Dear RG researchers
What is metamorphic rock and how it can be described by scientific way?
The purpose to ask the question make it a platform for young geological learners.
Reagrds
Ijaz
Dear Ijaz
A metamorphic rock is a igneous rock, sedimentary or other metamorphic rock that it have undergone pressure and heat. These causes of metamorphism such as heat more than 200°C (but below the boiling point of the rock) and pressures higher than 300Mpa break down the atoms in the rock’s minerals and recrystalize the rock into something different with many interesting and useful properties.
Exposure to these extreme conditions has altered the mineralogy, texture, and chemical composition of the rocks. All this leads to the formation of metamorphic rocks.
I hope to help your question.
Best regards
Irving
Metamorphic rocks arise from the transformation of existing rock types, in a process called metamorphism, which means "change in form".[1] The original rock (protolith) is subjected to heat (temperatures greater than 150 to 200 °C) and pressure (100 megapascals (1,000 bar) 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.[2] They are classified by texture and by chemical and mineral assemblage (metamorphic facies). They may be formed simply by being deep beneath the Earth's surface, subjected to high temperatures and the great pressure of the rock layers above it. They can form from tectonic processes such as continental collisions, which cause horizontal pressure, friction and distortion. They are also formed when rock is heated by the intrusion of hot molten rock called magma from the Earth's interior. The study of metamorphic rocks (now exposed at the Earth's surface following erosion and uplift) provides information about the temperatures and pressures that occur at great depths within the Earth's crust. Some examples of metamorphic rocks are gneiss, slate, marble, schist, and quartzite.
Literally the rock formed from partial melting/transformation of pre-existing igneous, sedimentary or metamorphic rocks due to changing temperature, pressure condition or action of fluid. Ijaz Ahmad
Hello Ahmad,
you can follow any standard book of metamorphic petrology to know it. for primary introduction you can follow the link: https://brocku.ca/earthsciences/people/gfinn/petrology/metaintr.htm
Metamorphic rocks are result of Metamorphism is a subsolidus process leading to changes in mineralogy and/or texture (for example grain size) and often in chemical composition in a rock. These changes are due to physical and/or chemical conditions that differ from those normally occurring at the surface and in zones of cementation and diagenesis below the surface. They may coexist with partial melting.
The most important Metamorphic Agents and respective changes are as follows
Temperature
1.Promotes recrystallization ® increased grain size 2.Drive reactions (endothermic) consume unstable mineral(s) and produces new minerals that are stable under the new conditions 3.Overcomes kinetic barriers that might otherwise preclude the attainment of equilibrium
Pressure
1.Lithostatic pressure = uniform stress (hydrostatic) 2.Deviatoric stress = pressure unequal in different directions. 3.This affects the textures/ structures, but not the equilibrium mineral assemblage ex: Foliation
Dear Ijaz:
Practically in any geology or petrology textbook there is a definition of metamorphic rocks and metamorphism. Here I state the one given by the Glossary of the American Geological Institute:
"Metamorphic rocks are those which are derived from preexitisting rocks of any type, having suffered mineralogical, chemical, or textural changes due to marked variations of temperature, pressure, and chemical conditions which occur at depth in the crust, below the zones of weathering and diagenesis".
We may add too: those conditions mentioned differ from those in which the rocks originated; and also, the process occurrs in the solid state, as a recrystallisation of preexisting minerals, mineraloids and/or volcanic glass, called blastesis. And, furthermore, metamorphism tends to be isochemical, and most rocks attain chemical equilibrium, generating a diagnostic mineral association, which is called metamorphic facies. You can also add that there are several types of metamorphism: dynamothermal, burial, and, sea-floor (of regional extent, related to plate limits and interactions); and contact-metasomatic, cataclastic, impact, and pyrometamorphism (of local extent). It is a very complex topic, no simple definition can be made. Schistosity or foliation is a common characteristic of metamorphic rocks, but it is not universal, as it depends on the mineralogical composition of the original rock and the type of metamorphism it has undergone.
Regards, Sebastián.
Are those that have originated from the transformation (changes in the mineralogy, chemical composition and texture) of other rocks preexisting (igneous, sedimentary and metamorphic), commonly under the surface, at great depths, by action of heat, pressure and the chemical activity of fluids.
Excellent definitions by all. As a result of the 12 km-long drill hole at Kola, by the Soviets, may I add the importance of the hot-water fluids circulating in rocks under high temperature and pressure in the formation of metamorphic rocks.
In other words, no fluids, no metamorphism.
https://en.wikipedia.org/wiki/Metamorphic_rock
Best Regards@ Ijaz Ahmad
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