1. Chapter 7 Metamorphism and Metamorphic Rocks
Metamorphic rock is formed when existing rocks change due to subjection to pressure and or temperature
Any rock can undergo metamorphism
Metamorphism is the process by which heat, pressure, and chemical reactions deep within the earth alter the mineral content and or structure of existing rock without melting it down

2. METAMORPHISM & METAMORPHIC ROCKS
NORMAL DEPTHS FOR METAMORPHISM: >10-KM FROM SURFACE (BELOW SEDIMENTARY DEPTHS & ABOVE IGNEOUS DEPTHS)
METAMORPHISM: MINERAL CONTENT & STRUCTURE OF SOLID ROCK ALTERED BY HEAT, PRESSURE & CHEMICALLY ACTIVE FLUIDS – DOESN’T MELT
CONDITIONS PROMOTING METAMORPHISM:
ROCK STABILITY IS RELATED TO FORMATION ENVIRONMENT
METAMORPHISM BREAKS SOME BONDS, BUT DOES NOT INCLUDE MELTING `

3. Sedi., meta., igne. rocks

4. Metamorphic Rocks in North America

5. CONDITIONS-CONTD PRESSURE HEAT – MOST IMPORTANT FACTOR
GEOTHERMAL GRADIENT (20-30 DEG C/KM-200 DEG C TO METAMORPHOSE ROCKS)
SOURCES OF HEAT FOR METAMORPHISM:
CONDUCTION FROM DEEP INTERIOR
RISING MAGMA
RADIOACTIVE ISOTOPES
FRICTION BETWEEN ROCK BODIES
PRESSURE

6. Pressure-contd.
Lithostatic: Confining pressure in all directions, rock becomes compressed
Directed Pressure: Acts in one principal plane
Results of Pressure:
Compaction – Smaller & Denser
Ion migration of unbonded ions (recrystallization)
Foliation – Preferred alignment of minerals -Subjected to direct pressure
Units of Pressure: 1 Bar = 1 Atm. Pressure = 1.02 kg/cm2 = 14.7 lbs/inch2 = 105 Pascal

7. Circulating Fluids
Often necessary for chemical reactions (Facilitates movement of ions and atoms)
Sources of Water
Surface Infiltration
Pores in Sedimentary Rocks
Cracks on Subducting Plates
Magmas
Decomposing Minerals
ALL METAMORPHIC ROCKS ARE CATEGORIZED AS ‘FOLIATED’ OR ‘NON FOLIATED’

8. PARALLEL CLEAVAGE

9. MINERAL GRAINS

10. MINERAL GRAINS-CONTD.

11. Deep burial of rocks

12. What Drives Metamorphism
Heat
Accelerate pace of chemical reactions
Pressure
Lithostatic (confining)- rock becomes smaller and denser
Directed- minerals become aligned- Foliation
Circulating Fluids
Ions in water- change mineral composition
Parent Rocks
Original rock’s composition will affect the outcome of metamorphism

13. CONFINING PRESSURE

14. DIRECTED PRESSURE

15. TYPES OF METAMORPHISM Contact
Heat is the dominant factor
Area affected generally smaller than regional metarmorphism
Regional are two types with extensive coverage
Burial- occurs in deep sedimentary basins- no plate tectonics involved
Dynamothermal- occurs where converging plates squeeze a rock caught between them
Others
Hydrothermal- involves hot water from magma
Fault-zone- rocks grinding past one another
Shock- meteorites strike
Pyrometamorphism- lightning

16. CONTACT METAMORPHISM

17. DYNAMOTHERMAL METAM.

18. HYDROTHER. METAM-CONTD

19. Hydrothermal Metamorphism

20. METAMORPHIC ROCK TYPES
Foliated- based on type of foliation
Slate- fine grain
Phyllite- fine grain with sheen
Schist- has ‘split’ appearance
Gneiss- layers/bands of minerals
Non-foliated- based on mineral composition
Marble
Quartzite
Hornsfel
Mixed Rock
Migmatite- indicates partial melting

21. Quartz-Quartzite

22. Quartz-Sandstone

23. Metamorphism Temperature & Pressure
Information about degree to which a metamorphic rock differs from its parent material
Metamorphic Grade-
low ( ) slate
high ( ) gneiss
Index minerals/metamorphic Zones are used to determine metamorphic condition of temperature and pressure
Chlorite, muscovite-low grade (low P/T)
Garnet, staurolite- intermediate
Sillianite- high grade (high P/T)

24. Common Metamorphic Rocks
FOLIATED ROCKS DERIVED FROM SHALE OR MUDSTONES:
SLATE (FINE GRAINED)
SLATY CLEVAGE
SLATE COLORS (RED: IRON OXIDE; GREEN: CHLORITE; PURPLE: MANGANESE OXIDES; BLACK: CARBON)
PHYLLITE: FINE-GRAINED
SCHIST: COARSE GRAINED
GNEISS: COARSE GRAINED

25. Relationships that produce crystallization

26. Three main metamorphic environments

27. Relationships that produce metamorphic rocks

28. Metamorphic Surface Rocks

29. Rock Slide of 1959

30. St. Francis Dam