1.4 Metamorphic Rocks and Processes Flashcards
What are metamorphic rocks a result of?
Increased temperature and/or pressure on existing rock - causing recrystallisation to form new minerals and textures
Which metamorphic rocks are crystalline?
All of them
Difference between lamination and foliation?
- lamination used for sedimentary rocks
* foliation used for metamorphic rocks
Description of marble?
- crystalline
* 1mm crystals
Description of schist?
- crystalline
- 1-5 mm crystals
- layered - foliated
- mica and possibly garnet
Description of slate?
- crystalline
- crystals too small to measure
- foliation >0.5 mm thick
- mica and small amounts of quartz
What gives slate its cleavage?
Mica
Description of chiastolite slate?
- crystalline
- white specs - chiastolite (mineral)
- 10-20 mm crystals
Description of gneiss?
- crystalline
- pink crystals
- large crystals - 1-20 mm
- foliated - big layers
- mica, quartz, orthoclase feldspar (pink) and plagioclase (white)
Description of metaquartzite?
- crystalline
- crystals so big you can’t see - when you can see crystals 1 mm
- quartz
What factors control metamorphism?
- heat
- pressure
- time
- parent rock
What are the main agents of metamorphism?
Heat and pressure
What effect will greater heat have during metamorphism?
Larger crystals
What effect will greater pressure have during metamorphism?
Rock will have layering or foliation - pressure at right angles to the foliation
What are the two types of metamorphism?
- thermal or contact
* regional
What does thermal/contact metamorphism usually form?
An area of baked rocks called a metamorphic aureole
What is a metamorphic aureole?
An area of baked rocks
What agent does thermal metamorphism involve?
Just heat
Where does the heat come from usually in thermal metamorphism?
Bodies of magma
As a rock progresses closer to a granite intrusion, what happens in terms of thermal metamorphism?
- limestone becomes marble
* shale becomes slate, then schist, then gneiss
What agents does regional metamorphism involve?
Heat and pressure
What is regional metamorphism usually a result of?
Earth movements over a wide area
What are rocks formed by regional metamorphism divided into?
Low, medium and high grade - depending on the temperature and pressure in which they were formed
Difference between rocks formed by thermal and regional metamorphism?
Regionally metamorphosed rocks will show foliation due to pressure, while thermally will not
Which metamorphic rock is formed under low pressure and high temperatures?
Marble
Which metamorphic rock is formed under relatively low pressures and low temperatures?
Slate
Which metamorphic rock is formed under high pressure and high temperatures?
- schist
* chiastolite slate
What rocks are formed by contact or thermal metamorphism?
Marble
What rocks are formed by regional metamorphism?
- slate
- schist
- gneiss
What rocks are formed by contact and regional metamorphism?
Chiastolite slate
What mineral can be seen in marble?
Calcite
What mineral can be seen in schist?
Mica, garnet
What mineral can be seen in slate?
Mica, quartz
What mineral can be seen in chiastolite slate?
Chiastolite, mica (dominant) and quartz (less dominant)
What is the parent rock of marble?
Limestone
What is the parent rock of schist?
Shale
What is the parent rock of slate?
Shale
What is the parent rock of chiastolite slate?
Shale
Which minerals are most easily changed due to metamorphism?
Clay minerals (that make up shale) are most easily changed
If there is a lot of folding in a rock, what does this suggest about the conditions it was formed under?
Formed under high pressures
Examples of metamorphic rocks?
- schist
- marble
- slate
- metaquartzite
What does low-grade regional metamorphism involve?
High pressure but relatively low temperatures
What does medium-grade regional metamorphism involve?
Occurs during development of mountain chains - high pressure and moderately high temperatures
What does high-grade regional metamorphism involve?
Takes places at depth during formation of mountain chains - intense pressure and heat
