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EAS 100 > L7: Igneous Rocks > Flashcards

L7: Igneous Rocks Flashcards

1
Q

Define rock

A

A cohesive aggregate on one or more minerals, which are held firmly together in a solid mass

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2
Q

Intrusive

A
  • Underground; has time to form big crystals

- Magma cools very slowly bc its covered by insulated rocks

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3
Q

Extrusive

A
  • Cools above ground

- Does not have time to form crystals

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4
Q

In what 2 ways can rocks form?

A
  1. texture/crystal structure

2. Composition

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5
Q

Phenocryst

A

Crystals have enough time to form and grow into large grains (aka plutonic or intrusive)

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6
Q

Igneous = __________, sedimentary = ___________

A

I: Crystals
S: Grains

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7
Q

How are igneous rocks formed?

A
  • Through the crystallization of a cooling magma

- Classified according to texture (intrusive, extrusive)

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8
Q

Define dikes

A
  • Cut across layers of country rock
  • Cross-cut the bedding
  • Formed when magma forces its way through open fractures
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9
Q

Define sills

A
  • Run parallel to country rocks
  • Think of 2 L’s being parallel to one another
  • Tubular, sheetlike body formed
  • Injection of magma between parallel layers of pre-existing sedimentary rock
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10
Q

Define veins

A
  • Deposits of minerals found within a rock fracture

- Big crystals

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11
Q

Define country rock.

A

Any rock into which the sill/dike has gone into

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12
Q

Examples of pyroclasts

A
  • Volcanic ash
  • Volcanic bomb
  • Pumice
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13
Q

Examples of mafic rocks

A
  • Basalt
  • Gabbro
  • Both differ in crystal size
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14
Q

Examples of felsic rocks

A

Rhyolite: extrusive
Granite: intrusive

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15
Q

What are batholiths?

A
  • The largest forms of plutons

- They’re intrusive rocks that take on enormous sizes often exceeding thousands of km

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16
Q

Define lava

A
  • Magma that flows quickly to the Earth’s surface still partially or wholly molten
  • Cools quickly therefore there is less time for crystallization to take place
  • Very fine grained
  • Only a glass may be formed due to quick cooling
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17
Q

Volcanic/extrusive rock

A

Given to an igneous rock formed close to, or at, the Earth’s surface

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18
Q

What is a pyroclast?

A
  • Any volcanic rock ejected into the air

- Viscous, siliceous rhyolitic and andesitic lavas; typically trap more gas

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19
Q

What does pyroclastic mean?

A

Erupts violently, very quick

20
Q

Volcanic tufts

A

Rocks resulting from smaller fragment

21
Q

Volcanic breccias

A

Rocks resulting from larger fragments

22
Q

How are tephra rocks formed?

A

Pyroclasts that eventually fall and are often lithified together upon cooling

23
Q

Define lithification

A

The process by which sediment and soil become rock

24
Q

What is a porphyry?

A
  • When a melt may occasionally begin to slowly crystallize at depth and grow some large crystals
  • May after be subjected to rapid cooling following a volcanic eruption
25
Q

How can igneous rocks be classified?

A
  • According to composition; more particularly silica content
  • More siliceous
  • Least siliceous
26
Q

Give examples of more siliceous rock

A
  • Granites

- Rhyolites

27
Q

Give examples of least siliceous rock

A
  • Gabbros
  • Basalts
  • This is because these rocks are higher in FeMg
28
Q

What are found in Mafic and Felsic rocks?

A

MA: Magnesium Ferric
FEL: Feldspar Silica

29
Q

Examples of convergent plate boundaries.

A
  • Ocean-ocean
  • Ocean-continent
  • Continent-continent
30
Q

Higher silica content + lower lava temperatures = ______________

A

More viscous lava therefore it flows slower

31
Q

Lower silica content + higher lava temperatures = ______________

A

Less viscous lava therefore it flows faster

32
Q

The more _______ lava claims the more _________ it erupts.

A
  • Gas

- Violently

33
Q

Basaltic (mafic) lavas

A
  • High FeMg and low silica content (dark in color)
  • Erupt at 1000°-1200°
  • Highly fluid (can travel at speeds of 100km/hr)
34
Q

Rhyolitic (felsic) lavas

A
  • Low FeMg and high silica content
  • Erupt at 800°-1000°
  • Highly viscous, therefore speed is 10x slower than basaltic
  • Viscosity causes it to resist flow and build up as thick, bulbous deposits
  • Pumice = vesicular variety
35
Q

Intermediate (andesitic) lavas

A
  • Have an intermediate composition between basalt and rhyolite
  • Intrusions of intermediate magma form diorite
36
Q

List the 3 types of lavas.

A
  • Basaltic (mafic)
  • Rhyolitic (felsic)
  • Intermediate
37
Q

How do magmas form?

A
  • Magma is derived from subducting rock, partially undergoes melting bc the minerals it is composed of undergo melting at different temperatures
  • Water melts rock faster; it acts as a lubricant
38
Q

Why can’t everything be magma?

A

Pressure henny!!!!

39
Q

Density of melted rock = _______ than density of solid rock with the same _______

A
  • Lower

- Composition

40
Q

What happens to partial melts?

A

Rise upwards through pores, along grain boundaries and in any fractures in the overlying rocks

41
Q

How are large pools of magma chambers formed?

A

Molten materials mixes with other liquids as it ascends

42
Q

What makes lava more explosive?

A

More silica content

43
Q

Rocks = _________, which means that . . .

A
  • Buoyant

- Able to melt or move through

44
Q

What happens when magma rises but the temperature decreases? This is known as . . .

A
  • Solid rock may begin to melt without any additional heat
  • Decompressional Melting
  • Occurs at a certain point
  • These produce the greatest volume of molten rock anywhere on earth
45
Q

Define magmatic differentiation.

A
  • Occurs when different minerals crystallize at different temperatures
  • During the crystallization process, the composition of the parent magma changes as it becomes depleted of the chemical elements that comprise the crystals
  • First to form cooling magma were last to melt
46
Q

Why does magma composition change overtime?

A
  • It’s constantly moving/changing, sinks, and so it starts over
  • When it begins to cool is when we may be able to get mafic -> felsic and VV
47
Q

What was Bowen’s reaction series?

A
  • Studied the order of crystallization of the common silicate minerals to form a magma
  • Found that they begin to cool and settle out, therefore begin to get cumulates
  • Shows that the composition of the magma chamber is changing because crystals present are settling out over time

EAS 100 (17 decks)

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