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EAS 210 > CHPTR 7 Metamorphic Rocks > Flashcards

CHPTR 7 Metamorphic Rocks Flashcards

1
Q

protolith

A

parent rock

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2
Q

metamorphism

A

transformation of rocks as the result of heat, pressure, or fluid activities

  • below melting point BUT higher pressure and temp. than lithification
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3
Q

lithostatic pressure

A

uniform stress/confining pressure
uniform field of pressure experienced by most rocks beneath Earth’s surface

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4
Q

directed pressure (differential stress

A

pushes mineral grains into one direction

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5
Q

geothermal gradient

A

25-30 degrees C

the rate at which the Earth’s temperature increases with depth

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6
Q

what can provide heat for the metamorphic process + how

A

burial increases temp. - the deeper you go, the hotter it is

volcanoes - heat from intrusions and lava flow heats underlying rocks

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7
Q

confining pressure + example

A

uniform stress in all direction - lithostatic stress

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8
Q

lithostatic stress

A

pressure experienced by rocks under the Earth’s surface

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9
Q

pressure due to 1km of rock

A

25 - 30 MPa

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10
Q

directed pressure

A

differential stress - pushes mineral grains into one direction

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11
Q

metastomatism

A

metamorphism due to fluid activity

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12
Q

how does fluid activity affect metamorphism

A

accelerate chemical change which can cause new minerals to form

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13
Q

origins of fluids that influence metamorphic activity (4)

A
  1. trapped in pore space in rocks
  2. released by magma
  3. dehydration reactions
  4. hydrothermal circulation
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14
Q

metamorphic processes (7)

A
  1. orientation of mineral grains
  2. recrystallization of existing minerals
  3. growth of new minerals
  4. segregation of minerals
  5. baking
  6. shearing
  7. partial melting
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15
Q

controlling factors in metamorphism

A

heat, pressure, fluids

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16
Q

index minerals for metamorphism grade

A

low to high
chlorite
muscovite
biotite
garnet / kyanite
staurolite
sillimanite

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17
Q

3 horrible index minerals for metamorphism

A

andalusite, quartz, feldspar

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18
Q

what do andalusite, kyanite and sillimanite have in common

A

polymorphs

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19
Q

what causes kyanite vs sillimanite

+ why don’t i care about andalusite

A

kyanite - high pressure
sillimanite - high temperature

andalusite is a bad index mineral

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20
Q

foliated texture

A

stripes - produced by the preferred orientation of platy minerals

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21
Q

non-foliated texture

A

do not exhibit preferred orientation of minerals

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22
Q

burial metamorphism

A

low temp, low pressure, just rocks underground

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23
Q

contact metamorphism

A

high temp, low pressure
near a magma chamber and the surface

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24
Q

aureoles

A

metamorphosed zones that surround plutons or other intrusions - its from contact metamorphism

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25
Q

how does distance from a pluton affect metamorphic grade

A
  • high grade metamorphism close to pluton, low grade farther away
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26
Q

regional metamorphism

A

most common metamorphism
occurs during subduction or continent-continent collision

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27
Q

Barrovian metamorphism protolith

A

shale

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28
Q

pelitic protolith

A

shale protolith

29
Q

Barrovian metamorphic process

A

shale
slate
phyllite
shist
gneiss

30
Q

what metamorphic grade does biotite and garnet signify

A

intermediate

31
Q

what metamorphic grade does chlorite signify

A

low grade

32
Q

economic significance of plutons/contact metamorphism

A

as pluton cools, hydrothermal circulation occurs by the fluids released from crystallizing rock and groundwater.

This fluid concentrate minerals and form deposits of economic minerals

33
Q

slate features?

A
  • foliated
  • created through grain reorientation
34
Q

phyllite features?

A

foliated - platy minerals cannot be seen by eye

  • identified by glossy, lustrous sheen
  • recrystallization; results in coarser grains
35
Q

what metamorphic grade does sillimanite signify

A

high grade

36
Q

slate foliated?

A

foliated

37
Q

schist features + what’s unique about it at a higher grade

A

foliated - schistocity
>50% platy material
garnet and staurolite porphyroblasts appear at higher grade

38
Q

most common metamorphic rock formed by regional metamorphism

A

schist

39
Q

porphyroblasts

A

large mineral crystal that disrupts the mineral grain in metamorphic rocks

40
Q

gneiss features

A

foliated
banding - bandss of black and white rock
more granular minerals than platy minerals

41
Q

minerals present in the light colour in gneiss

A

quartz, feldspar

42
Q

minerals present in the dark colour in gneiss

A

biotite, amphibole

43
Q

oldest dated rock

A

Acasta Gneiss

44
Q

migmatite

A

has a mixture of apparently igneous and metamorphic components. Like liquid stripes

  • signifies partial melting
45
Q

prograde metamorphism

A

increasing grade

46
Q

retrograde metamorphism

A

decreasing grade

47
Q

metamorphic zone

A

area with same degree of metamorphism

48
Q

is marble foliated

A

nope

49
Q

marble’s predominant minerals

A

calcite/dolomite

50
Q

what does limestone metamorphise into

A

marble

51
Q

what does quartz metamorphise into

A

quartzite

52
Q

what does mafic igneous rocks metamorphise into

A

greenstone, amphibolite, granulite eclogite

53
Q

eclogite features

A
  • often contains pink garnet
  • stable at mantle pressures
  • high density
54
Q

what does felsic rocks metamorphis into

A

gneiss

55
Q

impact metamorphism

A

asteroid hit Earth/underground nuclear explosions
- lots of pressure

56
Q

when the Earth was hit by an asteroid what rocks were formed

A
  • shocked quartz
  • coesite
  • stishovite
57
Q

dynamic metamorphism

A

formed in fault zones due to high strains

58
Q

cataclasites

A

forms in shallow part of faults

59
Q

what causes cataclastic texture

A

shallow faults which result in crushing and grinding of rocks

60
Q

mylonites

A

forms in deeper part of faults (10-20km)

61
Q

hydrothermal metamorphism - mid ocean ridges process

A
  • freshly erupted basalt and gabbro are erupted from ocean volcano and still hot
  • salt water percolates into the rocks. it cools into a new oceanic crust
  • mineral reaction occurs: olivine into serpentine
62
Q

hydrothermal metamorphism - plutons

A
  • plutons cools, releasing water from the magma
  • water invades surrounding rocks creating pegmatite
63
Q

blueschist facies

A

low T, high P - the upper part of a subduction zone

64
Q

zeolite facies

A

burial metamorphism

65
Q

eclogite facies

A

high T, high P. the lower part of a subduction zone

66
Q

shield

A

area where pre-Cambrian igneous and metamorphic rocks are exposed at the surface

67
Q

platform

A

area where igneous-metamorphic basement overlain by sedimentary rocks

68
Q

cratons

A

formed by a combination of shield and platform

69
Q

distribution of metamorphic rock

A
  1. shields
  2. cores of mountain ranges - (continent continent collision)

EAS 210 (20 decks)

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