IX metamorphic rocks

IX. Metamorphic Rocks
A.
B.
C.
D.
E.

Evidence of metamorphism
The recipe for metamorphism
Prograde metamorphism of shale
Classification of Metamorphic Rocks
Metamorphism and Plate Tectonics


The
Rock Cycle



Geological Materials
Transformation Processes


Rock
Metamorphism
(Icreased
& P)



T

Metamorphic
rock
Partial
Meltig



Magma


Metamorphism
Metamorphic Rocks
Defiitio:







Re-crystallization of
minerals
While still solid
Into minerals that are
stable at different
temperatures and
Different pressures
(Usually progressively
higher temperatures

and pressures)


A. Evidence of Metamorphism
E.g.,
Sedimetary
Rocks








Made of minerals derived from
weathering of a parent rock
Stable at atmospheric
temperatures and pressures (low
T & P)
Originally horizontal, continuous
and uniform layers

1. Bet
(deformed)
layers


Fig. 8-1, p. 168

Evidence of Metamorphism


Differetia
l pressure
“squashes”
rock ad
icluded
features

2.
Flatteed
Pebbles


Evidence of Metamorphism



3. Crystallie
Texture
Minerals tightly interlocking
due to recrystallization under
pressure


Evidence of Metamorphism


4.

New

mieral
assemblages

E.g., Shale:
Clay mierals
(some
quartz) 
Metamorphism
Forms Schist:
Mica, Feldspar
ad other silicate
mierals 


B. Recipe of Metamorphism


1. Paret
Rock






Even though minerals

will change
Most elements are
provided by parent
rock
Except water and
some dissolved ions

Shale

Schist


B. Ingredients of Metamorphism
Temp. (ºC)
0 500 1000

A B C



2.

Icreased

Temperature

(high geothermal gradiets)
 Minerals stable at lower temperatures converted to
 minerals stable at higher temperatures


Ingredients of Metamorphism



3. Icreased Pressure
(ad stresses)



Increased Lithostatic Pressure as rocks are buried
Differential Pressure at convergent plate boundary


Fig. 8-3, p. 169


Results of Stress (Pressure)


Differetial
Pressure



Parallel
aligmet of
platy mierals
(e.g., micas)

ad eedlelike mierals
(e.g.,
amphiboles)



Forms
Foliatio


Ingredients of Metamorphism



4. Additio or removal
fluids (ad elemets)







of

Water (and other fluids) within rocks and minerals
Moving during metamorphism
Accelerates solid-state chemical reactions and
May change rock composition

5.

Time



Millios

of

years!


C. Prograde Metamorphism of
Shale (and the classification of
metamorphic rocks)

Shale: Fie graied
Clay
(ad
quartz)
 Mierals stable
uder low T&P
(atmospheric)
 Compactio
due to
accumulatio of
sedimet
 Fissility
alog

lamiatios
 Water boud i
crystallie structure
of clay


Prograde Metamorphism of
Shale


Me tamorphic
grade
1: Low Grade  Rock:
Slate
Low grade
metamorphic T&P
(Water is expelled from
crystallie structure of
clay)



Mierals stable uder
low grade
metamorphic coditios

Fie

graied



Mieral compositio :
Mica (ad Quartz)



Foliatio: Slaty Cleavage due
realigmet of platy mierals

to


Prograde Metamorphism of
Shale
2: Medium-Grade
Metamorphism 
Phillite
 Courser graied
Mica ad
quartz
 Medium-grade
metamorphic
T&P Causes
 Slaty cleavage becomes
mierals to grow
rippled ad rock has
a shee

Prograde Metamorphism of
Shale
3: Medium to
High-Grade
Metamorphism
 Schist
 Course
graied Mica
ad Quartz
 Medium-grade
metamorphic
 Mierals
stable uder medium grade
metamorphic
T&P Causescoditios appear:
Garet,
amphibole
ad biotite
mierals
to
 Schistosity
due to aligmet of
grow
platy

ad

eedle

likemierals

Prograde Metamorphism of
Shale
4: High-Grade
Metamorphism 
Geiss
 Course graied
Feldspar,
Quartz,
Amphibole,
Biotite
Fig 7.12
 High-grade
metamorphic
T&P Causes
 Mierals stable uder high
mierals to
grade
metamorphic
coditios
separate
ito
appear:
feldspar
bads
 Geissic
badig bads of
dark ad light mierals

Prograde Metamorphism of
Shale
5: Very HighGrade
Metamorphism ad
partial meltig
Migmatite
 Silica rich
mierals melt
first (quartz
ad feldspar)
 Formig silicic
magma
 Ijected ito
fractures
resultig i
silicic veis if
itrusive igeous
rock

Fig 7.12


Metamorphic Rocks of other
Parent Rocks


Limestoe

Marble



Bioclastic calcite
Crystallie calcite




Metamorphic Rocks of other
Parent Rocks


Quartz

Sadstoe





Graular quartz 
Crystallie quartz

Quartzite


Metamorphic Rocks of other
Parent Rocks


Basalt


Amphibole



Graite

Schist


Geiss



Uiform texture

Foliatio (schistosity ad
geissic badig)


Where does Prograde
Metamorphism occur?

Temp. (ºC)
0 600 1200

A B C






Where temperatures ad pressures
are progressively icreased:
Subductio zoes ad Moutai belts
Regioal Metomorphism at
Coverget plate boudaries


Prograde Metamorphism in
Mountain Belts