metamorphic rocks

Question 1

definition

metamorphism

Answer 1

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

Question 2

factors that control

agents of metamorphism

Answer 2

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

Question 3

prograde metamorphism

Answer 3

due to increasing T and P, burial

Question 4

retrograde metamorphism

Answer 4

due to decreasing T and P, exhumation

Question 5

conditions for metamorphism

Answer 5

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

Question 6

mineralogical changes

neocrystallization

Answer 6

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

old minerals become unstable and change

Question 7

mineralogical changes

recrystallization

Answer 7

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

Question 8

mineralogical changes

phase transitions

Answer 8

structural changes in minerals (polymorphs)

Question 9

metamorphic grade

Answer 9

intensity of metamorphism, discussed in terms of temp

Question 10

textural changes

Answer 10

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

Question 11

foliation

Answer 11

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

Question 12

lineation

Answer 12

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

Question 13

non-foliated rocks

Answer 13

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

Question 14

porphyroblastic texture

Answer 14

large crystals, prophysoblasts, surrounded by matrix

similar to porphyritic texture in igneous rocks

Question 15

special rock names

quartzite

Answer 15

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

protolith typically sandstone

Question 16

special rock names

marble

Answer 16

metamorphic rock composed predominantly of calcite or dolomite

protolith typically limestone or dolostone

Question 17

special rock names

amphibolite

Answer 17

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

protolith typically basalt

Question 18

special rock names

migmatite

Answer 18

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

Question 19

metamorphic environments

thermal (contact) metamorphism

Answer 19

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

Question 20

metamorphic environments

regional metamorphism

Answer 20

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

creates foliated rocks

Question 21

metasomatism

Answer 21

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

Question 22

regional metamorphism

dynamothermal metamorphism

Answer 22

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

creates foliated rocks

Question 23

regional metamorphic environments

subduction

Answer 23

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)

Question 24

collisional metamorphic belts

Answer 24

often thousands of km long, hundreds of km wide

Question 25

# regional metamorphic environments sea floor metamorphism

Answer 25

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)

Question 26

# regional metamorphic environments shock

Answer 26

extreme high P attending a bolide (meteorite) impact | quartz low pressure tolerance, changes to coesite (SiO)

Question 27

metamorphic facies

Answer 27

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

Question 28

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

Answer 28

# definition metamorphism

Question 29

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

Answer 29

# factors that control agents of metamorphism

Question 30

due to increasing T and P, **burial**

Answer 30

prograde metamorphism

Question 31

due to decreasing T and P, **exhumation**

Answer 31

retrograde metamorphism

Question 32

* temp: between ~200°C and melting (~650°-1200°) * time: millions of years

Answer 32

conditions for metamorphism

Question 33

new minerals form through solid state, chemical changes, from old | old minerals become unstable and change

Answer 33

# mineralogical changes neocrystallization

Question 34

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

Answer 34

# mineralogical changes recrystallization

Question 35

structural changes in minerals (**polymorphs**)

Answer 35

# mineralogical changes phase transitions

Question 36

intensity of metamorphism, discussed in terms of temp

Answer 36

metamorphic grade

Question 37

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

Answer 37

textural changes

Question 38

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

Answer 38

foliation

Question 39

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

Answer 39

lineation

Question 40

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

Answer 40

non-foliated rocks

Question 41

large crystals, **prophysoblasts**, surrounded by matrix | similar to porphyritic texture in igneous rocks

Answer 41

porphyroblastic texture

Question 42

metamorphic rock composed predominantly of **quartz**, recrystallized to make coarser, non-foliation | protolith typically sandstone

Answer 42

# special rock names quartzite

Question 43

metamorphic rock composed predominantly of **calcite or dolomite** | protolith typically limestone or dolostone

Answer 43

# special rock names marble

Question 44

metamorphic rock dominated by hornblende + plagioclase, may be foliated or not | protolith typically basalt

Answer 44

# special rock names amphibolite

Question 45

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

Answer 45

# special rock names migmatite

Question 46

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

Answer 46

# metamorphic environments thermal (contact) metamorphism

Question 47

vast areas of *metamorphic belts*, often associated with compressional tectonics (subduction and collision) | creates foliated rocks

Answer 47

# metamorphic environments regional metamorphism

Question 48

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

Answer 48

metasomatism

Question 49

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

Answer 49

# regional metamorphism dynamothermal metamorphism

Question 50

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)

Answer 50

# regional metamorphic environments subduction

Question 51

often thousands of km long, hundreds of km wide

Answer 51

collisional metamorphic belts

Question 52

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)

Answer 52

# regional metamorphic environments sea floor metamorphism

Question 53

extreme high P attending a bolide (meteorite) impact | quartz low pressure tolerance, changes to coesite (SiO)

Answer 53

# regional metamorphic environments shock

Question 54

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

Answer 54

metamorphic facies