Metamorphic rocks process of formation 2014

S6E5. Students will investigate the scientific view of how the earth’s surface is formed.
c. Classify (metamorphic) rocks by their process of formation.

1. Learning Goal: Understand how metamorphic rocks are formed and classified.

2. S6E5. Students will investigate
the scientific view of how the
earth’s surface is formed
c. Classify (group) rocks
(metamorphic) by their process
of formation (formed)

3. Rocks that have changed (metamorphism) due
to HEAT and PRESSURE.
These rocks form
DEEP underground!
Pressure from plate movement
folds and buckles the crust.
Magma heats up surrounding
rock.

4. Metamorphic rocks are formed by the effect of heat
and pressure on existing rocks.
This can greatly affect the hardness, texture or
layer patterns of the rocks.
Magma
metamorphic
rock
forming
here
heat
Pressure from surface
rocks

5. Metamorphic rocks are classified by texture in 2
ways…
1.Foliated
2.Non-Foliated

6. The processes of compaction and recrystallization change the
texture of rocks during metamorphism.
Compaction
The grains move closer together.
The rock becomes more dense.
Porosity is reduced.
Example: clay to shale to slate
Recrystallization
Growth of new crystals. No changes in overall chemistry.
New crystals grow from the minerals already present. A
preferred orientation of minerals commonly develops under
applied pressure. Platy or sheet-like minerals such as
muscovite and biotite become oriented perpendicular to the
direction of force. This preferred orientation is called
foliation.

7. Mineral grains flatten and line up in parallel
bands OR layers.
Slate:
Foliated (with layers)
Gneiss:
Foliated (with banding)
That are formed under directed pressure

8. Foliated TextureFoliated Texture

9. Foliated TexturesFoliated Textures
• Slatey
- looks like blackboard
> dull surface
- smooth, thin layering
- breaks into flat slabs
> referred to as slatey cleavage
- no mineral grains visible
• Phyllitic
- looks like waxed surface
> has a "sheen" to it
- may have little "waves" on
surface
> referred to as crenulations
- some small grains visible
• Slatey
- looks like blackboard
> dull surface
- smooth, thin layering
- breaks into flat slabs
> referred to as slatey cleavage
- no mineral grains visible
• Phyllitic
- looks like waxed surface
> has a "sheen" to it
- may have little "waves" on
surface
> referred to as crenulations
- some small grains visible
• Schistose
-
- visible grains
> garnets, staurolites
- may have shiny
> due to mica minerals
• Gneissic
- larger grains
- may look like igneous rock
- may have crude banding
> intensely distorted
- different minerals than
schistose
• Schistose
- distinct bands of minerals
- visible mineral grains
> garnets, staurolites
- may have shiny
appearance
> due to mica minerals
• Gneissic
- larger grains
- may look like igneous rock
- may have crude banding
> intensely distorted
- different minerals than
schistose

10. QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Foliated MM RocksFoliated MM Rocks
slateslate
schistschist gneissgneiss
phyllitephyllite
MM Rocks that could form as a shale (sedimentary) parent rock isMM Rocks that could form as a shale (sedimentary) parent rock is
exposed to increasing directed pressure and temperature

11. Mineral grains change, grow, and rearrange,
but don’t form bands or layers.
Quartzite Marble
Formed under uniform pressures

12. • Marble:
- metamorphosed
limestone
•
Quartzite:
-
metamorphosed sandstone
•
-
Non-foliated RocksNon-foliated Rocks Examples
Quartzite forms in two different ways.
In the first way, under the high pressures
and temperatures of deep burial,
sandstone

13. Metamorphic ZonesMetamorphic Zones

14. • Metamorphism is common along most plate boundaries like this.
Metamorphic ZonesMetamorphic Zones

15. The Types of Metamorphism
Read this slide
Then use the next two sides to
complete the chart
Regional Orogenic Metamorphism is the type of metamorphism
associated with convergent plate margins
•Dynamo-thermal: one or more episodes of
orogeny with combined elevated geothermal
gradients and deformation (deviatoric stress)
•Foliated rocks are a characteristic product

16. Depth,
km
0
35
75
A
s
t
h
e
n
o
s
p
h
e
r
e
C
o
n
tin
e
n
ta
l c
r
u
s
t
Regional
metamorphism
Oceanic
crust
Oceanic
lithosphere
ShockShock
metamorphismmetamorphism
RegionalRegional
metamorphismmetamorphism
RegionalRegional
high-pressurehigh-pressure
metamorphismmetamorphism
ContactContact
metamorphismmetamorphism
C
o
n
tin
e
n
ta
l m
a
n
t
le
lit
h
o
s
p
h
e
r
e
Water
SeafloorSeafloor
metamorphismmetamorphism
Types of metamorphism

17. Depth,
km
0
35
75
A
s
t
h
e
n
o
s
p
h
e
r
e
C
o
n
tin
e
n
ta
l c
r
u
s
t
Regional
metamorphism
Oceanic
crust
Oceanic
lithosphere
ShockShock
metamorphismmetamorphism
RegionalRegional
metamorphismmetamorphism
RegionalRegional
high-pressurehigh-pressure
metamorphismmetamorphism
ContactContact
metamorphismmetamorphism
BurialBurial
metamorphismmetamorphism
C
o
n
tin
e
n
ta
l m
a
n
t
le
lit
h
o
s
p
h
e
r
e
Types of metamorphism

20. Sedimentary Igneous
or Metamorphic
Pressure Pressure
H
e
a
t H
e
a
t
Metamorphism
Effect
Classification
based on Texture
G r
a
in
s
Heat & Pressure
Foliated Nonfoliated
NO
Layers Bands
Gneiss
Schist
Phyllite
Slate
PRESSURE
HEAT
↑ Flatten Grains ↑
Layers
Bands
Gneiss
Slate
Quartzite
Marble
Sedimentary Igneous
or Metamorphic Rock
Pressure
H
e
a
t H
e
a
tt

Heat

22. Learning Goal: Understand how metamorphic
rocks are formed and classified.
Do Now Q: What features do foliate metamorphic
rocks show?