EAS 100 > L7: Igneous Rocks > Flashcards

L7: Igneous Rocks Flashcards

(47 cards)

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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?

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A

Erupts violently, very quick

20
Q

Volcanic tufts

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A

Rocks resulting from smaller fragment

21
Q

Volcanic breccias

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A

Rocks resulting from larger fragments

22
Q

How are tephra rocks formed?

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A

Pyroclasts that eventually fall and are often lithified together upon cooling

23
Q

Define lithification

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A

The process by which sediment and soil become rock

24
Q

What is a porphyry?

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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
How can igneous rocks be classified?
- According to composition; more particularly silica content - More siliceous - Least siliceous
26
Give examples of more siliceous rock
- Granites | - Rhyolites
27
Give examples of least siliceous rock
- Gabbros - Basalts - This is because these rocks are higher in FeMg
28
What are found in Mafic and Felsic rocks?
MA: Magnesium Ferric FEL: Feldspar Silica
29
Examples of convergent plate boundaries.
- Ocean-ocean - Ocean-continent - Continent-continent
30
Higher silica content + lower lava temperatures = ______________
More viscous lava therefore it flows slower
31
Lower silica content + higher lava temperatures = ______________
Less viscous lava therefore it flows faster
32
The more _______ lava claims the more _________ it erupts.
- Gas | - Violently
33
Basaltic (mafic) lavas
- High FeMg and low silica content (dark in color) - Erupt at 1000°-1200° - Highly fluid (can travel at speeds of 100km/hr)
34
Rhyolitic (felsic) lavas
- 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
Intermediate (andesitic) lavas
- Have an intermediate composition between basalt and rhyolite - Intrusions of intermediate magma form diorite
36
List the 3 types of lavas.
- Basaltic (mafic) - Rhyolitic (felsic) - Intermediate
37
How do magmas form?
- 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
Why can't everything be magma?
Pressure henny!!!!
39
Density of melted rock = _______ than density of solid rock with the same _______
- Lower | - Composition
40
What happens to partial melts?
Rise upwards through pores, along grain boundaries and in any fractures in the overlying rocks
41
How are large pools of magma chambers formed?
Molten materials mixes with other liquids as it ascends
42
What makes lava more explosive?
More silica content
43
Rocks = _________, which means that . . .
- Buoyant | - Able to melt or move through
44
What happens when magma rises but the temperature decreases? This is known as . . .
- 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
Define magmatic differentiation.
- 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
Why does magma composition change overtime?
- 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
What was Bowen's reaction series?
- 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
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