Deck 6: Up From the Inferno: Magma and Igneous Rocks

Question 1

Differentiation of the Earth's iron core and collisions of planetesimals 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.

Answer 1

C

Question 2

The difference between magma and lava is

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

Answer 2

C

Question 3

Injecting hot fudge into ice cream and causing the ice cream to melt 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) flux melting

Answer 3

C

Question 4

As compared to mafic igneous rocks,felsic igneous rocks

A) cool and solidify more quickly.
B) cool and solidify more slowly.
C) solidify at higher temperatures.
D) have a higher proportion of silica relative to Mg oxide and Fe oxide.

Question 5

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) are highly flammable.
D) evaporate easily and exist as gases.

Question 6

In general,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.
D) The melt composition is not predictable.

Question 7

Important volatiles in magmas include

A) mafic minerals,such as olivine.
B) potassium and aluminum.
C) water and carbon dioxide.
D) silicon and iron.

Question 8

When magma solidifies below the surface of the Earth,________ are formed.

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

Question 9

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

A) increase.
B) decrease.
C) stay the same.
D) Chemical composition has no effect on viscosity.

Question 10

In general,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 11

The geotherm is the rate of change of

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

Question 12

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

A) increase.
B) decrease.
C) stay the same.
D) Volatile content has no effect on viscosity.

Question 13

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 14

Which type of magma has the greatest silica content?

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

Question 15

Which of the following processes is not responsible for the formation of magma within the Earth?

A) decompression (due to a 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 16

Viscosity does NOT depend on

A) temperature.
B) volatile content.
C) silica content.
D) the total volume of the magma body.

Question 17

A fragmental,extrusive igneous rock is referred to as which of the following?

A) crystalline
B) vitric
C) pyroclastic
D) vesicular

Question 18

Igneous rocks are formed

A) through the freezing or crystallization of a melt.
B) by changing existing rock by the application of heat and pressure.
C) by depositing loose material into layers.
D) by chemically precipitating from solutions.

Question 19

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 20

A body of rock starts at location A in the graph below.The rock,over a period of time,moves to location B and begins to melt.This is an example of melting due to

A) fractional crystallization.
B) heat transfer.
C) addition of volatiles.
D) decompression.

Question 21

A pegmatite is a course-grained igneous rock that forms primarily because the melt

A) is water-rich.
B) cools very slowly.
C) cools at great depth.
D) cools under specific pressure conditions.

Question 22

The boundary formed between new intrusive igneous rock and the host rock around it is called a

A) dike.
B) contact.
C) sill.
D) laccolith.

Question 23

During fractional crystallization of a magma body,the first rock that is expected to crystallize from the magma will be

A) identical in chemical composition to the magma.
B) more mafic than the magma.
C) more felsic than the magma.
D) The composition of the rock is not predictable.

Question 24

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

A) porphyritic.
B) phaneritic.
C) aphanitic.
D) vitric.

Question 25

Shiprock,New Mexico,seen in the photo below is a(n)

A) sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock.
B) cooled layer of lava.
C) intrusion that represents the eroded remnant of an extinct volcano.
D) sheet-like intrusion that cuts across preexisting layers.

Question 26

A magma body with a ________ volume and a ________ shape cools fastest.

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

Question 27

The continuous series in Bowen's reaction series describes the crystallization behavior of which mineral?

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

Question 28

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

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

Question 29

Which of the following statements cannot be applied to the extrusive igneous rock obsidian?

A) It is composed of volcanic glass.
B) It possesses conchoidal fracture.
C) It is typically felsic in composition.
D) It cools very slowly.

Question 30

Pegmatites,which often 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 basalt.
D) are glassy,cooling so rapidly that crystals do not have time to form.

Question 31

A _________ is an irregular or blob-shaped intrusive body; a ___________ is a blister-shaped intrusion.

A) pluton; batholith
B) pluton; laccolith
C) batholith; laccolith
D) batholith; pluton

Question 32

A vast,composite intrusive igneous body that covers hundreds of square kilometers (in a map view)is called a

A) pluton.
B) dike.
C) batholith.
D) sill.

Question 33

Which of the following does not affect the cooling rate of magma?

A) depth of intrusion
B) shape and size of magma body
C) presence of circulating groundwater
D) tectonic setting

Question 34

Because of its physical properties,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 35

In the figure provided below,what type of igneous intrusion is the horizontal rock unit shown by letter A?

A) dike
B) sill
C) pluton
D) laccolith

Question 36

As compared to coarse-grained igneous rocks,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 37

Bombs,ash,and cinders are all examples of

A) intrusive igneous rocks.
B) lava flows.
C) volatiles.
D) pyroclastic debris.

Question 38

Intrusive rocks that form deep within the 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) are less dense

Question 39

As compared to aphanitic igneous rocks,phaneritic rocks are

A) coarser grained.
B) finer grained.
C) more mafic.
D) more felsic.

Question 40

In the figure provided below,what type of igneous intrusion is the vertical rock unit shown by letter A?

A) dike
B) sill
C) pluton
D) laccolith

Question 41

If you find a tuff in the field,what type of geologic activity could you reasonably assume has occurred?

A) an igneous intrusion
B) sea-level rise
C) a volcanic eruption
D) tectonic uplift

Question 42

Rhyolite and granite are both felsic igneous rocks,although they have different cooling histories,and consequently different textures.Explain the difference between the two rock types from a cooling perspective and be specific about which igneous texture can be applied to which rock.

Question 43

Describe the process of decompression melting.Be sure to include an example of where this type of melting occurs within the Earth.

Question 44

Granite,an intrusive igneous rock,is most similar in mineral composition to which extrusive equivalent?

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

Question 45

Vesicles in an igneous rock are evidence for which of the following?

A) a highly felsic composition
B) degassing of volatiles
C) fractional crystallization
D) magma mixing

Question 46

Label the cross-section of the convergent boundary shown below.Be sure to use all of the following words/phrases: down-going plate,overriding plate,volcanic arc,volatiles being released,magma forming,Moho,magma rising.

Question 47

Flood basalts such as those found in the Columbia Plateau and the Deccan region are associated with

A) subduction zones.
B) superplumes.
C) mid ocean ridges.
D) rifts.

Question 48

The figure below shows mafic magma as it meets the seafloor,which cools to form an igneous rock called

A) pegmatite.
B) pillow basalt.
C) laccolith.
D) pluton.

Question 49

Briefly explain why and how magmas rise within the Earth.

Question 50

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

A) flood basalts
B) sills
C) super plumes
D) highly explosive eruptions

Question 51

List the four major magma compositions in order of silica content.

Question 52

Compare and contrast a dike and a sill.How do they relate to surrounding rock layers?

Question 53

What is obsidian? How does it form?

Question 54

A felsic,highly-vesicular volcanic rock is termed

A) pumice.
B) granite.
C) tuff.
D) scoria.

Question 55

Fragments of material erupted from a volcano eventually settle and lithify to form an extrusive igneous rock called

A) basalt.
B) andesite.
C) hyaloclastite.
D) tuff.

Question 56

A volcanic arc results from __________ tectonic movements and is associated with a __________.

A) divergent; mid ocean ridge
B) convergent; subduction zone
C) divergent; hot spot
D) convergent; mid ocean ridge

Question 57

What is a tuff? How does a tuff form?

Question 58

What is fractional crystallization? Briefly explain how it works and why different types of magmas result.

Question 59

Which of the following is not typically associated with the eruption of a Large Igneous Province (LIP)?

A) sea-level rise
B) climate change
C) extinction
D) emplacement of large granite batholiths

Question 60

Describe the difference between the relative viscosity of felsic versus mafic magma and how this affects the rate of flow of each type.