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

2. The Rock Cycle Geological Materials Transformation Processes Rock
Metamorphism
(Increased T & P)
Meta-
morphic
rock
Partial Melting
Magma

3. Metamorphism Metamorphic Rocks
Definition:
Re-crystallization of minerals
While still solid
Into minerals that are stable at different temperatures and
Different pressures
(Usually progressively higher temperatures and pressures)

4. A. Evidence of Metamorphism
E.g., Sedimentary 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. Bent (deformed) layers

5. Evidence of Metamorphism
2. Flattened Pebbles
Differential pressure “squashes” rock and included features

6. Evidence of Metamorphism
3. Crystalline Texture
Minerals tightly interlocking due to recrystallization under pressure

7. Evidence of Metamorphism
4. New mineral
assemblages
E.g., Shale: Clay minerals
(some quartz) 
Metamorphism
Forms Schist: Mica, Feldspar and other silicate minerals 

8. B. Recipe of Metamorphism
1. Parent Rock
Even though minerals will change
Most elements are provided by parent rock
Except water and some dissolved ions
Shale
Schist

9. B. Ingredients of Metamorphism
Temp. (ºC)
500
1000 A B C
2. Increased Temperature (high geothermal gradients)
Minerals stable at lower temperatures converted to
minerals stable at higher temperatures
Solid state chemical reactions are accelerated

10. Ingredients of Metamorphism
3. Increased Pressure (and stresses)
Increased Confining Pressure as rocks are buried
Compression at convergent plate boundary or
Shearing as plates slide past each other

11. Results of Stress (Pressure)
Cause Foliation
Compressive Stress
Shear Stress

12. Ingredients of Metamorphism
4. Addition or removal of fluids (and elements)
Water (and other fluids) within rocks and minerals
Moving during metamorphism
Accelerates solid-state chemical reactions and
May change rock composition
5. Time  Millions of years!

13. C. Prograde Metamorphism of Shale (and the classification of metamorphic rocks)
Shale: Fine grained Clay (and quartz)
Minerals stable under low T&P (atmospheric)
Compaction due to accumulation of sediment
Fissility along laminations
Water bound in crystalline structure of clay

14. Prograde Metamorphism of Shale
Metamorphic grade
1: Low Grade  Rock: Slate
Low grade metamorphic T&P (Water is expelled from crystalline structure of clay)
Minerals stable under low grade metamorphic conditions
Mineral composition: Fine grained Mica (and Quartz)
Foliation: Slaty Cleavage due to realignment of platy minerals

15. Prograde Metamorphism of Shale
2: Medium-Grade Metamorphism  Phillite
Courser grained Mica and quartz
Medium-grade metamorphic T&P Causes minerals to grow
Slaty cleavage becomes rippled and rock has a sheen

16. Prograde Metamorphism of Shale
3: Medium to High-Grade Metamorphism  Schist
Course grained Mica and Quartz
Medium-grade metamorphic T&P Causes minerals to grow
Minerals stable under medium grade metamorphic conditions appear: Garnet, amphibole and biotite
Schistosity due to alignment of platy and needle likeminerals

17. Prograde Metamorphism of Shale
4: High-Grade Metamorphism  Gneiss
Course grained Feldspar, Quartz, Amphibole, Biotite
High-grade metamorphic T&P Causes minerals to separate into bands
Fig 7.12
Minerals stable under high grade metamorphic conditions appear: feldspar
Gneissic banding bands of dark and light minerals

18. Prograde Metamorphism of Shale
5: Very High-Grade Metamorphism and partial melting Migmatite
Silica rich minerals melt first (quartz and feldspar)
Forming silicic magma
Injected into fractures resulting in silicic veins if intrusive igneous rock
Fig 7.12

19. Metamorphic Rocks of other Parent Rocks
Limestone  Marble
Bioclastic calcite  Crystalline calcite

20. Metamorphic Rocks of other Parent Rocks
Quartz Sandstone  Quartzite
Granular quartz  Crystalline quartz

21. Metamorphic Rocks of other Parent Rocks
Basalt  Amphibole Schist
Granite  Gneiss
Uniform texture  Foliation (schistosity and
gneissic banding)

22. Where does Prograde Metamorphism occur?
Temp. (ºC)
600
1200 A B C
Where temperatures and pressures are progressively increased: Subduction zones and Mountain belts
Regional Metomorphism at
Convergent plate boundaries

23. Prograde Metamorphism in Mountain Belts

24. High Low Northeastern North America Northwestern Africa Metamorphic
Grade
High
Low
Northeastern
North America
Northwestern
Africa

26. Review for Exam For each rock type discussed know:
Grain size (rounding and sorting if sedimentary)
Texture (clastic or crystalline)
Other characteristics
Various types of metamorphic foliation
Various sedimentary structures
Environment of formation
History of formation
Classification
Rock

27. Reading the Grand Canyon

28. The Grand Canyon 5. Coconino Sandstone 4. Redwall Limestone
Fig. 8.16
The Grand Staircase
5. Coconino Sandstone
4. Redwall Limestone
Sedimentary Rocks
Intrusive Igneous
Metamorphic
3. Bright Angel Shale
2. Grand Canyon
Pink Granite
1. Vishnu Schist (and gneiss)

29. The Grand Staircase
Fig. 8.16

30. Eastern Zion National Park

31. Checkerboard Butte Zion National Park

32. Vishnu Schist and Pink Granite