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

Question 1

The incorporation or partial melting of pieces of wall rock into a magma is termed:

A) homogenization
B) fractional crystallization
C) assimilation
D) extrusion

Answer 1

C

Question 2

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

Answer 2

C

Question 3

Which type of magma has the greatest silica content?

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

Answer 3

A

Question 4

Felsic magmas commonly

A) contain more iron and magnesium than intermediate magmas.
B) contain more silica than intermediate magmas.
C) are less viscous than mafic magmas.
D) form later and at higher temperatures than mafic magmas

Question 5

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 6

The linking together of silica tetrahedra into chains that do not easily move past each other affects the ________ of a magma.

A) temperature
B) color
C) volatile content
D) viscosity

Question 7

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 8

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 9

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 10

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 11

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 12

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 13

The difference between magma and lava is that

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.

Question 14

Adding volatiles such as water or carbon dioxide to the mantle can cause it to

A) migrate through the subsurface.
B) cool down.
C) warm up.
D) transform into magma.

Question 15

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 16

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 17

Geologists distinguish between two main categories of igneous rock-extrusive and intrusive-based on

A) how fast the magma migrated.
B) whether or not the rock contains volatiles.
C) where the rock solidified.
D) if it has a high or low melting point.

Question 18

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 19

Injecting hot fudge into ice cream and causing the ice cream to melt is an appropriate analogy for which cause of magma generation?

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

Question 20

During fractional crystallization of a magma body,the first mineral 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 mineral is not predictable.

Question 21

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

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

Question 22

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 23

Igneous rocks with a glassy texture contain few if any _________.

A) volatiles
B) mineral crystals
C) xenoliths
D) silica tetrahedra

Question 24

What is the term for felsic extrusive igneous rock with glassy texture?

A) scoria
B) rhyolite
C) granite
D) obsidian

Question 25

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

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

Question 26

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

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

Question 27

As compared to aphanitic igneous rocks,phaneritic rocks are

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

Question 28

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

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

Question 29

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 30

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 31

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 32

As compared to mafic igneous rocks,felsic igneous rocks

A) have a higher Fe and Mg content.
B) have higher density.
C) melt at higher temperatures.
D) have a higher Si content.

Question 33

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 34

A _________ is an irregular or blob-shaped intrusive igneous rock that formed from cooling of a magma chamber.

A) xenolith
B) pluton
C) batholith
D) lava plateau

Question 35

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 36

A pegmatite is a coarse-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 37

Pumice and scoria are examples of glassy igneous rocks that contain a lot of ______.

A) vesicles
B) phenocrysts
C) volatiles
D) xenoliths

Question 38

What is a xenolith?

A) a sheet-like intrusion that lies parallel to surrounding layers of sedimentary rock
B) a cooled magma chamber that has been eroded
C) a fragment of wall rock that broke off and was surrounded by magma
D) a very coarse-grained igneous rock

Question 39

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 40

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

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

Question 41

What is a tuff? How does a tuff form?

Question 42

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

Question 43

Igneous rocks at hot spots are formed by ________ extending deep into the Earth's mantle.

A) mantle plumes
B) subduction zones
C) rift zones
D) groundwater

Question 44

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

Question 45

What is obsidian? How does it form?

Question 46

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

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

Question 47

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 48

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 49

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

Question 50

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 51

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

A) a highly felsic composition
B) abundant volatiles that formed gas bubbles
C) fractional crystallization
D) magma mixing

Question 52

What is the source of volatiles that lead to magma formation at subduction zones?

Question 53

A mafic,highly-vesicular volcanic rock is termed

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

Question 54

Briefly explain why and how magmas rise within the Earth.

Question 55

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

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

Question 56

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

Question 57

Igneous rocks formed at mid-ocean ridges are primarily

A) mafic.
B) volatile-rich.
C) glassy.
D) felsic.

Question 58

What is the reason for a solidus line and a liquidus line on a pressure-temperature graph in the context of partial melting and fractional crystallization?

Question 59

Magma and igneous rocks formed at subduction zones originate due to _______

A) decompression melting
B) fractional crystallization
C) addition of volatiles
D) loss of volatiles

Question 60

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

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