Deck 3: Igneous Rocks, Intrusive Activity, and the Origin of Igneous Rocks

Question 1

Basaltic magmas crystallize at higher temperatures than granitic magmas.

Answer 1

True

Question 2

A dike is a discordant intrusive igneous structure.

Answer 2

True

Question 3

A mineral's melting point generally increases with increasing pressure.

Answer 3

True

Question 4

Partial melting of the lower continental crust produces a silicic magma that eventually solidifies into granite or rhyolite.

Question 5

A pluton is an igneous structure that crystallized at very shallow depths.

Question 6

Lava is magma on the Earth's surface.

Question 7

The geothermal gradient is the rate at which pressure increases with increasing depth beneath the surface.

Question 8

The continuous branch in Bowen's Reaction Series contains the ferromagnesian minerals.

Question 9

Rhyolite is considerably more common than granite.

Question 10

The geothermal gradient for a volcanic region is greater than that for the continental interior.

Question 11

Diorite and andesite are composed of similar amounts of feldspars and ferromagnesian minerals.

Question 12

Extrusive igneous rocks are typically fine grained because they crystallized slowly, deep below the Earth's surface.

Question 13

Mafic igneous rocks are silica-poor.

Question 14

Igneous rock names are based on grain shape and chemical composition.

Question 15

Although batholiths may contain mafic and intermediate rocks, they almost never composed of granite.

Question 16

An ultramafic rock is composed almost entirely of quartz.

Question 17

Pegmatites are extremely coarse-grained igneous rocks.

Question 18

The sequence in which minerals crystallize in a cooling igneous melt is called Bowen's Reaction Series.

Question 19

The melting point of a rock decreases with increasing pressure.

Question 20

The term mafic comes from the terms magnesium and ferric.

Question 21

___ are igneous rocks that are silica-deficient but high in iron and magnesium.

A) Felsic
B) Intermediate
C) Oxide
D) Mafic
E) Sulfate

Question 22

______ are extremely coarse-grained with crystal up to 10 meters across.

A) Granites
B) Ultramafic
C) Basalts
D) Pegmatites
E) Marbles

Question 23

Mineralogically and chemically equivalent rocks are ___ and __.

A) granite; rhyolite
B) gabbro; basalt
C) diorite; andesite
D) mafic; ultramafic
E) intermediate; felsic

Question 24

A useful tool illustrating the relationships among igneous, sedimentary, and metamorphic rocks is called the ___.

A) weathering and erosion of surface features
B) plate tectonic cycle
C) relationships between preexisting rock
D) rock cycle
E) Bowen's reaction series

Question 25

___ is a coarse-grained igneous rock (grains > 1 mm diameter) with visible grains of quartz.

A) Gabbro
B) Granite
C) Basalt
D) Peridotite
E) Andesite

Question 26

A ______ is an intrusive structure that formed from magma that solidified within the "throat" of a volcano.

A) volcanic neck
B) sill
C) laccolith
D) batholith
E) diapir

Question 27

Fine-grained igneous rocks (grains < 1.0 mm) that have small grains cooled rapidly and are likely to be _______.

A) extrusive
B) reclusive
C) intrusive
D) obtrusive
E) preclusive

Question 28

Both andesite and ___ are composed of feldspars and 30% to 50% ferromagnesian minerals.

A) granite
B) diorite
C) pegmatite
D) gabbro
E) rhyolite

Question 29

______ are fragments of country rock that are distinct from the body of igneous rocks in which they are enclosed.

A) Clasts
B) Chill zones
C) Phenocrysts
D) Xenoliths
E) Necks

Question 30

Ultramafic igneous rocks are composed almost entirely of __.

A) feldspar
B) quartz
C) ferromagnesian minerals
D) calcite
E) diamonds

Question 31

______ igneous rocks, like gabbro and basalt, are silica-deficient with high magnesium and iron.

A) Felsic/silicic
B) Intermediate
C) Mafic
D) Intrusive
E) Extrusive

Question 32

______ is the predominant igneous rock of the continents.

A) Basalt
B) Granite
C) Rhyolite
D) Gabbro
E) Limestone

Question 33

The geothermal gradient, on average, is about _____.

A) 0.004 $\degree$ C/km
B) 2.5 $\degree$ C/km
C) 25 $\degree$ C/km
D) 30 $\degree$ C/km
E) 2500 $\degree$ C/km

Question 34

Igneous rocks that are silica-rich with high aluminum, sodium, and potassium are _____ rocks.

A) silicic
B) ultramafic
C) mafic
D) extraterrestrial
E) intermediate

Question 35

Under ideal conditions rock can melt and yield a granite composition at temperatures as low as ___.

A) 100 $\degree$ Celsius
B) 225 $\degree$ Celsius
C) 333 $\degree$ Celsius
D) 450 $\degree$ Celsius
E) 650 $\degree$ Celsius

Question 36

Igneous rocks may be either ____ if they form on or near Earth's surface, or ___ if they solidify under ground.

A) intrusive; volcanic
B) volcanic; extrusive
C) extrusive; intrusive
D) plutonic; intrusive
E) intrusive; extrusive

Question 37

_____, a coarse-grained rock composed of pyroxene and olivine, is the most abundant ultramafic rock.

A) Diorite
B) Gabbro
C) Granite
D) Peridotite
E) Hematite

Question 38

A _______ is a tabular (thin but large area) intrusive body that is concordant (parallel to the host rock structure).

A) dike
B) mantle
C) threshold
D) sill
E) neck

Question 39

_____ rocks have coarse crystals in a fine-grained matrix.

A) Ultramafic
B) Granite
C) Sill
D) Pegmatite
E) Porphyritic

Question 40

The most common minerals in a granite are the ______.

A) oxides
B) carbonates
C) feldspars
D) ferromagnesians
E) micas

Question 41

What type of melting takes place when a body of hot mantle rock moves upward and the pressure is reducted to the extent that the melting point drops to the temperature of the body?

A) decompression melting
B) subduction melting
C) depressurized melting
D) exfoliational melting
E) mantle plume melting

Question 42

The huge volume of mafic magma that erupted to form the Columbia plateau basalts of Washington and Oregon are attributed to ___.

A) sea floor spreading
B) a hot mantle plume
C) subduction
D) magma mixing
E) meteorite impact

Question 43

The melting point of a mineral generally _____ with increasing pressure (or depth).

A) does not change
B) decreases
C) increases
D) becomes dependent on rock type
E) is unknown

Question 44

The first plagioclase crystals to form as a hot melt cools are high in ______.

A) iron
B) calcium
C) manganese
D) carbonate
E) lead

Question 45

What is the sequence of crystallization along the discontinuous branch of Bowen's reaction series?

A) sodium-rich to calcium-rich plagioclase
B) quartz, potassium feldspar, biotite
C) silicic, felsic, mafic, intermediate
D) olivine, pyroxene, amphibole, biotite
E) framework, double chain, single chain, sheet, isolated

Question 46

The coarse-grained equivalent of basalt is a(n) ______.

A) andesite
B) gabbro
C) granite
D) diorite
E) rhyolite

Question 47

Imagine two magmas that are identical in all respects (for example, same chemistry, pressure, volume) except that one magma is hotter than the other. Which magma will have the higher viscosity?

A) The hotter magma will be more viscous.
B) The cooler magma will be more viscous.
C) The magmas will have the same viscosity.
D) There is not sufficient information to establish the relative viscosities of these magmas.
E) Temperature does not affect magma viscosity.

Question 48

On its slow journey through the crust, mafic magma evolves into intermediate magma by differentiation and assimilation of ______.

A) mantle rocks
B) basalt
C) gabbro
D) silicic rocks

Question 49

________ lava is largely restricted to narrow zones along convergent plate boundaries.

A) Granite
B) Andesite
C) Rhyolite
D) Ultramafic
E) Carbonate

Question 50

Geologists regard basaltic magma (Hawaiian lava, for example) as the result of the partial melting of ultramafic rock in the ____.

A) oceanic crust
B) continental crust
C) mantle
D) outer core
E) inner core

Question 51

Hawaii and __________ eruptions are related to intraplate igneous activity.

A) Japan
B) Cascade
C) Yellowstone
D) Honduras
E) California

Question 52

Crystal settling accounts for important deposits of ______.

A) chromium and platinum
B) gold
C) lead and zinc
D) iron
E) aluminum and silicon

Question 53

Granite and ______ are composed predominantly of feldspar and quartz.

A) oceanic crust
B) diorite
C) basalt
D) rhyolite
E) ultramafics

Question 54

Mafic magma generated in the _______ rises to the base of the crust.

A) continental crust
B) outer core
C) asthenosphere
D) spreading ridges
E) mantle plumes

Question 55

How is a sill different from a dike?

A) The sill is tabular in shape.
B) Dikes are intrusive structures.
C) Dikes are fine-grained and sills are coarse-grained.
D) Sills are parallel to the layering in the country rock.
E) A sill is shaped like a mattress, while a dike is shaped like a pillow.

Question 56

Most of the basalt and gabbro on the ocean floor is created at mid oceanic ridges, which are also ____.

A) divergent plate boundaries
B) ocean-ocean convergent plate boundaries
C) transform plate boundaries
D) ocean-continent plate boundaries
E) intraplate igneous areas

Question 57

What is the process through which magma differentiation takes place?

A) crystal settling
B) partial melting
C) viscosity of the magma
D) heating of the country rock
E) subduction

Question 58

To explain the great volumes of granite plutonic rocks, most geologists think that partial melting of the _______ must take place.

A) core
B) lower mantle
C) lower continental crust
D) oceanic crust
E) asthenosphere

Question 59

Viscosity is a property of a fluid that relates to how easily the fluid flows. A material that is viscous __.

A) flows easily
B) flows less easily
C) is always hot
D) is always a solid
E) is always cold

Question 60

The crust beneath the world's oceans is mafic ________.

A) iron
B) asthenosphere
C) granite and rhyolite
D) basalt and gabbro
E) Answers iron, asthenosphere, and granite and rhyolite are all correct.