Metamorphism student copy

Metamorphism


Metamorphic Rocks & the Rock Cycle


Types of Metamorphism

Patterns of
Metamorphic
Grade

Mineral Assemblages in
Metamorphic Rocks

METAMORPHIC ROCKS

Metamorphic
Textures

Index Minerals

Phase Diagrams

Factors affecting type
of metamorphic rock


Metamorphic Rocks
By the end of this lesson you will be able to:

• Classify metamorphic rocks into two groups.
• Explain the concept of metamorphic grade.
• Describe the causes of the different types of metamorphism.
• Explain how metamorphic reactions occur during metamorphism.


Metamorphic Rocks
List down as many metamorphic rocks as you can remember:

• spotted rock
• hornfels
• marble
• metaquartzite
• slate
• phyllite
• schist
• gneiss


Metamorphic Rocks
Which ones are foliated and which ones are unfoliated?

• spotted rock
• hornfels
• marble

unfoliated

• metaquartzite
• slate

• phyllite
• schist
• gneiss

foliated


Metamorphic Rocks
Which can be formed due to contact metamorphism & which
can be formed due to regional metamorphism?

• spotted rock
• hornfels
• marble

unfoliated

Contact
metamorphism

• metaquartzite
• slate
• phyllite
• schist

foliated

Regional
metamorphism

• gneiss
• mylonite/fault breccia

Dynamic
metamorphism


Metamorphic Processes

• Mineral alignment
• Recrystallisation

• New minerals formed from metamorphic reactions


Metamorphic Reactions
Low temperature minerals

Change in stability

High temperature minerals

PROGRADE REACTION

reactants

temp by 550 °C

products

(increase in metamorphic grade)

muscovite + quartz = feldspar + sillimanite + water vapour
products

temp by 550 °C

reactants

(decrease in metamorphic grade)

RETROGRADE REACTION
Low temperature minerals

Change in stability

High temperature minerals


Metamorphic Reactions
Low temperature minerals

Change in stability

High temperature minerals

PROGRADE REACTION

reactants

temp by 550 °C

products

Escapes from
rock

(increase in metamorphic grade)

muscovite + quartz = feldspar + sillimanite + water vapour

Metamorphic
mineral


Phase Diagrams
Kyanite stability field.
Phase boundary

Sillimanite stability field.

Andalusite stability field.

Al2SiO5

All have same formula but each
mineral has a different crystal
structure = POLYMORPH

Metamorphism & Metamorphic Reactions
1.

Define metamorphism.

2. What does the term metamorphic grade mean?
3. Why do metamorphic reactions occur?
4. What do these reactions typically form?
5. Explain prograde and retrograde reactions using the muscovite + quartz
metamorphic reaction.
6. In reality most metamorphic reactions do not return to their original
starting point. Why?

7. Metamorphic reactions are slow. What could cause them to speed up and
how is this done?
8. What is a phase diagram and what does it show?

(note: explain these words phase/phase transformation/ stability field - using the kyanite, andalusite & sillimanite example)

9. Why might a mineral be termed metastable?
10. Describe the differences between the three types of metamorphism.


Metamorphic Rocks
The intended learning outcomes from last lesson were to be able to:

• Classify metamorphic rocks into two groups.
• Explain the concept of metamorphic grade.
• Describe the causes of the different types of metamorphism.
• Explain how metamorphic reactions occur during metamorphism.

• Classify metamorphic rocks into two groups.
Put these metamorphic rocks into 2 groups – unfoliated &
foliated.
Unfoliated
• schist
1. Fault breccia
• mylonite
2. Spotted rock
• fault breccia
3. Hornfels
4. Marble
• spotted rock
5. Metaquartzite
• hornfels
• slate
Foliated
• phyllite
1. Schist
• marble
2. Mylonite
• gneiss
3. Slate
• metaquartzite
4. Phyllite
• migmatite
5. Gneiss
6. Migmatite

• Classify metamorphic rocks into two groups.
Put these metamorphic rocks into a Venn diagram to show
whether they are formed by contact metamorphism or
regional metamorphism, or by both.
•
•
•
•
•
•
•
•
•
•
•

schist
mylonite
fault breccia
spotted rock
hornfels
slate
phyllite
marble
gneiss
metaquartzite
migmatite

Marble

Spotted rock
Metaquartzite
Hornfels

Contact

Schist
Slate
Phyllite
Gneiss
Migmatite

Regional

Fault Breccia
Mylonite

Dynamic


• Explain the concept of metamorphic grade.
Put these regional metamorphic rocks into a linear order to
show increasing metamorphic grade.
•
•
•
•
•

schist

slate
phyllite
migmatite
gneiss

slate

phyllite

schist

gneiss

Increasing metamorphic grade

migmatite


• Describe the causes of the different types of
metamorphism.
Write the cause of the metamorphic change next to the
types of metamorphism below.
Dynamic metamorphism -

Localised deformation along
fault zones.

Contact metamorphism -

Heat from igneous

intrusions.

Regional metamorphism -

Heat & pressure due to
orogenesis.


• Explain how metamorphic reactions occur during
metamorphism.
Use clay & its polymorph andalusite to show how
metamorphic reactions occur.
Prograde reaction

Clay

Andalusite

Clay

Andalusite
Retrograde reaction


Metamorphic Rocks
By the end of this lesson you will be able to:

• Identify & describe the metamorphic textures associated with the
different types of metamorphism.
• Explain how these metamorphic textures form.

Dynamic Metamorphism

large, angular fragments (fault breccia)

fine-grained matrix (fault gouge)

Mylonite
Fault Breccia
elongation of minerals

foliation


Contact
Metamorphism

A

B
E

G

D

C

F

Contact
Metamorphism

A

B
F

E

D

C

H

Interlocking quartz,
feldspar & mica
grains (granoblastic)

F

Cordierite minerals
(porphyroblastic)

Recrystallised mica
minerals (unfoliated)

E

G

Interlocking coarse
calcite crystals
(granoblastic)

Partially
recrystallised
clay minerals
(unfoliated)

H

D

Interlocking quartz
grains (granoblastic)

B


Metamorphic
Texture
• Recrystalline
•
•
•
•

Interlocking
Medium-grained
Granoblastic
Non-foliated

Metamorphic
Minerals
• Quartz

• Feldspar
• Mica
• Sillimanite


Metamorphic
Texture
• Recrystalline
•
•
•
•

Interlocking
Medium-grained
Granoblastic
Non-foliated

Metamorphic
Minerals

• Calcite


Regional Metamorphism
Schistosity
(foliation)

Schist

Slaty cleavage
(foliation)
Clay &
mica

Phyllite

Slate
Increasing
metamorphic grade