Earth Science 2.4 : Metamorphic Rock
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Transcript of Earth Science 2.4 : Metamorphic Rock
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METAMORPHIC ROCK
Earth Science
Chapter 2.4
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Objectives:
1. Describe two ways a rock can undergo metamorphism.
2. Explain how the mineral composition of rocks changes as the rocks undergo metamorphism.
3. Describe the difference between foliated and non-foliated metamorphic rock.
4. Explain how metamorphic rock structures are related to deformation.
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Origins of Metamorphic Rock
Metamorphic rocks Rocks in which the structure, texture, or
composition of the rock have changed○ All three types of rock can be changed by heat, pressure,
or a combination of both
A rock’s texture or mineral composition can change when its surroundings changeIf the temperature or pressure of the new
environment is different from the one in which the rock formed○ the rock will undergo metamorphism
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1. Contact metamorphism When magma moves through the crust, the
magma heats the surrounding rock and changes it.○ Some minerals in the surrounding rock are changed into
other minerals by this increase in temperature.○ The greatest change occurs where magma comes into
direct contact with the surrounding rock.
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2. Regional metamorphism occurs when pressure builds up in rock that is
buried deep below other rock formations or when large pieces of the Earth’s curst collide
with each other.○ The increased pressure and temperature causes rock
to become deformed and chemically changed.
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Composition of Metamorphic Rock As rocks undergo metamorphism
Original minerals in a rock change into new minerals that are more stable within the new pressure and temperature conditions.
Index minerals (form only in metamorphic rock)○ Are used to estimate
1. Temperature
2. Depth
3. Pressure ---- at which a rock undergoes meta-morphism.
calcite
quartz
++ +hematite
Heat and Pressure
Garnet
=
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Texture of Metamorphic Rock
Two types:1. Foliated Metamorphic Rock
○ Mineral grains are arranged in planes or band○ Usually contains aligned grains of flat minerals, such
as biotite, mica or chlorite Metamorphic rocks can become other metamorphic rocks if
the environment changes again.
2. Nonfoliated Metamorphic Rock ○ Mineral grains are not arranged in planes or band○ commonly made of one or only a few minerals.
Recrystallization - Process in which crystals of these minerals may change in
size or the mineral may change in composition
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This shows what happens to shale, a sedimentary rock, when it is exposed to more and more heat and pressure.
Shale Slate Phylite
SchistGneiss
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Two examples of nonfoliated metamorphic rock
Marblelimestone
metamorphism
undergoes
Sandstone Quartzite
metamorphism
undergoes
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Metamorphic Rock Structures Metamorphic rock has features that indicates its
history. These features are caused by deformation:Change in the shape of a rock caused by a force
placed on it.○ These forces may cause a rock to be squeezed or stretched.○ Folds, or bends, in metamorphic rock are structures that
indicate a rock has been deformed.