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Answered 2009-06-07 02:56:35

Contact metamorphism does not cause profound compaction, which is the reduction in size of the spaces between mineral particles due to increases in pressure. Regional metamorphism causes compaction and possibly recrystallization, increasing the density of the rock.

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Why are metamorphic rocksformed by contact metamorphism usually not as dense as those formed by regional metamorphism?

Because contact metamorphism usually occurs because of an increase in temperature. In contrary, regional metamorphism is usually the result of compression. Compression makes a rock more dense.


How would you describe Metamorphic rocks?

Metamorphic rock can be describe in many ways. Contact or regional metamorphism. They are usually formed from high temp/pressure and can be sub devided into foliation and non foliation.


Where are rubies formed?

Ruby, a variety of the mineral corundum, is formed as a metamorphic mineral associated with regional and contact metamorphism. Contact metamorphism involves the exposure of pre-existing rock to high temperatures from close proximity to magma underground at various depths. Regional metamorphism is due to intense pressures and varying degrees of heat due to the compressional force of tectonic plate collisions, and is usually a deep underground phenomenon.


What are two ways that can poduce metamorphic rocks?

Two ways in which metamorphic rocks are 1) contact metamorphism (thermal) where magma comes in direct contact with surrounding igneous rock and changes it due to high temperatures and usually low pressure. 2) Regional metamorphism (dynamothermal) ,high pressures and low temperature eg mountain ranges. or 3) Cataclastic metamorphism, heat as a result of friction due to two plate meeting or passing each other.


Where does contact (prograde) occur?

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 where the contact metamorphism effects are present is called the metamorphic aureole. Contact metamorphic rocks are usually known ashornfels. Rocks formed by contact metamorphism may not present signs of strong deformation and are often fine-grained.


What is the most common type of metamorphism?

Regional metamorphism, usually as a result of tectonic plate collisions.


One more example of metamorphic rock?

One of the most popular metamorphic rocks is marble. Originally limestone, marble is generally created through regional metamorphism, which is when pressure and heat from where magma is pushing up through the Earth's crust effect rocks which are close by, but not actually touching the magma. Contact metamorphism changes the rocks that do actually touch the magma, this is how shale is usually metamorphosed into gneiss.


Why are metamorphic rocks formed by contact metamorphism usually not as dense as those formed by reg?

Because in contact the rock actually comes in contact with magma, this joins with the rock, so when it cools and become igneous rock, it's denser. In regular, or regional, the rock is formed from intense heat and pressure, but does not actually come in contact with magma.


What is slate?

Slate is shale that has been subjected to heat and intense pressure deep under the surface, usually in plate collision settings.Slate is a metamorphic rock. It is created by regional, low-grade metamorphism of shale.


Why don't we find fossils in metamorphic rocks?

The processes of metamorphism will usually destroy any fossils in the protolith.


What are metamorphic rocks?

== == Rocks that have undergone a change in mineral structure or composition, without melting, through heat and/or pressure are metamorphic rocks. Examples are slate, anthracite, and gneiss.How does contact (prograde) occur? the changes in mineral assemblage and mineral composition that occur during burial and heating are referred to as prograde metamorphism.Where does contact (prograde) occur? 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 where the contact metamorphism effects are present is called the metamorphic aureole. Contact metamorphic rocks are usually known ashornfels. Rocks formed by contact metamorphism may not present signs of strong deformation and are often fine-grained.Why does contact (prograde) occur? 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 where the contact metamorphism effects are present is called the metamorphic aureole.[5] Contact metamorphic rocks are usually known ashornfels. 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 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 ofpelitic 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 oreminerals and thus are of economic interest.Prograde and retrograde metamorphism[edit]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 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 conditions. This is a relatively uncommon process, because volatiles must be present.Garnets with Mn-rich cores and Mn-poorer rims record growth zoning that represents the change from the lower-T conditions at which the garnet core grew to the higher-T conditions at which the garnet rim grew (i.e., prograde metamorphism involving increasing temperature and pressure). Mn is preferentially partitioned into garnet relative to most other common minerals, so Mn is sequestered in early-formed garnet, depleting the local environment of the growing garnet in Mn.(b) Minerals that show major element growth zoning probably did not experience very high metamorphic temperatures. At high temperature (> 700 C) and sufficient duration, zoning may be homogenized as intracrystalline diffusion becomes more effective at eliminating compositional variation. An unzoned mineral that is typically zoned at low-medium metamorphic grades has either experienced high temperature conditions or was never zoned (owing to a simple reaction history at limited P-T or to growth entirely at high-T).


Is slate extrusive igneous rock?

Slate is a metamorphic rock which originated typically as a shale, or mudstone/claystone, and is usually associated with Regional Metamorphism (intense pressure with heat). This can be due to overburden, continental collision or other large scale compressional geological processes.


What happens each time a metamorphic rock is exposed to extreme heat and pressure?

Metamorphic Rock Metamorphism means to change form; this is exactly what metamorphic rocks do. This paper will take a look at the Earth's rock cycle to examine exactly where the metamorphic rock fits into it. It will also look at how metamorphic rocks are formed and the relationship between metamorphic rocks and igneous rock and sedimentary rocks. This paper will examine the geological characteristics and materials of metamorphic rocks, and examine some examples of metamorphic rocks and will describe mineral composition of some examples and explain its economic uses. The Rock Cycle The rock cycle helps people to understand the starting point of the igneous, sedimentary, and metamorphic rocks. In addition to explaining how each of the rocks are connected through the process. The rock cycle explains to us how the Earth assists in changing one type of rock into another type of rock. The process begins when magma, found from beneath the Earth's surface or from a volcano, cools and crystallizes. This process forms rocks called igneous rocks. When an igneous rock is exposed to weathering and erosion and compacted by the weight of the groundwater, which is otherwise known as lithification, it creates a sedimentary rock. When sedimentary rocks are buried deep within the Earth and evolve into mountains or are exposed to extreme pressure and intense heat it will then turn into the last cycle of rock, the metamorphic rock. Metamorphic rocks can even evolve from other metamorphic rocks. How Metamorphic Rocks Are Formed Within the Rock Cycle Metamorphic rocks are created when they are exposed to extreme heat, pressure, and chemicals. Rocks are usually exposed to extreme heat, pressure, and chemicals at the same time. Metamorphism occurs in one of two situations, contact metamorphism or regional metamorphism. Contact metamorphism occurs when a rocks experience a rise in temperature when it is exposed to magma. Heat is the most important source of metamorphism because... [continues]


Where would metaphoric rocks form?

Usually deep underground from heat and pressure, at regional metamorphic zones in areas of continental collisions, and in contact zones where parent rock is metamorphosed from proximity to an intrusive igneous body.


Why regional (prograde) occur?

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.


What are some types metamorphic rock?

These rocks get their name from the Greek words 'meta' and 'morph', meaning 'change of form'. Metamorphic rocks are produced by the alteration of pre-formed rocks by pressure, temperature and migrating fluids, often in environments deep in the Earth's crust. Because of the severe conditions which rocks undergo during metamorphism, the original minerals may become unstable and change to maintain equilibrium with the new environment. This can involve changes in mineralogy (recrystallization of existing minerals or formation of new ones) and usually changes in texture from the original rock. Three main types of metamorphism are recognized. Regional metamorphism results from mountain-building events with large scale folding and burial of pre-formed rocks. Contact metamorphism is produced by direct heating of rocks around an igneous intrusion, baking the surrounding country rocks. Dynamic metamorphism occurs where large scale faulting breaks and deforms rocks next to the fault.


What is the process of rocks turning into metamorphic rocks?

When the rock is in a high temperature and pressure environment for a long time, their properties changes as much that you can't say that it's the same rock, so we call it a metamorphic rock. There are 3 ways: Hydrotermal, by contact or differential pressure metamorphosis.


Where regional (prograde) occur?

Retrograde metamorphism involves the reconstitution of a rock via revolatisation under decreasing temperatures (and usually pressures),


What is the origin and composition of marble stone?

Marble is metamorphosed limestone or dolomite, and is predominately calcitic in composition. Marble usually forms from regional metamorphism associated with plate collisions.


What is the environment of quartzite?

Quartzite is a Metamorphic Rock that undergos extreme heat and pressure forcing pre-existing rocks to recrystalize. It forms through contact metamorphism. It's formed at an igneous intrusion cutting through existing rock in a small area; usually along cooled igneus intrusions.


What is metomorphism?

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. Metamorphism produced with increasing pressure and temperature conditions is known as prograde metamorphism. Conversely, decreasing temperatures and pressure characterize retrograde metamorphism. Kinds of 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. Metamorphic faciesMetamorphic 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). 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 : EclogiteIn 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 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. 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. Dikes generally have small aureoles with 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 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. 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. 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. 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. 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. 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. 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. 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. 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. 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. == ==


A metamorphic rock is from where?

Metamorphic rock usually forms when a rock is altered under heat and pressure without melting. Some rocks may be metamorphosed by contact with hot water,


How long does it take to form a metamorphic rock?

Although the process of rock metamorphism usually involves a process taking millions of years, rocks could be metamorphosed in the lab in minutes with the right equipment.


How do metamorphic rocks form?

Metamorphic rocks are formed from igneous, sedimentary, or other metamorphic rocks. The change is brought about by either contact with an intrusive plutonic body, or by enormous pressure and heat usually derived from lithospheric plate collisions.


What state is metamorphic rock formed in?

Metamorphism is the name of the process (of heat and pressure) that causes the chemical; and therefore mineralogical; properties of a rock to change. Marble (changed from limestone) may represent the lowest grade of metamorphism, whilst the schists are a more common higher grade of that same process. At the extreme, the rocks will melt, but that is considered beyond the definition of metamorphism, for it will change the actual chemical nature of the rock. So - it is the application of heat and pressure; perhaps accompanied by shear; that are the metamorphic change agents. Usually caused by deep burial.


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