Transcript METAMORPHISM

REPORTERS:
♥IVAN FRITZ ESGUERRA♥
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♥PRINCESS DANIELLE MATAS♥
METAMORPHISM
 Metamorphism (“meta” means
change and “morph” means form)
is a change that occurs in rocks
involving a recrystallization of
minerals and crystallization of new
minerals.
Agents of metamorphism :
1. Heat
- Minerals expand so that ions are separated from one
another, stretching and weakening the bond and enable
freed ions to migrate through the rock to form the seeds of
metamorphic minerals.
2. Pressure
- compresses the rocks and minerals, forcing their ions
closer together rearranged into more compact mineral
structure.
Two types of pressure:
A. Lithostatic pressure (“lithos” meaning rock and “status”
meaning position)
- is the pressure exerted on a rock as it is burried
deeper and deeper in the earth and is of equal intensity in
all directions.
B. Direct pressure
- greater pressure in some directions and can therefore
deform and flatten rocks.
A.
a. Lithostatic pressure
B.
b. Directed pressure
3. Chemically active fluids
-the solutions of active fluids change the
composition of a rock and form new minerals during
metamorphism.
THE AGENTS OF METAMORPHISM:
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A.HEAT
B. PRESSURE
C. ACTIVE FLUIDS
Regional metamorphism:
 Regional or Barrovian metamorphism
covers large areas of continental crust
typically associated with mountain ranges,
particularly subduction zones or the roots of
previously eroded mountains. Conditions
producing widespread regionally
metamorphosed rocks occur during an
orogenic event.
Contact metamorphism
 Rocks can also be heated by intruding magmas,
and the increase in their temperature can cause
them to become metamorphosed. Because
magmas often rise to very shallow levels in the
crust (and of course often erupt), they carry their
heat into low pressure environments. This heat is
conducted into the rocks the magmas intrude.
 Consequently, contact metamorphic rocks are
found adjacent to plutonic rocks. The metamorphic
grade is highest at the contact and lessens with
increasing distance from the contact. Thin bands
of contact metamorphic rocks are sometimes
formed beneath lava flows.
Blueschist metamorphism
 occurs under conditions of low
temperatures and a range of pressures. It
seems that conditions of low T and high P
exist only in special places. The high
pressures required to produce some of the
characteristic mineral assemblages found in
blueschists imply that the metamorphism
occurs deep in the Earth where
temperatures normally are also high.
The two lines shown on the figure set the P-T boundary of the conditions of regional
metamorphism. Where the temperature is low, the pressure is low; where the
temperature is high, the pressure is high. The terms low grade, intermediate grade, and
high grade metamorphism refers to these P-T conditions. At the highest grades of
regional metamorphism, rocks can begin to melt in the presence of sufficient water.
FOLIATION
 Foliation is any penetrative planar fabric
present in rocks. Foliation is common to
rocks affected by regional metamorphic
compression typical of orogenic belts. Rocks
exhibiting foliation include the typical
sequence formed by the prograde
metamorphism of mudrocks; slate, phyllite,
schist and gneiss.
GNEISS,a foliated metamorphic rock
Three common types of foliation are:
GNEISS
 a compositional banding that is manifested
by alternating bands of different minerals,
such as light color bands rich in feldspars
and quartz and dark bands rich in biotite or
amphiboles. Rocks possessing this type of
foliation have the name
Gneiss is a typical rock type formed by regional metamorphism, in which a
sedimentary or igneous rock has been deeply buried and subjected to high
temperatures and pressures. Nearly all traces of the original structures (including
fossils) and fabric (such as layering and ripple marks) are wiped out as the minerals
migrate and recrystallize. The streaks are composed of minerals, like hornblende
SCHIST
 Rocks possessing a foliation resulting
from the parallel alignment of flat
minerals such as mica. The planes of
this alignment are perpendicular to the
principle compressional stress during
the deformation.
Schist is formed by regional metamorphism and has
schistose fabric—it has coarse mineral grains and is
fissile, splitting in thin layers
SLATE
 an incipient plane of weakness along which
a rock easily breaks to yield flat, smooth (in
the absence of other complications)
surfaces. These are planes in which
microscopic size mica grains crystallize
during metamorphism. This type of foliation
also forms perpendicular to the principle
compressional stress.
SLATE
FLOW DIAGRAM FOR METAMORPHISM OF PELITIC ROCKS
GNEISS
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MYLONITE
Grains recrystallize,
COMPACTION AND REORIENTATION
Micas and chlorite form
SHALE REGIONAL
SLATE
coarsen
PHYLLITE
SCHIST
Porphyroblasts form
GRANOFELS
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GRANOFELS
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FLOW DIAGRAM METAMORPHISM FOR MAFIC ROCKS
MAFIC GNEISS
Plagioclase, pyroxenes, garnet
MYLONITE
Dehydration reactions
begin
Hydration reactions
BASALT REGIONAL
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COMPLETE
DEHYDRATION
GREENSCHIST
AMPHIBOLITE
ALBITE,EPIDOTE,
CHLORITE,ACTINOLITE
HORNBLENDE,
PLAGIOCLASE,GARNET
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GREENSTONE
ALBITE,EPIDOTE,
CHLORITE,ACTINOLITE
AMPHIBOLITE
HORNBLENDE,
PLAGIOCLASE,GARNET
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COMPLETE
DEHYDRATION
PYROXENE GRANOFELS
Plagioclase, pyroxenes, garnet
GOD BLESS!!!