Protolith
A pre-existing rock
Metamorphic rock
Solid- state alteration of a protolith
What are three agents of metamorphism?
- Temperature
- Pressure
- Stress
Metamorphism can alter any protolith. What two things in the rock can it alter?
Texture and mineralogy
How does heat affect metamorphism?
The heat energy breaks and reforms atomic bonds
What is the trend of pressure and depth?
Pressure increases with depth
How does pressure affect metamorphism?
An increase in presure packs the atoms more tightly together. This causes denser minerals or a phase change / crystallization
Hydrothermal fluid metamorphism
Hot water with dissolved ions and volatiles
How do hydrothermal fluids affect metamorphism?
- it accelerates chemical reactions
- alters rocks by adding / subtracting elements
what is another name for hydrothermal fluid metamorphism?
Metasomatism
Foliation
alternating light and dark bands
recrystyalization
- minerals change size and shape
- type does not change
neocrystallization
- new minerals form from old
- old minerals become unstable
Can metamorphism happen more than once?
yes
What are the two main groups of metamorphic rocks?
Foliated and non-foliated
In a foliated rock, minerals have a ___ ___
preferred orientation
A non-foliated rock contains minerals that have ____ but DO NOT have a preferred orientation
recrystallized
How do you define metamorphic intensity?
Metamorphic grade
What does metamorphic grade mainly depend on?
Temperature
Low temperature = ___ grade
low
High temperature = ____ grade
high
Thermal / contact metamorphism
- magma heats the wall of a magma chamber
- high grade form immediately
- low grade form farther away
Metamorphism in a subduction zone
- rock at the base of the zone has high pressure
- subducted oceanic lithosphere is cool, temperatures remain relatively low
Shock metamorphism
Meteorites impact the earth, extreme compression is felt
exhumation
the process in which deeply buried rocks end up back at the surface
shield
broad region of stable continental crust where the sedimentary cover was eroded away and the Precambrian "basement" rocks are exposed