Types of metamorphism
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Transcript of Types of metamorphism
Contents: •Introduction •Agents of metamorphism •Types of metamorphism
•Thermal metamorphism
•Cataclastic metamorphism
•Dynamo thermal metamorphism
•Plutonic metamorphism
•Conclusions
•References
Introduction Metamorphism may be defined as the response in the solid rocks to pronounced changes of temperature , pressure and chemical environment.
The rocks which subjected to metamorphism, may be either igneous , sedimentary, or other metamorphic rocks.
The changes in three factors of temperature pressure and chemical environment, upset the physical and chemical equilibrium of a mineral assemblages and effort to establish new mineral equilibrium.
Agents of metamorphism: The agents which are mostly responsible for bringing about metamorphic changes are
1).Temperature 2).Hydrostatic (or)uniform pressure 3).Directed pressure4).Chemically active fluids
Agents of metamorphism: The agents which are mostly responsible for bringing about metamorphic changes are
1).Temperature 2).Hydrostatic (or)uniform pressure 3).Directed pressure4).Chemically active fluids
Agents of metamorphism: The agents which are mostly responsible for bringing about metamorphic changes are
1).Temperature 2).Hydrostatic (or)uniform pressure 3).Directed pressure4).Chemically active fluids
Volume changes
Agents of metamorphism: The agents which are mostly responsible for bringing about metamorphic changes are
1).Temperature 2).Hydrostatic (or)uniform pressure 3).Directed pressure4).Chemically active fluids
Changes in shape
Agents of metamorphism: The agents which are mostly responsible for bringing about metamorphic changes are
1).Temperature 2).Hydrostatic (or)uniform pressure 3).Directed pressure4).Chemically active fluids
•Fluids present in the original rock or introduced from the magma, create metamorphic rocks with water and gas molecules
•Carbon dioxide, hydro-fluoric acid, bromine, fluorine and some other gases may present and can induce many changes in rocks
Types of metamorphism: •Depending upon the dominance of one or more agencies , the process of metamorphism can be broadly classified into several type
Thermal metamorphism
Cataclastic metamorphism
Dynamo thermal metamorphism
Plutonic metamorphism
Hydrothermal metamorphism
Burial metamorphism
Shock metamorphism
Thermal metamorphism: Temperature dominated, pressure and fluids place only secondary role
Pyrometamorphism:
This metamorphism resulted by the effect of highest degree of heat, without fusion. The original minerals are forced to recrystallise or re rearrange themselves.
Optalic metamorphism:
The indurating burning and fritting effects of lava-flows on neibouring rocks is known as caustic or optalic metamorphism.
Kimmeridge on the Dorset coast of England
Burned shale
Contact metamorphism:
Contact metamorphism caused due to local heating of rocks by the intrusion of hot igneous body to the surrounding rocks
Pneumatolytic metamorphism Injection metamorphism
The Purcell Sill, in Montana.
Intruded Igneous rock
Marble
Lime stone
Thermal metamorphism
Cataclastic metamorphism:
It is a type of metamorphism in which only the directed pressure plays dominant role. They operate mainly in the upper part of the earth’s crust where the temperature is moderately low.
Due to this metamorphism the rocks are crushed, grained ,and deformed. New rocks thus formed are called cataclastic rocks.
Some times parallel lenticular and banded structures forms by cataclastic metamorphism.
Cataclastic metamorphism
Conversion of shale into slate
Devils Punchbowl County Park, southern California.
Crush breccia
Shattered and pulverized due to directed pressure
Reru valley in the Zanskar range. This range is located in the north. East of India in the state of Jammu and Kashmir
Mylonite
Augen structure
Dynamo-thermal metamorphism:
Dynamo-thermal metamorphism is due to the co-operation of directed pressure and high temperature.
High temperature facilitates the recrystallisation, directed pressure facilitates deforming effects.
New parallel textures and structures are usually oriented perpendicular to the direction of greatest stress
both temperature and directed pressure
regional metamorphism
Clay Regional metamorphism Mica schist
schist
Acid igneous rocks Regional metamorphism Schist (or) gneiss
Flaser granite
Augen structure
Meta-conglomerate
Plutonic metamorphism:
The plutonic metamorphism is meant the changes which are produced in rocks by great heat and uniform pressure. The changes necessarily at depths where the directed pressure become less.
Rocks formed from this metamorphism give place to granulose, even grained, direction less structures.
Formation of anti-stress minerals of small specific volume and high density, will be favored by these conditions.
Rocks from locality at Kodaikanal,
Eclogite
The specimen from Queen Canyon in the northern White Mountains of California.
sericite
Hydrothermal metamorphism:
Hydrothermal metamorphism is defined as the alteration due to the super-heated fluids passes through the permeable rock.
Chapel Hill - Hillsborough area, Florida
composted of sericite and quartz with red and yellow mottling.
Burial metamorphism:
Sedimentary rocks buried more than a few kilometers, experience not only an increase in pressure but a gradual rise in temperature resulting in formation of metamorphic rocks.
Some times processes such as compaction, solution, cementation, accompanied by chemical changes.
At low temperature At high temperature
When an extraterrestrial body, such as a meteorite or comet impacts with the Earth or if there is a very large volcanic explosion, ultrahigh pressures can be generated in the impacted rock. These ultrahigh pressures can produce metamorphic changes.
Shock metamorphism:
Northwest Territories of Canada
Shatter cones in limestone
conclusions: Different structural, textural, mineralogical changes due to
metamorphism is depends on the metamorphic agents.
Orogenic activities plays an important role in the metamorphism
During the metamorphism recrystallisation takes place and new minerals and new textures may produced.
Minerals and rocks are stable only under the conditions at which they form.
Each rock can be metamorphosed by several different combinations of heat, pressure and fluids.
References : 1)G.W.Tyrrell(1958), Principles of petrology Publishers Chapman and Hall, P:105-1202)Donald.W.Hyndman(1972), Petrology of igneous and metamorphic rocks, Published by McGraw-Hill, P:541-545
3)P.K.Mukerjee(1931), A Test book of Geology Published by Sri D.Chakraborty, P:122-129.