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

2. Read each slide then fill in the blanks or chart.
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. How do they form?
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
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
Pressure from surface rocks
metamorphic
rock
forming
here
heat

5. How are they Classified?
Metamorphic rocks are classified by texture in 2 ways…
Foliated
Non-Foliated

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

8. Foliated Texture
Foliated Texture

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

10. Foliated MM Rocks Foliated MM Rocks phyllite phyllite slate slate
schist
gneiss
schist
gneiss
MM Rocks that could form as a shale (sedimentary) parent rock is
MM Rocks that could form as a shale (sedimentary) parent rock is
exposed to increasing directed pressure and temperature

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

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

13. Metamorphic Zones
Metamorphic Zones

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

15. Then use the next two sides to complete the chart
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
Island arcs, active continental margins, and continental collision zones
Most studies focus on orogenic belts, and the term, “regional metamorphism” is often used synonymously with “orogenic metamorphism”

16. Types of metamorphism Regional high-pressure metamorphism Shock
Contact
metamorphism
Regional
metamorphism
Depth, km
Oceanic
crust 35
Continental crust
Oceanic
lithosphere 75
Continental mantle lithosphere
Asthenosphere
Water
Seafloor
metamorphism

17. Regional high-pressure metamorphism Shock metamorphism Regional
Types of metamorphism
Regional
high-pressure
metamorphism
Shock
metamorphism
Regional
metamorphism
Contact
metamorphism
Regional
metamorphism
Depth, km
Oceanic
crust 35
Continental crust
Oceanic
lithosphere 75
Continental mantle lithosphere
Asthenosphere
Burial
metamorphism

20. Heat Pressure Pressure Visual Summary Use this to complete Foliated
Heatt
Heat
Pressure
Pressure
Pressure
Sedimentary Igneous
or Metamorphic Rock
Sedimentary Igneous
or Metamorphic
Metamorphism
Effect
Classification
based on Texture a s G r i n
Foliated
Nonfoliated
Heat & Pressure NO
↑ Flatten Grains ↑
Layers
Bands
Layers
Slate
HEAT
Phyllite
Bands
PRESSURE
Schist
Slate
Gneiss
Quartzite
Marble
Gneiss

21. Images of content/ The End/ Thanks?

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