Metamorphism and metamorphic rocks

1
Metamorphism and metamorphic rocks
2
Goals

• To understand what drives metamorphism, the
  different types of metamorphism that can occur,
  and to interpret metamorphic rocks in terms of
  plate-tectonic setting.

3
The rock cycle
4
Metamorphism

• Metamorphism is like baking cookies

5
Driving forcesHeat from burial

• Average thermal gradient in crust is 25 C/km

Estimated temps 6 km deep
6
Driving forcesHeat from magma

• Contact metamorphism

7
Driving forcesStatic pressure
Crust, weighs 2.63 metric-tons/m2
8
Driving forcesDirected pressure
9
Directed pressure

• Metamorphic foliations

10
Play foliation animation
11
Think-pair-share activity

• What do you think the dominant direction of
  directed pressure is at A) convergent plate
  boundaries, B) divergent plate boundaries, and C)
  transform plate boundaries?
• Hint Think about the relative plate motions at
  each.
• Answer the question
• Compare, discuss, and refine your answer with one
  or two of your neighbors.
• Write up your results and pass them in.

12
Common metamorphic rocks

• Type of metamorphic rock dictated by
• Rock type before metamorphism
• Temperature and pressure conditions

13
Metamorphic facies
Increasing temperature
Greenschist
Increasing pressure
Amphibolite
Blueschist
Ecologite
14
Metamorphic facies
15
Pressure-temperature paths (P-T paths)
Temperature (Celsius)
Pressure (kbars)
Depth (km)
16
Pressure-temperature paths (P-T paths)

• Subduction zones Paired metamorphic belt

17
Pressure-temperature paths (P-T paths)

• Paired metamorphic belt in California

Sierra Nevada
SF
LA
18
Pressure-temperature paths (P-T paths)

• Continent-continent collisions Regional
  dynamothermal metamorphism

19
Metamorphism in New England
gt550 C
450550 C
Up to 450 C
Sediments
20
Pressure-temperature paths (P-T paths)

• Mid-ocean ridges characterized by hydrothermal
  metamorphism

21
Play black smokers video
22
Asbestos
23
Asbestos
24
Asbestos and your health
25
Asbestos and your health