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EOS 120 > Meatamorphic Processes and Rocks > Flashcards

Meatamorphic Processes and Rocks Flashcards

1
Q

what is metamorphism?

A

Change that occurs when pre-existing rocks (protoliths) experience conditions different from those in which they formed

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2
Q

during metamorphism what changes in the rock?

A

Texture and/or Mineralogy/Composition

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3
Q

What controls metamorphic processes?

A

Composition of parent rock
Fluids (-> composition changes)
Temperature
Pressure

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4
Q

what are the 2 main types of metamorphism?

A

(1) Contact metamorphism (local)

2) Regional metamorphism (large-scale

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5
Q

what is Contact metamorphism?

A

Magma intrusions bake (T increase) surrounding rock

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6
Q

what is Regional metamorphism?

A

Associated with plate interactions (usually involves P & T increases, depth increases)

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7
Q

where does contact metamorphism occur?

A

magma chambers of volcanoes

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8
Q

where does regional metamorphism occur?

A

volcanoes and mountains at subduction zones

mid-ocean ridges

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9
Q

how does pressure change occur to metamorphic rocks?

A

rock is subducted

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10
Q

how does temp. change occur to metamorphic rocks?

A

magma rises and heats rocks

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11
Q

how does composition change occur to metamorphic rocks?

A

fluid gets into rock fractures

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12
Q

how does pressure and temp. change occur to metamorphic rocks?

A

Orogens (e.g., continent-continent collision)
Crustal thickening
Rocks move up/down P and/or T

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13
Q

what does compression lead to?

A

thickening, burial (or uplift)

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14
Q

How do high-P high-T metamorphic rocks get to the surface?

A

Uplift

Erosion

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15
Q

what are the drivers of metamorphism?

A

(1) Pressure
(2) Temperature
(3) Fluids

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16
Q

what is Confining Pressure (uniform stress)?

A

the load of the overlying rock= 1 kilobar for 3 km of burial

17
Q

what is Directed Pressure (differential stress)?

A

unequal pressure from plate tectonics (compression, tensional, shear) -> distortion

18
Q

what do Increases in Pressure favour?

A

dense, compact crystal structures

19
Q

what is foliation?

A

Under directed pressure (stress), rocks develop a foliation due to the alignment of minerals
Minerals realign at right angles to P
Equidimensional minerals get squashed
New minerals crystallise in the preferred orientation

20
Q

give some examples of metamorphic rocks from those formed in lower pressure, lower temps. to those formed in higher pressures, higher temps

A 
Shale
Slate
Phyllite
Schist
Gneiss
21
Q

temp. increases with…

A

depth (geothermal gradient)

22
Q

geothermal varies with…

A

tectonic setting

23
Q

temp in the crust is (also) influenced by…

A

intrusion of magma bodies

24
Q

what do increases in temp. promote?

A

reactions to form new minerals, lower density phases, increased ductility

25
Q

what happens during recrystallisation?

A

Pre-existing grains may recrystallise into larger crystals of the same mineral

e. g. limestone -> marble
e. g. quartz sandstone -> quartzite

26
Q

give some examples of rocks from least metamorphic grade to most?

A 
slate
phyllite
blueschist/schist
gneiss
migmatite
27
Q

what does the mineralogy of metamorphic rocks depend on?

A

bulk composition, P–T conditions (& action of hot fluids)

28
Q

Metamorphic minerals…

A

Nearly all minerals in igneous and sedimentary rocks can occur in metamorphic rocks but some minerals occur exclusively in metamorphic rocks

29
Q

Metamorphic Index Minerals form at…

A

distinct P and T conditions
e.g. Andalusite (Al2SiO5), Sillimanite (Al2SiO5), Kyanite (Al2SiO5) all have the same formula but they form at different pressure and temp.

30
Q

which minerals are not useful as index minerals?

A

ones with a wide stability range e.g. quartz, feldspar

31
Q

what is an example of fluid metamorphism?

A

Hydrothermal metamorphism at mid-ocean ridges
basalt -> greenstone
H2O is added

32
Q

when H2O is added what does pyroxene turn into?

A

Chlorite
Epidote
Actinolite

EOS 120 (24 decks)

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