Metamorphic Rocks ppt.ppt - Wikispaces

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					Metamorphic Rocks
     Metamorphic Rocks
The Greek word meta means “change” and morph
meaning “shape”.

Metamorphic rocks were previously either
sedimentary or igneous rocks, but they have
been subjected to very high temperature and
pressure. (Below the surface of the Earth)
     Metamorphic Rocks
The temperature was not high enough to make
the rock melt (Metamorphic changes occur as
the rock is in solid-state), but it was high
enough to allow some crystals to grow, and
for the minerals to begin to re-crystallize
and thus form a new rock.
As temperature rises,
crystal lattices are
broken down and reformed
with different
combinations of atoms.
New minerals are formed.
      Metamorphic Rocks
The types of metamorphism
Regional metamorphism
Contact metamorphism

Contact metamorphism        Regional metamorphism
    Metamorphic Rocks
Contact metamorphism
In the case of contact metamorphism heat
comes from contact with molten magma.
-This type of metamorphism has a limited and
local effect.
    Metamorphic Rocks
Regional metamorphism
When rocks are forced toward
the mantle during the formation
of a mountain range and/or
other tectonic activity,
regional metamorphism occurs.
-Large volumes of rock are
altered in this way.
    Metamorphic Rocks
Metamorphism does not take place on the
Earth’s surface.

Rocks under the Earth’s surface are under
great pressure from overlying rock layers.

Deep burial- as depth increases, in the
Earth’s crust, the temperature also

Tectonic forces in the Earth may apply
lateral pressure to large volumes of rock.
Metamorphic Rocks
Metamorphic Rocks
      Metamorphic Rocks
Metamorphic rocks have
been exposed to the
surface of the Earth
because erosion has
striped away overlying

So, when we see a large
area of metamorphic
rocks we know we are
looking at the core of
an ancient mountain
                     Changes During Metamorphism

                                                       High temperature
Parent rock   Low temperature   Medium temperature                         Higher temp.
                                                        High pressure
(protolith)    Low pressure      Medium pressure                          Higher pressure

   shale           slate             phyllite     schist    gneiss


limestone                           marble                                  MELTING

                                        amphibolite or schist

  granite                                                    gneiss
  Metamorphic Rocks
Change in metamorphic grade with depth

  Increasing Directed Pressure and increasing Temps
    Metamorphic Rocks
Foliated metamorphic rock

Foliation forms when pressure squeezes the
flat or elongate minerals within a rock so
they become aligned. These rocks develop a
platy or sheet-like structure that reflects
the direction that pressure was applied in.

Foliation: minerals have been rearranged
into visible bands.
Metamorphic Rocks

Increasing Directed Pressure and increasing Temps
      Metamorphic Rocks
Directed Pressure causes rocks to become folded, and minerals to reorient
                  perpendicular to the stress: “foliation”
    Metamorphic Rocks
Non-foliated metamorphic rock

Non-foliated metamorphic rocks do not have a
platy or sheet-like structure.

Metamorphic rock that does not show bands.

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