1. Metamorphic Rocks

2. Metamorphic Rocks Recrystallization in the solid state
Caused by changes in T, P or fluids
New environment = new minerals
Growing minerals create a new texture

3. Sources of metamorphic change

4. Metamorphism Recrystallization
T, P or change in pore fluids initiate change in the mineral assemblage
Reaction occur entirely in the solid state
Shale
Schist
Initiate: وارد کردن assemblage:اجتماع

5. Textural changes occur during metamorphism
New minerals grow during metamorphism
Precursor rock textures are modified
Precursor rock:سنگ جدید

6. Protolith The parent rock subjected to Metamorphism
-can be any rock type: igneous, sedimentary, or metamorphic
Shale
Schist
Protolith: سنگ منشا دگرگونی

7. Protolith
For example, limestone is the protolith of marble

9. Origin of Metamorphic Rocks
Metamorphism
Temperature exceeds 200OC
Pressure exceeds 300 M Pa (approx. 10,000 ft deep)
Metamorphism ends when melting begins
Melting begins at ~700oC

10. Stability ranges for Al2 SiO5 minerals

11. Source of heat Proximity to igneous intrusions Depth of burial
Contact metamorphism
Different metamorphic grade ring the intrusion
Depth of burial
15-30oC increase per km
Geothermal Gradient

13. Zone of Contact
Metamorphism
Magma Body
-source of heat

14. -equal in all directions: uniform stress
Pressure and Stress
Lithostatic Pressure- pressure increases with depth due to the weight of the overlying rocks.
-equal in all directions: uniform stress
-a cubic foot of granite weighs pounds.

16. Tectonic Pressure/Stress
-directional/non-uniform
-referred to as deviatoric stress
Deviator: منحرف شونده

17. Folded Metamorphic Rocks -subjected to non-uniform deviatoric stress
uniform stress: تنش همه جانبه ، تنش یک نواخت
subjected to: در معرض
Folded Metamorphic Rocks
-subjected to non-uniform deviatoric stress

18. T & P determine degree of metamorphism
Low-grade metamorphism- 200 to 350 OC
Intermediate-grade metamorphism-350 to 550 OC
High-grade metamorphism - very high temperatures, above 550OC

19. Progressive metamorphism of shale
Conspicuous foliation: برگوارگی آشکار

20. Fig. 6.5. Stability ranges for Al2O5 minerals

21. Index Minerals

22. Metamorphic Rocks Classified by texture and composition
Texture is divided into foliated & nonfoliated rocks
Mineral composition qualifies textural name
Qualifies: توصیف کردن

23. Foliated Nonfoliated textures

24. Foliation:
-preferred orientation
or location of minerals

25. Slate

26. Phyllite Similar to slate More Recrystallization Common Protolith:
Crystals are larger
Common Protolith:
shales

27. Schist Strongly foliated rock Medium to coarse grained
-dominated by platy minerals
Protoliths: multiple??

28. [Garnet] Schist w/porphyroblasts

29. Gneiss Coarse grained granular rock
Foliation: alternating bands of light & dark minerals
Quartz, feldspar, amphibole,
biotite
Protoliths: ??

30. Nonfoliated Rocks Marble Interlocking, coarse grained calcite
Recrystallization of limestone or dolostone
Sedimentary features
destroyed

31. Quartzite Metamorphism of quartz sandstone
Entire rock is recrystallized

32. Amphibolites & Eclogites
Metamorphism of mafic rocks
Mineral assemblage
gives green color
Amphibolite [pillow basalt]
Eclogite from Norway

33. Regional Metamorphic Zones
Index minerals
A mineral that forms within a specific,often narrow range of conditions
Identifies a specific grade of metamorphism
Allows further subdivision of rock types

34. Metamorphic Index Minerals

35. Protolith controls final mineral assemblage
Different mineral assemblages form at a given P & T for various parent rocks
Metamorphic facies describe a group of minerals formed under similar conditions
May be found in different rocks
Assemblage: اجتماع

36. Regional
Metamorphic
Gradients

37. Metamorphic facies

38. Metamorphic Rocks & Tectonics
Most metamorphic rocks develop due to plate collisions
Processes are not observable in the field
Conditions at various plate boundaries define possible P & T range
Parent rocks present control mineral assemblages
plate collisions: برخورد صفحات