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metamorphic rocks Flashcards

1
Q

metamorphism

A

changing an existing rock into a new rock through exposure to temperature and pressure different to those in which it formed

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2
Q

name given to rock before metamorphism

A

protolith

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3
Q

stages of metamorphism

A
  1. protolith exposed to different pressure and temperature
  2. the molecules in the protolith are no longer in equilibrium
  3. molecules remobilise
  4. recrystallisation
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4
Q

in what state does recrystallisation occur

A

solid

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5
Q

TRUE/FALSE

melting occurs before recrystallisation

A

FALSE, no melting

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6
Q

what forms from protolith? how different is the metamorphic rock?

A

new mineral or same mineral in different orientation.

bulk chemistry doesn’t change

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7
Q

metamorphic rock crystalline or amorphous?

A

crystalline

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8
Q

3 main things that force the change in metamorphism

A
  1. temperature - most important factor
  2. pressure
  3. chemically active pore fluids - increase speed of reaction
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9
Q

3 types of metamorphism

A
  1. contact
  2. dynamic (cataclastic)
  3. regional
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10
Q

contact metamorphism

A

due to heat from igneous intrusions. high temperature and low pressure. Generally localised

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11
Q

dynamic (cataclastic) metamorphism

A

due to high local stresses along fault zones. high pressure, low temp

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12
Q

regional metamorphism

A

occurs over large areas and generally occurs deep in the crust. high temp and pressure are important

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13
Q

metamorphic grade

A

refers to the relative intensity of metamorphism. Increases with temperature and pressure

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14
Q

____ grade characterised by hydrous minerals. _______ grade non-hydrous. And _______ grade less hydrous.

A

low, high, medium

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15
Q

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 _________ ______.

A

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.

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16
Q

contact metamorphism in mudstone produces….?

A

hornfels, a dark, finely crystalline rock which is granular.

17
Q

contact metamorphism of protoliths of dominantly one mineral

A

mineral recrystallises to fill previous voids

18
Q

marble formation

A

protolith is limestone.

19
Q

quartzite formation

A

protolith is sandstone with a very high quartz content (SiO2)

20
Q

what causes the colours in marble and quartzite

A

Impurities cause the colour

21
Q

Dynamic/ cataclastic metamorphism details of action.

A

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.

22
Q

mylonite

A

formed at fault at great depth. foliated - very fine grained with large isolated crystals (porphyroblasts) ‘smeared’

23
Q

type of pressure and consequences of it, in regional metamorphism

A

differential stress which causes volume and shape change leading to foliated rocks

24
Q

platy minerals (e.g micas) tend to grow with sheet structures ___________ to direction of max pressure

A

perpindicular

25
Q

order these with low grade metamorphism first ‘ slaty cleavage’ ‘gneissic layering’ ‘schistosity’

A
  1. slaty cleavage
  2. schistosity
  3. gneissic layering
26
Q

slate: grade and protolith

A

low grade.
sheet silicates (mica)
mudstone, basalt

27
Q

phyllite: grade and protolith and structure.

A 
low grade (higher than slate). mudstone basalt
structure is crinkled continuous foliation. mica minerals (sheet silicates)
28
Q

schist: grade, protolith and structure.

A

medium grade.
continuous foliation, due to sheet silicates, with some minerals visible.
Protolith mudstone, igneous rocks.

29
Q

Gneiss: grade, protolith and structure.

A

HIgh grade.
discontinuous foliation, with segregated bands.
Protolith: felsic igneous rock (granite)

30
Q

Migmatite: grade, protolith and structure

A

very high grade.

coarse grained and wavy baby.

31
Q

strength of granular vs foliated rocks

A

granular rocks are strong if unaltered, whereas foliated rocks are similar to sedimentary rocks in that they have a tendancy to fail.

32
Q

granular rocks have similar properties to what?

A

intrusive igneous rocks

yeah rocks (16 decks)

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