Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Intro to Earth Science > New From Old: Metamorphism - Lec 11 > Flashcards

New From Old: Metamorphism - Lec 11 Flashcards

You may prefer our related Brainscape-certified flashcards:
Biology 101 flashcards
1
Q

What does metamorphism do?

A

Changes the texture and/or mineral assemblage in rocks in the solid state

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the cause of metamorphism?

A

Changes in temperature and/or pressure, differential stress (compression or shear) plus hydrothermal fluids may also be involved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What does the composition of a protolith control?

A

What minerals form

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are the processes involved in forming metamorphic rocks? (5)

A 
Recrystallisation
Phase Change
Neocrystallisation
Pressure solution
Plastic Deformation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Where does metamorphism occur and how can it be identified?

A

In various settings

On the basis of the mineral assemblage

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How does contact metamorphism occur?

A

By an increase in temperature

Heating by an intrusion creates an aureole surrounding it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

How does regional metamorphism occur?

A

Involves both Temperature and Pressure and is associated with orogenesis

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How does subduction metamorphism occur?

A

Characterised by low temperature and high pressure

Occurs at subduction zones

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Name 3 other types of metamorphism

A 
Shock metamorphism (asteroid impact)
Burial metamorphism (as sediments accumulate the succession passes from diagenesis to metamorphism) 
Dynamic metamorphism (localised deformation via ductile behaviour along faults)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

How do prograde and retrograde metamorphism occur?

A

As temperature and pressure increase, and decrease, respectively

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is metamorphism?

A

Pre-existing rock (protolith) undergoes solid state (no change of state) change as response to modification of its environment (change in temp/pressure etc)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What metamorphism is associated with igneous intrusion?

A

Contact metamorphism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What are porphyroblasts?

A

Outsized large crystals that grow in a metamorphic rock

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is foliation?

A

The alignment of minerals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Are there textures in hand specimens that are diagnostic of metamorphism?

A 
Metamorphic minerals (indicative of Temp/Pressure conditions)
Metamorphic textures (foliation - garnet porphyoblasts cross-cutting foliation)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does metamorphism often result in?

A

Foliation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is planar foliation?

A

The parallel alignment of platy minerals (clays/micas)
Minerals oriented perpendicular to compression
Sometimes with alterations of differently coloured layers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

List the different types of foliation from very fine foliation to fine foliation to medium scale foliation to banding

A

Slaty Cleavage (individual minerals not visible)
Phyllitic foliation
Schistosity (minerals clearly visible)
Gneissic Banding (alternating bands of light and dark coloured minerals)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

In relation to texture, list 3 types of metamorphic rocks from low grade metamorphism (fine) to high grade metamorphism (coarse)

A

Slate
Schist
Gneiss

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is non-foliated texture?

A

No preferred orientation of the minerals in rocks

Occurs when deformation is low and clay/mica content is low (quartzite has poor foliation at best)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

What is involved in recrystallisation?

A

Changes shape and size of grains
No change in mineral identity
(Protolith to metamorphic rock: quarts sand to quartzite)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What is involved in phase change?

A

One mineral transformed into another with same composition but different crystal structure
(Andalusite: low t and p, kyanite: low t high p, sillimanite: high t and p)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is involved in neocrystallisation?

A

Growth of new minerals different from protolith

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What is involved in pressure solution?

A

Mineral grains dissolve where their surfaces are pressed against other grains
Ions produced migrate
Precipitation where grains under less pressure
Can shorten grains in one direction and lengthen them in another
Also occurs under non-metamorphic conditions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is involved in plastic deformation?

A

Rock sheared/squeezed at high temps/pressures
Minerals change shape without breaking: plastic behaviour
Can occur without change to composition or crystal structure
Can occur when metamorphic reactions are happening

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Role of heat in metamorphism

A

Atoms vibrate
Chemical bonds between them stretch and break
Atoms detach
Results in rearrangement of atoms within grains and migration of atoms into/out of grains
Results in recrystallisation and/or neocrystallisation
(product depends on protolith)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

Role of pressure in metamorphism

A

Greater pressure = closer packing of atoms
Density increases
Results in phase changes and/or neocrystallisation
(product depends on protolith)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What is differential stress?

A

Stress applied unequally in all directions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

What is normal stress?

A

Applied perpendicular to a surface

30
Q

What do compression and tension do to a material?

A

Compression: flattens a material
Tension: stretch a material

31
Q

What is shear stress?

A

Moves one particle sideways relative to another

32
Q

How does preferred orientation form?

A

Develops via alignment of inequant grains
(at elevated temps rock changes shape without breaking - internal texture changes sympathetic to stresses applied)
Inequant grains may be pre-existing or form during the metamorphic episode

33
Q

What is equant?

A

Roughly the same in all dimensions

34
Q

What is inequant?

A

Dimensions not all the same

35
Q

Name and describe to types of inequants

A

Elongate (cigar-shaped) : one dimension notably longer than the other 2
Platy (pancake-like): one dimension notably shorter than the other 2

36
Q

How does preferred orientation form in relation to pressure solution?

A

Occurs on faces perpendicular to direction of compression (grains shorten in that direction)

37
Q

How does preferred orientation form in relation to neocrystallisation?

A

Precipitation occurs where rock is stretching

38
Q

How does preferred orientation form in relation to plastic deformation?

A

At high temp accompanied by differential stress

39
Q

How does preferred orientation form in relation to shear stress?

A

It flattens grains and rotates them into alignment

As rock undergoes flattening, rigid inequant grains in ‘soft matrix’ rotate and flatten as overall rock changes shape

40
Q

How does preferred orientation form in relation to compressive stress?

A

It flattens grains into alignment

As rock undergoes flattening, rigid inequant grains in ‘soft matrix’ rotate and flatten as overall rock changes shape

41
Q

What are 3 hydrothermal fluids?

A

Hot water
Steam
Supercritical fluids

42
Q

What are supercritical fluids?

A

Fluids under high temp and pressure with characteristics of fluid and gas. They are very pervasive

43
Q

What is the role of hydrothermal fluids in metamorphism?

A

Accelerate reactions (atoms migrate faster through fluids than solids)
Provide water that becomes absorbed by minerals during metamorphic reactions
Metasomatism

44
Q

What is metasomatism?

A

A metamorphic process that by which the chemical composition of a rock is altered by introduction and/or removal of chemical components as a results of its interaction with aqueous fluids

45
Q

What are sources of water?

A

Groundwater (lots of rocks contain water at great depths)
Released from rising magmas
Products of metamorphic processes

46
Q

Where does burial metamorphism occur?

A

Deep burial in a basin

47
Q

Where does dynamic metamorphism occur?

A

Shearing in a fault zone

48
Q

Where does contact (thermal) metamorphism occur?

A

Hating by an intrusion

49
Q

Where does hydrothermal metamorphism occur?

A

Alteration by hot water leaching

50
Q

Where does regional metamorphism occur?

A

Pressure and Temp change due to orogenesis

51
Q

Where does subduction metamorphism occur?

A

High pressure and low temperature alteration

52
Q

Where does shock metamorphism occur?

A

Extreme high pressure from a bolide impact

53
Q

Burial metamorphism

A

Pressure and temp increase as sediments are buried in a basin due to the weight of overburden and the geothermal gradient (20-40 degrees per km)
Typical metamorphism starts at temp >200 degrees - before that only get diagenesis
Below depths of 8-15km,metamorphic changes replace diagenesis

54
Q

Dynamic metamorphism

A

Breakage of rock by shearing within a fault zone
At shallow depths (up to 15km) rocks are brittle, crushing to form fault breccia
At deeper levels rocks are ductile, rocks in fault zones smear to form mylonite

55
Q

Contact (Thermal) metamorphism

A

Thermal - develops in response to heat without change in pressure
Contact - position adjacent to an intrusion
Magma intrusion affects ‘country rock’ - heat transferred and hydrothermal fluids circulated - metamorphic aureole generated

56
Q

Give an example of contact metamorphism in Ireland

A

Leinster granite (400mya)

57
Q

Give an example of hydrothermal metamorphism in Ireland

A

Lithium deposits in S. Wexfird
Pb deposits in N. Wicklow
Avoca Gold (400 mya) - formed in association with volcanic arc

58
Q

What are mineral deposits an indication of in relation to metamorphic rocks?

A

Hydrothermal metamorphism - indicates circulation of hydrothermal fluids

59
Q

Hydrothermal metamorphism at mid-ocean ridges and example

A

Cold ocean water seeps into fractured oceanic crust
Heated by magma, hot aggressive water chemically alters the basalt
Hot water from black smokers provides mineral deposits and life
Serpentinite: (480 mya) Altered mantle from ancient ocean in Clew Bay

60
Q

Regional Metamorphism

A

Pressure and temp change due to orogensis
At continent-continent convergent boundary
Protolith subjected to increased temp (geothermal gradient and igneous activity), greater pressure (weight of overburden) and more compression and shearing

61
Q

What is orogenesis?

A

Mountain building

62
Q

Give an example of regional metamorphism

A

Grampian orogeny 470mya (ductile deformation of old rocks) - Connemara to Donegal

63
Q

Subduction metamorphism

A

At subduction zones
Trenches and accretionary prisms (wedges shaped build up of sediments scraped off descending plates)
Subduction introduces colder rocks to depth so low geothermal gradient
These conditions produce a unique low temp high pressure mineral assemblage called blueschist

64
Q

Give an example in Ireland of subduction metamorphism

A

Achill

65
Q

Shock metamorphism

A

Impact of comet/asteroid
Extremely high pressure and temp
High pressure minerals (eg. stishovite - highly dense polymorph of SiO2)

66
Q

What are metamorphic facies?

A

A set of mineral assemblages indicative of certain pressure and temp conditions

67
Q

What is metamorphic grade?

A

A measure of the intensity of temp and pressure conditions that lead to alterations

68
Q

What is metamorphic grade reflected in?

A

What minerals are formed - protolith exerts control

69
Q

What is prograde metamorphism?

A

Temp and pressure progressively increase
As grade increases, reactions release water
Therefore, high grade rocks tend to be ‘drier’ (lack minerals with -OH in their chemical formula)

70
Q

What is retrograde metamorphism?

A

Temp and pressure progressively decrease AND
Hydrothermal fluids MUST enter the system to add water
Retrograde reactions do not take place under ‘cold and dry’ conditions
Thus high grade rocks can be exhumed and visible on surface today

Intro to Earth Science (13 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions