Metamorphic Rocks

1. Metamorphic Rocks

2. Metamorphic Rock • “Meta” means Change • “Morph” means Form • Definition: A sedimentary/igneous/metamorphic rock that has been changed from its original form by heat, pressure, and/or fluid activity, into a new rock.

3. Formation of Metamorphic Rock • Previously existing rock (parent rock) usually recrystallized. • Recrystalization is the process of increasing the size of the minerals crystals or rock clasts and/or changing the mineral composition without melting. • 2 ways of recrystalizing parent rock. • Contact metamorphism • Regional metamorphism

4. Contact Metamorphism • When older rocks come in contact with the magma of an intrusion or lava of an extrusion , the heat and mineral fluids of the liquid rock alter the older rock.

5. Characteristics of Contact Metamorphism • In the contact metamorphism zone there will be 3 distinct layers Parent Rock Parent Rock Metamorphic rock Metamorphic rock Magma Parent rock changed to metamorphic rock

6. Regional Metamorphism • Colliding tectonic plates often result in mountain building. The closer an area is to the boundary of the colliding plates, the greater the increase in temperature and pressure. • The increase in temperature and pressure transforms older rocks to a series of metamorphic rocks. • This is called Regional metamorphism, because it takes place over a large region of the earth.

7. Regional Metamorphism

8. Regional Metamorphism

9. Textures of Metamorphic Rocks • 2 major types of textures • Foliated • Non-foliated

10. Metamorphic Textures Metamorphic Textures Foliated Foliated • • - - Folios = page or leaf-like Folios = page or leaf-like - - rock has distinct banding or layering rock has distinct banding or layering > often not smooth like in sedimentary rocks > often not smooth like in sedimentary rocks - - formed under directed pressure formed under directed pressure Non-foliated Non-foliated • • - - no distinct layering character no distinct layering character - - often a massive crystalline texture often a massive crystalline texture - - formed under uniform pressures formed under uniform pressures

11. Banding vs Layering

12. Which texture banding or layering?

13. Which texture banding or layering?

14. Foliated rocks • These rocks have layers of minerals crystals that have formed by recrystallization usually under regional metamorphism • These rocks are composed of two or more minerals and are made of interconnected mineral crystals. • There are 4 types of foliations

15. Foliated Textures Foliated Textures Slate • Schist • - looks like blackboard - distinct bands of minerals > dull surface - visible mineral grains - smooth, thin layering > garnets, staurolites - breaks into flat slabs - may have shiny > referred to as slatey cleavage appearance - no mineral grains visible > due to mica minerals Phyllite Gneiss • • - looks like waxed surface - larger grains > has a "sheen" to it - may look like igneous rock - may have little "waves" on - may have crude banding surface > intensely distorted - different minerals than - - some small grains visible schistose

16. Foliated MM Rocks Foliated MM Rocks phyllite phyllite slate slate gneiss gneiss schist schist MM Rocks that could form as a shale (sedimentary) parent rock is MM Rocks that could form as a shale (sedimentary) parent rock is exposed to increasing directed pressure and temperature

17. Non-foliated metamorphic rocks • These rocks are not layered because the minerals are not flat, or sheet like, and/or the rocks were not subjected to directional pressure. • These rocks are composed of interconnected mineral crystals

18. Non-foliated Rocks Non-foliated Rocks Marble: • - metamorphosed limestone Quartzite: Quartzite: • • - - metamorphosed metamorphosed quartz sandstone quartz sandstone