Metamorphic Rocks

Question 1

What are metamorphic rocks?

Answer 1

• Metamorphic rocks are produced through the recrystallisation of pre existing rocks due to changes in: Heat, Pressure and Differential pressure.
• This causes the sedimentary/igneous/metamorphic rocks to change in form, producing a new metamorphic rock.

Question 2

How do heat, pressure and differential pressure change inside Earth?

Answer 2

• Heat = increases with depth, or when in contact with igneous intrusions.
• Pressure = increases with depth.
• Differential pressure = tectonic activity leads to horizontal stresses being larger than vertical stresses, producing faults and crystals.

Question 3

What is the difference between high and low graded metamorphic rocks?

Answer 3

Low grade:

• Produced under low temperatures/pressures.
• Therefore have small crystals and fine foliation.

Low grade:

• Produced under high temperatures/pressures.
• Therefore have large crystals and coarse foliation.

Question 4

What are the different types of metamorphism?

Answer 4

• Contact metamorphism
• Regional metamorphism
• Hydrothermal metamorphism
• Burial metamorphism
• Impact metamorphism

Question 5

What is contact metamorphism?

Answer 5

• Contact metamorphism is when rock is in contact with another high temperature rock, leading to recrystallisation.
• It only occurs at shallow depths.
• It is related to high temperatures.

Question 6

What is regional metamorphism?

Answer 6

• Regional metamorphism is when rocks are under high pressures and temperatures at significant depths, affecting large volumes of rock.
• It only occurs at significant depths.
• It is related to high temperatures and pressures.

Question 7

What is hydrothermal metamorphism?

Answer 7

• Hydrothermal metamorphism is when high temperatures associated with the presence of water leads to chemical reactions occurring.
• It only occurs near mid-ocean ridges.
• It is related to high temperatures.

Question 8

What is burial metamorphism?

Answer 8

• Burial metamorphism is when an increase in sedimentation increases the pressure, causing recrystallisation to occur.
• It is related to high pressures.

Question 9

What is impact metamorphism?

Answer 9

• Impact metamorphism is when a meteor strike causes the recrystallisation of rocks impacted by the strike.
• It is related to high temperatures and pressures.

Question 10

What are the differences between foliated and non-foliated rocks?

Answer 10

Foliated:

• Name is based on the kind of foliation.
• Examples: Slaty -> Slate

Schistose -> Schist

Gneissic -> Gneiss

Non-foliated:

• Name is based on the mineral content of the rock.
• Examples: Limestone -> Marble

Shale -> Hornfels

Basalt -> Hornfels

Question 11

Metamorphic rock diagram

Answer 11

Question 12

How is foliation produced?

Answer 12

• Minerals are deformed or realigned due to the pressures during recrystallisation.
• This produces distinct layering within a rock.

Question 13

Schist

Answer 13

• Schist is a regional metamorphic, medium grained foliated rock.
• It is weak and easily sheared.

Question 14

Hornfels

Answer 14

• Hornfels is a thermal contact metamorphic, non-foliated rock.
• It is very strong.