1. Metamorphism and Metamorphic Rocks

2. Daily Question Correctly place the following
Igneous
Rocks
Contact
Metamorphic
Regional
rocks
Correctly place the following
statements in the Venn Diagram.
Occurs at divergent boundaries
Occurs at convergent boundaries
Forms as a result of melting (magma)
Temperature is an agent
Pressure is an agent
Generates foliated rocks
Forms as a result of being near an intrusion of magma
Found in mountain belts
May have been originally been a metamorphic rock
Form at temperatures above 200 oC
May underlie several adjacent states

3. Definitions
Metamorphism – mineralogical, chemical, and physical changes that occur in solid rocks.
Occurs at depths greater than that of lithification (Diagenesis).
Solid state recrystallization – changes that occur without the rock melting (rocks that melt are igneous).

4. Factors influencing Metamorphism
Temperature
Pressure
Fluid
Time
Agents of Metamorphism

6. Factors influencing Metamorphism
Temperature
below about 150oC, most minerals are stable (little or no metamorphism)
above 150oC, reaction rate increases as temperature increases, new minerals begin to form
above 600oC, some minerals begin to melt (transition to igneous rocks)
Temperature a function of depth within the Earth and the presence of a magma

7. Factors influencing Metamorphism
Pressure
as pressure increases, pore spaces reduced and density increases, pore fluids are expelled
Minerals recrystallize and begin to realign
Differential stress
pressure is greater in one direction than in another

8. Temperature, Pressure and Rock Type

10. Effects of Stress
Uniform
Differential

11. Factors influencing Metamorphism
Pore fluids (water and carbon dioxide)
as pressure increases, pore fluids are expelled
Pore fluids increase the rate of metamorphic reactions by:
storing ions involved in reactions
moving ions from one place to another
Chemical Fluids from Magmas
Carry ions from the melt
Fluids increase the temperature in the rock

12. Veins
Solutions are deposited in fractures and joints

13. Factors influencing Metamorphism
Time
solid state recrystallization is a slow process
in general, size of minerals increases with time

14. Types of Metamorphism Burial Metamorphism 2. Contact Metamorphism
3. Regional Metamorphism

15. Metamorphism & Plate Tectonics

16. Types of Metamorphism Burial Metamorphism
most common type, occurs where crust is greater than 5 km thick
Relatively low temperature and pressure (low grade metamorphism)
Maximum stress vertical, foliation parallel to ground surface

18. Types of Metamorphism Contact metamorphism
Occurs in rocks around a magma body
High temperature (heat from magma) “bakes” the rock around the magma creating an alternation
High temperature & fluid primary agents, little to no pressure (occurs at shallow depths in the crust)

19. Non-foliated Metamorphic Rocks
Granular texture
Interlocking grains
Composed primarily of one mineral
Uniform grain size

20. Contact Metamorphism

21. Contact Metamorphism

22. Types of Metamorphism Regional metamorphism
Large scale – large volume of rock is affected
Associated with convergent plate margins and mountain building
Folding and faulting increase thickness of the crust
Occurs over a range of temperatures and pressures
Fluids are also present
Low grade to high grade metamorphism
Will have zones of contact metamorphism

23. Regional Metamorphism

24. Metamorphic Grade

26. Metamorphic Grade
As pressure and/or temperature increases, the grade of metamorphism increases

27. Low Grade Metamorphism
Example: Slate
Rocks become more dense and compact
forms at low temperature and pressure
microscopic crystals
dull luster
clay and mica minerals
foliated

28. Low Grade - Slate

29. Metamorphic Grade

30. Intermediate Grade Metamorphism
Example: Phyllite
intermediate temperature and pressure
small crystals
shiny luster
mostly mica minerals
foliated

31. Intermediate Grade – Phyllite

32. Metamorphic Grade

33. High Grade Metamorphism
Example: Schist
high temperature and pressure
large crystals
mica-rich
foliated

34. High Grade - Schist

35. Metamorphic Grade

36. High Grade Metamorphism
Example: Gneiss
high temperature and pressure
large crystals
mica-poor
foliated

37. High Grade - Gneiss

38. Rock Cycle

39. Regional Revisited
Slate
Phyllite
Schist,
Gneiss
Magma

40. Nonfoliated - Marble metamorphosed limestone (CaCO3)
bedding and fossils obliterated

41. Nonfoliated - Quartzite
metamorphosed quartz-rich sandstone
Pore spaces filled with SiO2

42. Metamorphic Facies
Different minerals form at different temperatures and pressures
Group of stable minerals define a facies