Metamorphic rocks Flashcards
What is a metamorphic rock?
transformations of existing rock types (e.g. igneous and sed) through METAMORPHOSIS - heat, pressure, and chem reactions
How does metamorphism work?
- Minerals are stable at the temp they form at
- If temp changes, they become unstable. They then recrystallise into new minerals - 200 degrees
How does recrystallisation work?
- powered by heat energy and pressure
- higher the temp, faster the recrystallisation
What are the two kinds of metamorphism?
Regional
Contact
What are the conditions for regional metamorphism?
Give an example of where occur
- high temp
- high pressure
- caused by plate tectonics
e.g. fold mountains
What are the conditions for contact metamorphism?
Give an example of where occur
- high temp
- low pressure
- small and localised
- actual contact with heat e.g. pluton
e.g. metamorphic aureole
affected by: size, temp (mafic crystallise at 1200, silicic at 700)
What is the protolith?
the parent rock
- what the rock was before it was metamorphosed
What is texture?
The relationship between the grains
Give some metamorphic textures
Granoblastic
Porphyroblastic
Porphyroblasts
Foliation
What does granoblastic mean?
All grains are a similar size
What does porphyroblastic mean?
larger grains in a finer groundmass
What are porphyroblasts?
the larger grains in a porphyroblastic rock
What does foliation mean?
- any alignment in the rock
- caused by regional metamorphism
Give 3 examples of metamorphic foliation
Slaty cleavage
Gneissose banding
Schistosity
How does regional metamorphism work?
pressure causes platy minerals to recrystallise at right angles to the sigma max
- because of the pressure the platy mins are all aligned = FOLIATION = right angles to sigma max
Give an example of regional metamorphism
Shale = clay (mica), quartz
Under huge pressure and temp, mica (the platy min) recrystallises 90 degrees to the sigma max, and the quartz interlocks
What is the sigma max?
the direction of maximum pressure
What is the difference between slate and shale?
SLATE
- metamorphic
- sonorous
SHALE
- sedimentary
- falls apart
How would I tell the difference between marble and metaquartzite?
- Marble will fizz with HCl
- Metaquartzite has a hardness of 7, marble is 3
What are hornfells?
high grade contact metamorphosed mudstone
What is a metamorphic aureole?
an area of rock altered in composition/structure/texture by contact with an igneous intrusion
