Chap 4 Magma and Igneous Rocks Flashcards

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

Geothermal gradient

A

The rate at which the Earth’s temperature increase with
dept

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

Formation of Magma

A

 Pressure release = decompression melting= Geothermal gradient

 Heat transfer from rising magma

 Addition of volatiles
Wet magma = up to 15% volatiles ∴ melts at lower temps
Dry Magma = no volatiles ∴ melts at higher temps

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

What is magma made of?

A
  1. Liquid = melt
  2. Solids = silicates
  3. Volatiles ( AND )
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Magma types:

A

Felsic,
Intermediate,
Mafic,
Ultramafic

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

Felsic magma

A

%: 66-76%
Density: Very low
Temp: Very low
Viscosity: Very high: Explosive
Plutonic: Granite
(Obsidian
=glass)
Volcanic: Rhyolite

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

Intermediate magma:

A

%: 52-66%
Density: Low
Temp: Low
Viscosity: High: Explosive
Plutonic: Diorite
Volcanic: Andesite

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

Mafic magma:

A

%: 45-52%
Density: High
Temp: High
Viscosity: Low: thin,
hot, runny
Plutonic: Gabbro
Volcanic: Basalt

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

Ultramafic magma:

A

%: 38-45%
Density: Very High
Temp: Very high
Viscosity: Very low
Plutonic: Peridotite
Volcanic: Komatiite

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

Processes involved in magma variation

A

 Partial melting
 Assimilation
 Mixing magmas
 Fractional crystallisation

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Partial melting

A

= different types of rock melt/partially melt by different amounts
∴ partial melting of: Ultramafic –> Mafic –> Intermediate –> Felsic

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

Assimilation

A

= rock surrounding magma may partially melt and mix with original magma

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

Mixing magmas

A

= one magma composition can be derived from another during
crystallisation

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

Fractional crystallisation

A

= magmas of different compositions can mix to produce new, inbetween compositions

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

Characteristics of intrusive igneous rock

A

 Baked zone
 Chill margin
 Xenoliths

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

Baked zone

A

= rim of heat
altered country rock

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Chill margin

A

= magma at
contact that cooled rapidly

17
Q

Xenoliths

A

= country rock
fragment in magma
∴ magma cooled before xenolith could
be assimilated

18
Q

Invasion in colder country rock

A

 Thermal metamorphism and melting
 Inflation of fractures pushing the rock aside
 Incorporation of country rock fragments (xenolith)
 Hydrothermal (hot water) alteration

19
Q

Intrusive rock bodies

A

 Concordant
 Discordant
 Tabular
 Plutonic

20
Q

Concordant Intrusive rock body

A

= does not cut across rock layers (sill, locolith, lopolith)

21
Q

Discordant Intrusive rock body

A

= cuts across rock layers (batholith, stock, dyke)

22
Q

Tabular Intrusive rock body

A

= flat with uniform thickness (sill, dyke)

23
Q

Plutonic Intrusive rock body

A

= body/blob of intrusive igneous rock (batholith, stock, lopolith, locolith)

24
Q

Factors affecting the cooling time of magma

A
  1. Depth of intrusion
  2. Shape and size
  3. Presence of circulating ground water
25
Q

Types of textures

A
  1. Glassy
  2. Interlocking mineral crystals/ crystalline
  3. Fragmental
26
Q

Glassy texture

A

= fast cooling OR highly viscous; made of solid glass or solid shards

27
Q

Interlocking mineral crystals/ crystalline texture

A

= slow cooling; minerals that fit like jigsaw pieces

28
Q

Fragmental texture

A

= pieces of pre-existing rocks

o Aphanitic = finely crystalline, only microscopically visible ∴ rapid cooling

o Phaneritic = coarsely crystalline, mm-cm

o Porphyritic = a mixture of coarse and fine grained (Indicates a 2-stage history ∴ initial slow cooling and subsequent eruption cools magma quickly)

o Pegmatitic = exceptionally coarse mineral crystals; form from water rich melts in
which atoms can move around so rapidly (not very viscous) that large crystals can
grow very quickly