Metamorphism: Contact and Regional Flashcards
Define Metamorphism
The mineralogical and physical change of a rock in the solid state
At what depth does metamorphism usually occur?
10-30km
At what temperature does metamorphism usually occur?
200 degrees C
What three things does metamorphism depend on?
Original composition of rock, Amount of change in pressure and temperature, Length of time
What three things must we know that?
Increases in pressure and temperature are factors responsible for changes, Metamorphic reactions take place in the solid state, Metamorphism is an isochemical process - the rock chemistry doesn’t change
Define Contact Metamorphism
Occurs when the country rock surrounding an intrusion is heated, causing the rock to recrystallise
What changes to cause contact metamorphism?
Just temperature
What are four types of contact metamorphosed rock?
Metaquartzite, Marble, Spotted rock, Hornfels
What is the original rock of metaquartzite?
Sandstone
What is the original rock of marble?
Oolitic limestone
What is the original rock of spotted rock?
Shale
What is the original rock of hornfels?
Shale
What five factors does the size of the metamorphic aureole depend on?
Initial temperature of the igneous body, Size of the igneous body, Composition of the country rock, Amount of water in the country rock, Dip of the contact affecting outcrop width on a map
What trend can develop within a metamorphic aureole?
The higher the temperature reached by the country rock, the greater the amount of recrystallisation can take place and the bigger the crystals will become
What is an indication that metamorphism has started?
Development of porphyroblasts of minerals e.g. andalusite
Define Regional Metamorphism
Occurs on a large scale and is associated with increases in both pressure and temperature
What are three types of regional metamorphosed rocks?
Slate, Schist, Gneiss
What is the original rock of slate, schist and gneiss?
Shale
Define Porphyroblastic
Crystals are of unequal sizes in metamorphic rocks
Define Granoblastic
Crystals are of equal size in metamorphic rocks
Define Non-Foliated
No layers, crystals are randomly orientated
Define Foliated
Layers formed from the alignment of crystals in metamorphic rocks, only occurs in regionally metamorphosed
Define Slaty Cleavage
Well defined, flat planes of weakness in a slate
Define Schistose
Thin, wavy lines made from mica, in a schist
Define Gneissose
Alternation of black and white monomineralic banding
