Metamorphic Rock

Question 1

metamorphic change (3)

Answer 1

Neo-crystallization
Foliation
Re-crystallization

Question 2

Plastic deformation

Answer 2

mineral grains soften and deform
increased temperature and pressure
dont break, behave plastically

Question 3

Agents of metamorphism (4)

Answer 3

1) Heat (T)
2) Pressure (P)
3) Compression and shear
4) Hot water

Question 4

Sources of heat (3)

Answer 4

1) Geothermal gradient
2) Magmatic intrusions
3) Tectonic compression

Question 5

Where does metamorphism occur?

Answer 5

2-12 Kbars = 6.5-40km

Question 6

Kinds of differential stress (2)

Answer 6

Normal stress

Shear stress

Question 7

Normal stress

Answer 7

operates perpendicular to surface

Tension-compression

Question 8

Shear stress

Answer 8

moves one part of the material sideways

causes material to be smeared out

Question 9

Shape changes due to differential stress (2)

Answer 9

Equant: equal in all dimensions
Inequant: not equal in all dimensions

Question 10

Do metamorphic rocks prefer equant of inequant dimensions

Answer 10

Inequant dimensions

Question 11

How does preferred mineral orientation develop?

Answer 11

• Shear rotation and flattening
• Shear flattens grains in a manner similar to compression
• Shear rotates grains into alignment

Question 12

Hydrothermal alteration is called _______

Answer 12

Metasomatism

Question 13

Major divisions of Metamorphic rocks (2)

Answer 13

1) foliated

2) non-foliated

Question 14

Foliated metamorphic rocks

Answer 14

• through going planar fabric
• crystallized with differential stress
• planty minerals

Question 15

Non-foliated metamorphic rocks

Answer 15

• no planar fabric
• crystalized without differential stress
• equant minerals only

Question 16

Foliation

Answer 16

• Parallel planar surfaces
• Streaked or striped appearance
• Foliated rocks often break along foliation planes

Question 17

Slate

Answer 17

Fine grained

low grade metamorphic shale

Question 18

Schist

Answer 18

Fine to course rock with larger Mica’s
medium to high grade metamorphism
shistosity (type of foliation)

Question 19

Large non-mica minerals

Answer 19

porphyroblasts

Question 20

Gneiss

Answer 20

distinct banded foliation
light bands: Feldspar/quartz
dark bands: biotite/amphibole

Question 21

compositional banding development (3)

Answer 21

1) Original layering in the protolith
2) Extensive high T shearing
3) Metamorphic differentiation

Question 22

Migmatite

Answer 22

Partially melted gneiss

feature of igneous and metamorphic rock

Question 23

Hornfels

Answer 23

alteration by heating (contact metamorphism)

baked contact by igneous rock

Question 24

Amphibolite

Answer 24

protolith of gabbro or basalt
High is Mg and Fe
foliation under differential stress

Question 25

Quartzite

Answer 25

pure quartz in composition
formed by alteration in quartz sandstone
conchoidal fractures

Question 26

Marble

Answer 26

crystalline calcite or dolomite

limestone or dolostone protolith

Question 27

Broad compositional classes (4)

Answer 27

1) Pelitic
2) Mafic
3) Calcareous
4) Quartzo

Question 28

Pelitic class

Answer 28

derived from shale protolith

Al rich so form Micas

Question 29

Mafic

Answer 29

basalt or gabbro protolith

Question 30

Calcareous

Answer 30

carbonate protolith

Question 31

Quartzo-feldspathic

Answer 31

granite protolith

Question 32

Metamorphic grade is a measure of ______

Answer 32

Intensity

Question 33

Low metamorphic grade

High metamorphic grade

Answer 33

Low T and P

High T and/or P

Question 34

Prograde metamoprphism

Answer 34

Metamorphism with increasing T and P

burial process

Question 35

Retrograde metamorphism

Answer 35

Metamorphism with decreasing T and P
Requires addition of H2O
Rocks move towards surface

Question 36

Metamorphic Facies

Answer 36

Grew in association with other rock in the same P and T
Derived from the same:
1) protolith
2) P and T conditions

Question 37

Types of Metamorphic environments (7)

Answer 37

1) Thermal
2) Burial
3) Dynamic
4) Regional
5) Hydrothermal
6) Subduction
7) Shock

Question 38

Thermal metamorphism

Answer 38

• Thermal baked contact
• Grades of alteration form aureoles around the pluton
• contact between magma and other rock

Question 39

Burial metamorphism

Answer 39

As sediments are buried in sedimentary basin: T increases due to geothermal gradient; P increase due to overburden
~8-15Km deep

Question 40

Dynamic metamorphism

Answer 40

breakage of rock due to shear forces at fault zone
Shallow (<15km): Fault Breccia
Deep (<15km): Fault Mylonite

Question 41

Regional metamorphism

Answer 41

collisions form huge “mobile belts”
Compression adds to mountain ranges
creates foliated rocks

Question 42

Hydrothermal metamorphism

Answer 42

hot water deformation

mid-ocean ridge magma

Question 43

Subduction metamorphism

Answer 43

bluesheist facies
trenches and accretionary prisms
High P - Low T
- Glaucophale: Blue amphibole

Question 44

Shock Metamorphism

Answer 44

asteroid
compressional shockwave
heat vapourizes large amount of ground
- Coesite, schisovite

Question 45

Exhumation

Answer 45

how rocks return to the surface

1) uplift
2) extensional collapse
3) erosional unrooting

Question 46

Where are most metamorphic rocks found?

Answer 46

continental interiors