Metamorphic Rocks

Question 1

What is metamorphism?

Answer 1

The recrystallisation of pre-existing rock in a solid solution via pressure and/or heat

Question 2

What is contact metamorphism?

Answer 2

Localised in a metamorphic aureole. The predominant force is heat (pressure present too). When magma intrudes country

Question 3

Are we likely to see alignment/foliation with contact metamorphism?

Answer 3

No, as there is little pressure

Question 4

What is regional metamorphism?

Answer 4

Larger regional area. The predominant force is pressure. Happens at convergent boundaries at subduction and collision zones

Question 5

Are we likely to see alignment/foliation with regional metamorphic?

Answer 5

Yes, as there is significant pressure

Question 6

What is dynamic metamorphism also known as?

Answer 6

Cataclasis

Question 7

What is dynamic metamorphism?

Answer 7

Happens in fault zones, where rocks are moving past each other suddenly. Rocks are old, cold, brittle - causing rocks to be crushed, resulting in angular clasts. (cataclasis)
Then recrystallisation to hold clasts together

Question 8

What is foliation?

Answer 8

Formed by the preferred alignment of flat, platy minerals (micas, clays). These must be present along with pressure. Usually formed during regional metamorphism

Question 9

What is the sequence of regional metamorphic rocks starting with shale?

Answer 9

Shale - Parent rock
Slate, phyllite, schist, gneiss

Question 10

What would happen if gneiss undergoes more pressure?

Answer 10

It would melt

Question 11

What is shale made up of?

Answer 11

clays and quartz

Question 12

What is slate?

Answer 12

Foliated and has slaty cleavage. Made of micas. Low grade metamorphism

Question 13

What is phyllite?

Answer 13

Wavy foliation, made of micas

Question 14

What is schist?

Answer 14

Foliated and schistosity. Made of micas. May have garnet porphyroblasts

Question 15

If garnet is found, what rock type is it?

Answer 15

Always metamorphic

Question 16

What is gneiss?

Answer 16

Dark and light bands. Foliation and gneissose banding. Made of micas

Question 17

What is the daughter rock of shale in contact metamorphism?

Answer 17

Spotted rock. But at an intrusion, hornfels (closest) then andalusite then spotted rock

Question 18

When undergoing contact metamorphism, sandstone becomes…?

Answer 18

metaquartzite

Question 19

When undergoing contact metamorphism, limestone becomes…?

Answer 19

Marble

Question 20

What is marble?

Answer 20

White, granoblastic with medium grain size, but the size increases with metamorphic grade. Calcite crystals

Question 21

What is metaquartzite?

Answer 21

White or grey. Granoblastic with medium grain size, but increases with metamorphic grade. Quartz crystals

Question 22

What is spotted rock?

Answer 22

Darker spots with poorly formed minerals. Poorly developed with slaty cleavage and fine grained. Clay and micas

Question 23

When does diagenesis occur? (According to the metamorphic grade graph)

Answer 23

<200°C
<10 km depth pressures

Question 24

When does contact metamorphism happen? (According to the metamorphic grade graph)

Answer 24

> 200°C
Shallow depth and pressure. Heat is the main source

Question 25

When do igneous rocks form? According to the metamorphic grade graph)

Answer 25

When pressure and temps are both high.
>600°C. They can form at a range of depth depending on pressure and heat. It can happen at lower temps if pressure is significant

Question 26

What did George Barrow discover?

Answer 26

Index minerals in metamorphic rocks

Question 27

What index minerals did George Barrow discover in metamorphic rocks?

Answer 27

Chlorine (low)
Biotite
Garnet (mid)
Kyanite
Silimanite (high)

Question 28

What is granoblastic?

Answer 28

Metamorphic texture. Interlocking equidimensional crystals

Question 29

What is schistosity?

Answer 29

Metamorphic texture.
Medium-coarse rocks. Preferred alignment of flat/tabular minerals. Alignment perpendicular to stress. No traces of original bed remain

Question 30

What is gneissose banding?

Answer 30

Light and dark layers. Mm or cm thick.
Light = granoblastic
Dark = schistosity

Question 31

What is the difference between porphyritic and porphyroblastic?

Answer 31

Porphyritic = igneous texture. Two stage cooling.

Porphyroblastic = metamorphic. Recrystallisation

Question 32

What is a common metamorphic porphyroblast?

Answer 32

Garnet in mica schist