Basics of Metamorphic Rocks
- Created by: Mellissa True
- Created on: 09-02-13 14:34
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- Metamorphic Rock
- Change d by Heat and/or pressure
- Heat:Rocks close to an intrusion of magma will become heated, Rocks buried deep in the crust will become heated.
- Pressure: Rocks in active zones (continental edges/mountain chains), Rocks buried deep will be affected by pressure
- Mineralogy is changed, minerals react and recrystallize to suit new conditions
- Texture is changed; as new minerals develop, their size, shape and arrangement will change
- Grades
- High grade: greatly changed and looks very different from its original form
- Medium grade or low grade metamorphism would mean less change has taken place
- Thermal Metamorphism
- Heat only
- Occurs mostly around igneous intrusions
- The amount of change depends on the amount of heat. Large batholiths cause more metamorphism than smaller dykes and sills.
- Zone around a batholith is called a metamorphic aureole.
- Variations can occur within an aureole because rocks closer to the intrusion will be changed more then those further away.
- Around smaller intrusions, or beneath lava flows, there is not enough heat to produce an aureole so it is called a baked margin
- Against it you will find the rapidly cooled edge of the igneous rock called the chilled margin
- The original rocks into which a magma has intruded are called the country rocks.
- Regional Metamorphism
- Heat and Presure
- Whole region is altered-occurs when a large volume of continental crust is deformed into a mountain chain.
- This formation process is called an orogeny and regional. met. is a vital part of this process.
- The most intense changes occur at great depth
- Only in uplifted and eroded remains of ancient mountains can can the full effects be seen.
- When a whole region of rock is altered. the grade differences throughout the area.
- Because if the high amounts of pressure, minerals become aligned and show a foliated (banded) texture.
- Example: Schist
- Example: gneiss
- Identifying Metamorphic Rocks
- Because igneous rocks where formed under high temperatures thermal met. has little effect on them.
- Regional met. can cause fine-grained volcanics to recrystallise under pressure
- Because igneous rocks where formed under high temperatures thermal met. has little effect on them.
- Change d by Heat and/or pressure
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