Hello guys!!!!
I'll discuss briefly an important process that occurred millions of years ago.
The term metamorphism is derived from the Greek word "meta-morphe" meaning "change of form". Metamorphism can be defined as the sum total of all the processes,that cause changes in mineral composition, texture and structures of rocks below the zone of sedimentary activities without passing through the fluid phase.
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That is,change of a rock to another rock type by factors such as temperature and pressure, without melting(fluid phase).
On the other hand, metamorphism can be defined as the process responsible for all the changes that take place in an original rock under the influence of changes in the surrounding conditions of temperature, pressure and chemically active fluids.
NOTE
•These temperatures are greater than those of sedimentary processes,but lower than those of igneous processes(melting)
•These changes take place only in a solid state
FACTORS THAT AFFECT METAMORPHIC REACTIONS
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•The resistance of the rock to pressure
•The size of the constituent grains of the rocks
•The degree of porosity of the rocks
•The solubility of the constituents of the rocks
•The chemical reactions of the minerals in the rock
•The stability of the mineral assemblage that is produced
•The resistance of the rock to temperature change
•The length of time the rock is subjected to temperature,pressure and chemically active fluids.
TYPES OF METAMORPHISM
•CONTACT METAMORPHISM:
This is the metamorphism that takes place at increased temperature without any significant role from other sources. This metamorphism occurs when there is a contact with a hot invading magmatic body which releases it's heat to the surrounding country rock.
The bigger the size of the intrusion,the higher the grade of the metamorphism,and the part of the host rock close to them agmatine body is metamorphosed the most,while farther away from the magma,the effect of metamorphism is less.
•DYNAMIC METAMORPHISM:
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This is the type of metamorphism due to great mechanical and physical pressure on the upper part of the continental crust,causing dislocation,crushing and grinding.
•REGIONAL METAMORPHISM:
Metamorphism occurs on a very large scale,covering cast areas. It's usually associated with orogenic belts and igneous intrusion.
•PYROMETAMORPHISM:
It takes place usually at very high temperatures,and may develop partial melting.
•BURIAL METAMORPHISM:
Occurs due to deep burial. At deeper depth,it's difficult to make a distinction between burial metamorphism and regional metamorphism.
CAUSES OF METAMORPHISM
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There are three major causes of metamorphism
•Temperature
•Pressure
•Chemically active fluid and
•Time(passive factor)
TEMPERATURE
Rocks are made up of minerals,that are normally stable at temperatures below 200°C. A change,increase or decrease would make these minerals unstable and metamorphism can occur. There are two sources of heat required for metamorphism
*The internal heat
*Magmatic intrusion/heat
PRESSURE
This is the second most important cause of metamorphism after temperature. The most important cause of pressure acting on rock is the hydrostatic pressure. The hydrostatic pressure changes from 0kb on the surface of the Earth to about 10kb beneath the Earth's crust.
Any rock below the surface of the Earth is usually subjected to pressure from two sources
*Load of the overlying burden
*Crustal movements during the convergence of tectonic plates.
FLUID
They increase pressure and can also act as catalysts. The bulk chemistry determines the possible minerals,that can be present,while temperature and pressure determines the actual mineral formed. An example would be H20,which is water.
EXAMPLES OF METAMORPHIC ROCKS
•Slate
•Phyllite
•Schist
•Gneiss
•Hornfels
•Marbles
•Quartzite
•Greenschist
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I hope you find this post educative and interesting...Thanks for reading.