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Geology > metamorphism > Flashcards

metamorphism Flashcards

1
Q

what are the agents of metamorphism

A

heat
pressure and stresses
hot fluids
not all required, they co-occur

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2
Q

recrystallization

A

minerals change size and shape
mineral identity doesn’t change
eg. limestone -> marble

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3
Q

phase change

A

new minerals forms with same chemical formula and different crystal structure
andalusite -> kyanite

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4
Q

neocrystallization

A

new minerals form from old
initial minerals became unstable, changed to new minerals
original protolith minerals digested in reaction
shale -> garnet mica schist

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5
Q

pressure solution

A

mineral grains partially dissolve
small amounts of water
minerals dissolve where surfaces press together

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6
Q

plastic deformation

A

mineral grains soften and deform
elevated p and t
change shape without breaking

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7
Q

heat metamorphism

A

between 250 and 850 degrees celcius
heat energy breaks and reforms atomic bonds
solid-state diffusion: movement of ions and atoms w/in a solid

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8
Q

pressure metamorphism

A

5-40 km depth
2-12 kbar
increase in p packs atoms more tightly together
denser minerals

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9
Q

compression

A

stress grated in one orientation
not same as pressure which is equal in all directions
common result of tectonic forces

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10
Q

shear

A

moves one part of material sideways
material is smeared out (like deck of cards)

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11
Q

equant inequant

A

equant: roughly equal in all dimensions
inequeant: uneven dimensions: platy (pancake, one dimensions shorter), elongate (cigar, one dimension longer)

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12
Q

preferred orientation

A

compression and shear combine with elevated P and T. rocks change shape without breaking. internal textures can also change

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13
Q

hydrothermal fluid metamorphism

A

hot water dissolves ions and volatiles
facilitates metamorphism (accelerate chemical reactions and alter rocks by adding subtracting elements)

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14
Q

foliated rocks

A

parallel surfaces or layers in metamorphic rocks
inequant grains or compositional banding alignment

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15
Q

slate

A

FMR
fine grained
low grade metamoprhic shale
slaty cleavage develops perpendicular to compression
slate breaks along parallel foliation

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16
Q

phyllite

A

FMR
fine-grained
mica-rich
made from slate
clay minerals neocrystallize into tiny micas
silky sheen

17
Q

schist

A

FMR
larger micas
formed at higher temp than phyllite
distinct foliation from large micas

18
Q

gneiss

A

FMR
destinct compositional bands, often contorted
light bands of FELSIC
dark bands of MAFIC

19
Q

how does gneissic banding develop?

A

original layering in protolith
extensive high T shearing
metamorphic differentiation (minerlas segregate into layers)

20
Q

compositional banding

A

solid-state differentiation
chemical reactions segregate light and dark layers

21
Q

migmatite

A

partially melted gneiss
features of igneous and metamorphic rocks

22
Q

felsic vs mafic mineralogy

A

LIGHT = FELSIC = MELT AT LOWER T
DARK = MAFIC = MELT AT HIGHTER T
felsic banfs melt and recrystallize in gneiss

23
Q

nonfoliated metamorphic rocks

A

no planar fabric evident
recrystallized without compression or shear
equant minerals

24
Q

hornfels

A

NFMR
fine grained
metamorphic clay minerals sedimented as mudstone protolith
plutonic intrusions

25
Q

quartzite

A

almost pure quartz
alteration of quartz sandstone
sand grains recrystallize and fuse
hard glassy and resistant
breaks by conchoidal fracture

26
Q

marble

A

coarsely crystalline calcite or dolomite
forms from limestone protolith
recrystallization changes rock
original textures and fossils OBLITERATED

27
Q

metamorphic grade

A

low: weak metamorphism
high: intense metamorphism
as grade increases, new and larger minerals form

28
Q

increasing metamorphism of shale protolith

A

low: shale protolith (recrystallize into slate, neocrystallize into micas in a phyllite)
intermediate: micas recrystallize and grow to form schist
high grade: micas decompose, neocrystallization yields quartz and feldspars in gneiss

29
Q

index minerals

A

specific P and T range
metamorphic zones defined by index minerals

30
Q

CBD SHRS

A

contact
burial
dynamic
shock
regional
hydrothermal
subduction

31
Q

contact metamorphism

A

heat from magma invading host rock
zoned bands of alteration in host rock
aureole surrounds plutonic intrusion

32
Q

burial metamorphism

A

p increases because of weight of overburden
t increases because of geothermal gradient
8-15 km depth, sediments metamorphose

33
Q

dynamic metamorphism

A

breakage of rock by shearing at fault zone
shallow: brittle - minerals crush
deeper: ductile - minerals smear

34
Q

regional metamorphism

A

tectonic collisions deform huge mobile belts
rocks are heated, squeeze, smashed and deformed

35
Q

hydrothermal metamorphism

A

alteration by hot chemically agressive water
dominant near MOR magma
cold ocean water seeps into fractured crust
heated water reacts with mafic rock
hot water rises and ejected via black smoker

36
Q

subduction metamorphism

A

creates blueschist facies
low T high P (low geothermal gradient)

37
Q

exhumation

A

due to CUE
collapse, uplift, erosion
how metamorphics rocks return to surface

38
Q

shields

A

large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas

Geology (19 decks)

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