Metamorphism Flashcards

1
Q

Define metamorphism.

A

Rocks changing in response to changes in temperature and pressure

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2
Q

What factors does the product rock of metamorphism depend on?

A

Chemical composition of original rock, temperature, pressure, and stress

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3
Q

What are the two ways a rock can be heated as part of metamorphosis?

A

Burial and nearby igneous intrusion

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4
Q

What is the temperature range of heat metamophism?

A

Starts around 200ºC and ends around 650-800ºC

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5
Q

Why does metamorphism stop around 650-800ºC?

A

Because that’s the temperature where crustal rocks start to melt

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6
Q

What types of rocks does metamorphism usually affect?

A

Sedimentary

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7
Q

What happens to carbonates when they are heated?

A

Carbon dioxide is expelled.

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8
Q

What happens to clays when heated as part of a metamorphic process?

A

Water is expelled to produce mica

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9
Q

What generally happens to the grainsize of a mineral under metamorphosis?

A

Becomes coarser.

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10
Q

With increasing pressure, _________ minerals are formed.

A

Denser

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11
Q

What is the distinction between high and low grade metamorphism?

A

Low = 200-500ºC and mostly low pressures
High = >500ºC with high pressures

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12
Q

What temperatures does low grade metamorphism usually occur at?

A

200ºC to 500ºC

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13
Q

Above what temperature is metamorphism usually high grade?

A

500ºC

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14
Q

Why does high temperatures usually mean high pressures too, in terms of metamorphism?

A

High temperature metamorphism is usually the result of burial, which usually has higher pressures.

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15
Q

What is differential stress?

A

When pressure on a rock varies in different directions.

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16
Q

What does differential stress cause?

A

Foliation

17
Q

What is foliation?

A

A planar fabric where grain aligns at a normal to the direction of highest pressure

18
Q

What is foliation on a large scale?

A

Cleavage

19
Q

What is foliation called in lower grade metamorphism?

A

Slaty cleavage

20
Q

What is foliation called in higher grade metamorphism?

A

Schistosity

21
Q

What are the 3 types of low grade metamorphism?

A

Cataclastic metamorphism
Burial metamorphism
Contact metamorphism

22
Q

Describe cataclastic metamorphism. Is it low or high grade?

A

Mechanical deformation of a rock with only minor recrystallisation.
- low grade

23
Q

Describe burial metamorphism. Is it low or high grade?

A

Caused by an increase in temperature with depth, but only a small increase in pressure, only minor recrystallisation.
- Can be both

24
Q

Describe contact metamorphism.

A

Occurs when hot magma intrudes into cool rocks, mechanical deformation is minor or absent

25
Q

What is a metamorphic aureole? What size is it normally?

A

The heated region around an igneous intrusion
Usually <100m

26
Q

What are the Siberian Traps?

A

A region of Siberia dominated by coals, hydrocarbon course rocks, evaporites and remnants of large scale volcanic activity

27
Q

What did contact metamorphism produce post-eruption in the Siberian Traps? What was concerning about this?

A

Organohalogens
Which were linked to Stratosphere ozone destruction

28
Q

What is regional metamorphism? Is it high grade or low grade?

A

A type of metamorphism caused by mountain building and continental changes which causes very pronounced foliations and new minerals.
High grade

29
Q

What are metamorphic rocks?

A

A way of grouping metamorphic rocks by what temperature and pressure their minerals were formed at

30
Q

What are the 3 metamorphic facie groups?

A

1) High T, low P usually in the vicinity of igneous intrusion in the shallow crust
2) High T, high P most common
3) Low T, high P very rare

31
Q

What do shale/mudstone metamorphose to? (in order)

A

Shale -> Slate -> Phyllite -> Schist -> Gneiss

32
Q

What does sandstone/sandy sediments metamorphose to?

A

Psammite

33
Q

What does quartz sandstone metamorphose to?

A

Quartzite

34
Q

What does limestone metamorphose to/

A

Marble

35
Q

Which type of igneous rocks show a change after metamorphism? Examples?

A

Less silica rich igneous rocks
e.g. Basalt or Gabbro

36
Q

What does basalt/gabbro metamorphose to? What is this composed of?

A

A metabasite
made of amphiboles

37
Q

What is contact metamorphic rock known as?

A

Hornfels