1. METAMORPHIC ROCKS

2. TERMS Subduction – Descent of one crustal plate beneath another – Creates intense horizontal pressure Preferred orientation – Parallel alignment of elongated mineral crystals

3. TERMS Recrystallization – Replacement of original mineral crystals with new ones Equant – Having the same measurements in all directions – E.g. a sphere or a cube

4. METAMORPHIC ROCKS What is Metamorphism? What Drives Metamorphism? Metamorphic Textures Common Metamorphic Rocks

5. Metamorphic Rocks What Is Metamorphism?

6. WHAT IS METAMORPHISM? “meta” = change; “morph” = shape Change of one rock type into another – Heat and (usually) pressure Parent rock – Rock that gets metamorphosed into something else – ANY rock type can be a parent rock, including a metamorphic rock GEOL 131: Metamorphic Rocks

7. Metamorphic Rocks What Drives Metamorphism?

8. Three Metamorphic Agents Heat: most critical Pressure Chemically active fluids GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

9. Heat A form of energy Vibration of atoms and molecules Hotter = faster vibration GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

10. Role of Heat in Metamorphism Provides energy for chemical reactions Weakens atomic bonds in mineral crystals GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

11. Sources of Heat Geothermal – Remnant heat of formation – Radioactive decay Magmas GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

12. Pressure Confining pressure Differential stress GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

13. Confining Pressure Equal in all directions Deep burial GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

14. Differential Stress Higher pressure from sides Converging tectonic plates GEOL 131: Metamorphic Rocks: What Drives Metamorphism? Zone of intense differential stress

15. Chemically Active Fluids Some minerals are hydrated – E.g. gypsum CaSO 4 + 2H 2 0 Water driven out by heat Circulating water promotes transport of atoms GEOL 131: Metamorphic Rocks: What Drives Metamorphism?

16. Metamorphic Rocks Metamorphic Textures

17. Foliation Created by differential stress Preferred orientation of elongated minerals GEOL 131: Metamorphic Rocks: Textures

18. Foliated Textures Slaty cleavage Schistosity Gneissic texture GEOL 131: Metamorphic Rocks: Textures

19. How Foliation Develops: Three Ways Rotation Recrystallization Elongation GEOL 131: Metamorphic Rocks: Textures

20. How Foliation Develops: Rotation Elongated crystals rotate into alignment GEOL 131: Metamorphic Rocks: Textures

21. How Foliation Develops: Recrystallization Original grains replaced by more stable ones New grains are elongated and aligned GEOL 131: Metamorphic Rocks: Textures

22. How Foliation Develops: Elongation Original equant grains are “squashed” into elongated ones GEOL 131: Metamorphic Rocks: Textures

23. Nonfoliated Textures Confining pressure Absence of pressure Equant grains, usually interlocking GEOL 131: Metamorphic Rocks: Textures

24. Nonfoliated Textures Marble, made of interlocking equant calcite grains. Limestone metamorphoses into the nonfoliated rock marble. GEOL 131: Metamorphic Rocks: Textures

25. Metamorphic Rocks Common Metamorphic Rocks

26. Common Foliated Rocks Slate Phyllite Schist Gneiss GEOL 131: Metamorphic Rocks: Common Types From: radford.edu

27. Common Nonfoliated Rocks GEOL 131: Metamorphic Rocks: Common Types Marble Parent: limestone Quartzite Parent: sandstone Anthracite Parent: coal

28. End of Metamorphic Rocks