This document discusses metamorphic rocks, which form from the alteration of existing rocks (parent rocks) due to changes in pressure, temperature, and exposure to chemically active fluids. Metamorphism can occur within the earth's crust through processes like deep burial and mountain building, which increase pressure and temperature. This causes minerals in the parent rock to change and recrystallize into new forms suited to the new conditions. The document describes different types of metamorphic conditions and textures, and provides examples of common metamorphic rock transformations.

1. Metamorphic Rocks
Chapter 7

2. Metamorphic Rx
“meta” = change
“morphos” = shape/form
Parent rock = pre-existing rock
that is subject to metamorphism

3. Metamorphic Rx
Form by alteration of parent rock
due to:
- increase in pressure
- increase in temperature
- exposure to chemically active
fluid

4. Metamorphism
Occurs within Earth’s crust
- minerals change until they are
________ under the new
conditions

5. Metamorphic Conditions
1) Increasing pressure (stress)
- occurs for two reasons:
a) deep burial
b) mountain building

6. Rx reaction to pressure
Behave differently depending
upon temperature
Shallow depths = cooler temp
- rx are brittle and tend to break
Ex: fault breccia
Called “cataclastic metamorphism”

7. Rx reaction to pressure
Deep burial = higher temp’s
- rx behave plastically and fold
under pressure (Fig. 7.1)

8. Types of pressure
a) Differential stress
- applied unequally from different
directions
- produces foliated texture

9. Foliated texture
Foliation = parallel alignment of
minerals w/in a rock
- creates a layered appearance
- associated w/mountain building

10. Types of pressure
b) Confining pressure
- applied equally from all sides
- associated with deep burial
- nonfoliated texture

11. Metamorphic Conditions
2) Increasing temperature
NOTE: Temperature cannot
exceed the melting point of all
minerals in rock
Why?

12. Increasing temperature
- occurs for two reasons:
a) deep burial
- geothermal gradient
- increases 30o C per km
b) magma intrusion

13. Increasing temperature
Changes to parent rock:
a) Compositional change
- unstable minerals either melt or
rearrange into new minerals
- partial melting: remaining rock is
metamorphic rock

14. Compositional Change
Ex: Shale
(clay minerals)
Slate
(microscopic
micas)

15. Increasing temperature
b) Textural Change
- partial melting allows minerals to
recrystallize
- produces nonfoliated texture

16. Textural Change
Ex: Sandstone
(quartz)
Quartzite
(quartz)
Note: The composition is still the
same

17. Metamorphic Conditions
3) Chemically active fluid
- superheated water with ions in
solution
- “hydrothermal solution”
- occurs near magma chambers

18. “Microscopic Water”
Water in crystalline structure
- necessary for atoms to rearrange
themselves

19. Sources of Water
a) Groundwater
b) Magma chambers
c) Crystalline structure of hydrous
minerals
Ex: Gypsum = CaSO4 2H2O

20. Metamorphic Rock
Classification
Foliated textures
- degrees of increasing
metamorphic intensity
(temperature, pressure)

21. Foliated textures
Parent rock = shale
Low degree
Slate
(microscopic micas)
Low degree
Phyllite
(light reflects from
larger micas)

22. Foliated textures
Low degree
Medium degree
Phyllite
Schist
(visible micas)

23. Foliated textures
Low degree
Slate
Medium degree
Schist
High degree
Gneiss
(black & white layers)

24. Transitional change
Migmatite
- rock w/both igneous &
metamorphic characteristics
- represents high degree of
metamorphism (Fig. 7.23)

25. Foliated textures
Most schists have muscovite &
biotite = mica schists
Accessory minerals w/micas
indicate degree of
metamorphism w/in schist range

26. Accessory minerals
Referred to as “index minerals”
Ex: chlorite mica schist
Low grade mm (~200oC)
Ex: garnet mica schist
Intermediate grade mm

27. Nonfoliated textures
Composition controlled by parent rock
Parent Rock
Meta. Rock
Sandstone
Quartzite
Limestone
Marble

28. Regional metamorphism

30. Index minerals

31. Regional Metamorphism
Foliated rocks are often folded

32. One rock is the raw material for another