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geology 209 > metamorphic rocks > Flashcards

metamorphic rocks Flashcards

1
Q

definition

metamorphism

A

solid state changes in a rock when it is subjected to conditions other than that in which it formed

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2
Q

factors that control

agents of metamorphism

A

temperature and pressure, fluids (change the minerology/composition)

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3
Q

prograde metamorphism

A

due to increasing T and P, burial

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4
Q

retrograde metamorphism

A

due to decreasing T and P, exhumation

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5
Q

conditions for metamorphism

A
  • temp: between ~200°C and melting (~650°-1200°)
  • time: millions of years
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6
Q

mineralogical changes

neocrystallization

A

new minerals form through solid state, chemical changes, from old

old minerals become unstable and change

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7
Q

mineralogical changes

recrystallization

A

pre-existing minerals change size and shape
- mineral identity doesnt change
- forming bigger crystals reduces the energy of the system (when heat is added)

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8
Q

mineralogical changes

phase transitions

A

structural changes in minerals (polymorphs)

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9
Q

metamorphic grade

A

intensity of metamorphism, discussed in terms of temp

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10
Q

textural changes

A

compression and shear at elevated T and P cause changes in internal texture of rocks
- minerals rotate into preferred orientations

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11
Q

foliation

A

minerals lined up in planes in metamorphic rocks, streaked or striped appearance
- direct pressure aligns minerals
- foliated rocks break along foliation planes
- foliation form by preferred orientation of minerals with an inequant habit

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12
Q

lineation

A

linear alignment of minerals within a metamorphic rock, like a bundle of drinking straws
- direct pressure aligns minerals during metamorphism

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13
Q

non-foliated rocks

A

metamorphic minerals randomly orientated
- no directed pressure during formation, equal stresses
- no preferred shape

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14
Q

porphyroblastic texture

A

large crystals, prophysoblasts, surrounded by matrix

similar to porphyritic texture in igneous rocks

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15
Q

special rock names

quartzite

A

metamorphic rock composed predominantly of quartz, recrystallized to make coarser, non-foliation

protolith typically sandstone

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16
Q

special rock names

marble

A

metamorphic rock composed predominantly of calcite or dolomite

protolith typically limestone or dolostone

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17
Q

special rock names

amphibolite

A

metamorphic rock dominated by hornblende + plagioclase, may be foliated or not

protolith typically basalt

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18
Q

special rock names

migmatite

A

composite silicate rock, commonly has dark gneissic matrix and lighter felsic portions
- high grade rock that underwent some melting
- first stages of magma
- granitite melt pods

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19
Q

metamorphic environments

thermal (contact) metamorphism

A

due to heat from magma invading country rock, creates zones of metamorphism in country rock called contact aureole
- aureole typically concentric with the pluton
- zoned from high (near pluton) to low grade (far from pluton)
- dominant rock is hornsfels

aureole zone typically < 1km in width, usually no foliated rocks

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20
Q

metamorphic environments

regional metamorphism

A

vast areas of metamorphic belts, often associated with compressional tectonics (subduction and collision)

creates foliated rocks

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21
Q

metasomatism

A

bulk composition of rock changes often due to fluids adding or removing elements
- fluids from magma can affect country stone

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22
Q

regional metamorphism

dynamothermal metamorphism

A

rocks caught up in mountain building are
- heated via geothermal gradient and plutonic intrusions
- squeezed and sheared by different stresses

creates foliated rocks

23
Q

regional metamorphic environments

subduction

A

basalt is metamorphosed
subducting plate - low T high P
- blueschiest (only forms here)
- eclogite (high density, causes slab pull)
volcanic arc - high T high P (overriding plate)

24
Q

collisional metamorphic belts

A

often thousands of km long, hundreds of km wide

25
Q

regional metamorphic environments

sea floor metamorphism

A

low-med T low P
- magma from MOR heats up plate/water
- current of hot water can metamorphose rocks (hydrothermal metamorphism)
- chlorite common (green mica)

26
Q

regional metamorphic environments

shock

A

extreme high P attending a bolide (meteorite) impact

quartz low pressure tolerance, changes to coesite (SiO)

27
Q

metamorphic facies

A

the names of facies on a P-T diagram reflect minerals and mineral-assemblages that are stable at these conditions and provide info on the metamorphic processes that have affected the rocks

useful to interpret the history of a metamorphic rock

28
Q

solid state changes in a rock when it is subjected to conditions other than that in which it formed

A

definition

metamorphism

29
Q

temperature and pressure, fluids (change the minerology/composition)

A

factors that control

agents of metamorphism

30
Q

due to increasing T and P, burial

A

prograde metamorphism

31
Q

due to decreasing T and P, exhumation

A

retrograde metamorphism

32
Q
  • temp: between ~200°C and melting (~650°-1200°)
  • time: millions of years
A

conditions for metamorphism

33
Q

new minerals form through solid state, chemical changes, from old

old minerals become unstable and change

A

mineralogical changes

neocrystallization

34
Q

pre-existing minerals change size and shape
- mineral identity doesnt change
- forming bigger crystals reduces the energy of the system (when heat is added)

A

mineralogical changes

recrystallization

35
Q

structural changes in minerals (polymorphs)

A

mineralogical changes

phase transitions

36
Q

intensity of metamorphism, discussed in terms of temp

A

metamorphic grade

37
Q

compression and shear at elevated T and P cause changes in internal texture of rocks
- minerals rotate into preferred orientations

A

textural changes

38
Q

minerals lined up in planes in metamorphic rocks, streaked or striped appearance
- direct pressure aligns minerals
- foliated rocks break along foliation planes
- foliation form by preferred orientation of minerals with an inequant habit

A

foliation

39
Q

linear alignment of minerals within a metamorphic rock, like a bundle of drinking straws
- direct pressure aligns minerals during metamorphism

A

lineation

40
Q

metamorphic minerals randomly orientated
- no directed pressure during formation, equal stresses
- no preferred shape

A

non-foliated rocks

41
Q

large crystals, prophysoblasts, surrounded by matrix

similar to porphyritic texture in igneous rocks

A

porphyroblastic texture

42
Q

metamorphic rock composed predominantly of quartz, recrystallized to make coarser, non-foliation

protolith typically sandstone

A

special rock names

quartzite

43
Q

metamorphic rock composed predominantly of calcite or dolomite

protolith typically limestone or dolostone

A

special rock names

marble

44
Q

metamorphic rock dominated by hornblende + plagioclase, may be foliated or not

protolith typically basalt

A

special rock names

amphibolite

45
Q

composite silicate rock, commonly has dark gneissic matrix and lighter felsic portions
- high grade rock that underwent some melting
- first stages of magma
- granitite melt pods

A

special rock names

migmatite

46
Q

due to heat from magma invading country rock, creates zones of metamorphism in country rock called contact aureole
- aureole typically concentric with the pluton
- zoned from high (near pluton) to low grade (far from pluton)
- dominant rock is hornsfels

aureole zone typically < 1km in width, usually no foliated rocks

A

metamorphic environments

thermal (contact) metamorphism

47
Q

vast areas of metamorphic belts, often associated with compressional tectonics (subduction and collision)

creates foliated rocks

A

metamorphic environments

regional metamorphism

48
Q

bulk composition of rock changes often due to fluids adding or removing elements
- fluids from magma can affect country stone

A

metasomatism

49
Q

rocks caught up in mountain building are
- heated via geothermal gradient and plutonic intrusions
- squeezed and sheared by different stresses

creates foliated rocks

A

regional metamorphism

dynamothermal metamorphism

50
Q

basalt is metamorphosed
subducting plate - low T high P
- blueschiest (only forms here)
- eclogite (high density, causes slab pull)
volcanic arc - high T high P (overriding plate)

A

regional metamorphic environments

subduction

51
Q

often thousands of km long, hundreds of km wide

A

collisional metamorphic belts

52
Q

low-med T low P
- magma from MOR heats up plate/water
- current of hot water can metamorphose rocks (hydrothermal metamorphism)
- chlorite common (green mica)

A

regional metamorphic environments

sea floor metamorphism

53
Q

extreme high P attending a bolide (meteorite) impact

quartz low pressure tolerance, changes to coesite (SiO)

A

regional metamorphic environments

shock

54
Q

the names of facies on a P-T diagram reflect minerals and mineral-assemblages that are stable at these conditions and provide info on the metamorphic processes that have affected the rocks

useful to interpret the history of a metamorphic rock

A

metamorphic facies

geology 209 (8 decks)

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