METAMORPHIC
ROCKS
These are the
secondary rocks that are created by the transformation of existing rocks by
heat and pressure. The term metamorphic comes from the word “metamorph” meaning
“change”. All rocks may be subjected to metamorphism. Granite can be re-melted
and re-crystallized sand stone can be transformed by heat and pressure into a
much harder rock material. Metamorphic rocks themselves can be changed again
and again.
This phenomenon
usually happens in the tectonic movements zones of the earth crust where due to
the volcanic action when tectonic plates are disturbed and one plate is pushed
up and other slides under. As a result rocks in zones of both plates are
subjected to different temperature and pressure and resultant is the
Metamorphic Rock.
Similarly when
the sheet of lava flows over the surface, the bedrocks of that surface
experience excessive heat and changes its form.
TYPES OF
METAMORPHISM
Thermal
Metamorphism
This is the
metamorphism in which the existing rocks are changed into new rocks under high
temperature or intense heat.
Dynamic
Metamorphism
When the rocks
change in form under high pressure it is called Dynamic Metamorphism
Regional
Metamorphism
When the change
in rock occurs in a particular region under high temperature and pressure it is
called Regional Metamorphism. It can be easily distinguished from adjacent
rocks.
Contact
Metamorphism
When molten
magma or lava comes in contact with already existing rocks it changes their
composition and color of the rocks. The remaining rock materials that do not
come in contact with lava remain unchanged. This is called Contact Metamorphism
Cataclastic
Metamorphism
This happens at
the boundaries of tectonic plates. When heavy plate collide with a lighter one
it result in breaking and pulverization of the rock material which after
sometimes re-group into some different rock. This is Cataclastic Metamorphism.
Burial
Metamorphism
When the Igneous
or Sedimentary Rocks are buried under the layers of the earth material, they
are subjected to change due to rise in temperature and pressure. This is known
as Burial Metamorphism
Hydrothermal
Metamorphism
This Phenomenon
occur in oceans as the ocean ridges are situated at the edge of tectonic plate
which result in small cracks and faults in the ocean floor. At this point of
the ridge water percolates in those cracks and faults and reaches at depth
where temperature is high enough to change liquid water into steam and the
steam rushes upwards and comes in contact with the adjacent rock material. It
change color and composition of rock and metamorphic rock is formed
ECONOMIC
IMPORTANCE OF METAMORPHIC ROCKS
·
These
are used as raw material in Industry and Construction
·
Slate
is used for writing and for roofing and painting
·
Graphite
is used in pencil and crucible making
·
Precious
minerals are obtained
·
Quartz
is used in glass making