Deck 4: Up From the Inferno: Magma and Igneous Rocks

Question 1

Not all magmas have the same initial composition.Which of the following is LEAST likely to cause variation in the composition?

A) source of magma
B) amount of partial melting
C) amount of magma mixing
D) depth in the Earth

Answer 1

D

Question 2

All other factors being equal,intrusive rocks that form deep within Earth ____________ than intrusive rocks that cool near the surface.

A) are more felsic
B) contain a smaller proportion of volatiles
C) cool more slowly
D) cool more rapidly

Answer 2

C

Question 3

Volatiles refer to substances that ____________.

A) crystallize most rapidly out of a melt
B) melt immediately upon contact with a hot body of magma
C) have a tendency to evaporate and are stable as gases

Answer 3

C

Question 4

Important volatiles in magmas include ____________.

A) iron- and magnesium-rich minerals, such as olivine
B) potassium and aluminum
C) water and carbon dioxide
D) trinitrotoluene and nitroglycerin

Question 5

If the volatile content of magma is increased,its viscosity will ____________.

A) increase
B) decrease
C) stay the same

Question 6

The difference between lava and magma is that magma ____________.

A) is light in color, whereas lava is dark
B) usually has mafic composition, whereas lava usually has felsic composition
C) is found beneath Earth's surface, whereas lava has reached the surface
D) flows more quickly than lava

Question 7

A majority of the melts in the Earth form through the partial melting of ultramafic mantle rock.These newly formed magmas are ____________.

A) ultramafic
B) mafic
C) felsic
D) intermediate

Question 8

When rock is partially melted,the chemistry of the melt is ____________.

A) more mafic than the original chemistry of the rock that was partially melted
B) more felsic than the original chemistry of the rock that was partially melted
C) identical to the original chemistry of the rock that was partially melted
D) completely unpredictable (it could be more mafic or more felsic)

Question 9

Igneous rocks ____________.

A) are formed through the freezing of melt
B) can be produced at the surface of the Earth as well as deep below the surface
C) are the most common type of rocks within Earth
D) All of the above are correct.

Question 10

All of the Earth's internal heat was acquired very early in its history through meteoric impact and differentiation of the core.The Earth's interior loses heat to space but does not currently receive heat through any known process.

Question 11

Radioactive isotopes,differentiation of Earth's iron core,gravity-driven compression,and meteoric bombardment all caused early Earth to ____________.

A) glow brighter than the Sun
B) be much cooler than at present
C) be much hotter than at present
D) be much more oblong than at present

Question 12

Most commonly,felsic igneous rocks ____________.

A) contain more iron and magnesium than intermediate rocks
B) are lighter in color than mafic rocks
C) are darker in color than mafic rocks
D) are found in oceanic crust

Question 13

Very early in Earth's history,it was so hot that the surface was likely entirely molten.

Question 14

Geologically,melts are equivalent to both ____________ and ____________.

A) felsic magma; mafic magma
B) felsic lava; mafic lava
C) lavas; magmas
D) fine-grained igneous rocks; coarse-grained igneous rocks

Question 15

As compared to mafic igneous rocks,all felsic igneous rocks ____________.

A) cool and solidify more quickly
B) cool and solidify more slowly
C) solidify at higher temperatures
D) solidify at lower temperatures

Question 16

Injecting hot fudge into ice cream is an appropriate analogy for which cause of magma melt?

A) melting due to a decrease in pressure
B) melting due to an addition of volatiles
C) melting due to heat transfer from rising magma
D) All of the above are correct.

Question 17

The difference between magma and lava is ____________.

A) that magma cools more rapidly than lava
B) that magma is found at the surface, whereas lava is found below the surface
C) that magma is found beneath the surface, whereas lava is found at the surface
D) There is no difference; the two terms mean the same thing.

Question 18

The geotherm is the rate of change of ____________.

A) pressure with depth in Earth's interior
B) temperature with depth in Earth's interior
C) temperature with altitude in Earth's atmosphere
D) temperature with latitude on Earth's surface

Question 19

The formation of magma within Earth is NOT caused by which of the following processes?

A) decompression (drop in pressure)
B) addition of volatiles
C) transfer of heat from adjacent magma or very hot rocks
D) loss of volatiles to the atmosphere

Question 20

Which type of magma has the greatest silica content?

A) felsic
B) intermediate
C) mafic
D) ultramafic

Question 21

A volcanic neck,such as that seen at Shiprock,New Mexico (below),is a(n)____________.

A) sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock
B) cooled layer of lava
C) intrusion formed within a volcano
D) sheet-like intrusion that cuts across preexisting layers

Question 22

Consult the figure below.A sill is a(n)____________.

A) sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock
B) cooled layer of lava
C) intrusion formed within the magma chamber of a volcano
D) sheet-like intrusion that cuts across preexisting layers

Question 23

Which of the following is NOT a factor controlling the cooling rate of magma?

A) depth of intrusion
B) shape and size of magma body
C) presence of circulating groundwater
D) All of the above are factors.

Question 24

A blob-like igneous rock body that has cooled beneath the surface of Earth is ____________.

A) guyot
B) pluton
C) lava flow
D) andesite

Question 25

In regard to the cooling of molten rock,a __________ volume and a __________ shape cools faster.

A) larger; spherical
B) larger; pancake
C) smaller; spherical
D) smaller; pancake

Question 26

If a body of magma is subjected to fractional crystallization,the rock that results is expected to be ____________.

A) identical in chemical composition to the magma
B) more mafic than the magma
C) more felsic than the magma

Question 27

Magma tends to _____________.

A) move upward, away from where it formed
B) move downward, away from where it formed
C) move laterally
D) stay in one place

Question 28

Obsidian,shown below,____________.

A) is volcanic glass
B) possesses conchoidal fracture
C) typically is felsic in composition
D) All of the above are correct.

Question 29

If a volcano erupted and its resultant lava flowed to a great distance at a relatively fast rate,what properties would you expect of the lava?

A) high temperature
B) volatile-rich
C) mafic
D) Both a and b are correct.
E) All of the above are correct.

Question 30

Why are intrusive igneous rocks exposed today?

A) Mountain building events uplift belts of mantle.
B) Wind, water, and ice erode overlying rock to expose igneous rocks.
C) Dikes and sills bring intrusive igneous rocks above the surface.
D) There are many theories to explain this, but none have been widely accepted.

Question 31

Consult the figure below.A dike is a(n)____________.

A) sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock
B) cooled layer of lava
C) intrusion formed within the magma chamber of a volcano
D) sheet-like intrusion that cuts across preexisting layers

Question 32

Viscosity depends on ____________.

A) temperature
B) volatile content
C) silica content
D) All of the above are correct.

Question 33

Consult the figure below.If you found deposits of tuff at an ___________ igneous setting,you could conclude that the lava had a ___________ viscosity content.

A) intrusive; high
B) intrusive; low
C) extrusive; high
D) extrusive; low

Question 34

Which is the best analogy for the rate at which magma cools inside of the Earth?

A) coffee poured into mug
B) coffee spilled on the table
C) coffee poured into a sealed thermos
D) creamer poured into coffee in a mug

Question 35

If a body of igneous (source)rock is subjected to partial melting,the magma that is produced is expected to be ____________.

A) identical in chemical composition to the source rock
B) more mafic than the source rock
C) more felsic than the source rock

Question 36

If magma did not move up from where it was formed,which of the following would be true?

A) No new oceanic crust would be made.
B) Volcanoes would not erupt.
C) Plates would not move.
D) Both a and b are correct.
E) All of the above are correct.

Question 37

If a body of magma becomes more felsic,its viscosity will ____________.

A) increase
B) decrease
C) stay the same

Question 38

Why don't all igneous rocks contain all the minerals listed in Bowen's Reaction Series?

A) Minerals degrade with time, leaving only some of the series behind in igneous rocks.
B) Crystallization may be complete before all of the minerals in the series have had time to form.
C) Not all of the minerals in the series have the ability to form in every rock.
D) Bowen's Reaction Series only applies to some igneous rocks, not all.

Question 39

Due to fractional crystallization and assimilation of surrounding host rock,most magmas that rise slowly through the crust chemically evolve to become ____________.

A) more felsic
B) more mafic
C) dominated by nonsilicate minerals

Question 40

Stoping by magmas occurs when ____________.

A) pieces of surrounding country rock are broken off and assimilated
B) the magma stops flowing and starts to solidify
C) the magma becomes fully solidified to form intrusive rock
D) the magma alters a thin rind of surrounding country rock

Question 41

Pegmatites,which occur in dikes,are unusual among shallow intrusive rocks in that they ____________.

A) possess porphyritic texture
B) possess exceptionally coarse grains
C) are mineralogically identical to the extrusive rock basalt
D) are glassy, cooling so rapidly that crystals do not have time to form

Question 42

As compared to coarse-grained igneous rocks,all fine-grained igneous rocks ____________.

A) cool and solidify more quickly
B) cool and solidify more slowly
C) solidify at higher temperatures
D) solidify at lower temperatures

Question 43

Large igneous provinces are formed by ___________,which can flow tens to hundreds of kilometers.

A) flood basalts
B) sills
C) super plumes
D) None of the above are correct.

Question 44

Why are igneous rocks important?

A) They provide information about the mantle.
B) They can be used to reconstruct tectonic activity.
C) They host important mineral deposits.
D) All of the above are correct.

Question 45

As compared to aphanitic igneous rocks,phaneritic rocks are ____________.

A) made of crystals big enough to see
B) made of crystals that can't be seen
C) more mafic
D) more felsic

Question 46

A famous example of hot-spot volcanism occurs at ____________.

A) the Aleutian Islands of Alaska
B) the Andes Mountains
C) the island of Hawaii
D) Mt. St. Helens, Washington

Question 47

When magma crystallizes,____________ are formed.

A) intrusive igneous rocks
B) extrusive igneous rocks
C) volatiles
D) pyroclastic debris

Question 48

A volcanic island arc occurs at ____________.

A) the Aleutian Islands of Alaska
B) the Andes Mountains
C) Hawaii
D) Mt. St. Helens, Washington

Question 49

Volcanoes that do not occur along present plate boundaries are associated with ____________.

A) continental rifts
B) mantle hot spots
C) mid-ocean ridges
D) subduction zones

Question 50

Vesicles is a term used mostly to describe a texture in __________ igneous rocks.

A) crystalline
B) glassy
C) pyroclastic

Question 51

Consult the figure below.Large igneous provinces can cause ______________.

A) sea-level rise
B) climate change
C) extinction
D) All of the above are correct.

Question 52

If you determine the composition of an igneous rock,you can deduce a number of things about the rock's origin.Which one of these is NOT one of those things?

A) the rate at which it cooled
B) the environment in which it formed
C) the original source of the magma
D) the exact age of the rock

Question 53

Coarse-grained granite is most similar in mineral composition to fine-grained ____________.

A) andesite
B) basalt
C) komatiite
D) rhyolite

Question 54

A volcano emits ash,which falls from the sky,settles in layers,and is eventually cemented.The resulting rock is termed ____________.

A) pumice
B) granite
C) tuff
D) ignimbrite

Question 55

Which of these is an example of a continental volcanic arc?

A) the Aleutian Islands of Alaska
B) the Andes Mountains
C) Hawaii
D) Japan

Question 56

Without igneous rocks,which of the following would not be significantly different on our planet?

A) sea-floor spreading
B) volcanic eruptions
C) formation of deserts
D) mountain building
E) evolution of continents

Question 57

An igneous rock with a mixed texture of coarse grains (phenocrysts)surrounded by fine crystals (groundmass)is termed ____________.

A) porphyritic
B) phaneritic
C) aphanitic
D) necrotic

Question 58

The silicate mineral that is found in the greatest variety of igneous rocks is ____________.

A) olivine
B) plagioclase
C) pyroxene
D) quartz

Question 59

In Bowen's discontinuous reaction series,the first mineral to crystallize from a mafic melt is ____________.

A) olivine
B) plagioclase
C) pyroxene
D) quartz

Question 60

Bombs,ash,and cinders are all examples of ____________.

A) intrusive igneous rocks
B) hot spots
C) volatiles
D) pyroclastic debris

Question 61

Which of the following would help distinguish continental hot spots from oceanic hot spots?

A) the presence of water
B) the presence of both mafic and felsic magmas
C) the presence of other, extinct or active, volcanoes nearby
D) the presence of basalt

Question 62

Bowen's continuous reaction series describes the crystallization behavior of a single mineral (with variable chemical composition),____________.

A) olivine
B) plagioclase
C) pyroxene
D) quartz

Question 63

Pillow basalts,shown below,attain their distinctive blob-like shapes because their parent lavas do not travel far prior to solidification.This is because the parent lavas ____________.

A) are completely devoid of volatiles and thus travel slowly
B) erupt underwater and thus cool very quickly
C) are highly felsic and thus travel slowly
D) are ultramafic and thus freeze at exceptionally high temperatures

Question 64

Mt.Kilimanjaro and the Basin and Range Province are the result of _____________.

A) converging plates
B) subducting plates
C) rifting
D) None of the above are correct.