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What is metamorphism?
to change from one form to another
What is metamorphic rock?
any rock that has undergone changes in texture, mineralogical, or chemical composition in the solid state
Why do we study metamorphic rocks?
- -exposed metamorphic rocks make up large parts of continents
- -certain minerals in metamorphic rocks give clues about the conditions existing when they are formed
- -used widely as building materials and manufacturing
Conditions of metamorphism:
- solid state- rocks does not melt
- isochemical-chemistry does not change
Composition of metamorphic rock determined by
composition of parent rock
Parent rocks are changed in mineralogy or physical texture by:
- -heat and pressure
- -tectonic forces
- -fluid activity
What are the agents of metamorphism?
- 1. Temperature
- 2. Pressure
- 3. Fluid gases
- 4. Time
Temperature: why? how?
- -increases rate of chemical reactions
- -minerals are stable over temperature range
- *conditions of metamorphism can be reconstructed
- -increasing temperature with depth
- -radioactive decay
- -migrating magmas
Pressure: Why? How?
- -mineral grains are more closely packed
- -recrystallization may occur, producing smaller and denser minerals
- -confining pressure: equally applied on all surfaces
- -lithostatic pressure results from the weight of overlying rocks
Fluids and Gases
increase metamorphic reactions
How are metamorphic rocks classified?
- -Foliated: Identified by grain size, separation of light and
- dark minerals, and finally partial melting. Comes down
- to increasing temperature and pressure-Slate, Phyllite, Gneiss, Migmatite
- -Non-foliated: Identify by mineral content or original (parent) rock
- Quartzite, Marble
- Igneous rock metamorphism:
- Gabbro, Basalt, Granite and Diorite
What are the types of metamorphism?
- 1. Contact-takes place when a body of magma alters the surrounding country rock
- 2. Regional-occurs over a large area and is usually caused by tremendous temperatures, pressures and deformations within the deeper portions of the crust.
Index Minerals- what are they and can we use them?
Index minerals form under specific conditions of temperature and pressure
Geologists use index minerals to recognize low, intermediate, and high grade metapmorhic zones
What are hydrothermal processes?
- -rocks altered by hot water
- -divergent plate boundaries
- *water penetrates through cracks
- *converts mafic minerals into hyrdrous (water bearing) minerals
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