1. Metamorphic Rocks Fig. 3-CO, p.44
Gneiss, a metamorphic Rock from Baffin Island, Canada.
Fig. 3-CO, p.44

2. Figure 3. 4 The rock cycle shows that rocks change over geologic time
Figure 3.4 The rock cycle shows that rocks change over geologic time. The arrows show paths that rocks can follow as they change.
Fig. 3-4, p.46

3. Metamorphism
The transition of one rock into another by temperatures and/or pressures unlike those in which it formed.
Metamorphic rocks are produced from
Igneous rocks
Sedimentary rocks
Other metamorphic rocks

4. Metamorphism Progresses incrementally from low to high-grade
Rock must remains essentially solid throughout process
Agents of metamorphism include heat, pressure and chemically-active fluids

5. Metamorphic settings
Contact or thermal metamorphism – driven by a rise in temperature within the host rock
Hydrothermal metamorphism – chemical alterations from hot, ion-rich water
Regional metamorphism (mountain building)

6. Agents of metamorphism
Heat: The most important agent
recrystallization of mineral grains and chemical precipitates
Formation of new, stable minerals
Two sources of heat
Contact metamorphism – heat from magma
An increase in temperature with depth due to the geothermal gradient

7. Geothermal Gradient

8. Agents of metamorphism
Pressure (stress) increases with depth
Confining pressure: applies forces equally in all directions
Example: depositional environment
Differential stress: applies unequal forces in different directions
Example: mountain-building environment

9. Figure 7.3a

10. Agents of metamorphism
Pressure (stress) increases with depth
Confining pressure: applies forces equally in all directions
Example: depositional environment
Differential stress: applies unequal forces in different directions
Example: mountain-building environment

11. Figure 7.2b

12. Figure 7.4

13. Result of differential stress
Gneiss, a metamorphic Rock from Baffin Island, Canada.

14. Role of Parent Rock
Mineral composition of parent rock determines mineral composition of metamorphic daughter rock (often the same or similar:
Sandstone and quartzite
Limestone and marble
Mineral composition of parent rock determines grade of metamorphism that takes place:

15. Quartz sandstone, sedimentary parent rock of quartzite

16. Quartzite – Metamorphosed Sandstone

17. Limestone, sedimentary parent rock of marble

18. Marble – Metamorphosed Limestone

19. Low grade to high grade Metamorphism (left-right)

20. Figure 7.17