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Environmental Geoscience > Igneous Processes > Flashcards

Igneous Processes Flashcards

1
Q

Define an igneous rock.

A

One formed through the cooling and solidification of magma

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2
Q

What is the difference between magma and lava?

A

Magma = Molten rock below the earth’s surface
Lava = Magma once it reaches the surface

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3
Q

What conditions are required for melting the Earth’s crust and mantle?

A

Depressurisation
Adding water or other volatiles
Heating to the melting point

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4
Q

What are the three types of magma?

A

Basaltic, Andesitic, Rhyolitic

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5
Q

Which magma type is most mafic?

A

Basaltic magma

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6
Q

What type of magma is most felsic?

A

Rhyolitic lava

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7
Q

What are the typical magma temperatures of the 3 main types?

A

Basaltic - 1200C +
Andesitic - 800-1000C
Rhyolitic - 600-900C

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8
Q

What does viscosity of magma depend on?

A

Temperature and composition

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9
Q

The lower something’s viscosity is…..

A

The easier it flows

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10
Q

Does greater silicate content in magma raise or lower viscosity?

A

Raise (harder to flow due to silicate chains)

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11
Q

What is magmatic differentiation by fractional crystallisation?

A

A process by which crystals of certain minerals form, removing this mineral from the magma
- so later crystals have a different composition

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12
Q

What are two ways crystals and magma can become separated?

A

Compression
Sinking of dense, early minerals

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13
Q

What type of magma did Bowen notice to be more common?

A

Basaltic magmas.

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14
Q

What did Bowen figure out about andesitic and rhyolitic magmas?

A

They are derived from basaltic magmas (the primary magma) by magmatic differentiation

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15
Q

What mineral did Bowen study to reach his conclusion?

A

Plagioclase Feldspars

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16
Q

What did Bowen call the process of continual reaction between magma and crystals?

A

A continuous reaction series

17
Q

What did Bowen describe as a ‘discontinuous reaction series’?

A

Processes where already-formed minerals react with magma to form new minerals

18
Q

Which is more coarse grained; intrusive or extrusive rocks? Why?

A

Intrusive, Because the magma crystallises slower

19
Q

What are phenocrysts?

A

isolated grains within igneous rocks

20
Q

What are igneous rocks with phenocrysts called?

A

Porphyritic

21
Q

What’s the difference between vesicles and amygdales

A

Vesicles are bubbles preserved in igneous rocks, when filled with another mineral they are called amygdales

22
Q

What’s the difference in eruption between high viscosity and low viscosity magmas?

A

High viscosity (hard to flow) - explosive eruptions with fragments
Low viscosity (easy to flow) - non-explosive eruptions

23
Q

What are basalt eruptions like?

A

They produce low, broad, gently sloping shield volcanoes with non-explosive flows

24
Q

What is tephra?

A

Airborne volcanic debris

25
Q

What are the 3 types of tephra? How are they differentiated?

A

Differentiated by particle size

Bombs >64mm
Lapilli 2-64mm
Ash <2mm

26
Q

What is the angle of rest of a volcano?

A

The angle between the slope and flat ground

27
Q

What are andesitic eruptions like?

A

The volcano emits viscous lava and tephra
- Usually alternating to form a stratovolcano

28
Q

What are pyroclastic flows?

A

Mixture of hot gases and pyroclasts denser than the atmosphere
- Hot highly mobile flow of tephra

29
Q

What are rhyolitic eruptions like?

A
  • Very silica rich
  • Usually form calderas
30
Q

What are calderas?

A

Steep walled basin usually >1km in diameter created by volcano collapse

31
Q

During what type of eruption are calderas common?

A

Rhyolitic eruptions

32
Q

What is the order of Bowen’s continuous reactions series?

A

Peridotite
Gabbro
Diorite
Granite

33
Q

What is the order of Bowen’s discontinuous reaction series?

A

Olivine
Pyroxene
Amphibole
Biotite/Quartz

Environmental Geoscience (10 decks)

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