metamorphism

Question 1

what are the agents of metamorphism

Answer 1

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

Question 2

recrystallization

Answer 2

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

Question 3

phase change

Answer 3

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

Question 4

neocrystallization

Answer 4

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

Question 5

pressure solution

Answer 5

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

Question 6

plastic deformation

Answer 6

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

Question 7

heat metamorphism

Answer 7

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

Question 8

pressure metamorphism

Answer 8

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

Question 9

compression

Answer 9

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

Question 10

shear

Answer 10

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

Question 11

equant inequant

Answer 11

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

Question 12

preferred orientation

Answer 12

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

Question 13

hydrothermal fluid metamorphism

Answer 13

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

Question 14

foliated rocks

Answer 14

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

Question 15

slate

Answer 15

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

Question 16

phyllite

Answer 16

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

Question 17

schist

Answer 17

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

Question 18

gneiss

Answer 18

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

Question 19

how does gneissic banding develop?

Answer 19

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

Question 20

compositional banding

Answer 20

solid-state differentiation
chemical reactions segregate light and dark layers

Question 21

migmatite

Answer 21

partially melted gneiss
features of igneous and metamorphic rocks

Question 22

felsic vs mafic mineralogy

Answer 22

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

Question 23

nonfoliated metamorphic rocks

Answer 23

no planar fabric evident
recrystallized without compression or shear
equant minerals

Question 24

hornfels

Answer 24

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

Question 25

quartzite

Answer 25

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

Question 26

marble

Answer 26

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

Question 27

metamorphic grade

Answer 27

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

Question 28

increasing metamorphism of shale protolith

Answer 28

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

Question 29

index minerals

Answer 29

specific P and T range metamorphic zones defined by index minerals

Question 30

CBD SHRS

Answer 30

contact burial dynamic shock regional hydrothermal subduction

Question 31

contact metamorphism

Answer 31

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

Question 32

burial metamorphism

Answer 32

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

Question 33

dynamic metamorphism

Answer 33

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

Question 34

regional metamorphism

Answer 34

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

Question 35

hydrothermal metamorphism

Answer 35

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

Question 36

subduction metamorphism

Answer 36

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

Question 37

exhumation

Answer 37

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

Question 38

shields

Answer 38

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