Metamorphic Rocks:

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Metamorphic Rocks

• Meta change Morph form
• Metamorphic rocks form from changes to
  pre-existing rock caused by heat and pressure
• Metamorphism can occur locally over a small area,
  or over a large area covering many kilometers

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Two Types of Metamorphism...

• Regional Metamorphism - heat and pressure are
  significant over a wide area (many kilometers)
• Contact Metamorphism - occurs over a small area
  when pre-existing rocks come into contact with
  hot liquid magma from an igneous intrusion.

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Metamorphic Rocks...

• Classified on the basis of type of metamorphism
  (Regional or Contact) and texture
• Foliated (occurs w/regional metamorphism)
• Non-foliated (usually occurs w/ contact
  metamorphism)

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Regional Metamorphism

• Changes to rock over a large area
• Layers of rock deep in the Earths crust
  experience the following
• 1. High temperatures (depth and friction)
• 2. High pressures (weight and crustal movement)
• 3. Exposure to hot liquids, water, and gases
• Results
• Mineral grains are compressed
• minerals migrate through rock and begin to
  separate
• minerals are aligned within rock in response to
  pressures to produce foliation

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Regional Metamorphism...

• Foliation - the alignment of minerals within a
  rock caused by heat and pressure

This sample is clearly foliated. see the mineral
alignment???
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Draw the foliation that results from regional
metamorphism
AFTER
BEFORE
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Metamorphic Grade (degree of metamorphism)
Medium-Grade Metamorphic Rock
HIGH-Grade Metamorphic Rock
Low-Grade Metamorphic Rock
Medium-Grade Metamorphic Rock
Sedimentary Rock
GNEISS
SCHIST
PHYLLITE
SLATE
SHALE
Clearly banded appearance as minerals separate
into alternating bands
Visible mica grains foliation obvious other
minerals may be seen.
Micas still microscopic, but begin to reflect
more light silky sheen in appearance
Harder, microscopic mica minerals begin to form,
less air space dull shine
Clay minerals, stratified, soft, and fragile,
dull in appearance
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This nice piece of schist has large, visible
garnet crystals in it.
This sample of schist shows mica minerals that
have grown large enough to reflect light.
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Here is another gneiss which shows distinct
banding due to mineral alignment. The arrows
indicate how this sample was squeezed by pressure
at great depth below ground.
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Contact Metamorphism

• Occurs over as small area around magma (igneous
  bodies)
• country rock (pre-existing, in-place) is baked by
  the hot temperatures associated with magma
• hot liquids and gases mix with country rock
• Results
• minerals migrate and fuse together
• no foliation or alignment since pressure is not
  significant

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Contact metamorphism has occurred around this
igneous intrusion.
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Draw layers of rock getting metamorphosed by
coming into contact with magma
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Metamorphism Parent Rock Definition

• Parent Rock - the pre-existing rock from which a
  metamorphic rock forms

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Metamorphism
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Metamorphic Rock Quiz...

• Metamorphic Rocks form from changes to other
  rocks in response to pressure and heat
• TRUE

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Metamorphic Rock Quiz...

• Metamorphic rocks are classified by their mineral
  composition primarily
• FALSE. Metamorphic rocks are classified on the
  basis of texture and type of metamorphism

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Metamorphic Rock Quiz...

• Foliation in metamorphic rocks is the alignment
  of minerals in response to high temperatures
  along with great pressure.
• TRUE!

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Metamorphic Rock Quiz...

• Only contact metamorphic rocks experience
  foliation.
• FALSE. Regional metamorphic rocks become
  foliated due to high pressure in addition to high
  temperatures

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Metamorphic Rock Quiz...

• Shale is a low-grade metamorphic rock
• FALSE. Shale is a sedimentary rock.

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Metamorphic Rock Quiz...

• Middle to high grade metamorphic rocks appear
  shiny because as mica minerals crystallize they
  begin to reflect light.
• TRUE!

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Metamorphic Rock Quiz...

• Extremely high grade metamorphic rocks experience
  more alignment of minerals into distinct bands.
• TRUE.

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Metamorphic Rock Quiz...

• Rocks that come into contact with an igneous
  intrusion will only change into igneous rocks.
• FALSE. The high heat near an igneous intrusion
  will burn the surrounding rock and change it
  into metamorphic rock.

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Metamorphic Rock Quiz...

• The pre-existing rock that was changed into a
  metamorphic rock is called the Grandma rock.
• FALSE. The original rock is called the parent
  rock.

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Metamorphic Rock Quiz...

• The sedimentary rock limestone can become changed
  by metamorphism into a metamorphic rock called
  marble.
• TRUE.