Geology: Metamorphic Rocks

  1. Do rocks melt during metamorphism?
  2. Define the term protolith and give several specific examples of metamorphic rocks and their protoliths. Explain.
    A protolith is the parent rock of a metamorphic rock. May be sedimentary, igneous, or other metamorphic rocks.

    • Marble - Limestone
    • Quartzite - Quartz Sandstone
    • Slate - Shale
    • Phylite - Shale
    • Schist - Phylite
    • Gneiss - Schist
    • Serpentine - Peridotite
  3. List the three agents of metamorphism.
    • Heat
    • Pressure
    • Chemically Active Fluids
  4. Discuss each agent of metamorphism, including how it affects the rock and where (tectonically) it might be important.
    • Heat
    • Heat energy drives chemical reactions that recrystallize individual mineral grains(increases)

    • Pressure
    • Confining pressure applies forces equally in all directions. Causes new minerals to form.

    Differential Stress applies force the exerts in a particular direction. Causes foliation.

    • Chemically Active Fluids
    • Mainly water or other volatile compounds
  5. Which “agent” causes foliation?
    Pressure - Differential stress
  6. What 3 things can happen to a rock as it undergoes metamorphism? Give examples.
  7. List and describe the specific metamorphic textures. How does each originate?
    • Foliated
    • Non-foliated

    Foliation - planar arrangement of mineral grains or structural features within a metamorphic rock

    Non-foliated Texture - develops where deformation is minimal

    • Crystalline
    • Microcrystalline
    • Porphyroblastic
  8. Give examples of metamorphic rocks with specific textures.
    • Foliated
    • Slate - Slaty cleavage
    • Phylite - Phyllitic texture
    • Schist - Schistone
    • Gneiss - Gneissic

    • Non-Foliated
    • Crystalline - Marble, Quartzite
    • Microcrystalline - Hornfels, Serpentine
  9. Discern between high and low grade metamorphism and give examples.
    Increase in metamorphism increases crystal size and coarseness of foliation.

    • Low Grade: Slate, Phyllite
    • Intermediate Grade: Schist
    • High Grade: Gneiss, Migmatite
  10. List/briefly describe common metamorphic environments.
    Contact/Thermal: results from heat and pressure in a small area

    Burial: confining pressure and increase in temperature as sediments are gradually buried deeper in the crust

    Regional: high temperatures and high pressure. Differential stress.

    Hydrothermal: hot water
  11. Explain the concept of metamorphic zones and index minerals.
  12. Name at least two metamorphic rocks commonly found in Sonoma County and describe where/how each formed.
Card Set
Geology: Metamorphic Rocks
Geology Exam for Metamorphic Rocks