) and metamorphism. These changes happen at relatively low temperatures and pressures and result in changes to the rock's original mineralogy and texture. There is no sharp boundary between diagenesis and metamorphism,

neg: Metamorphic rock introduction of new chemicals is not necessary for recrystallization to occur. Contact metamorphism is the name given to the changes that take place when magma is injected into the surrounding solid rock (country rock). The changes that occur are greatest wherever the magma comes into contact with the rock because the temperatures are highest at this boundary and decrease with distance from it. Around the igneous rock that forms from the cooling magma is a metamorphosed zone called a "contact metamorphism aureole". Aureoles may show all degrees of metamorphism from the contact area to unmetamorphosed (unchanged) country rock some distance

neg: Migmatite Migmatite Migmatite is a rock that is a mixture of metamorphic rock and igneous rock. It is created when a metamorphic rock such as gneiss partially melts, and then that melt recrystallizes into an igneous rock, creating a mixture of the unmelted metamorphic part with the recrystallized igneous part. They can also be known as "diatexite". Migmatites form under extreme temperature conditions during prograde metamorphism, where partial melting occurs in pre-existing rocks. Migmatites are not crystallized from a totally molten material, and are not generally the result of solid-state reactions. Commonly, migmatites occur within extremely deformed rocks that represent the

neg: Metamorphic rock metamorphism, is the name given to changes in great masses of rock over a wide area. Rocks can be metamorphosed simply by being at great depths below the Earth's surface, subjected to high temperatures and the great pressure caused by the immense weight of the rock layers above. Much of the lower continental crust is metamorphic, except for recent igneous intrusions. Horizontal tectonic movements such as the collision of continents create orogenic belts, and cause high temperatures, pressures and deformation in the rocks along these belts. If the metamorphosed rocks are later uplifted and exposed by erosion, they may occur

neg: Cataclastic rock Cataclastic rock A cataclastic rock is a type of metamorphic rock that has been wholly or partly formed by the progressive fracturing and comminution of existing rock, a process known as "cataclasis". Cataclasis involves the granulation, crushing, or milling of the original rock, then rigid-body rotation and translation of mineral grains or aggregates before lithification and any metamorphism. Cataclastic rocks are associated with fault zones and impact event breccias. Various classification schemes have been proposed for the cataclastic rocks, but changes in understanding of the processes involved in their formation and better knowledge of the variety of such rocks has

neg: Pressure-temperature-time path paths often reflect various stages of the metamorphic cycle. A metamorphic cycle implies the series of processes that a rock experienced from burial, heating to uplift and erosion. The P-T conditions experienced by a rock throughout these processes can be classified into three main stages according to temperature changes: However, retrograde metamorphism may not always be observed in metamorphic rocks. This is due to the loss of fluids (e.g. CO, HO) from prograde metamorphism, after which there is insufficient fluid to permit reverse reaction of the mineral assemblages. Another reason is that the rocks are of inappropriate composition to generate

neg: Rock cycle or chemically to form a different rock, called metamorphic. Regional metamorphism refers to the effects on large masses of rocks over a wide area, typically associated with mountain building events within orogenic belts. These rocks commonly exhibit distinct bands of differing mineralogy and colors, called foliation. Another main type of metamorphism is caused when a body of rock comes into contact with an igneous intrusion that heats up this surrounding country rock. This "contact metamorphism" results in a rock that is altered and re-crystallized by the extreme heat of the magma and/or by the addition of fluids from the magma

neg: Pressure-temperature-time path Pressure-temperature-time path The Pressure-Temperature-time path (P-T-t path) is a record of the pressure and temperature (P-T) conditions that a rock experienced in a metamorphic cycle from burial and heating to uplift and exhumation to the surface. Metamorphism is a dynamic process which involves the changes in minerals and textures of the pre-existing rocks (protoliths) under different P-T conditions in solid state. The changes in pressures and temperatures with time experienced by the metamorphic rocks are often investigated by petrological methods, radiometric dating techniques and thermodynamic modeling. Metamorphic minerals are unstable upon changing P-T conditions. The original minerals are commonly destroyed

neg: Metamorphism 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 special type of contact metamorphism, associated with fossil fuel fires, is known as pyrometamorphism. Hydrothermal metamorphism is the result of the interaction of a rock with a high-temperature fluid of variable composition. The difference in composition between an existing rock and the invading fluid triggers a set of metamorphic

neg: Unconformity disconformity in which the separation is a simple bedding plane with no obvious buried erosional surface. A nonconformity exists between sedimentary rocks and metamorphic or igneous rocks when the sedimentary rock lies above and was deposited on the pre-existing and eroded metamorphic or igneous rock. Namely, if the rock below the break is igneous or has lost its bedding due to metamorphism, the plane of juncture is a nonconformity. An angular unconformity is an unconformity where horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers. The whole

neg: Metamorphic rock in metamorphic rocks indicates the approximate temperatures and pressures at which they formed. The change in the particle size of the rock during the process of metamorphism is called recrystallization. For instance, the small calcite crystals in the sedimentary rock limestone and chalk change into larger crystals in the metamorphic rock marble; in metamorphosed sandstone, recrystallization of the original quartz sand grains results in very compact quartzite, also known as metaquartzite, in which the often larger quartz crystals are interlocked. Both high temperatures and pressures contribute to recrystallization. High temperatures allow the atoms and ions in solid crystals to migrate,

neg: Metamorphic rock minerals are formed. Many complex high-temperature reactions may take place, and each mineral assemblage produced provides us with a clue as to the temperatures and pressures at the time of metamorphism. Metasomatism is the drastic change in the bulk chemical composition of a rock that often occurs during the processes of metamorphism. It is due to the introduction of chemicals from other surrounding rocks. Water may transport these chemicals rapidly over great distances. Because of the role played by water, metamorphic rocks generally contain many elements absent from the original rock, and lack some that originally were present. Still, the

neg: Metamorphic rock develops with increasing temperature: slate is a very fine-grained, foliated metamorphic rock, characteristic of very low grade metamorphism, while phyllite is fine-grained and found in areas of low grade metamorphism, schist is medium to coarse-grained and found in areas of medium grade metamorphism, and gneiss coarse to very coarse-grained, found in areas of high-grade metamorphism. Marble is generally not foliated, which allows its use as a material for sculpture and architecture. Another important mechanism of metamorphism is that of chemical reactions that occur between minerals without them melting. In the process atoms are exchanged between the minerals, and thus new

neg: Metamorphism minimal metamorphism whereas large ultramafic intrusions can have significantly thick and well-developed contact metamorphism. 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 aluminosilicate 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. An extensive addition of magmatic fluids can significantly modify the chemistry of the affected rocks. In this case the metamorphism grades into metasomatism. If

neg: Metamorphic zone Metamorphic zone In geology, a metamorphic zone is an area where, as a result of metamorphism, the same combination of minerals occur in the bedrock. These zones occur because most metamorphic minerals are only stable in certain intervals of temperature and pressure. The temperature and pressure at which the mineralogical composition of a rock equilibrated can vary laterally through a metamorphic terrane. The two parameters together determine the metamorphic grade. The difference in grade between two locations is called the metamorphic gradient. Planes that connect points with the same metamorphic grade are called isograds. The secant lines of isograds with

neg: Slate Slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. Foliation may not correspond to the original sedimentary layering, but instead is in planes perpendicular to the direction of metamorphic compression. The foliation in slate is called "slaty cleavage". It is caused by strong compression causing fine grained clay flakes to regrow in planes perpendicular to the compression. When expertly "cut" by striking parallel to the foliation, with a specialized tool in the quarry, many slates

neg: Metamorphism excludes diagenetic changes due to compaction and the formation of sedimentary rocks. The upper boundary of metamorphic conditions is related to the onset of melting processes in the rock. The maximum temperature for metamorphism is typically 700 – 900 °C, depending on the pressure and on the composition of the rock. Migmatites are rocks formed at this upper limit, which contains pods and veins of material that has started to melt but has not fully segregated from the refractory residue. Since the 1980s it has been recognized that rocks are rarely dry enough and of a refractory enough composition to

neg: Metamorphism a result of the temperature increase caused by the intrusion of magma into cooler country rock. The area surrounding the intrusion 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. 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 intrusion, its size, and the temperature difference with the wall rocks. Dikes generally have small aureoles with

neg: Pressure-temperature-time path all the minerals that record their complete metamorphic events. On average, only one-in-twenty metamorphic rock samples display all the three stages of metamorphism. P-T-t paths can generally be classified into two types: "clockwise P-T-t paths" and "anticlockwise P-T-t paths". Metamorphic rocks with clockwise P-T-t paths are commonly associated with a near-isothermal decompressional P-T trajectory. Clockwise P-T-t path normally consists of three parts: One might expect that the rock reaches its peak metamorphism at the peak temperature and pressure at similar time, and near-isothermal decompression P-T-t path is observed at its stage 1 metamorphism. However, in reality, the rocks commonly experience

neg: Anthophyllite containing anthophyllite are indicative of at least greenschist facies metamorphism in the presence of carbon dioxide bearing metamorphic fluids. The typical metamorphic assemblage reactions for low-magnesian (<25% MgO) and high-magnesian (>25% MgO) ultramafic rocks are; Retrogressive anthophyllite is relatively rare in ultramafic rocks and is usually poorly developed due to the lower energy state available for metamorphic reactions to progress and also the general dehydration of rock masses during metamorphism. Similarly, the need for substantial components of carbon dioxide in metamorphic fluid restricts the appearance of anthophyllite as a retrograde mineral. The usual metamorphic assemblage of retrograde-altered ultramafic rocks is

neg: Rock (geology) of magma that heats the surrounding rock causes contact metamorphism—a temperature-dominated transformation. Pressure metamorphism occurs when sediments are buried deep under the ground; pressure is dominant, and temperature plays a smaller role. This is termed burial metamorphism, and it can result in rocks such as jade. Where both heat and pressure play a role, the mechanism is termed regional metamorphism. This is typically found in mountain-building regions. Depending on the structure, metamorphic rocks are divided into two general categories. Those that possess a texture are referred to as foliated; the remainders are termed non-foliated. The name of the rock is

neg: Metasomatism alter these rocks. This mechanism implies that metasomatism is open system behaviour, which is different from classical metamorphism which is the in-situ mineralogical change of a rock without appreciable change in the chemistry of the rock. Because metamorphism usually requires water in order to facilitate metamorphic reactions, metamorphism nearly always occurs with metasomatism. Further, because metasomatism is a mass transfer process, it is not restricted to the rocks which are changed by addition of chemical elements and minerals or hydrous compounds. In all cases, to produce a metasomatic rock some other rock is also metasomatised, if only by "dehydration" reactions

neg: Rock cycle the rocks involved. The result is regional metamorphism within the interior of the ensuing orogeny or mountain building event. As the two masses are compressed, folded and faulted into a mountain range by the continental collision the whole suite of pre-existing igneous, volcanic, sedimentary and earlier metamorphic rock units are subjected to this new metamorphic event. The high mountain ranges produced by continental collisions are immediately subjected to the forces of erosion. Erosion wears down the mountains and massive piles of sediment are developed in adjacent ocean margins, shallow seas, and as continental deposits. As these sediment piles are buried

neg: Metamorphic rock mineral particles while they are crystallizing in that directed pressure field. Rocks that were originally sedimentary and rocks that were undoubtedly igneous may be metamorphosed into schists and gneisses. If originally of similar composition they may be very difficult to distinguish from one another if the metamorphism has been great. A quartz-porphyry, for example, and a fine feldspathic sandstone, may both be metamorphosed into a grey or pink mica-schist. The five basic metamorphic textures with typical rock types are slaty (includes slate and phyllite; the foliation is called "slaty cleavage"), schistose (includes schist; the foliation is called "schistosity"), gneissose (gneiss;

neg: Metamorphic rock are those that form only at the high temperatures and pressures associated with the process of metamorphism. These minerals, known as index minerals, include sillimanite, kyanite, staurolite, andalusite, and some garnet. Other minerals, such as olivines, pyroxenes, amphiboles, micas, feldspars, and quartz, may be found in metamorphic rocks, but are not necessarily the result of the process of metamorphism. These minerals formed during the crystallization of igneous rocks. They are stable at high temperatures and pressures and may remain chemically unchanged during the metamorphic process. However, all minerals are stable only within certain limits, and the presence of some minerals

neg: Amphibolite amphibolite assemblage. Deposits containing dolomite and siderite also readily yield amphibolite (tremolite-schist, grunerite-schist, and others) especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalt creates "ortho-amphibolite" and other chemically appropriate lithologies create "para-amphibolite". Tremolite, while it is a metamorphic amphibole, is derived most usually from highly metamorphosed ultramafic rocks, and thus tremolite-talc schist is not generally considered as 'amphibolite'. A holocrystalline plutonic igneous rock composed primarily of hornblende amphibole is called a hornblendite, which is usually a crystal cumulate rock. Igneous rocks with >90% amphiboles, which have a feldspar groundmass, may be

neg: Geology of the Western Carpathians zone of core mountains is present. The core is formed by the Tatric unit composed predominantly by Paleozoic metamorphic rock, younger plutonic rock, and Carboniferous to Mesozoic sedimentary cover. Basement rock was formed during the Hercynian orogeny when a strong regional metamorphism affected the area. Paragneisses and amphibolites are most abundant, but low grade metamorphic rock is also present. Later, at the end of Hercynian orogeny in the Carboniferous and Permian, the area was intruded by granitic rock and strongly affected by erosion, which affected even the deeply situated granites. The autochthonous Carboniferous, Permian and most commonly Mesozoic sediments are

neg: Blueschist quarried in Agia Pelagia on the north coast of central Crete. In 1962, Edgar Bailey of the U.S. Geological Survey introduced the concept of "blueschist" into the subject of metamorphic geology. His carefully constructed definition established the pressure and temperature conditions which produce this type of metamorphism. Blueschist facies - Rock Library Glossary, Imperial College London Blueschist Blueschist (), also called glaucophane schist, is a metavolcanic rock that forms by the metamorphism of basalt and rocks with similar composition at high pressures and low temperatures (200 to ~500 degrees Celsius), approximately corresponding to a depth of 15 to 30 kilometers.

neg: Metamorphic zone the form of metamorphism. This is dependent on the geodynamic (tectonic and magmatic) setting in which metamorphism took place. The sequence of metamorphic zones is called a metamorphic facies series, and the most common of these is Barrovian (called after George Barrow who first mentioned it in 1912). In this series of zones, both pressure and temperature increase gradually along the metamorphic gradient. Barrovian metamorphism takes place during regional metamorphism, caused by crustal thickening in the roots of an orogenic belt (under mountain chains). Barrovian zones are especially easy to recognize in pelitic rocks. The prograde sequence of Barrovian zones

neg: High pressure metamorphic terranes along the Bangong-Nujiang Suture Zone as a microcontinent as the Qiangtang and Lhasa terranes rifted apart. The Amdo terrane includes: -"Rock Types:" Schists, marble, and mylonitic fabrics are present. Lower amphibolite-facies metamorphism. -"Rock Types:" Limestone, felsic volcanic rocks. Greenschist-facies metamorphism. -"Rock Types:" Shallow-water limestone. -"Rock Types:" Sandy slate with coral fossils. -"Rock Types:" Conglomerate, tuffaceous sandstone, and slate. Greenschist-facies metamorphism. Similar to the Dong Tso in the Gertse area, geochemical analysis of samples taken from the Amdo massif show arc-related features; thus, this area would have been under an active continental margin setting. The Basu massif, located east of the Amdo massif in the Dingqing-Nujiang

neg: Metamorphism record without melting "ultra-high" metamorphic temperatures of 900 – 1100 °C. The metamorphic process usually has to be over pressure of at least 100 mega pascals but below 300 mega pascals, the depth of 100 mega pascals varies depending on what type of rock is applying pressure. Regional or "Barrovian" metamorphism covers large areas of continental crust typically associated with mountain ranges, particularly those associated with convergent tectonic plates 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

neg: Foliation (geology) is usually a result of prograde metamorphic reactions during deformation. Often, retrograde metamorphism will not form a foliation because unroofing of a metamorphic belt is not accompanied by significant compressive stress. Thermal metamorphism in the aureole of a granite is also unlikely to result in growth of mica in a foliation, although growth of new minerals may overprint existing foliation(s). Alignment of tabular minerals in metamorphic rocks, igneous rocks and intrusive rocks may form a foliation. Typical examples of metamorphic rocks include porphyroblastic schists where large, oblate minerals form an alignment either due to growth or rotation in the groundmass.

neg: Monazite geochronology example, a metamorphic rock in the Neil Bay area of northern Saskatchewan underwent high grade (high P/T) metamorphism followed by exhumation (uplift). Porphyroblast garnet is formed during high grade metamorphism while porphyroblast cordierite is formed during exhumation afterwards. Both porphyroblasts contain monazite inclusions which dated 1910 Ma and 1840 Ma respectively. And matrix monazite is dated 1800 Ma. Thus, it is interpreted that high grade metamorphism occurred after 1910 Ma and before 1840 Ma, while exhumation after 1840 Ma, and the final annealing (cooling and coarsening of minerals) at 1800 Ma. Within the same setting as above, monazite inclusions in

neg: Geology of the Western Carpathians external Carpathians). Three main phases of the volcanic activity are distinguished: The occurrence of metamorphosed crystalline rock in the Western Carpathians is known from the Tatric, Veporic, Gemeric, and Zemplinic zones. Existing research has clearly demonstrated traces of the Hercynian and Alpine orogeny. Although some authors suggest the possible presence of the older Cadomian or Caledonian metamorphic cycles, existence of the Precambrian metamorphic cycles was not confirmed because of the later metamorphic overprint. Caledonian metamorphism has not been clearly proved, but some signs are present in amphibolites of the Malé Karpaty Mts. (about 395 million years old) or the granite

neg: Chlorite group mineral of existing ferromagnesian minerals, or it may be present as a metasomatism product via addition of Fe, Mg, or other compounds into the rock mass. Chlorite is a common mineral associated with hydrothermal ore deposits and commonly occurs with epidote, sericite, adularia and sulfide minerals. Chlorite is also a common metamorphic mineral, usually indicative of low-grade metamorphism. It is the diagnostic species of the zeolite facies and of lower greenschist facies. It occurs in the quartz, albite, sericite, chlorite, garnet assemblage of pelitic schist. Within ultramafic rocks, metamorphism can also produce predominantly clinochlore chlorite in association with talc. Experiments

neg: Metamorphism 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 rock characteristic of the maximum pressure and temperature experienced. Metamorphic rocks usually do not undergo further change when they are brought back to the surface. Retrograde metamorphism involves the reconstitution of a rock via revolatisation under decreasing temperatures (and usually pressures), allowing the mineral assemblages formed in prograde metamorphism to revert to those more stable at less extreme

neg: Metamorphic zone subduction zones, that are transported to great depths in relatively low temperatures, rare types of metamorphic zones can develop. Two facies series are the Franciscan and Sanbagawa types. The rocks are characterized by prehnite-pumpellyite, blueschist or eclogite facies minerals. Metamorphic zone In geology, a metamorphic zone is an area where, as a result of metamorphism, the same combination of minerals occur in the bedrock. These zones occur because most metamorphic minerals are only stable in certain intervals of temperature and pressure. The temperature and pressure at which the mineralogical composition of a rock equilibrated can vary laterally through a metamorphic

neg: Greenschist Greenschist Greenschists are metamorphic rocks that formed under the lowest temperatures and pressures usually produced by regional metamorphism, typically and 2–10 kilobars (). Greenschists commonly have an abundance of green minerals such as chlorite, serpentine, and epidote, and platy minerals such as muscovite and platy serpentine. The platiness causes the tendency to split, or have schistosity. Other common minerals include quartz, orthoclase, talc, carbonate minerals and amphibole (actinolite). It is a general field petrologic term for metamorphic or altered mafic volcanic rock. A greenstone is sometimes a greenschist but can also be rock types without any schistosity, especially metabasalt (spilite

neg: Metamorphic rock in long belts or other large areas at the surface. The process of metamorphism may have destroyed the original features that could have revealed the rock's previous history. Recrystallization of the rock will destroy the textures and fossils present in sedimentary rocks. Metasomatism will change the original composition. Regional metamorphism tends to make the rock more indurated and at the same time to give it a foliated, shistose or gneissic texture, consisting of a planar arrangement of the minerals, so that platy or prismatic minerals like mica and hornblende have their longest axes arranged parallel to one another. For that

neg: Sedimentary rock rock. Some biochemical processes, like the activity of bacteria, can affect minerals in a rock and are therefore seen as part of diagenesis. Fungi and plants (by their roots) and various other organisms that live beneath the surface can also influence diagenesis. Burial of rocks due to ongoing sedimentation leads to increased pressure and temperature, which stimulates certain chemical reactions. An example is the reactions by which organic material becomes lignite or coal. When temperature and pressure increase still further, the realm of diagenesis makes way for metamorphism, the process that forms metamorphic rock. The color of a sedimentary rock

neg: Metamorphic rock tendency for metasomatism between the igneous magma and sedimentary country rock, whereby the chemicals in each are exchanged or introduced into the other. Granites may absorb fragments of shale or pieces of basalt. In that case, hybrid rocks called skarn arise, which don't have the characteristics of normal igneous or sedimentary rocks. Sometimes an invading granite magma permeates the rocks around, filling their joints and planes of bedding, etc., with threads of quartz and feldspar. This is very exceptional but instances of it are known and it may take place on a large scale. Regional metamorphism, also known as dynamic

neg: Geology structure is called an overturned anticline or syncline, and if all of the rock units are overturned or the correct up-direction is unknown, they are simply called by the most general terms, antiforms and synforms. Even higher pressures and temperatures during horizontal shortening can cause both folding and metamorphism of the rocks. This metamorphism causes changes in the mineral composition of the rocks; creates a foliation, or planar surface, that is related to mineral growth under stress. This can remove signs of the original textures of the rocks, such as bedding in sedimentary rocks, flow features of lavas, and crystal

neg: Rubidium–strontium dating present during metamorphism or magmatism. Conversely, these fluids may metasomatically alter a rock, introducing new Rb and Sr into the rock (generally during potassic alteration or calcic (albitisation) alteration. Rb-Sr can then be used on the altered mineralogy to date the time of this alteration, but not the date at which the rock formed. Thus, assigning "age significance" to a result requires studying the metasomatic and thermal history of the rock, any metamorphic events, and any evidence of fluid movement. A Rb-Sr date which is at variance with other geochronometers may not be useless, it may be providing data on

neg: Coast Mountains granite intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of the Bridge River Ocean. This molten granite burned the old oceanic sediments into a glittering medium-grade metamorphic rock called schist. The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as gneiss. In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat, weight and stress to create unusual swirled patterns known as migmatite, appearing to have been

neg: Porphyroblast the rock. If a porphyroblastic mineral has small inclusions of minerals within it, the mineral is described as poikiloblastic. This observation can help interpret deformation history. A rock which has many porphyroblasts is described as having a "porphyroblastic texture". As porphyroblasts grow, the foliation may be preserved as oriented inclusions trapped by the porphyroblast as it overgrows them, and this is helpful for tracking changing deformation planes. In metamorphic rocks that experience deformation during metamorphism, porphyroblasts may grow before, during, or after the phase of deformation recorded by the matrix minerals. The relationship of porphyroblast growth to deformation is typically

neg: Pressure-temperature-time path because of losing heat in a downward direction. Thus, the lower segment and the upper thrust sheet are undergoing prograde metamorphism and retrograde metamorphism respectively. Nevertheless, special attention should be taken to the effect of multiple thrusting such as duplexes, where the initial lower plate in an earlier thrust would become the upper plate in a later thrusting event. Depending on the location of the rock, a variety of complex P-T trajectories can be found, which may make interpretation of a terrain challenging. Metamorphic facies is a classification system first introduced by Pentti Eskola in 1920 to classify particular metamorphic

neg: Geology of Hong Kong Geology of Hong Kong The Geology of Hong Kong is dominated by igneous rocks (including granitic rocks and volcanic rocks) formed during a major volcanic eruption period in the Mesozoic era. It made up 85% of Hong Kong's land surface. The remaining 10% are mostly sedimentary rocks located in the northeast New Territories. There are also a very small percentage (about 5%) of metamorphic rocks in New Territories. These are formed by deformation of pre-existing sedimentary rocks which changed the mineral assemblages in the rock (metamorphism). The geological history of Hong Kong started as early as the Devonian period (~420

neg: Pressure-temperature-time path environments can be found in the same rock specimen. As different minerals have different optical characteristics and textures, determination of the mineral compositions in metamorphic rocks is made possible. Common textures at different stages of metamorphism: It should be noted that not all rock samples exhibit all the P-T conditions they experienced throughout geological evolution. This is attributed to the complexity of the geological processes, which the samples may have undergone complicated thermodynamic histories, or of inappropriate mineral compositions to produce minerals that record their metamorphic events. Geothermobarometry is a "quantitative" measurement of the P-T conditions, which is widely used

neg: Metamorphism 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, characterized by paired metamorphic belts. 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 metamorphic zones of temperature/pressure conditions throughout the orogenic terrane. Contact metamorphism occurs typically around intrusive igneous rocks as

neg: Ultra-high-pressure metamorphism mafic rock (eclogite) or ultramafic rock (garnet-bearing peridotite). Some include sedimentary or rift-volcanic sequences that have been interpreted as passive margins prior to metamorphism. UHP rocks record pressures greater than those that prevail within Earth's crust. Earth's crust is a maximum of 70–80 km thickness, and pressures at the base are <2.7 GPa for typical crustal densities. UHP rocks therefore come from depths within Earth's mantle. UHP rocks of a wide variety of compositions have been identified as both regional metamorphic terrains and xenoliths. UHP ultramafic xenoliths of mantle affinity provide information (e.g., mineralogy or deformation mechanisms) about processes active

neg: Ultramafic rock pipes in Canada, Russia and South Africa have incompletely preserved tephra and agglomerate facies. These are generally diatreme events and as such are not lava flows although tephra and ash deposits are partially preserved. These represent low-volume volatile melts and attain their ultramafic chemistry via a different process to typical ultramafic rocks. Metamorphism of ultramafic rocks in the presence of water and/or carbon dioxide results in two main classes of metamorphic ultramafic rock; talc carbonate and serpentinite. Talc carbonation reactions occur in ultramafic rocks at lower greenschist through to granulite facies metamorphism when the rock in question is subjected to

neg: Metamorphic rock away. The formation of important ore minerals may occur by the process of metasomatism at or near the contact zone. When a rock is contact altered by an igneous intrusion it very frequently becomes more indurated, and more coarsely crystalline. Many altered rocks of this type were formerly called hornstones, and the term "hornfels" is often used by geologists to signify those fine grained, compact, non-foliated products of contact metamorphism. A shale may become a dark argillaceous hornfels, full of tiny plates of brownish biotite; a marl or impure limestone may change to a grey, yellow or greenish lime-silicate-hornfels or

neg: Slesse Mountain the US state of Washington. Most of Mount Slesse is made up of granitic rocks related to the Chilliwack batholith, which intruded the region 26 to 29 million years ago after the major orogenic episodes in the region. This is part of the Pemberton Volcanic Belt, an eroded volcanic belt that formed as a result of subduction of the Farallon Plate starting 29 million years ago. The primary rock comprising Slesse is grey diorite from the batholith. However the summit ridge and the west face are composed of Darrington Phyllite, a metamorphic rock, produced by contact metamorphism with the rock

neg: Schist to distinguish between sedimentary and igneous schists and gneisses. If, for example, the whole district occupied by these rocks has traces of bedding, clastic structure, or unconformability, then it may be a sign that the original rock was sedimentary. In other cases intrusive junctions, chilled edges, contact alteration or porphyritic structure may prove that in its original condition a metamorphic gneiss was an igneous rock. The last appeal is often to the chemistry, for there are certain rock types which occur only as sediments, while others are found only among igneous masses, and however advanced the metamorphism may be, it

neg: Anatexis aluminous crustal rocks), basalts (partially melted mantle peridotite), and migmatitic rock. Granitic rocks that come from the crust commonly contain xenoliths of metamorphic or sedimentary rocks when pieces of the wall rock are included into the magma during ascent or site of placement. Although a source of petrologic controversy, migmatites are thought to represent partial melting where melt and residual unmelted material are intertwined in layers (melt segregation). Migmatitic rocks "provide an example of the close relation between metamorphism, deformation, and melt generation and emplacement (El Bahariya, G.A; 2008;2009). Granites "are undoubtedly the result of extreme fractionation of mantle-derived parental

neg: Shale been alternatively attributed to input from hydrothermal fluids during or after sedimentation or to slow accumulation from sea water over long periods of sedimentation. Fossils, animal tracks/burrows and even raindrop impact craters are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite, or various carbonate minerals. Shales that are subject to heat and pressure of metamorphism alter into a hard, fissile, metamorphic rock known as slate. With continued increase in metamorphic grade the sequence is phyllite, then schist and finally gneiss. Before the mid-19th century, the terms slate, shale and schist were not sharply

neg: Country rock (geology) surrounding country rock. Sometimes, a fragment of country rock will break off and become incorporated into the intrusion, and is called a "xenolith", from Greek, , "xenos", "strange,", and , "lithos", the ancient Greek word for "stone." The heat of the intrusions usually changes the country rock, often to contact metamorphic rock. Commonly, hornfels is produced, or skarn. When describing recent alluvium, the material that has arrived through volcanic, glacial or fluvial action can be described as a veneer on the (older) country rock. Country rock (geology) Country rock is a geological term meaning the rock native to an area,

neg: Contact (geology) on the composition of the magma, the intrusive body may have a complex internal structure which can provide insight into its emplacement. The country rock responds to the immense heat from the intruding body numerous ways. Chill margins are created if the magma is cooled too quickly to fully crystallise. The result is a distinct boundary of very fine grain igneous rock along the border of the country rock. The surrounding rock may be "baked" through contact metamorphism, resulting in non-foliated metamorphic rocks. Rocks that were originally limestone, quartz sandstone, and shale become marble, quartzite, and hornfels, respectively . Fault

neg: Catalina Schist Catalina Schist The Catalina Schist is a metamorphic rock complex primarily exposed on Santa Catalina Island of the Channel Islands of California. It formed during the Cretaceous Period of the Mesozoic Era. The Catalina Schist is broadly correlated with the Franciscan Complex, a similar metamorphic complex formed along the California margin. Both of these units record high-pressure/low-temperature metamorphism associated with the subduction of the Farallon plate beneath North America during the Mesozoic Era. The Catalina Schist is differentiated from the Franciscan primarily in the style of mélange formed during subduction. In the Los Angeles Harbor Region, Catalina Schist is associated

neg: Diagenesis Diagenesis alters the proportions of organic collagen and inorganic components (hydroxyapatite, calcium, magnesium) of bone exposed to environmental conditions, especially moisture. This is accomplished by the exchange of natural bone constituents, deposition in voids or defects, adsorption onto the bone surface and leaching from the bone. Diagenesis Diagenesis () is the change of sediments or existing sedimentary rocks into a different sedimentary rock during and after rock formation (lithification), at temperatures and pressures less than that required for the formation of metamorphic rocks. It does not include changes from weathering. It is any chemical, physical, or biological change undergone by

neg: Catalina Schist with the Wilmington Oil Field. Catalina Schist The Catalina Schist is a metamorphic rock complex primarily exposed on Santa Catalina Island of the Channel Islands of California. It formed during the Cretaceous Period of the Mesozoic Era. The Catalina Schist is broadly correlated with the Franciscan Complex, a similar metamorphic complex formed along the California margin. Both of these units record high-pressure/low-temperature metamorphism associated with the subduction of the Farallon plate beneath North America during the Mesozoic Era. The Catalina Schist is differentiated from the Franciscan primarily in the style of mélange formed during subduction. In the Los Angeles Harbor

neg: Subduction zone metamorphism the subducting slab is known as the Wadati–Benioff zone. Paired metamorphic belts were envisaged as a set of parallel metamorphic rock units parallel to a subduction zone displaying two contrasting metamorphic conditions and thus two distinctive mineral assemblages. Nearest the trench is a zone of low temperature, high pressure metamorphic conditions characterized by blueschist to eclogite facies assemblages. This assemblage is associated with subduction along the trench and low heat flow. Nearest the arc is a zone of high temperature-low pressure metamorphic conditions characterized by amphibolite to granulite facies mineral assemblages such as aluminosilicates, cordierite, and orthopyroxenes. This assemblage is

neg: Foliation (geology) significant differential pressure or shear. Foliation is common in rocks affected by the regional metamorphic compression typical of areas of mountain belt formation (orogenic belts). More technically, foliation is any penetrative planar fabric present in metamorphic rocks. Rocks exhibiting foliation include the standard sequence formed by the prograde metamorphism of mudrocks; slate, phyllite, schist and gneiss. The "slatey cleavage" typical of slate is due to the preferred orientation of microscopic phyllosilicate crystals. In gneiss, the foliation is more typically represented by compositional banding due to segregation of mineral phases. Foliated rock is also known as S-tectonite in sheared rock masses.

neg: Metamorphic zone the surface form lines on a geologic map. Changes in mineralogical composition in a terrane reflect differences in metamorphic grade of the rocks. Minerals that are characteristic for a certain metamorphic grade are called index minerals. The first or last appearance of an index mineral (the place where a metamorphic reaction is observed) forms an easily recognizable isograd. A metamorphic zone is the region between two such easily recognizable isograds. Often they are named for the most characteristic index mineral of the zone. Whether a certain index mineral occurs is also dependent on the composition of the rock itself. Many

neg: Eclogite Eclogite Eclogite () is a mafic metamorphic rock. Eclogite forms at pressures greater than those typical of the crust of the Earth. An unusually dense rock, eclogite can play an important role in driving convection within the solid Earth. The fresh rock can be striking in appearance, with red to pink garnet (almandine-pyrope) in a green matrix of sodium-rich pyroxene (omphacite). Accessory minerals include kyanite, rutile, quartz, lawsonite, coesite, amphibole, phengite, paragonite, zoisite, dolomite, corundum, and, rarely, diamond. Plagioclase is not stable in eclogite. Eclogites typically result from high to ultrahigh pressure metamorphism of mafic rocks at low thermal gradients

neg: San Martín de los Andes the Lanín National Park. Its landscape is one of the most spectacular of Patagonia. The cities lies in an area of varied geology. Rocks in the area include metamorphic, plutonic and volcanic rocks. Metamorphic rocks found are schists, gneisses and migmatites, all of whom have sedimentary protoliths. Deposition of sediments occurred no earlier than in the Cambrian period and metamorphism occurred during the Devonian period as part of the Famatinian orogeny. Plutonic rocks around San Martín de los Andes crystallized from magma in the Devonian in connection to the onset of the Gondwanide orogeny. Plutonic rock types in the area

neg: Lithology of a rock or its component parts is a distinctive characteristic of some rocks and is always recorded, sometimes against standard colour charts, such as that produced by the Rock-Color Chart Committee of the Geological Society of America based on the Munsell color system. The fabric of a rock describes the spatial and geometric configuration of all the elements that make it up. In sedimentary rocks the main visible fabric is normally bedding and the scale and degree of development of the bedding is normally recorded as part of the description. Metamorphic rocks (apart from those created by contact metamorphism),

neg: Narryer Gneiss Terrane the margins, and preserves an amphibolite facies metamorphic assemblage. The gneiss is pervasively shot through with pegmatite veins. Within the low-strain zones, the Dugel Gneiss exists as a medium-grained leucocratic metagranite with phenocrysts of K-feldspar which has recrystallized into granulite facies. The rock is greasy-looking with annealed quartz and feldspar, and syn-granulite facies leucosomes cutting across metamorphic banding, and subsequently deformed by later metamorphism. The Dugel Gneiss is considered to be intruded into the older Meeberrie Gneiss, possibly as sheets or sills, but most contacts are overprinted by ductile metamorphic banding or mylonite zones. The Meeberrie Gneiss is a generally

neg: Kanoite type locality kanoite occurs along a joint that cuts a pyroxmangite-cummingtonite metamorphic rock in a manganese ore deposit. The region has undergone contact metamorphism as magma intruded the area. It was named to honor Hiroshi Kano, a petrology professor at Akita University in Japan. It has also been reported from Broken Hill, New South Wales, Australia, the Semail Ophiolite in Oman, and the Balmat–Edwards zinc district, Saint Lawrence County, New York. Kanoite Kanoite is a light pinkish brown silicate mineral that is found in metamorphic rocks. It is an inosilicate and has a formula of (Mg,Mn)SiO. It is a member

neg: Alleghanian orogeny the Atlas Mountains of Morocco and the western Sahara). Close to the boundary between the colliding plates, tectonic stresses contributed to the metamorphism of the rock (i.e. the transformation of igneous and sedimentary rock into metamorphic rock). The sedimentary rock in the eastern Appalachian Basin region was squeezed into great folds that ran perpendicular to the direction of forces. The greatest amount of deformation associated with the Alleghanian orogeny occurred in the Southern Appalachians (North Carolina, Tennessee, Virginia, and West Virginia). In that region, a series of great faults developed in addition to the folds. As the two continents collided,

neg: Monazite geochronology formed under similar temperature and pressure is called metamorphic facies. Actually, most mineral changes during rock burial, uplift, hydrothermal processes and deformation are associated with metamorphic reactions. Monazite is commonly found in many metamorphic rocks, especially in those formed from pelites and sandstones. The zonation in monazite reflects the successive monazite forming events. They may be formed from reactions along a single pressure-temperature (P-T) loop in a phase diagram, or reactions without changing P-T. For a metamorphic event, monazite is formed by the reactions with more than one P-T loop. The objective of monazite geochronology is to relate these monazite

neg: Paired metamorphic belts barometric conditions within these 2 regions are recorded and preserved through distinct types of metamorphism and mineral assemblages. Detailed research on constraints of metamorphic mineral stability fields allows accurate inference of previous regional thermal and barometric conditions. Metamorphic belts are a consequence of thermal perturbations, due to low temperature with respect to pressure ratios (dT/dP) in oceanic trenches and high temperature with respect to pressure ratios (dT/dP) in arcs. Paired metamorphic belts are the product of subducted colder crustal rocks, which are taken to depth, metamorphosed and then exhumed. However, if the rock unit is not exhumed relatively quickly after

neg: Cordillera Darwin Metamorphic Complex Cordillera Darwin Metamorphic Complex The Cordillera Darwin Metamorphic Complex is a geologic complex composed chiefly of metamorphic rocks located in southern Tierra del Fuego. It has been suggested that the Cordillera Darwin Metamorphic Complex is analogous to the Eastern Andes Metamorphic Complex. The Cordillera Darwin Metamorphic Complex is the only metamorphic complex in the southern Andes known to have amphibolite facies rocks containing kyanite and sillimanite which evidences high-grade metamorphism. High-grade metamorphism took place during the Cretaceous purportedly in association with the closure of the Rocas Verdes Basin. The protoliths of Cordillera Darwin Metamorphic Complex are unrelated to Tierra del

neg: Cordillera Darwin Metamorphic Complex Fuego Igneous and Metamorphic Complex despite present-day proximity. Cordillera Darwin Metamorphic Complex The Cordillera Darwin Metamorphic Complex is a geologic complex composed chiefly of metamorphic rocks located in southern Tierra del Fuego. It has been suggested that the Cordillera Darwin Metamorphic Complex is analogous to the Eastern Andes Metamorphic Complex. The Cordillera Darwin Metamorphic Complex is the only metamorphic complex in the southern Andes known to have amphibolite facies rocks containing kyanite and sillimanite which evidences high-grade metamorphism. High-grade metamorphism took place during the Cretaceous purportedly in association with the closure of the Rocas Verdes Basin. The protoliths of Cordillera

neg: Igneous rock after Vulcan, the Roman name for the god of fire. Intrusive rocks are also called "plutonic" rocks, named after Pluto, the Roman god of the underworld. Igneous rock Igneous rock (derived from the Latin word "ignis" meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava. The magma can be derived from partial melts of existing rocks in either a planet's mantle or crust. Typically, the melting is caused by one or more of three processes: an increase

neg: Geology of the Western Carpathians grade metamorphism. During the subduction of the Meliata-Halstatt Ocean in the Upper Jurassic, the back-arc basin evolved. This basin was later inverted and it was probably the root zone of the Mónosbél-Szarvaskő nappe. The Transdanubian or the Bakony Belt principal tectonic unit called the Transdanubicum occurs in the Transdanubian Mountains (Bakony, Gerecse, Vértes, and Buda Mountains). It consists of the low grade metamorphic Paleozoic and Mesozoic rock and Cenozoic sedimentary cover. A tectonic unit of uncertain position is the Zemplinic in the horst of the Zemplín Mts., emerging from the Cenozoic sedimentary fill of the Eastern Slovakia Basin. The Zemplinic

neg: Phyllite Phyllite Phyllite is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite. Phyllite has fine-grained mica flakes in a preferred orientation, whereas slate has extremely fine clay flakes that achieve a preferred orientation, and schist has large flakes in a preferred orientation. Among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a

neg: Authigenesis Authigenesis Authigenesis is the process whereby a mineral or sedimentary rock deposit is generated where it is found or observed. Such deposits are described as authigenic. Authigenic sedimentary minerals form during sedimentation by precipitation or recrystallization instead of being transported from elsewhere (allogenic) by water or wind. Authigenic sediments are the main constituents of deep sea sedimentation. Authigenic clays tend to reduce the porosity of sediments, thus reducing permeability. In metamorphic petrology an authigenic mineral is one formed "in situ" during metamorphism, again by precipitation from fluids or recrystallization. For any mineral to be precipitated, the water must be oversaturated

neg: Volcanology of Canada to have been widespread. It was also during this period when massive amounts of molten granite intruded highly deformed ocean rocks and assorted fragments from pre-existing island arcs, largely remnants of the Bridge River Ocean. This molten granite burned the old oceanic sediments into a glittering medium-grade metamorphic rock called schist. The older intrusions of the Coast Range Arc were then deformed under the heat and pressure of later intrusions, turning them into layered metamorphic rock known as gneiss. In some places, mixtures of older intrusive rocks and the original oceanic rocks have been distorted and warped under intense heat,

neg: Geology of Argentina craton rock. Throughout the late Proterozoic, sections of Argentina were part of a metamorphic mobile belt adjacent to the Brazilian Shield. Regional metamorphism produced scheelite belts and wolframite in parts of San Luis and Cordoba Provinces. To the north, along the Bolivian border in the Altiplano, drilling has revealed Precambrian horblende granoblastite and biotite granoblastite formed from magma during the Grenville orogeny 1.05 billion years ago metamorphosed around 530 million years ago. Granitoid and metamorphic rocks elsewhere in the El Cristo area in the southern Tandilia Range experienced intense folding more than two billion years ago and then metamorphosed to

neg: Illite crystallinity thin illite grains to thicker illite/muscovite grains. This low grade metamorphic technique can also be put into use when there is an absence in change of mineral structure which applies to higher grade metamorphism. Early use of illite crystallinity was in the petroleum industry to determine the transition from a dry gas phase to an unproductive rock. Recently, this technique has expanded in the field and now is used in areas such as palaeotectonics and geodynamic reconstructions. Rock sample preparation for illite crystallinity can vary slightly, but boils down to basically the same steps. Although for accurate returns in testing,

neg: Carbonate rock existing rock grains together or it can fill fractures. Karst topography and caves develop in carbonate rocks because of their solubility in dilute acidic groundwater. Cooling groundwater or mixing of different groundwaters will also create conditions suitable for cave formation. Marble is the metamorphic carbonate rock. Rare igneous carbonate rocks exist as intrusive carbonatites and even rarer volcanic carbonate lava. Carbonate rock Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO) and dolostone, which is composed of the