metamorphic rocks Flashcards
metamorphism
changing an existing rock into a new rock through exposure to temperature and pressure different to those in which it formed
name given to rock before metamorphism
protolith
stages of metamorphism
- protolith exposed to different pressure and temperature
- the molecules in the protolith are no longer in equilibrium
- molecules remobilise
- recrystallisation
in what state does recrystallisation occur
solid
TRUE/FALSE
melting occurs before recrystallisation
FALSE, no melting
what forms from protolith? how different is the metamorphic rock?
new mineral or same mineral in different orientation.
bulk chemistry doesn’t change
metamorphic rock crystalline or amorphous?
crystalline
3 main things that force the change in metamorphism
- temperature - most important factor
- pressure
- chemically active pore fluids - increase speed of reaction
3 types of metamorphism
- contact
- dynamic (cataclastic)
- regional
contact metamorphism
due to heat from igneous intrusions. high temperature and low pressure. Generally localised
dynamic (cataclastic) metamorphism
due to high local stresses along fault zones. high pressure, low temp
regional metamorphism
occurs over large areas and generally occurs deep in the crust. high temp and pressure are important
metamorphic grade
refers to the relative intensity of metamorphism. Increases with temperature and pressure
____ grade characterised by hydrous minerals. _______ grade non-hydrous. And _______ grade less hydrous.
low, high, medium
contact metamorphism. caused by localised _____ by an _________ ________. _________ is the dominant agency. generally occurs at _______ depths where pressure is ____. Produces ________ rocks. Heating occurs in a band around the intrusion called the _________ ______.
contact metamorphism. caused by localised heating by an igneous intrusion. temperature is the dominant agency. generally occurs at shallow depths where pressure is low. Produces granular rocks. Heating occurs in a band around the intrusion called the metamorphic aureole.
contact metamorphism in mudstone produces….?
hornfels, a dark, finely crystalline rock which is granular.
contact metamorphism of protoliths of dominantly one mineral
mineral recrystallises to fill previous voids
marble formation
protolith is limestone.
quartzite formation
protolith is sandstone with a very high quartz content (SiO2)
what causes the colours in marble and quartzite
Impurities cause the colour
Dynamic/ cataclastic metamorphism details of action.
occurs due to rupturing and movement of rocks along a fault. Rocks nearest the fault are often intensely deformed and reconstituted. Shear stress aligns minerals as they recrystallise.
mylonite
formed at fault at great depth. foliated - very fine grained with large isolated crystals (porphyroblasts) ‘smeared’
type of pressure and consequences of it, in regional metamorphism
differential stress which causes volume and shape change leading to foliated rocks
platy minerals (e.g micas) tend to grow with sheet structures ___________ to direction of max pressure
perpindicular
order these with low grade metamorphism first ‘ slaty cleavage’ ‘gneissic layering’ ‘schistosity’
- slaty cleavage
- schistosity
- gneissic layering
slate: grade and protolith
low grade.
sheet silicates (mica)
mudstone, basalt
phyllite: grade and protolith and structure.
low grade (higher than slate). mudstone basalt structure is crinkled continuous foliation. mica minerals (sheet silicates)
schist: grade, protolith and structure.
medium grade.
continuous foliation, due to sheet silicates, with some minerals visible.
Protolith mudstone, igneous rocks.
Gneiss: grade, protolith and structure.
HIgh grade.
discontinuous foliation, with segregated bands.
Protolith: felsic igneous rock (granite)
Migmatite: grade, protolith and structure
very high grade.
coarse grained and wavy baby.
strength of granular vs foliated rocks
granular rocks are strong if unaltered, whereas foliated rocks are similar to sedimentary rocks in that they have a tendancy to fail.
granular rocks have similar properties to what?
intrusive igneous rocks
